Acta pharmacol. et toxicol. 1978,43 (11), 69-73
From the Research Laboratories, AB Leo, S-251 00 Helsingborg, Sweden
The Effects of Anticholinergics on the Urinary Bladder Mechanism. BY Christer Sjogren
Abstract: A summary is given of the physiological conditions concerned with collection and expulsion of urine from the bladder. The role of afferent and efferent nerve activity from and to the urinary bladder
and urethra is discussed. When studying the effects of anticholinergics on the urinary bladder in animals an in situ model described here seems to be the most valid for conditions in man. This method involves recording of the intravesical pressure in conscious rabbits simultaneously with a bladder infusion. An assessment is made of the evidence for a purinergic transmission in the urinary bladder. Key-words: urinary bladder - nerve activity - anticholinergics - purinergic transmission.
Introduction
Afferent - efferent nerve activity
I will start with a note on the definition of the expression “anticholinergics”. This group of drugs includes compounds which exert their main effects on muscarinic receptor sites. But several anticholinergics, perhaps most of them, also exhibit an antagonistic action on the nicotinic receptor in the autonomic ganglia. The detrusor is richly endowed with muscarinic receptors. Stimulation of these gives rise to a forceful contraction of the detrusor and the functional role of this type of receptor seems so far completely clear. But I will return to this later, in connection with another aspect of the bladder mechanism. The active role in the micturition process (and for maintaining continence) played by the urethra is still under discussion. The supply of adrenoceptors is supposed to be crucial in this area and the evidence of a substantial influence of parasympathetic nerves under physiological conditions is poor.
For the sake of completeness I shall give a brief description of the afferent - efferent impulse flow during the collecting and expulsion phases of the bladder. Among others, Edvardsen (1968) has made interesting observations by cutting the nerves to the bladder at different levels. During the last part of the collecting phase an impulse flow from the tension receptors in the detrusor takes place. This nerve activity seems, at least in the cat, to run in fibres in the pelvic nerves. The afferent firing influences the lumbar symphathetic outflow, which reaches the bladder via the hypogastric nerves. This reflex subserves a n inhibitory function on the detrusor executed by the P-adrenoceptors, and perhaps also on parasympathetic ganglia by way of a-adrenoceptors. These mechanisms altogether considerably prevent the intravesical pressure from rising during the collecting phase in spite of a gradually increasing bladder volume. de Groat and Saum (1972) have shown by preganglionic
70
CHRISTER SJOGREN
stimulation of the pelvic nerve and postganglionic recordings of the discharge, that simultaneous stimulation of the hypogastric nerve causes an inhibition of the postganglionic discharge in the pelvic nerve. Administration of noradrenaline also prevents the transmission in the parasympathetic ganglion. This inhibitory action evoked by both electrical and chemical stimulation can be blocked by an a-adrenoceptor antagonist. However, when the critical limit for the detrusor compliance is approaching during the collecting phase, the activity in the efferent parasympathetic nerves substantially increases and the bladder expels its content. de Groat (1975) has observed that high-frequency stimulation of preganglionic pelvic nerves causes a marked facilitation of the nerve activity simultaneously evoked in the postganglionic nerve portion. At low-frequency stimulation, this facilitation does not seem to occur. From this observation de Groat assumed that the parasympathetic ganglia in the urinary bladder might have a filter function and that during the collecting phase the low-frequency firing is thus filtered away, but during the expulsion phase the efferent discharge is facilitated. Whether drugs can influence this mechanisms under physiological conditions is not yet known. Thus, it can be concluded that the efferent parasympathetic impulses do not seem to play any considerable role during the collecting phase.
The role of C N S It should also be kept in mind that in the different phases of the bladder mechanism, the CNS is largely involved. As early as in 1907 Elliot demonstrated that destruction of the brain in cats abolished the micturition reflex. Barrington (1925) came to the conclusion that seven different reflexes participated in the micturition process and that the centre for reflex coordination was located in the anterior pons. Other authors have more recently proved the existence of both facilitating and inhibitory areas for the bladder mechanism in the cerebral cortex, mes-
encephalon, pons and medulla oblongata (Tang 1955, Kuru 1965). From this argumentation it may be summarized that the parasympathetic bladder functions can be influenced at several levels and in different ways. It must therefore be emphasized that drugs are capable of acting at one o r more of these sites and can in this way mimick or conceal a purely anticholinergic mechanism of action. This gives prominence to the fact that it is important, when studying potential “bladder drugs”, to choose relevant experimental models. Some examples will be discussed here. The therapcutic use of anticholinergics is restricted to conditions with hyperactivity in the efferent parasympathetic nerve fibres innervating the urinary bladder, These disorders result in a decreased bladder capacity, urinary spasms and/or incontinence. The symptoms can be more or less completely cured by anticholinergics, but also by ganglionic blocking agents. A possible disadvantage of the latter group of compounds is that they may also abolish the efferent inhibitory activity accomplished by the sympathetic nerve fibres.
