Terbutaline-induced desensitization

Potential age-related differences in cardiovascular responsiveness and receptor regulation induced by short-term administration of a selective P2-adrenergic receptor agonist were investigated. Young (age range, 23 to 31 years) and elderly (age range, 64 to 73 years) healthy subjects were treated with terbutaline (5 mg, three times daily) for 5 days. Similar plasma terbutaline concentrations were achieved in the two age groups. The elderly group had higher baseline plasma norepinephrine concentrations and mean arterial pressures, neither of which were altered by terbutaline administration. During terbutaline treatment, heart rate increased in both age groups while subjects were supine but consistently increased only in the young group while subjects were standing. In both age groups, the density of P2-adrenergic receptors on polymorphonuclear leukocyte membranes was reduced by 50% during terbutaline administration and returned to baseline values at similar rates after drug administration was stopped. Isoproterenol-stimulated cyclic adenosine monophosphate accumulation in polymorphonuclear leukocytes from elderly subjects was regulated similarly. These findings suggest that the ability of terbutaline to increase standing heart rate is selectively impaired in the elderly, whereas the ability of polyrnorphonuclear leukocyte P,-adrenergic receptors to down-regulate and to return to baseline values is not. (CLIN PHARMACOLTHER1992;51:432-9.)

Nancy R. Zahniser, PhD, Anne Wiser, MS, Wayne A. Cass, PhD, Pam Curella, BS, John G. Gerber, MD, and Alan S. Nies, MD Denver, Colo. Prolonged exposure to P-adrenergic receptor agonists produces a long-lasting desensitization that is attributable to down-regulation, or loss, of P-adrenergic receptors.'22 Little is known about how aging affects P-adrenergic receptor agonist-induced desensitization in humans. By contrast, the occurrence of this compensatory mechanism has been well established in relatively young subjects (age range, 19 to 43 years). The first study to show that short-term administration of the agonist terbutaline to young humans diminishes radioligand binding to P-adrenergic receptors used From the Department of Pharmacology, Neuroscience Program, and Department of Medicine, Division of Clinical Pharmacology, University of Colorado Health Sciences Center. Supported by grants AGO4418 and RR00051 from the U.S. Public Health Service, Bethesda, Md. Received for publication July 16, 1991; accepted Nov. 5, 1991. Reprint requests: Nancy R. Zahniser, PhD, Department of Pharmacology, C-236, University of Colorado Health Sciences Center, 4200 E. Ninth Ave., Denver, CO 80262. 1311134797

polymorphonuclear leukocytes (PMNLs) for the receptor measurement^.^ Subsequently, it was shown that administration of terbutaline (5 mg, three times daily) for 1 week rapidly down-regulates the density of P-adrenergic receptors on PMNL membranes and that the receptors return to baseline densities 6 to 7 days after termination of drug admini~tration.~ For most studies of P-adrenergic receptor regulation in young humans, circulating mononuclear leukocytes (MNLs), primarily lymphocytes, have been used. Terbutaline administration also down-regulates MNL P-adrenergic receptors and diminishes MNL P-adrenergic receptor-stimulated cyclic adenosine However, monophosphate (CAMP) accumu~ation.~-~ MNL preparations are composed of several subpopulations that differ in P-adrenergic receptor density, and the extent of agonist-induced desensitization differs depending on the MNL subset m ~ n i t o r e d This .~ could complicate interpretation of the data unless MNL subsets are studied separately. The only study to investigate desensitization of P-adrenergic receptors as

