Effects of arachidonic acid and prostaglandins on lung function in the intact dog E. W. SPANNHAKE, R. J. LEMEN, M. J. WEGMANN, A. L. HYMAN, AND P. J. KADOWITZ Departments of Pharma.cology, Surgery, and Pediatrics, Tulane University School of Medicine, New Orleans, Louisiana SPANNHAKE, E. W.,R.

ALEMEN, M.J. WEGMANN, A.L. P. J. KADOWITZ. Effects of arachidonic acid and prostaglandins on lung function in the intact dog. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 44(3): 397-405, i978. -The effects of the prostaglandin (PG) precursor, arachidonic acid (AA), and the prim&y PG’s, PGF,,, and PGDz, on lung function were compared in 39 intact-chest, paralyzed, artificially ventilated dogs. Intravenous AA decreased dynamic compliance (Cdyn) and functional residual capacity and increased airway resistance (RL) and transpulmonary pressure at end-passive expiration. The decrease in Cdyn correlated closely with a rise in pulmonary arterial pressure (Ppa). Indomethacin abolished airway and vascular responses to AA, but did not attenuate responses to the PG’s. The effects of AA, PGD2, and PGF,, on lung function and Ppa were similar, whereas PGE, had little effect. Vagotomy attenuated the RL increase in response to AA, PGE2,-y, and PGD, and the Cdyn decrease in response to the PG’s. The effects of the PG’s on compliance were greater than those produced by mechanically increasing pulmonary venous pressure. The present studies suggest that the PG precursor is rapidly converted to agents that have marked effects on both pulmonary vessels and airways, particularly peripheral airways, in the dog. HYMAN,

AND

respiratory resistance; dynamic lung compliance; lung volume; pulmonary arterial pressure; vagotomy; pulmonary vascular congestion; prostaglandin synthesis inhibition

THE BIOSYNTHESISOF PROSTAGLANDTNS from arachidonic acid by homogenates of guinea pig lung was first described in 1965 by &g&d and Samuelsson (1). It was subsequently reported that a variety of pathophysiological stimuli, including anaphylaxis, asthma, embolization, hyperventilation, and mechanical injury, increase prostaglandin synthesis in the lung (28). Increased synthesis of prostaglandins involves the splitting off of arachidonic acid from phospholipids in the cell membrane by enhanced phospholipase A, activity (9) with subsequent conversion by a microsomal cyclooxygenase to prostaglandin intermediates, primary prostaglandins, and thromboxanes (25). The -effects of arachidonic acid, prostaglandin (PG) Ez, and PGF,, on the pulmonary and systemic circulations have been studied extensively (15, 17, 26). Little information is available, however, about the effects in the intact dog (16, 31) of PGDz, a third primary prosta0021~8987/78/0000-0000$01.25

Copyright

0 1978 the American

Physiological

70112

glandin formed from fatty acid precursor in a variety of tissues including lung (24). Furthermore, while the effects of PGF,, on lung function in the spontaneously breathing dog have been documented (30), those of the precursor, arachidonic acid, and the three primary prostaglandins have not been reported previously in the intact, artificially ventilated dog. The purpose of the present study was to investigate the effects of arachidonic acid and the primary prostaglandins on pulmonary mechanics in anesthetized, intact-chest dogs. These studies were carried out in paralyzed animals under conditions of controlled ventilation to permit study of alterations in mechanical properties of the lung in the absence of reflex ventilatory activity. In addition, the contribution of vagal reflexes to responsesto these lipids and the effects of vascular congestion on lung compliance were evaluated. METHODS

Thirty-nine microfilaria-free mongrel dogs, unselected as to sex, with a mean weight of 15.9 -5 0.4 kg, were used in this study. The animals were anesthetized with chloralose (50 mg/kg) and urethan (500 mg/kg) administered intravenously. Polyethylene catheters were advanced from the femoral artery and vein for the recording of aortic pressure (PAo) and the administration of drugs, respectively. A 6F Edslab double lumen thermodilution catheter (Edwards Laboratories) was passed from the external jugular vein into the main pulmonary artery under fluoroscopic guidance. Pulmonary arterial pressure (Ppa) was measured from the distal port of this catheter. In some experiments, left ventricular end-diastolic pressure was measured through a Cordis pigtail catheter advanced from a femoral artery, or alternately, left atria1 pressure was measured directly through a 7F Teflon catheter positioned transseptally in the left atrium. Cardiac output was determined with an Edwards Laboratories thermal dilution computer, model 9500A, after rapid injection of 5 ml normal saline (22-24°C) into the superior vena cava (SVC) by way of the proximal port on the Edslab catheter. All vascular pressures were measured with Statham P23BB or P23AC transducers zeroed at midright atria1 level. Mean pressures were *obtained from the pulsatile signal by electrical averaging. Society

397

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.186.138.035) on January 11, 2019.