Experimental models for testing anticholinergics in animals.
The most straightforward way of testing anticholinergics is by using bladder strips in v i m ) contracted by an agonist possessing a muscarine-like action. Such a test does not give information about the influence on the bladder mechanism in its entirety, and it is therefore more appropriate to apply methods where the bladder is infused in situ. Thus, we have recorded the intravesical pressure in rabbits by introducing two catheters - one for continuous infusion and one for pressure measurements - directly through the detrusor wall (Sjogren 1976 a). One of the advantages of this design of method is that the outlet region of the bladder is left intact. Fig. 1 shows the different phases of an infusion in a n anaesthetized rabbit. The mean hladder capacity was 18 ml, the threshold pressure 6 cm H2O and the micturition pressure 16 cm H 2 0 . Obvious drawbacks with this method are
URINARY BLADDER AND ANTICHOLINERGICS
that the depth of the sleep must be kept constant and that the rabbits usually void with residual volumes, already prior to treatment. Atropine (1 mg/kg i.v.) augmented the bladder capacity and threshold pressure by 90 and 70 %, respectively. The micturition pressure was decreased by 50 %, which caused an increase of the residual volume by 50 % (Fig. 2 ) . The figure also illustrates that the bladder made repeated contractions, without expelling any fluid, when the intravesical pressure and volume reached the preinjection bladder capacity and threshold pressure. Emeprone (Cetiprin@, AB Recip, Sweden) was
71
cm H70
infusron
micturlfion / M )
Fig. 1 Anaesthetizied rabbit. The intravesical pressure during infusion and micturition. T P = micturition threshold pressure. MP = micturition pressure. (Sjogren 1976 a)
1 2ol
A
t
10 n v -
t
t
atropine inf 1mgm
t
M
Fig. 2 Anaesthetized rabbit. The intravesical pressure (cm H a ) during infusion (inf. indicates the start of infusion) before (A) and after (B) intravenous injection of 1 mg/kg atropine. (Sjogren 1976 a)
Fig. 3 Unanaesthetized rabbit. T i e intravesical pressure during the last portion of the infusion. TP = micturition threshold pressure. MP = micturition pressure. R indicates the first distinct pressure rise. (Sjogren 1976 b)
yoL_!..I 72
CHRISTER SJOGREN
Imk, L
crn H20
20 0
,lrnin
,
t’
t
M
M
Fig. 4 Unanaesthetized rabbit. The intravesical pressure during infusion, before (A) and after (B) intravenous injection of 1 mg/kg atropine. (Sjogren 1976 b)
t
a f ropin e 12 mg/kg i a
Fig. 5 Electrically induced rabbit bladder contractions in vivo. Atropine 12 mg/kg given intraarterially has no apparent effect on the contractions. (Sjostrand ef at. 1972)
residual volume of 10-25 %. But, the fact that atropine (1 mg/kg i.v.) reduced the bladder capacity by 20-30 % and that no residual volume was left in the bladder were highly surprising observations (Fig. 4). This effect of atropine can probably b e ascribed to its central stimulating action (Winter 1941). It can be concluded that an intact CNS is crucial for the physiological bladder mechanisms and for yielding more reliable results in studies concerning the effects of drugs on the bladder. Purinergic transmission?
Fig. 6 Guinea-pig bladder in vifro. ATP (bath conc. lO--’M) added at the arrows. (Sjogren, unpublished results)
also tested and was found to increase the bladder capacity, threshold pressure and residual volume and to decrease the micturition pressure. In order t o eliminate the disadvantages associated with the recordings in anaesthetized animals, we carried out a similar experiment in unanaesthetized rabbits. The bladder capacity (45 ml), threshold pressure (17 cm H20), and micturition pressure (35 c m H2O) substantially exceeded those found in anaesthetized animals and the bladder did not contain any residual volume after micturition (Fig. 3). Anticholinergics, for example emeprone, increased the bladder capacity by only 5 - 10 %, decreased the micturition pressure by 15-40 % and caused a
However, the question can be raised whether cholinergic mechanisms alone are essential for the bladder emptying. If the bladder is stimulated electrically via pelvic nerves o r transmurally a forceful contraction is elicited. In most animal species this contraction can be inhibited by atropine, but only to a maximal extent of 20-30 % (Fig. 5). (Ambache and Zar 1970; Sjostrand e t al., 1972). The cause of this atropine resistance has been the subject of several discussions. Burnstock (1972) has contributed with an interesting explanation for the phenomenon. H e postulates the existence of a nerve type which he terms purinergic nerves and which might have ATP as transmitter. ATP evokes a detrusor contraction both in vivo and in viiro (Fig. 6). The evidence presented by Burnstock for a purinergic transmission in the urinary bladder is summarized below.