VOLUME 5 1 NUMBER 4

a function of subject age used a 2-hour in vitro exposure of isolated lymphocytes to a maximally effective concentration of i s ~ ~ r o t e r e n oThat l . ~ study found that subsequent stimulation of cAMP accumulation by isoproterenol was reduced to the same extent in young and elderly subjects; however, long-term regulation of P-adrenergic receptors in response to agonist treatment was not investigated. Interestingly, findings from experiments in which animals were treated with drugs suggest that downregulation or restoration of P-adrenergic receptors is impaired with aging. P-Adrenergic receptors in cerebral cortex and pineal gland down-regulate equally well in young and aged rats, but the recovery of receptors to their normal complement is considerably slower in aged rats.9 Regeneration of P-adrenergic receptors after irreversible receptor blockade is also delayed in heart and lung of aged rats.'' In response to repeated stress, sequestration and down-regulation of P-adrenergic receptors on MNLs from aged rats is impaired. ' The goals of this study were to investigate potential age-related differences in agonist-induced cardiovascular responsiveness and regulation of P-adrenergic receptors in humans. PMNLs were used as the source of receptors. PMNLs represent a largely homogeneous cell population, which is composed primarily of neutrophils, and possess only the P2-adrenergic receptor subtype.12 By contrast with MNLs, PMNLs show no age-related differences in baseline density of P-adrenergic receptors.13.14 Terbutaline was the agonist used because it is selective for P2-adrenergic receptors, has previously been shown to cause receptor desensitization, is used clinically as a bronchodilator, and has limited central nervous system side effects. It is unlikely that changes in PMNL P2-adrenergic receptors induced by terbutaline will reflect changes in the predominant population of (3,-adrenergic receptors in the heart; however, they may reflect changes in P2-adrenergic receptors present in right atrium, saphenous vein, and lung. l 5

'

METHODS Experimental protocol and hemodynamic measurements. Eight young subjects ranging in age from 23 to 31 years (mean age, 27; four men and four women) and seven elderly subjects ranging in age from 64 to 73 years (mean age, 69; three men and four women) participated in this study at the University of Colorado Clinical Research Center (Denver, Colo.). This study was reviewed and approved by the Human Subjects Committee, University of Colorado

&-Receptors in young and elderly subjects 433 School of Medicine. Each volunteer gave written informed consent, had a medical history taken, and was given a physical examination. All were in good health, and none was taking any medications. On day 1, after an overnight fast, an intravenous cannula was placed in each of the volunteers, who rested supine for 45 minutes. Baseline arterial pressure was measured in triplicate, heart rate was determined, and a 50 ml blood sample was drawn. After 5 minutes of standing, arterial pressure and heart rate were again measured. The arithmetic mean of the three systolic and diastolic pressure measurements was used for data analysis. The mean arterial pressure (MAP) was calculated as the diastolic pressure plus one third of the difference between the systolic and diastolic pressures (pulse pressure). After the baseline measurements, the subjects took their first 5 mg dose of terbutaline sulfate (Brethine, Geigy Pharmaceuticals, Ardsley, N.Y.). The subjects continued to self-administer the standard therapeutic dose of terbutaline sulfate (5 mg every 8 hours) for the next 5 days. On days 3, 5, 7, 9, and 11, the subjects returned to the Clinical Research Center after an overnight fast and just before the next scheduled dose of terbutaline; and the hemodynamic parameters were measured and blood samples were drawn as on day 1. Plasma terbutaline and norepinephrine concentrations. Concentrations of terbutaline were determined in plasma samples by high performance liquid chromatography coupled with electrochemical detection. l 6 Concentrations of norepinephrine were determined in plasma samples by radioenzymatic assay. " PMNL isolation, P-adrenergic receptor assay and cAMP assay. PMNLs were isolated by use of a two-phase discontinuous (42%/51%) plasma Percoll (Pharmacia AB, Uppsala, Sweden) gradient, and P-adrenergic receptors were assayed as described prev i ~ u s l y . The ' ~ washed cells were counted by use of a hemocytometer; three fourths were used for the receptor binding assays and one fourth were used for the cAMP assays. The receptor affinity and density were measured by generating saturation curves with 1251-iodopindolol (nine final concentrations ranging from 7 to 700 pmol/L) in PMNL membranes and by use of the curve-fitting program Ligand to estimate the nonspecific binding and to determine the binding parameters.18 Binding assays contained approximately 20 to 50 k g protein from 1 to 4 million cells. Membrane protein concentrations were measured with the spectrophotometric dye-binding assay of Bradford.19 Concentrations of cAMP were determined in freshly isolated PMNLs. Assay conditions were those of

CLIN PHARMACOL THER APRIL 1992

434 Zahniser et al.

TIME (days)

Fig. 1. Similar plasma terbutaline concentrations in young

and elderly subjects. The 5 days of terbutaline treatment (5 mg, t.i.d.) commenced after the blood samples were drawn on day 1. Mean values + SEM are shown for young subjects (n = 8) and elderly subjects ( n = 7).

RESULTS Plasma terbutaline concentrations. Similar plasma

a-• YOUNG

50 0

1 -

TERBUTALINE

.

0

2

.

'

.

4

-

- A ELDERLY

A-

'

.

6

.