398

SPANNHAKE

The animals were ventilated with a Harvard respirator through a short tracheal tube (2-3 cm diameter) introduced by tracheostomy (Fig. 1). Transpulmonary pressure (Ptp) was measured by a Statham PMSE differential transducer bridged between the tracheal tube and a Harvard pleural cannula inserted through the chest wall at the 4th or 5th intercostal space. Pneumothorax was adjusted to lo-20 ml immediately after introduction of the pleural cannula. Airflow (ii) was measured with a Fleisch no. 1 pneumotachograph heated above body temperature and coupled to a Grass PI’SA differential transducer. Ptp and V signals were fed into a Hewlett-Packard 8816A respiratory analyzer which provided on line, volume (V), dynamic compliance (Cdyn), and resistance of the lung (RL). Cdyn was computed between points of zero flow by dividing the volume of each breath by the difference between endinspiratory and end-expiratory Ptp. RL was computed at early expiration by the method of Mead and Whittenberger (19) in which instantaneous resistive pressure was divided by instantaneous flow. Resistive pressure is derived by subtracting the ratio of volume to computed compliance from Ptp. Using these methods, the mean RL and Cdyn during base-line periods for all experiments were: RL = 2.18 t 0.04 cmH,O/(l/s) and Cdyn = 0.037 t 0.001 l/cmH,O. Percent CO, in endtidal air was monitored periodically with a Beckman LB-Z medical gas analyzer connected to a tap between the respirator and the pneumotachograph. Ptp, i7, V, RL, Cdyn, and vascular pressures were recorded on a Grass model 7C eight-channel polygraph. When all surgical procedures were completed (approximately 1 h), the animals were heparinized with sodium heparin (Upjohn), 500 U/kg iv. Spontaneous breathing was arrested with succinylcholine chloride (Anectine, Burroughs Wellcome), 30-40 mg, iv, repeated as needed. After neuromuscular blockade, increments of anesthetic were given when an increase was observed in arterial pressure, heart rate, or salivation, Minute volume was set with tidal volume at 12 ml/kg at a rate sufficient to maintain end-tidal CO, near 35 Torr and blood gases in a normal range. A lung volume history was established by hyperinflating the lung to three times the tidal volume 3 min prior to each injection. Arachidonic acid, PGD2, PGE2, and PGFZ, were each injected as a bolus into the SVC through the proximal port of the Edslab catheter and flushed immediately with 5 ml saline. Sufficient time was allowed

Po/ygmph

FIG.

volume (See

1. Schematic determinations,

METHODS).

diagram of the experimental a plastic syringe was

system. For lung attached to point A

ET

AL.

between administration of the test agents for Ppa and PA0 to return to control levels (generally lo-15 min). Measurements of functional residual capacity (FRC) were made at end-passive expiration in five dogs by a closed-circuit equilibration method. A plastic syringe containing 300 ml of 99.9% 0, was attached to a port on the tracheal tube (Fig. l), and the lungs were rapidly inflated and deflated until a nitrogen meter (HewlettPackard model 4730211nitrogen analyzer) indicated the nitrogen concentration had reached equilibrium. FRC was calculated from the expression: FRC = &FE,*/ WA - FE~J where V1 = 300 ml, FEDS = equilibrium N, !iaction, and FAN = initial alveolar N, fraction. This value was then corrected for equipment dead space (110 ml). Animals were hyperinflated to three times their tidal volume 3 min prior to injection of arachidonic acid and again 10 min after injection, FRC measurements were made 60 s after hyperinflation (control), 30 s after the first rise in Ptp elicited by the arachidonic acid (peak), and 60 s after the hyperinflation at 10 min. The peak measurement always corresponded in time to the period of maximal Ptp change. Six successive determinations of FRC in one dog, using this method, ranged from 475 to 491 ml (mean & SE, 484 2 2 ml). The eight dogs used to study the effects of vascular engorgement were prepared as previously described (14) in the following manner. In addition to the placement of the Edslab catheter, a specially designed 20F balloon perfusion catheter was positioned in the artery of the left lower lobe under fluoroscopic guidance. A Teflon catheter with its tip extending about 2 cm distal to the balloon was used to measure pressure in the perfused lobar artery. A Dotter-Lukas no. 1 balloon catheter, (&5F, US Catheter), was passed transseptally into the left atrium from a jugular vein and positioned in the vein draining the left lower lobe. Left atria1 pressure was measured through a second transseptal catheter (4F, Teflon). After all catheters were positioned, the balloon on the perfusion catheter was distended with 2-4 ml Hypaque (sodium diatrizoate, 50%, Winthrop Laboratories) until pressure in the lobar artery and intrapulmonary lobar vein decreased to near left atria1 pressure. The vascularly isolated left lower lung lobe was then perfused with blood withdrawn from the right atrium by a Sarns roller pump (model 3500). The pumping rate was adjusted so that pressure in the perfused lobar artery approximated pressure in the main pulmonary artery and thereafter was not changed. In these dogs, a Carlens endobronchial divider (no. 39) was inserted through a tracheostomy, thereby isolating the left lower lobe from the rest of the lung. Each side of the divider was ventilated separately at a constant volume with a Harvard dual-cylinder respirator. Translobar pressure was determined by bridging the transducer between a Harvard pleural tap in the chest wall and the lobar side of the divider. Lobar venous pressure was elevated to various levels by slowly distending the Dotter-Lucas balloon in the lobar vein for 40-60 s. These experiments permitted us to evaluate the passive effects of increased venous and arterial pressure on dynamic compliance of the left lower lung lobe under conditions of controlled blood flow in intact,

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.186.138.035) on January 11, 2019.

ARACHIDONIC

ACID

AND

PROSTAGLANDINS:

LUNG

399

FUNCTION

paralyzed, and artificially ventilated dogs. Arachidonic acid (NuChek), 99% pure, and indomethacin (Merck) were freshly prepared as sodium salts: AA in 10% ethanol in 100 mM sodium carbonate; and indomethacin in 100 mM sodium carbonate in normal saline. Linoleic acid (Sigma), 99% pure, was prepared in the same way as AA. Prostaglandins DZ, Eel and FZ, (Upjohn) were dissolved in absolute ethanol and stored at -20°C under nitrogen gas. Working solutions were freshly prepared in saline. All values were expressed as the means * SE, unless otherwise indicated. The existence of dose-related changes in variables was tested for by using regression analysis. These analyses and tests of significance for group and paired comparisons were done according to standard statistical methods (29). A P value less than 0.05 was considered significant.

pliance shown in Fig. 2 attained a peak 5-10 s later than RL. After a short delay, AA produced a marked decrease in systemic arterial pressure. Arachidonic acid f6

PTP

8

(CMw)