URINARY BLADDER AND ANTICHOLINERGICS
I . A T P is taken u p and stored in terminal axons. 2 . Large opaque vesicles are present in terminal axons. 3. ATP produces bladder contraction in vivo and in v i t r o . 4. Both ATP- and nerve-mediated contractions can be blocked by quinidine. 5. Tetrodotoxin does not influence the A T P contraction.
6. Tachyphylaxis caused by high doses of A T P reduces the nerve mediated contraction.
7 . Inactivating enzymes exist. There are also arguments against a purinergic transmission. Anyhow, it is an interesting aspect, which might explain observations disaccordant with the established concept of the autonomic nervous system.
References Ambache, N. And M.A. Zar: Non-cholinergic nature of the postganglionic motor neurones in guinea-pig bladder. J . Physiol. 1970,209, 10- 12. Barrington, F.J.F.: The effect of lesions of the hindand midbrain on micturition in the cat. Quart. J . Exp. Physiol. 1925,15,81- 102. Burnstock, G.: Purinergic nerves. Pharmacol. Rev. 1972,24, 509-581.
73
Edvardsen, P.: Nervous control of urinary bladder in cats. I. The collecting phase. Act0 physiol. scnnd. 1%8,72, 157-171. Elliott, T.R.: The innervation of the bladder and urethra. J . Physiol. (London), 1907,35,367-445. de Groat, W.C. and W.R. Saurn: Sympathetic inhibition of the urinary bladder and of pelvic ganglionic transmission in the cat. J . Physiol. 1972, 220, 297 - 3 14. de Groat, W.C.: Nervous control of the urinary bladder of the cat. Brain Research, 1975,87,201- 1 1 . Kuru, M.: Nervous control of micturition. Physic>/. Rev. 1%5,45,425-494. Sjogren, C.: The effects of some anticholinergic compounds on the infused urinary bladder of anaesthetized rabbits. Acta Pharmacol. et Toxicol. 1976 a, 39, 167-176. Sjogren, C.: The effects of some anticholinergic compounds on the infused urinary bladder of unanaesthetized rabbits. Acta pharmacol. et toxicol. 1976 b. 39, 177-185. Sjogren, C.: Unpublished results. Sjostrand, S.E., C. Sjogren and C.G. Schmiterlow: Responses of the rabbit and cat urinary bladders in situ to drugs and to nerve stimulation. Acta pharmacol. et toxicol. 1972,31p 241 -254. Tang, P.C.: Levels of brain stem and diencephalon controlling micturition reflex. J . Neurophysiol. 1955,18,583-595. Winter, I.C.: The pharmacology of micturition. The effect of drugs on the bladder and urethra with autonomic supply intact. J . Urol. 1941,46,925-980.
From the Research Laboratories, AB Leo, S-251 00 Helsingborg, Sweden
The Effects of Anticholinergics on the Urinary Bladder Mechanism. BY Christer Sjogren
Abstract: A summary is given of the physiological conditions concerned with collection and expulsion of urine from the bladder. The role of afferent and efferent nerve activity from and to the urinary bladder
and urethra is discussed. When studying the effects of anticholinergics on the urinary bladder in animals an in situ model described here seems to be the most valid for conditions in man. This method involves recording of the intravesical pressure in conscious rabbits simultaneously with a bladder infusion. An assessment is made of the evidence for a purinergic transmission in the urinary bladder. Key-words: urinary bladder - nerve activity - anticholinergics - purinergic transmission.
Introduction
Afferent - efferent nerve activity
I will start with a note on the definition of the expression “anticholinergics”. This group of drugs includes compounds which exert their main effects on muscarinic receptor sites. But several anticholinergics, perhaps most of them, also exhibit an antagonistic action on the nicotinic receptor in the autonomic ganglia. The detrusor is richly endowed with muscarinic receptors. Stimulation of these gives rise to a forceful contraction of the detrusor and the functional role of this type of receptor seems so far completely clear. But I will return to this later, in connection with another aspect of the bladder mechanism. The active role in the micturition process (and for maintaining continence) played by the urethra is still under discussion. The supply of adrenoceptors is supposed to be crucial in this area and the evidence of a substantial influence of parasympathetic nerves under physiological conditions is poor.