8

'

10

50 mmol/L sodium acetate buffer (pH 4.0) and 0.2 mmol/L isobutylmethylxanthine, and denaturation by boiling for 3 to 5 minutes. The samples were stored at -70" C until CAMP was measured by radioimmunoassay (Biomedical Technologies, Stoughton, Mass.) Statistics. For single analysis between two means, the two-way unpaired Student t test was used. Analysis of variance (ANOVA) with repeated measures was used to assess statistical significance in all other cases. Age of the subjects was a between-groups variable. Depending on the parameter measured, days, differences in position (supine or standing), and differences in arterial pressure (diastolic or systolic) were repeated groups variables. Significant interactions were further analyzed with ANOVA after they were collapsed across the nonsignificant variables. Significant main effects of age were further analyzed with the Tukey test to compare data points between the two age groups. Significant main effects of time were further analyzed with the Dunnett multiple comparison test to compare data from day 1 (baseline) with the data on the remaining days.

.

12

TIME (days)

Fig. 2. No effect of terbutaline treatment on plasma norepi-

nephrine concentrations in either age group. The treatment protocol was the same as that described in the legend to Fig. 1. With the exception of day 11, the elderly subjects had significantly higher plasma norepinephrine concentrations. Mean values ? SEM are shown for young subjects (n = 8) and elderly subjects (n = 7). A two-factor ANOVA revealed only a significant effect of age (F,,,, = 10.51, p < 0.01). + p < 0.05 differences between the two age groups, Tukey test. Szefler et a1.20 PMNLs (60 p g protein or 4.5 million cells per assay) were preincubated for 10 minutes at 37" C in Krebs-Ringer phosphate buffer (pH 7.2) containing 0.1 mmol/L Ro20-1724 (gift of Hoffman-La Roche Co., Nutley, N.J.), 0.1 mmol/L isobutylmethylxanthine, superoxide dismutase (20 pglml) and catalase (20 pglml). Next, the cells were incubated either in the absence or presence of 100 pmol/L 1-isoproterenol for an additional 10 minutes. The reaction was terminated by centrifugation at 10,000g for 20 seconds, aspiration of the supernatant, resuspension of the pellet in

terbutaline concentrations were achieved in the two age groups (Fig. 1). The mean plasma concentration of the drug was 25 nmol/L. One day after drug treatment was terminated, 14 of 15 subjects had low but detectable concentrations of drug still present. However, 2 days later only one elderly subject still had a measurable terbutaline concentration. Plasma norepinephrine concentrations. Plasma concentrations of norepinephrine were significantly higher on day 1 (baseline) in the elderly group and, with the exception of the last day, remained elevated throughout the course of this experiment (Fig. 2). Terbutaline treatment had no effect on this parameter in either age group. When collapsed across days, the mean plasma concentration of norepinephrine in the young was 170 ng/L, and the concentration in the elderly was 60% higher. Hemodynamic measurements. Baseline blood pressure was also higher in the elderly group. While subjects were supine, baseline systolic pressure was 13% higher and diastolic pressure was 17% higher in the older age group (Fig. 3, A). This age-related difference is evident in the MAP (Fig. 3, B). While subjects were standing, only baseline systolic pressure was significantly higher (19%) in the elderly (data not shown). Terbutaline treatment had no effect on blood pressure in either age group whether the blood pressure was measured when the subjects were supine or

VOLUME 51 NUMBER 4

&-Receptors in young and elderly subjects 435

O0

1

+

+

DIASTOLIC

+

Li

5:0 d

*-•

-

20 0

TERBUTALINE

-

A-

8

6

-A

YOUNG ELDERLY

10

12

TIME (days) 160

*-•

0

-

TERBUTALINE

-

A-

-A

SUPINE

STANDING

YOUNG ELDERLY

Fig. 3. No effect of terbutaline treatment on blood pressure in either age group. The treatment protocol was the same as that described in the legend to Fig. 1 . The systolic and diastolic pressures for both age groups while subjects were in the supine position are shown in panel A. The