F

,320

0

(L/SEC) v v

,8000 t .200

@I

0 I

I

TIM EM

I

RESULTS

Effects of arachidonic acid ti The effects of arachidonic acid (AA) on the airways and on vascular pressures in the dog in a typical experiment are illustrated in Fig. 2 and the airway data from 10 experiments are summarized in Table 1. Rapid bolus injection of 10 mg of AA into the SVC caused a marked rise in Ppa within 15 s of administration (Fig. 2). Simultaneously, APtp increased to twice control level, attaining a maximum within 20 s, and gradually returned toward base line. As the Ptp swing increased, Ptp at end-passive expiration rose by 1.5 cmH,O. Since pressure at the tracheal tube was zero at end-passive expiration, this increase was due to a more negative intrapleural pressure. The magnitude of this effect varied with the dose, ranging from 0.2 to 1.6 cmH,O and was consistently seen after AA injection. Associated with the increase in APtp was a rise in RL of short duration and a marked and more prolonged decrease in Cdyn. The 50% decrease in com-

.064 "yn

-----%

,032

(1-m H20)

, '7

+

0 10 mg ARACHIDQNIC 45 i-

ACID

(MM HG) ppA

':I~

FIG. 2. Record from an experiment illustrating effects of arachidonic acid on transpulmonary pressure (Ptp) (inspiration up), airflow (v) (inspiration upward from zero, expiration downward), tidal volume (V), lung resistance (RL), dynamic compliance (Cdyn), mean pulmonary arterial pressure (Ppa) and mean aortic pressure (PAo) in the anesthetized and ventilated dog. Injection was made as a bolus into the superior vena cava at point indicated.

TABLE 1. Effects of precursor arachidonic acid and bisenoic prostuglandins m lung resistance and dynamic compliance in the intact artificially ventilated dog

Control

Arachidonic acid 3x 6mg 10 mg

Cdyn,

RL, cmH,O/(l/s)

n

Response

%A

Control

l/cmH,O Response

%A

10 10 10

2.21 zk 0.44 2.42 k 0.42 2.27 k 0.36

4.72 k 0.7?* 5.83 -+ 1.08* 7.81 A 1.07*

144 t 45 166 f 50 297 f 70

0.036 0,040 0.036

k 0.004 2 0.003 -+ 0.004

0.027 0.027 0.020

+ 0.003* f 0.009* 2 0.002"

-23-t-4 -32k4 -43k4

7 7 7

2.28 k 0.30 2.33 + 0.33 2.10 + 0.24

2.84 + 0.44* 4.93 k 0.61* 6.70 k 0.57*

23 k 9 129 2 36 244 L+_55

0.038 0.037 0,037

5 0.004 3- 0.003 2 0.003

0.033 0.024 0.020

+ 0.003* -t- 0.002* 2 0.002*

-13 + 3 -34*4 -45&4

7 7 7

2.05 k 0.60 2.01 k 0.51 2.17 5 0.59

2.05 + 0.60 3.44 + o.ss* 4.49 + 0.48*

0 71 + 23 139 -+ 22

0.038 0.039 0.039

+ 0.004 -c 0.005 f om4

0.035 -+ 0.004 0.032 k 0.004* 0.027 f 0.002*

7 7

2.01 2 0.28 2.14 3- 0.52

2.01 + 0.28 2.19 2 0.44

0 9 IL 11

0.034 0.036

2 0.005 t 0.005

PGD,

PGE, 30 Pg ml fig

All agents were injected RL = lung resistance;

group.

as a bolus into the superior Cdyn = dynamic compliance.

vena

0.032 0.032

+ 0.004 t 0.005

-723 -2Ok3 -29-t-4

-3k2 -10 2 4

cava. All values are expressed as means * SE; n. = number of animals * Significantly different (P < 0.05) from control, paired t-comparison.

per

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.186.138.035) on January 11, 2019.

400 caused a significant increase in cardiac output (CO), but had no consistent effect on left atria1 or left ventricular end-diastolic pressures. Table 1 compares changes in RL and Cdyn in response to three doses of AA. Both variables showed a significant dose-related change in response to the prostaglandin precursor. Hyperinflating the lung lo-15 min after administration of AA usually returned Cdyn and RL to precisely the control value. The effect of AA on arterial blood oxygen tension was studied nine times in seven dogs. Blood samples were withdrawn from the thoracic aorta prior to injection of AA and within 20 s following the peak of the airway response. There was no significant change in P%Z in response to AA (control = 77 t- 4 Torr; peak = 78 * 6 Torr). The effect of the IO-mg dose of AA on FRC was measured 11 times in five dogs. FRC significantly decreased from 444 -+ 54 to 397 t 48 ml at the peak of the airway response (statistical YL = 5). This change was associated with a 40% decrease in Cdyn and a 92% rise in Ppa. The magnitude of the Cdyn decrease was similar to that obtained for this dose in the dose-response studies (Table l), in which Ptp at end-passive expiration was found to increase 1.0 t 0.1 cmH,O in 10 dogs. Specific conductance of the airways (SGaw) decreased significantly from 0.79 * 0.10 to 0.55 t 0.09 (s/ cmH,O)+ at the peak of the airway response. Values of FRC, Cdyn, and SGaw returned to within control limits after hyperinflation at 10 min postinjection. Linoleic acid, an 18-carbon fatty acid that is not a prostaglandin precursor, was used to determine the nonspecific effects of a bolus injection of a nonsubstrate fatty acid. Injection of linoleic acid, 10 mg, into the WC of six dogs did not affect any of the variables measured. Effects of classical prostaglandins. The effects of PGD, on the airways and on vascular pressures in a typical experiment are illustrated in Fig. 3, and the airway data from seven experiments are summarized in Table 1. Bolus injection of a mid-range dose of PGD, (3 pg) into the SVC increased Ppa significantly but had little or no effect on PAO or CO (Fig. 3). PGDz, 10 pg, did not significantly affect CO in seven experiments (2.6 -+ 0.4 l/min before and 2.5 t 0.4 l/min at peak response). The 53% rise in Ppa shown in Fig. 3 reached a maximum by 20 s and gradually declined toward base line. Associated with the increase in Ppa, APtp rose 53%. As seen with AA, the increases in Ptp and Ppa were closely related. A small but consistent increase in Ptp at FRC, which ranged from 0.2 to l-6 cmH,O, was observed in dogs receiving 3 or 10 ,ug of PGD,. Associated with the Ptp response was a small increase in RL and a gradual, more sustained decrease in Cdyn. The effect of PGD, on RL and Cdyn was dose related at 1, 3, and 10 pg (Table 1). In six experiments in five dogs, blood was withdrawn from the thoracic aorta prior to PGD, injection and within 20 s following the peak airway response. As was seen with AA, PzJ,, was not significantly changed during the response to PGD, (control = 75 -F- 3 Torr). The effects of PGFZti on lung mechanics were less than those of PGD,. Although 3 pg of PGFZ, was

SPANNHAKE

ET

AL.