mean arterial pressure (MAP) calculated from these data are shown in panel B. The pulse pressures, derived from the data collapsed across all of the days while the subjects were either supine or standing, are shown in panel C. Y, Young (hatched bars); E, elderly (open bars). These data showed that the elevated blood pressure of the elderly group was largely attributable to higher systolic pressure and that blood pressure was higher whether the elderly subjects were supine or standing. Mean values ? SEM are shown for young subjects ( n = 8) and elderly subjects ( n = 7). For the data shown in panel A, a three-way ANOVA revealed only significant main effects of arterial pressure (F,,,, = 684, p < 0.001) and age (F,,,, = 6.60, p < 0.05). For the data in panel B, a two-way ANOVA revealed only a significant effect of age (F,,,, = 7.67, p < 0.05). +p < 0.05 differences between the two age groups, Tukey test (panels A and B) or t test (panel C). standing (Figs. 3, A and B , and data not shown). Because there was no effect of the drug treatment, the data were collapsed across days to evaluate the effect of the subject being supine versus standing on pulse pressure (Fig. 3, C). The systolic and diastolic pressures were approximately 15 and 8 mm Hg higher, respectively, in the elderly group throughout the experiment; however, statistical analyses revealed that while the subjects were supine, both the systolic and diastolic pressures were significantly higher but while the subjects were standing, only the systolic pressure was significantly higher (Fig. 3, C). By contrast with baseline blood pressures, baseline

heart rates in the two age groups were similar (Fig. 4). This was true whether the pulse was measured while the subjects were supine or standing. Hzart rate was approximately 12 beatslmin higher in both groups while standing. When subjects were taking terbutaline, heart rates were elevated by 26% in both groups while the subjects were supine (Fig. 4, A). While subjects were standing, heart rate in the young group was significantly increased during terbutaline treatment; and this increase persisted for 1 day after treatment was terminated (Fig. 4, B). Thereafter, heart rate returned to baseline levels. By contrast, while subjects were standing, heart rate in the elderly group was ele-

CLIN PHARMACOL THER APRIL 1992

436 Zahniser et al.

-$ +

80 -

Pa

1

YOUNG

0-0 A-

-

A

ELDERLY

F

> A-

-

VI J

3

0

a

0

A

TERBUTALINE

2

-

A

X

ELDERLY

-

m

20

8

10

A-

-

TERBUTALINE

5 a

01 0

2

6

4

-

TERBUTALINE

-

YOUNG

- A ELDERLY

6

2

4

6

8

10

12

TlME (days)

0-0

VI

0

12

TlME (days)

W

-

0

6

4

40

8

10

I 12

TIME (days)

Fig. 4. Effect of terbutaline treatment on heart rate in young and elderly subjects while subjects were supine (A) or standing (B). The treatment protocol was the same as that described in the legend to Fig. 1. The increase in heart rate during terbutaline treatment was similar in both age groups when measured while the subjects were supine; however, the increase was more persistent in the young group when measured while the subjects were standing. Mean values SEM are shown for young subjects (n = 8) and elderly subjects (n = 7 ) . A three-factor ANOVA revealed significant interactions of position times age (F,.,, = 20.02, p < 0.001) and position times days (F,,,, = 2.68, p < 0.05) and significant main effects of position (F,,,, = 207, p < 0.001) anddays (F = 5,651 = 2 1 . 3 2 , ~< 0.001). *p < 0.05 compared with their respective baseline value on day 1, Dunnett test.

*

,,,,

vated only on the second day of terbutaline administration and returned to baseline values throughout the remainder of the experiment (Fig. 4, B ) . P-Adrenergic receptors. On PMNL membranes isolated from both age groups, the baseline affinity of the P-adrenergic receptor for '25~-iodopindololwas approximately 35 pmol/L. Terbutaline administration did not affect this parameter (range for young, 28 to 34 pmol/L; range for elderly, 26 to 30 pmol/L). In agreement with our previous o b ~ e r v a t i o n s , ' ~ there .'~ were no differences in the baseline density of P-adrenergic receptors on PMNL membranes from young and

Fig. 5. Similar down-regulation and recovery of polymorphonuclear leukocyte (PMNL) P-adrenergic receptor density in young and elderly subjects in response to terbutaline. The treatment protocol was the same as that described in the legend to Fig. 1 . Values for the density of receptors (B,,,) were determined from 1251-iodopindololsaturation binding curves. Mean values 2 SEM are shown for young subjects (n = 8) and elderly subjects (n = 7 ) . A two-factor ANOVA revealed only a significant effect of days in both age groups (F = 16.27 (young) and F,,,, = 6.08 (elderly), p < 0.001). *p < 0.05 compared with their respective baseline value on day 1, Dunnett test.

,,,,

elderly subjects (Fig. 5). Initially, the density of receptors was approximately 70 fmollmg protein or 800 siteskell. By day 3 of the terbutaline treatment, the density of receptors was reduced by 50% in both age groups. After termination of drug treatment, the receptor density remained significantly reduced for 3 days but returned to the baseline density in both the young and elderly groups by day 1 1 (Fig. 5). Neither basal cAMP concentrations nor the ability of a maximally active concentration of isoproterenol (100 p.mol/L) to stimulate cAMP accumulation differed in PMNLs isolated from young or elderly subjects on day 1 (Fig. 6). Basal cAMP concentrations remained constant throughout the experiment (data not shown). By contrast, isoproterenol-stimulated cAMP accumulation was reduced by 70% in the elderly group by the second day of terbutaline treatment and remained depressed for at least 1 day after the drug treatment was terminated (Fig. 6). Isoproterenolstimulated cAMP accumulation was also reduced by 50% in the young group at the same time points; however, this decrease was not statistically significant (Fig. 6). Individual variability. There were no differences observed in any of the responses measured between the groups of male and female subjects. Only one subject differed markedly in several parameters. This elderly male subject had consistently higher (approxi-

VOLUME 51 NUMBER 4

mately double) plasma norepinephrine concentrations throughout the experiment compared with other elderly subjects. His MAP (both supine and standing) averaged over the course of the experiment was the highest, whereas his heart rate (both supine and standing) was the second or third lowest when compared with all other subjects. Also, this subject's density of PMNL P-adrenergic receptors was one of the highest of any of the subjects throughout the experiment, but more remarkable was the observation that his were the only receptors that did not down-regulate in response to the terbutaline treatment. Also, no desensitization of the isoproterenol-stimulated cAMP response was observed in this subject's PMNLs. Nonetheless, the data from this subject was included in this study because his plasma terbutaline concentrations were similar to the those of the other subjects. The fact that a high density of receptors was present despite the high circulating concentrations of norepinephrine and that these receptors were not susceptible to regulation by agonist suggests that the receptors of this subject were already maximally regulated.

DISCUSSION Two of the baseline parameters measured in this study differed between the two age groups. The elderly group had higher plasma norepinephrine concentrations and mean arterial pressures. These age-related differences have been commonly reported in the literature. However, this is the first study to show that neither of these parameters was altered by terbutaline administration. By contrast, no baseline differences between the two age groups were observed in heart rate, density of P-adrenergic receptors on PMNL membranes, and isoproterenol-stimulated cAMP accumulation in PMNLs. All three of these parameters were affected by terbutaline administration; however, only heart rate showed a differential change in the two age groups. During terbutaline treatment, heart rate increased in both age groups while subjects were supine but consistently increased only in the young group while subjects were standing. Our findings suggest that the ability of terbutaline to increase the standing heart rate is selectively impaired in the elderly, whereas the regulation of PMNL P2-adrenergic receptor density and responsiveness is not. Also, plasma terbutaline concentrations at steady state do not differ as a function of age. Hemodynamic changes. Terbutaline is classified as a selective 6,-adrenergic receptor agonist21'22;therefore, one might have predicted that blood pressure rather than heart rate would be affected by terbutaline treatment. A significantly greater decrease in blood pressure in elderly female subjects is observed after a

&-Receptors in young and elderly subjects 437

O

-

0

.

' 2

0-0

YOUNG

A-A

ELDERLY

.

' 4

.

' 6

8

10

12

TIME (days)

Fig. 6 . Effect of terbutaline treatment on isoproterenol-

stimulated cyclic adenosine monophosphate (CAMP) accumulation in PMNLs from young and elderly subjects. The treatment protocol was the same as that described in the legend to in Fig. 1. Accumulation induced by isoproterenol (100 pmolIL) is expressed as a percent increase above the basal cAMP level. Basal concentrations were 43.8 ? 6.8 and 56.3 9.0 pmollmg protein in the young and elderly groups, respectively, and were unaffected by the terbutaline treatment. Accumulation was significantly reduced in response to terbutaline treatment only in the elderly group. Mean values +- SEM are shown for young subjects (n = 8) and elderly subjects (n = 7). A two-factor ANOVA revealed only a significant effect of time in the elderly group (F,,,, = 2.64, p < 0.05). *p < 0.05 only for the elderly group compared with their baseline value on day 1, Dunnett test.