** lti

PTP (CMw)

8 0E .320 0

0

v (L/SEC)

,800 t .200

v IL)

0[

.,.,.,.l.l...

18.8 1,60L/MlN R

1.79 L/MN

L

(CM “2O/L/=c

)

“‘0”

E;

.064 cdyn (L/CM

I

:

THEE

ii20

j

032 1 0E 45

pp#4

1

MIN

4

3clsPGD2

25 J

(MMHG) 0t 200

PA0 (MM HG)

100 0 0E

3. Record from an experiment illustrating the effects of on transpulmonary pressure (Ptp), airflow (v), tidal volume lung resistance (RL), dynamic compliance (Cdyn), mean pulmoarterial pressure (Ppa) and mean aortic pressure (PAO). Numbelow time line represent cardiac output. Injection was made bolus into the superior vena cava.

FIG.

PGD, (V), nary bers as a

sufficient to cause a 45% increase in Ppa, this dose did not result in a significant airway response in terms of RL or Cdyn (Table 1). At a dose of 10 rug, the increase in RL in response to PGFZ, was less than 30% of that produced by PGD,. Likewise, this dose of PGFZ, was less than 50% as effective in decreasing Cdyn as was the equivalent dose of PGD,. Like PGDz, PGF,, had little or no effect on PAO or CO at the doses studied. As was observed with AA, hyperinflation 10-15 min after administration of either PGD, or PGF,. returned RL and Cdyn to the preadministrative value, Injection of 30 and 100 pg of PGE, resulted in a small but significant increase in Ppa that varied with the dose; however, neither dose had significant effect upon RL or Cdyn (Table 1). In addition to its pulmonary vascular effect, PGE, caused a sustained decrease in aortic pressure similar to that seen after AA (Fig. 2). Figure 4 illustrates the relative activities of AA and prostaglandins Dz, FZ,, and E, in the airways and on the pulmonary and systemic vascular bed. Arachidonic acid, PGD, and PGF,, were very active in increasing both APtp and Ppa in the doses studied. The doserelated increases in these two variables were markedly similar in the case of each agent, suggesting a close relationship between the airways and the vascular bed. Prostaglandins D, and FZ, were approximately equal in their ability to increase Ppa; however, PGD, was more than three times as active as PGF,, in increasing Ptp swing. Arachidonic acid was approximately 2,000 times

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.186.138.035) on January 11, 2019.

ARACHIDOMC

ACID

AND

PRUSTAGLANDINS:

LUNG

401

FUKTION

n=7

20

0 _--__-----_--__-_----_-_-_-__ A e40 fmmffg)

-20

---.mns

ns -__- -. - I

___--_- _-____ t ------------------

- 4O!

FIG. 4. Dose-response relationships fur arachidonic acid (AA) and prostaglandins DZ, F &, and E,. Changes in transpulmonary pressure swing (Ptp), mean pulmonary arterial pressure (Ppa> and mean aortic pressure (PAo) shown as changes from preinjection control

values. Control values (mean of all dogs in dose-response study, n = 10): Ptp = 5.4 5 &I, Ppa = 17.6 + 0.3, and PAU = 132 + 3. All changes (mean 2 SE) are significant (P < 0.05) unless labeled nonsignificant (ns).

less active in both airways and pulmonary vascular bed than was PGD,. Of the prostaglandins studied, the systemic vascular responses to AA were similar to those of PGE2, which also decreased PAO. Effects of indomethacin. The effects of indomethacin (2.5 mg/kg iv), a cycle-oxygenase inhibitor, on the airway and vascular responses were investigaled. Figure 5 summarizes data from several experiments, comparing responses in APtp, Ppa, and PAO to AA and prostaglandins Dz, Fz,, and E, before and 20 min after indomethacin infusion. While this synthesis blocker abolished responses to all doses of AA, the responses to prostaglandins were either unaffected or enhanced significantly, as in the case of Ppa for both PGDz and PGF,.. The increase in the systemic depressor effects of PGE, was not significant. Effects of vugotomy. To assess the importance of vagally mediated reflexes on the airway and vascular responses to AA, PGD2, and PGF,,, the effects of midrange doses of these agents were compared before and after bilateral cervical vagutomy in eight dogs. These results are summarized in Table 2. Vagotomy decreased control values of RL but had no effect on control Cdyn or Ppa. While the increases in RL in response to AA, PGDz, and PGF,, were still significant after vagotomy, the absolute increases were significantly less than those obtained in the animals with vagi intact. If viewed on

the basis of percent change in RL, however, the RL increases after vagotomy were similar to those obtained with the vagi intact. This difference between absolute and percent increases in RL is due to the reduction in control RL values caused by vagotomy. Vagotomy significantly attenuated the decrease in compliance (both absolute and percent decrease) seen after mid-range doses of PGD, and PGF,, but had no effect on the decrease in compliance following AA. Responses in the pulmonary artery were unaffected by sectioning of the vagi, except in the case of AA, where the pulmonary pressor response was significantly enhanced after vagotomy (Table 2). Pulmonary vascular congestion. A series of experiments was undertaken in eight dogs to evaluate the potential contribution of pulmonary vascular congestion to changes in airway mechanics produced by AA, PGDz, and PGF,, . In these experiments, the left lower lung lobe of the intact dog was ventilated separately from the remainder of the lung and was perfused at a constant rate. By inflating a balloon in the lobar vein draining the left lower lobe, lobar arterial pressure was passively elevated to levels similar to those resulting from bolus injections of AA, PGDz, and PGF,, into the perfusion circuit. The increases in translobar pressure (Ptl) swing resulting from injections of the active agents were then compared to those increases caused by

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.186.138.035) on January 11, 2019.