*

single dose of t e r b ~ t a l i n e .However, ~~ increases in myocardial oxygen consumption (heart rate-systolic blood pressure product) are produced by short-term terbutaline treatment.5 It has been well established that the elderly have a blunted heart rate response to P,-adrenergic receptor stimulation produced by intravenous i ~ o ~ r o t e r e n o lSome, . ~ ~ . ~but ~ not all, investigators have found an age-related reduction in P2-adrenergic receptor- mediated v a s o d i ~ a t i o n . ~ ~ ~ ~ ~ ~ The stimulation of heart rate observed here could be either direct by way of activation of P,- or P2-adrenergic receptors in the right atrium or indirect by way of reflex compensation after vasodilation. In favor of direct stimulation is the fact that no increase in plasma norepinephrine concentrations was observed at the time that the heart rates were stimulated above baseline values. P2-Adrenergic receptors are present in the right atrium but are not thought to control heart rate under normal conditions.15 In vitro binding studies show that terbutaline is only approximately twofold selective for p2- versus P, -adrenergic receptors. 3 1 Terbutaline appears more selective in vivo but can still produce some cardiac Reflex stimulation plays a role in determining heart rate while sub-

CLIN PHARMACOL THER APRIL 1992

438 Zahnzser et al. jects are standing but not while subjects are supine. The fact that there was a differential effect of terbutaline on heart rate in the two age groups while subjects were standing but not while subjects were supine suggests that this PI-adrenergic receptor- mediated reflex may be impaired in the elderly. Receptor and CAMP changes. In the rat central nervous system, up-regulation of 6,-adrenergic receptors induced by hormones or drug administration is impaired with aging, whereas in peripheral tissues such as rat heart (predominately PI-adrenergic receptors) and human PMNLs (P2-adrenergic receptors), it is not affected by In the rat central nervous system, recovery of P-adrenergic receptor number after agonist-induced down-regulation is also impaired with aging.' Our data suggest that this is not the case in human PMNLs (Fig. 5). However, regeneration of P-adrenergic receptors after irreversible blockade is impaired in heart and lung (predominantly P2-adrenergic receptors) from aged rats.'' It is not clear whether these discrepant observations are attributable to differences in tissues examined, species used, or underlying mechanisms for receptor recovery after prolonged agonist exposure or irreversible blockade. In a cell line derived from vas deferens, exposure to isoproterenol produces down-regulation of P2-adrenergic receptors by destabilizing the receptor messenger ribonucleic acid ( ~ R N A ) . TO ~ ~ date, , ~ ~ only the mechanism involved in glucocorticoidinduced up-regulation of P2-adrenergic receptors has been determined to be enhanced transcription of the receptor ~ R N A36,37 . In addition to aging-related differences in receptor density, coupling of these receptors to signal transduction systems could be altered. However, our findings indicate that the maximal stimulation of cAMP accumulation produced by isoproterenol was not reduced in the PMNLs isolated from elderly subjects. This is in contrast with reports from other groups that used different cell isolation procedures and assay conditions who have observed differences consistent with agerelated decreases in PMNL P-adrenergic receptor coupling or signal transduction. For example, agonist affinity and the proportion of high-affinity agonist binding sites have been observed to decrease in PMNLs from elderly subjects38; however, we have not observed similar differences.13 Also, stimulation of cAMP accumulation by isoproterenol in PMNLs has been found to be diminished in the elderly.39 We do not have an explanation for these discrepancies; however, there was a relatively large variability associated with our cAMP measurements. This may be a reflection of the high oxidative capacity of PMNLs because we do not find such large yariability with this

assay in other tissues such as brain.40 In any case, the terbutaline-induced desensitization was only statistically significant in the elderly group (Fig. 6), suggesting that this compensatory response is not impaired with aging. Our observations agree with the conclusions drawn by others that the effects of aging in humans are "cardioselective" (i.e., that PI-adrenergic receptors are selectively affected), and that P,-adrenergic receptors are not changed with aging.23*29They extend these conclusions to include agonist-induced downregulation of P2-adrenergic receptors and their recovery after down-regulation. We thank Ms. Bette Andros and Ms. Dianne Metcalf for technical assistance with this study, Drs. Lars-Erik Edholm and Britt-Marie Kennedy (AB Draco, Sweden) for the plasma terbutaline determinations, and Dr. Joanna Peris for help with the statistical analyses.

References 1. Harden TK. Agonist-induced desensitization of the P-adrenergic receptor linked adenylate cyclase. Pharmacol Rev 1983;35:5-32. 2. Hausdoff WP, Caron MC, Lefkowitz RJ. Turning off the signal: desensitization of P-adrenergic receptor function. FASEB J 1990;4:2881-9. 3. Galant SP, Duriseti L, Underwood S, Insel PA. Decreased beta-adrenergic receptors on polymorphonuclear leukocytes after adrenergic therapy. N Engl J Med 1978;299:933-6. 4. Sano Y, Watt G, Townley RG. Decreased mononuclear cell beta-adrenergic recepfors in bronchial asthma: parallel studies of lymphocyte and granulocyte desensitization. J Allergy Clin Immunol 1983;72:495-503. 5. Aarons RD, Nies AS, Gerber JG, Molinoff PB. Decreased beta adrenergic receptor density on human lymphocytes after chronic treatment with agonists. J Pharmacol Exp Ther 1983;224:1-6. 6. Brodde OE, Brinkmann M, Schemuth R, O'Hara N, Daul A. Terbutaline-induced desensitization of human lymphocyte P,-adrenoceptors. Accelerated restoration of P-adrenoceptor responsiveness by predisone and ketotifen. J Clin Invest 1985;76:1096-101. 7. Maisel AS, Fowler P, Rearden A, Motulsky HJ, Michel MC. A new method for isolation of human lymphocyte subsets reveals differential regulation of P-adrenergic receptors by terbutaline treatment. CLIN~ I A R M A C O LTHER 1989;46:429-39. 8. Oppenheim G, Mintzer J, Halperin Y, Eliakim R, Stessman J, Ebstein RP. Acute desensitization of lymphocyte beta-adrenergic-stimulated adenylate cyclase in old age and Alzheimer's disease. Life Sci 1984; 35: 1795-802. 9. Greenberg LH, Brunswick D, Weiss B. The effect of age on the recovery of beta-adrenergic receptors in rat brain following desmethylimipramine-induced subsensitivity. Brain Res 1985;328:81-8.

VOLUME 5 1 NUMBER 4

10. Pitha J, Hughes BA, Kusiak JW, Dax EM, Baker SP. Regeneration of P-adrenergic receptors in senescent rats: a study using an irreversible binding antagonist. Proc Natl Acad Sci USA 1982;79:4424-7. 11. De Blasi A, Fratelli M, Wielosz M, Lipartiti M. Regulation of beta adrenergic receptors on rat mononuclear leukocytes by stress: receptor redistribution and downregulation are altered with aging. J Pharmacol Exp Ther 1987;240:228-33. 12. Szefler SJ, Edwards CK 111, Haslett C, Zahniser NR, Miller JA, Henson PM. Effects of cell isolation procedures and radioligand selection on the characterization of human leukocyte (3-adrenergic receptors. Biochem Pharmacol 1987;36:1589-97. 13. Zahniser NR, Parker DC, Bier-Laning CM, Miller JA, Gerber, JG Nies AS. Comparison between the effects of aging on antagonist and agonist intereactions with beta-adrenergic receptors on human mononuclear and polymorphonuclear leukocyte membranes. J Gerontol 1988;43:M151-7. 14. Zahniser NR, Bier-Laning CM, Gerber JG, Nies, AS. Timolol-induced up-regulation of polymorphonuclear leukocyte P,-adrenergic receptors in the elderly. CLIN PHARMACOL THER1989;45:469-75. 15. Brodde OE, Beckeringh JJ, Michel MC. Human heart P-adrenoceptors: a fair comparison with lymphocyte P-adrenoceptors? Trends Pharmacol Sci 1987;8:403-7. 16. Edholm LE, Kennedy BM, Bergquist S. Multidimensional column liquid chromatography with electrochemical detection for the analysis of terbutaline in human plasma. Eur J Respir Dis Suppl 1984;134:33-40. 17. Passon PG, Peuler J. A simplified radioenzymatic assay for plasma norepinephrine and epinephrine. Anal Biochem 1973;51:618-31. 18. Munson PJ, Rodbard D. Ligand: a versatile computerized approach for characterization of ligand-binding systems. Anal Biochem 1980;107:220-39. 19. Bradford MM. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem 1976;72:248-54. 20. Szefler SJ, Ando R, Cicutto LC, Surs W, Hill MR, Martin RJ. Plasma histamine, epinephrine, cortisol and leukocyte P-adrenergic receptors in nocturnal asthma. THER1991;49:59-68. CLINPHARMACOL 21. Bergman J, Persson H, Wetterlin K. Two new groups of selective stimulants of adrenergic P-receptors. Experientia 1969;25:899-901. 22. Nelson HS. Beta-adrenergic therapy. In: Middleton E Jr, Reed CE, Ellis EF, Adkinson NF Jr, Yunginger JW, eds. Allergy principles and practice, Vol. 1. 3rd ed. St. Louis: C.V. Mosby Co., 1988:647-61. 23. Kendall MJ, Woods KL, Wilkins MR, Worthington DJ. Responsiveness to P-adrenergic receptor stimulation: the effects of age are cardioselective. Br J Clin Pharmacol 1982;14:821-6. 24. Vestal RE, Wood AJJ, Shand DG. Reduced betaadrenoceptor sensitivity in the elderly. CLINPHARMACOL THERl979;26: 181-6.