402

SPANNHAKE

I

Control

R Aher

Indomethacin

l

p

1

2o l5 10 5 0 -5

0 A PA* /hmHg~

AL.

co.05

I A PpA fmmffg/

ET

FIG. 5. Effects of indomethacin on the changes in transpulmonary pressure swing (Ptp), mean pulmonary arterial pressure @a>, and mean aortic pressure (PAo) in response to arachidonic acid and prostaglandins DY, Fti, and E,. Responses were obtained before and 30-60 min after slow infusion of indomethacin, 2.5 mg/kg iv. Numbers in parentheses indicate number of dogs studied.

=4 O

-ao-

1 -

(6)

TABLE 2. Effects of vagotomy on airway and pulmonary vascular responses to aruchidonic acid, PGD, and PGF,, in the intact artificially ventilated dog RL, cmH,O/(l/s)

n

Arachidonic acid, Vagi intact Vagi cut

6 mg

Ppa, Torr

l/cmH,O

Change*

Control

Control

Change*

2.99 2 0*37 1.83 2 0.14$

4.69 -+ LOW 3,44 k 0.61t$

0.038 + 0.002 0.039 k 0.003

-0.013 -0.014

5 0.002t k 0.002-t

14.9 f 0.7 14.4 k 1.0

15.9 k 2.3t 20.6 k 2.7t$

2.66 2 0,16 1.68 + 0.13$

1.99 k 0.39t 1.28 2 0.35-M

0.041 * 0.003 0.038 2 0.003

-0.012 -0.007

k 0.002t f o*oozt~

16.1 k 1.5 16aO k Ll

9.6 k 2.H 8.9 + 1.2t

2.62 2 0.26 1.68 2 0.13$

L79 -t- 0,4ot 1.01 t 0.39v$

0,041 -+- 0.003 0.039 -c 0.003

-0.009 -0.006

-t- 0.001t f 0.001-M

17.3 2 1.9 15.4 2 1.7

15.6 + 2.5t 13.3 5 1.9t

Change*

7

pm, 3 pg Vagi intact Vagi cut

8

PGF,,, Vagi Vagi

8

10 rug intact cut

Cdyn,

Control

Injections made as a bolus into the superior vena cava. All values lung resistance; Cdyn = dynamic compliance; Ppa = mean pressure decrease from control (preinjection) value. + Significantly different different (P < 0.05) from value with vagi intact, paired t-comparison.

congestion in the lobar vascular bed. Figure 6 shows the relationship between maximal changes in translobar and lobar arterial pressure induced by l-10 pg PGD, and by balloon inflation. Increasing lobar vascular pressure by inflating the balloon caused an immediate rise in peak Ptl throughout the range of vascular pressure studied. The relationship between vascular and translobar pressures was relatively flat, however, and increasingly larger elevations of vascular pressure within the lobe caused only small additional increases in Ptl swing (Fig. 6). The mean lobar arterial and corresponding Ptl increases for all balloon experiments were 96 -+ 8% and 12 -+ l%, respectively. Upon deflating the balloon, peak Ptl returned to the preinflation value. These airway responses to passively increased lobar vascular pressure were markedly different from those elicited by intralo-

are expressed as means in the pulmonary artery, (P < 0.05) from control

t SE; n. = number of animals per group. RL = * Change represents absolute increase or $ Significantly value, paired t-comparison.

bar injections of PGD2, AA, and PGF,,. Through the entire range of response to l-10 pg of PGD2, for any given rise in lobar arterial pressure the corresponding increase in Ptl swing produced by the prostaglandin was higher than that produced by balloon inflation (Fig. 6). Moreover, the airway and vascular responses in the lobe were highly proportional and dose dependent. This was also true for AA and PGF,, , The mean lobar arterial pressure and corresponding Ptl increases were, respectively: PGD2, 48 t 7% and 32 t 4%; AA, 57 t 7% and 50 + - 11%; PGF,,, 60 t 15% and 28 t 7%. DISCUSSION

Results of the present investigation show that the prostaglandin precursor, arachidonic acid, produced a sustained decrease in dynamic lung compliance and an

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.186.138.035) on January 11, 2019.

ARACHIDONIC

ACID

AND

PROSTAGLANDINS:

LUNG

FUNCTION

120 . PGD2 *

t

8o

1,

.

0

50

l

BALLOON

~=.649’.‘“”

L 4 a?

40

0 100

% A

150

200

250

PpLA

FIG. 6. Relationship between changes in translobar pressure (Ptl) and corresponding changes in pressure in the perfused lobar artery (Ppla). Comparison of changes induced by lobar arterial injection of l-10 r_Lg PGD, to those induced by mechanically increasing lobar pressures with a lobar venous balloon in eight dogs. m = Slope + standard error of estimate. Correlation coefficients were significant (P < 0.05): PGD2, 0,609; balloon, 0.772. *Significan tl y different from balloons P < 0.01.

initial transient increase in total lung resistance in the dog. The decrease in compliance corresponded closely in time with a rise in pulmonary arterial pressure, and these responses were followed by a delayed reduction in systemic arterial pressure. The increases in lung resistance and pulmonary arterial pressure and the reduction in compliance and systemic arterial pressure were attenuated after administration of indomethacin, a cyclooxygenase inhibitor, supporting the hypothesis that the precursor is transformed into active intermediates and/ or prostaglandins and thromboxanes. Moreover, linoleic acid, a nonsubstrate long chain fatty acid, had no significant cardiovascular or bronchopulmonary effects in the dog, suggesting that the effects of arachidonate were not related to a nonspecific action of the long chain fatty acid. The conversion of the substrate into vaso- and bronchoactive products in the lung was rapid since the time of onset of the pulmonary effects of the precursor and of PGD, or PGF,, was quite similar. Prostaglandins D, and Flzc,, when administered into the vena cava, also produced a rapid, sustained decrease in dynamic compliance of the lung and a less sustained increase in total lung resistance. The decrease in compliance corresponded closely in time and magnitude with the increase in pulmonary arterial pressure. It has been previously demonstrated that the primary prostaglandins increased pulmonary vascular resistance in the dog by constricting intrapulmonary veins and upstream segments (14). The present studies suggest that these agents constrict both pulmonary vascular and peripheral airway components simultaneously. The effects of PGD, and PGFI,, were not due to stimulation of prostaglandin synthesis, since their effects were not attenuated after indomethacin. Enhancement of vascular pressor responses by indomethacin has been reported previously (14) and may be due to decreased synthesis of a dilator prostaglandin or prostacyclin. The shift toward a more negative intrapleural pressure observed in response to arachidonic acid and PGD, is consistent with a decreased FRC in these animals. In the case of arachidonic acid, measurements of FRC showed that a small but statistically significant reduc-

403 tion did occur. Similar shifts in end-expiratory transpulmonary pressure after pulmonary arterial administration of histamine or acetylcholine have been reported to be associated with a decreased lung compliance and FRC in cats (5). Histological data suggested that FRC was reduced by constriction of smooth muscle in the peripheral airways (5). It has been reportedJ that intravenously administered acetylcholine and histamine decreased arterial O2 saturation in dogs while over-all ventilation and lung perfusion were kept constant (22). This effect was attributable to the ability of these bronchoconstrictor agents to alter ventilation-perfusion relationships. We have been unable to detect a similar decrease in arterial PO:! during the response to the highest doses of arachidonic acid or PGD2, suggesting that an inequality in the ventilation-perfusion relationship did not occur in the present studies. Pulmonary mechanics may be influenced by the presence of pulmonary vascular congestion in the dog (3,7). It has been demonstrated that acute vascular distention, in the absence of pulmonary edema, could decrease lung compliance. Since the prostaglandins increase small intrapulmonary vein pressure in the dog (14), which may produce congestion and decrease compliance, the effects of passively increasing vascular pressure in the lobe on translobar transpulmonary pressure were examined. Translobar pressure swing was consistently increased when vascular pressures were raised to levels similar to those seen after administration of prostaglandins. However, the increase in translobar pressure was far less than that seen in response to the prostaglandins. It was concluded that if the prostaglandins produced pulmonary vascular congestion in the present experiments, its contribution to the decreased compliance would be small when compared to the direct smooth muscle effects of these autacoids. Arachidonic acid, PGDz, and PGFz,, in the range of doses studied, increased lung resistance by 20-300%. The effects on resistance were shorter in duration and more variable than were those on compliance, suggesting that the mechanisms involved with the changes in lung resistance and those involved with the responses in the peripheral airways may be different. Base-line lung resistance was reduced by vagal section, an observation consistent with the presence of vagal tone in the resistance airways. It is not clear, however, to what extent vagal reflexes played a part in the resistance changes seen after administration of arachidonic acid and the prostaglandins. While the magnitude of the increase caused by each agent was attenuated by vagotomy, the percent increase in resistance was not attenuated. Nevertheless, the existence of prostaglandin-induced vagal reflexes cannot be ruled out. Such reflexes could be initiated by activation of rapidly adapting stretch (“irritant”) receptors of the type proposed to be involved in the ventilatory responses to histamine (2). Both irritant receptors and afferent C fibers of the canine lung have been reported to be responsive to stimulation by PGF2, and PGE, (6). Reported patterns of rapid shallow breathing in dogs after intravenous administration of PGF,, (30) are also consistent with the presence of reflex prostaglandin effects.

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.186.138.035) on January 11, 2019.

404

Vagotomy attenuated the decrease in lung compliance in response to PGD, and PGF&, suggesting that -the vagally mediated component of the response to exogenous prostaglandins produced constriction of airways peripheral enough to affect compliance of the lung. Roentgenographic studies by Nadel et al. (20) demonstrated that maximum airway narrowing in response to vagal stimulation in dogs occurred in ai.rways of 1-5 mm diameter. Constriction of airways at this level would be expected to decrease dynamic lung compliance. The present data are consistent with the reported attenuation by atropine of changes in both lung resistance and dynamic compliance in response to PGF2, (30). In contrast to the results with PGD, and PGF2,, the decrease in compliance seen after arachidonic acid administration was not significantly affected by vagotomy. The explanation for this difference is not clear. However, this observation may reflect subtle differences in the modes of action of exogenously administered, as opposed to endogenously formed, prostaglandins. Changes in resistance and compliance in response to the prostaglandins were only partially attenuated by vagotomy, suggesting local effects of these autacoids. Although changes in pulmonary mechanics could be brought about by accumulation of mucus in the airways, no evidence for this was found at autopsy. Furthermore, the observation that the changes in- resistance and compliance were reversed in time or by hyperinflation provides additional support for an effect on smooth muscle. Changes in resistance may have been secondary to the decreased FRC produced by the action of the prostaglandins on the peripheral airways. However, specific conductance decreased in our studies, indicating the increased resistance was not due to decreased FRC alone. Changes in resistance due to direct local stimulation would probably be associated with constriction of central conducting airways (18); however, extensive narrowing of more peripheral airways might also have contributed significantly to the increase in total lung resistance. A previous study by Wicks et al. (33) did not demonstrate an effect of arachidonic acid on airway inflation pressure in open-chest dogs. In their preparation, the precursor fatty acid was administered by injection to a single lung lobe. Airway effects in this lobe were probably not large enough to significantly alter measurements of total airway inflation pressure in their studies, and isolation of lobar venous blood prevented return of the arachidonic acid to the lung from the periphery. Although PGD, and PGF, were equally active as pressor agents in the pulmonary vascular bed, PGD, possessedmore than three times the activity of PGF2, in the airways under conditions of controlled ventilation. PGD, has previously been reported to be four to six times more active than PGF, in spontaneously breathing dogs (31) and guinea pigs (11, 12). While PGD, has been demonstrated to be synthesized in a variety of tissues in vitro (24) and to possessantiaggregatory (23) and local inflammatory (10) activity in vivo,