&Receptors in young and elderly subjects 439 25. Klein C, Gerber JG, Gal J, Nies AS. Beta-adrenergic receptors in the elderly are not less sensitive to timolol. CLINPHARMACOL THER1986;40: 161-4. 26. O'Donnell SR, Wanstall JC. Beta-1 and beta-2 adrenoceptor-mediated responses in preparations of pulmonary artery and aorta from young and aged rats. J Pharmacol Exp Ther 1984;228:733-8. 27. Duckles SP, Hurlbert JS. Effect of age on beta adrenergic relaxation of the rat jugular vein. J Pharmacol Exp Ther 1986;236:71-4. 28. Pan HYM, Hoffman BB, Pershe RA, Blaschke TP. Decline in beta-adrenergic receptor-mediated vascular relaxation with aging in man. J Pharmacol Exp Ther 1986;239:802-7. 29. Klein C, Hiatt WR, Gerber JG, Nies AS. Age does not alter human vascular and nonvascular P,-adrenergic responses to isoproterenol. CLINPHARMACOL THER1988; 44573-8. 30. Vanhoutte PM. Aging and vascular responsiveness. J Cardiovasc Pharmacol 1988;12:s 11-8. 31. Minneman KP, Hedberg A, Molinoff PB. Comparison of beta adrenergic receptor subtypes in mammalian tissues. J Pharmacol Exp Ther 1979;211: 502-8. 32. Scarpace PJ, Abrass IB. Thyroid hormone regulation of P-adrenergic receptor number in aging rats. Endocrinology 1981;108:1276-8. 33. Greenberg LH. Regulation of brain adrenergic receptors during aging. Fed Proc 1986;45:55-9. 34. Hadcock JR, Malbon CC. Down-regulation of P-adrenergic receptors: Agonist-induced reduction in receptor mRNA levels. Proc Natl Acad Sci USA 1988; 85t5021-5. 35. Hadcock JR, Wang HY, Malbon CC. Agonistinduced destabilization of P-adrenergic receptor mRNA. Attenuation of glucocorticoid-induced up-regulation of P-adrenergic receptors. J Biol Chem 1989; 264: 19928-33. 36. Collins S, Caron MG, Lefkowitz RJ. (3,-Adrenergic receptors in hamster smooth muscle cells are transcriptionally regulated by glucocorticoids. J Biol Chem 1988;263:9067-70. 37. Hadcock JR, Malbon CC. Regulation of P-adrenergic receptors by "permissive" hormones: glucocorticoids increase steady-state levels of receptor mRNA. Proc Natl Acad Sci USA 1988;85:8415-9. 38. Montamat SC, Davies AO. Physiological response to isoproterenol and coupling of beta-adrenergic receptors in young and elderly human subjects. J Gerontol Med Sci 1989;44:M100-5. 39. Cotter TG, O'Malley K. Decreased neutrophil cyclic AMP response to isoprenaline stimulation in the elderly. Clin Sci 1983;65:155-7. 40. Lupica CR, Cass WA, Zahniser NR, Dunwiddie TV. Effects of the selective adenosine A2 receptor agonist CGS 21680 on in vitro electrophysiology, CAMP formation and dopamine release in rat hippocampus and striatum. J Pharmacol Exp Ther 1990;252: 1134-41.

Terbutaline-induced desensitization of polymorphonuclear leukocyte beta 2-adrenergic receptors in young and elderly subjects.

Potential age-related differences in cardiovascular responsiveness and receptor regulation induced by short-term administration of a selective beta 2-...
551KB Sizes 0 Downloads 0 Views