SPANNHAKE

ET

AL.

a role for this prostaglandin in normal lung function has not yet been established. The potent pulmonary vascular and ail-way effects of PGD, may suggest contraindications in potential therapeutic use of this prostaglandin as an antithrombotic agent (23). The bronchopulmonary effects of arachidonic acid are probably not due to synthesis of PGE2, since this primary prostaglandin had minimal activity in the airways. The systemic effects observed after arachidonic acid were similar to those produced by PGE, and suggest that they may have been due to conversion of arachidonic acid to this prostaglandin or to the newly discovered autacoid, prostacyclin (PGI,). It seems unlikely that the changes in lung function observed in response to arachidonic acid were due to platelet aggregation. While this precursor has been shown to produce thrombocytopenia in several species (26, 27), it has been reported to be a poor aggregator of dog platelets (4). Furthermore, in the canine pulmonary vascular bed (13), and isolated hind limb (S), the pressor response to arachidonate was not diminished when platelet-free perfusate was substituted for blood. Finally, the effects of PGD2, which inhibits platelet aggregation (23), were similar to those of arachidonic acid in the airways and the pulmonary vascular bed. These results suggest that the pulmonary effects of arachidonic acid are not dependent upon platelet aggregation in the dog. The effects of arachidonic acid may be due in part to the conversion of the precursor to thromboxanes in the lung. In this regard, Wasserman and Griffin (32) reported that thromboxane B, had about 30% of the activity of PGF, on pulmonary mechanics in spontaneously breathing dogs; however, the effects of thromboxane A, on pulmonary mechanics are uncertain, Imidazole, an inhibitor of thromboxane synthesis in vitro (21), did not diminish the effects of arachidonic acid in experiments in three dogs when given in doses ranging from 25 to 25 mg/kg iv. The results of the current studies demonstrate that arachidonic acid may markedly alter both pulmonary mechanics and vascular resistance due to conversion of the precursor to vasoactive products within the lung. The alterations in lung mechanics, as well as those in the pulmonary circulation, appear to be associated principally with constriction of smooth muscle in the walls of vessels and peripheral airways. These findings are consistent with the hypothesis that arachidonic acid, released locally from cell membranes in response to various stimuli, could influence the distribution of perfusion and ventilation to specific areas of the lung. The present investigation further supports the proposal that locally synthesized prostaglandins may function as potent physiologicsl modulators in situations where free precursor levels increase in the lung. The authors acknowledge the excellent technical assistance of Mr. Michael W. Skinner. We wish to thank the Upjohn Company for the prostaglandins and Merck for the indomethacin used in this study. We also thank Ms. Elizabeth C. Thomason for her valuable aid in preparing the manuscript. This investigation was supported by National Institutes of Health

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.186.138.035) on January 11, 2019.

ARACHIDONIC

ACID

AND

PROSTAGLANDINS:

Grants HLB-15580, 11802, 18070 and grants Heart Association, Louisiana Heart Association, tic Fibrosis Foundation. E. W. Spannhake was awarded National

LUNG

405

FUNCTION

from the American and National Cys-

Postdoctoral Investigator

Institutes

Received

of Health

Fellowship HL-05455. of the American Heart for publication

27 June

P. J, Kadowitz Association.

is an Established

1977.

REFERENCES 1 w ANGG~RD, E . , AND B. SAMUELSSON. Biosynthesis of prostaglandins from arachidonic acid in guinea pig lung. J. Biol. Chem. 240: 3518-3521, 1965a 2. BLEECKER, E. R., D. J. COTTON, S. P. FISCHER, P. D. GRAF, W. M. GOLD, AND J. A. NADEL. The mechanism of rapid, shallow breathing after inhaling histamine aerosol in exercising dogs. Am. Rev. Respirat. Diseases 114: 909-916, 1976. 3. BORST, H. G., E. BERGLUND, J. L. WHITTENBERGER, M. MEAD, M. MCGREGOR, AND C COLLIER. The effect of pulmonary vascular pressures on the mechanical properties of the lungs of anesthetized dogs. J. CZin.. invest. 36: 1708-1714, 1957. 4. CHIGNARD, M., AND B. B. VARGAETIG. Dog platelets fail to aggregate when they form aggregating substances upon stimulation with arachidonic acid. European J. PharmacoZ. 38: 7-18, 1976. 5. COLEBATCH, H. J. H., C. R, OLSEN, AND J. A. NADEL. Effect of histamine, serotonin and acetylcholine on the peripheral airways. J. Appl. Physiol. 21: 217-226, 1966. 6. COLERIDGE, H. M., J, C. G. COLERIDGE, K. H. GINZEL, D + G. BAKER, R, I3. BANZETT, AND M. A. MORRISON. Stimulation of “irritant” receptors and afferent C-fibres in the lung by prostaglandins. Nature 264: 451-453, 1976, 7. COOK, C. D., J. MEAD, G. L. SCHREINER, N. R. FRANK, AND J. Ma CRAIG. Pulmonary mechanics during induced pulmonary edema in anesthetized dogs. J. Appl. Physiol. 14: 177-186, 1959. 8. FITZPATRICK, T. M., M, JOHNSON, P. A. KOT, P. W. RAMWELL, AND J. C, ROSE. Vasoconstrictor response to arachidonic acid in the isolated hind limb of the dog. Brit. J. Pharmacol. 59: 269273, 1977. 9. FLOWER, R. J., AND G. J. BLACKWELL. The importance of phospholipase-A2 in prostaglandin biosynthesis. B&hem. Pharmacol. 25: 285-291, 1976. 10. FLOWER, R. J., E. A. HARVEY, AND W. P. KINGSTON. Inflammatory effects of prostaglandin D, in rat and human skin. Bait. J. Pharmacol. 56: 229-233, 1976. 11. HAMBERG, M., P. HEDQVTST, K. STRANDBERG, J. SVENSSON, AND B. SAMUELSSON. Prostaglandin endoperoxides, IV. Effects on smooth muscle. Life Sci. 16: 451-462, 1975. 12. HEDQVIST, P., M. STRANDBERG, AND B. SAMUELSSON. Some actions of prostaglandin endoperoxides on airway and vascular smooth muscle (Abstract). Stand. J. Respirat. Diseases 88, Suppl.: 53, 1974. 13. ‘HYMAN, A. L., A. A. MATHE, E. W, SPANNHAKE, AND P, J. KADOWTIZ. Influence of arachidonic acid on the canine pulmonary vascular bed (Abstract). Pharmacologist 18: 224, 1976. 14. KADOWITZ, P. J., B, D. CHAPNICK, P. D. JOINER, AND A. L. HYMAN. Influence of inhibitors of prustaglandin synthesis on the canine pulmonary vascular bed. Am. J. Physiol. 229: 941946, 1975. 15. KADOWITZ, P, J,, P. D. JOINER, AND A. L. HYMAN. Physiological and pharmacological roles of prostaglandins. Ann. Rev. Pharmacol. 15: 203-306, 1975. 16. KADOWITZ, P, J., E, W. SPANNHAKE, S. GREENBERG, L P. FEIGEN, AND A. L. HYMAN. Comparative effects of arachidonic acid, bisenoic prostaglandins and an endoperoxide analog on the canine pulmonary vascular bed. Can. J. Physiol. Pharmuc&

In press. 17. KADOWITZ, P. J., E. WM. SPANNHAKE, D. S. KNIGHT, AND A. L. HYMAN. Vaso-active hormones in the pulmonary vascular bed. Chest 71, Suppl.: 257-261, 1977. 18. MACKLEM, P. T., AND J. MEAD. Resistance of central and peripheral airways measured by a retrograde catheter. J. Appl. Physiol. 22: 395-401, 1967. 19, MEAD, J., AND J. L. WHITTENBERGER. Physical properties of human lungs measured during spontaneous respiration. J. AppZ. Physiol. 5: 779-796, 1953. 20. NADEE, J. A., G. A. CABEZAS, AND 5. H. M. AUSTIN. In vivo roentgenographic examination of parasympathetic innervation of small airways. Use of powdered tantalum and a fmal focal spot X-ray tube. Invest. Radial. 6: 9-17, 1971. 21. NEEDLEMAN, P., A. RAZ, J. A. FERRENDELL~, A~JD M. MINKES. Application of imidazole as a selective inhibitor of thromboxane synthetase in human platelets. Proc. NatZ. Acad. Sci., US 74: 1716-1720,1977. 22. NIDEN, A. H., B. BURROWS, AND W. R. BARCLAY. Effects of drugs on the pulmonary circulation and ventilation as reflected by changes in the arterial oxygen saturation. Circukation Res. 8: 509-518, 1960. 23. NISHIZAWA, E. E., W. L. MILLER, R. R. GORMAN, G. L. BUNDY, J. SVENSSON, AND M. HAMBESG, Prustaglandin Dz as a potential antithrombotic agent. Prostuglandins 9: 109-121, 1975. 24. NUGTEREN, D I H., AND E. HAZELHOF. Isolation and properties of intermediates in prostaglandin biosynthesis. Biochim, Biophys. Acta 326: 448-461, 1973. 25. PACE-ASCIAK, C. R, Oxidative biotransformations of arachidonic acid. Prostaglandins 5: 811-817, 1977. 26. ROSE, J. C., M. JOHNSON, P. W. RAMWELL, AND P. A. KOT. Effects of arachidonic acid on systemic arterial pressure, myocardial contractility, and platelets in the dog. Proc. Sot. ExptZ, BioZ. Med. 147: 652-655, 1974. 27. SILVER, M. J., J. B. SMITH, C. INGERMAN, AND J. J. Kocsrs. Arachidonic acid-induced human platelet aggregation and prostaglandin formation. ProstagZandins 4: 863-875, 1973. 28. SMITH, A. P. Prostaglandins in the respiratory system. In: Prostaglandins: Physiological Pharmacological and PathologicaL Aspects, edited by S. S. M. Karim. Baltimore, Md.: University Park Press, 1976, p. 83-102. 29. SNEDECOR, G. E. Statistical Methods (5th ed.). Ames, Iowa: Iowa State College Press, 1956. 30. WASSERMAN, M. A. Bronchopulmonary pharmacology of some prostaglandin endoperoxide analogs in the dog. European J. Pharmacol. 36: x03-114, 1976. 31. WASSERMAN, M. A., D. W. DUCHARME, R. L. GRIFFIN, G. L. DEGRAAF, AND F. G. ROBINSON. Bronchopulmonary and cardiovascular effects of prostaglandin D, in the dog. ProstagZandins 13: 255-269, 1977. 32. WASSERMAN, M. A., AND R. L, GRIFFIN. Comparatively weak effects of thromboxane B, on pulmonary mechanics (Abstract). Pharmacokgist 18: 224, 1976. 33. WICKS, T. C., J. C. ROSE, M. JOHNSON, P. W. RAMWELL, AND P. A. KOT. Vascular responses to arachidonic acid in the perfused canine lung. Circulation Res. 38: 167-171, 1976.

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (129.186.138.035) on January 11, 2019.