For the sake of completeness I shall give a brief description of the afferent - efferent impulse flow during the collecting and expulsion phases of the bladder. Among others, Edvardsen (1968) has made interesting observations by cutting the nerves to the bladder at different levels. During the last part of the collecting phase an impulse flow from the tension receptors in the detrusor takes place. This nerve activity seems, at least in the cat, to run in fibres in the pelvic nerves. The afferent firing influences the lumbar symphathetic outflow, which reaches the bladder via the hypogastric nerves. This reflex subserves a n inhibitory function on the detrusor executed by the P-adrenoceptors, and perhaps also on parasympathetic ganglia by way of a-adrenoceptors. These mechanisms altogether considerably prevent the intravesical pressure from rising during the collecting phase in spite of a gradually increasing bladder volume. de Groat and Saum (1972) have shown by preganglionic
70
CHRISTER SJOGREN
stimulation of the pelvic nerve and postganglionic recordings of the discharge, that simultaneous stimulation of the hypogastric nerve causes an inhibition of the postganglionic discharge in the pelvic nerve. Administration of noradrenaline also prevents the transmission in the parasympathetic ganglion. This inhibitory action evoked by both electrical and chemical stimulation can be blocked by an a-adrenoceptor antagonist. However, when the critical limit for the detrusor compliance is approaching during the collecting phase, the activity in the efferent parasympathetic nerves substantially increases and the bladder expels its content. de Groat (1975) has observed that high-frequency stimulation of preganglionic pelvic nerves causes a marked facilitation of the nerve activity simultaneously evoked in the postganglionic nerve portion. At low-frequency stimulation, this facilitation does not seem to occur. From this observation de Groat assumed that the parasympathetic ganglia in the urinary bladder might have a filter function and that during the collecting phase the low-frequency firing is thus filtered away, but during the expulsion phase the efferent discharge is facilitated. Whether drugs can influence this mechanisms under physiological conditions is not yet known. Thus, it can be concluded that the efferent parasympathetic impulses do not seem to play any considerable role during the collecting phase.
The role of C N S It should also be kept in mind that in the different phases of the bladder mechanism, the CNS is largely involved. As early as in 1907 Elliot demonstrated that destruction of the brain in cats abolished the micturition reflex. Barrington (1925) came to the conclusion that seven different reflexes participated in the micturition process and that the centre for reflex coordination was located in the anterior pons. Other authors have more recently proved the existence of both facilitating and inhibitory areas for the bladder mechanism in the cerebral cortex, mes-
encephalon, pons and medulla oblongata (Tang 1955, Kuru 1965). From this argumentation it may be summarized that the parasympathetic bladder functions can be influenced at several levels and in different ways. It must therefore be emphasized that drugs are capable of acting at one o r more of these sites and can in this way mimick or conceal a purely anticholinergic mechanism of action. This gives prominence to the fact that it is important, when studying potential “bladder drugs”, to choose relevant experimental models. Some examples will be discussed here. The therapcutic use of anticholinergics is restricted to conditions with hyperactivity in the efferent parasympathetic nerve fibres innervating the urinary bladder, These disorders result in a decreased bladder capacity, urinary spasms and/or incontinence. The symptoms can be more or less completely cured by anticholinergics, but also by ganglionic blocking agents. A possible disadvantage of the latter group of compounds is that they may also abolish the efferent inhibitory activity accomplished by the sympathetic nerve fibres.
Experimental models for testing anticholinergics in animals.
The most straightforward way of testing anticholinergics is by using bladder strips in v i m ) contracted by an agonist possessing a muscarine-like action. Such a test does not give information about the influence on the bladder mechanism in its entirety, and it is therefore more appropriate to apply methods where the bladder is infused in situ. Thus, we have recorded the intravesical pressure in rabbits by introducing two catheters - one for continuous infusion and one for pressure measurements - directly through the detrusor wall (Sjogren 1976 a). One of the advantages of this design of method is that the outlet region of the bladder is left intact. Fig. 1 shows the different phases of an infusion in a n anaesthetized rabbit. The mean hladder capacity was 18 ml, the threshold pressure 6 cm H2O and the micturition pressure 16 cm H 2 0 . Obvious drawbacks with this method are
URINARY BLADDER AND ANTICHOLINERGICS
that the depth of the sleep must be kept constant and that the rabbits usually void with residual volumes, already prior to treatment. Atropine (1 mg/kg i.v.) augmented the bladder capacity and threshold pressure by 90 and 70 %, respectively. The micturition pressure was decreased by 50 %, which caused an increase of the residual volume by 50 % (Fig. 2 ) . The figure also illustrates that the bladder made repeated contractions, without expelling any fluid, when the intravesical pressure and volume reached the preinjection bladder capacity and threshold pressure. Emeprone (Cetiprin@, AB Recip, Sweden) was
71
cm H70
infusron
micturlfion / M )
Fig. 1 Anaesthetizied rabbit. The intravesical pressure during infusion and micturition. T P = micturition threshold pressure. MP = micturition pressure. (Sjogren 1976 a)
1 2ol
A
t
10 n v -
t
t
atropine inf 1mgm
t
M
Fig. 2 Anaesthetized rabbit. The intravesical pressure (cm H a ) during infusion (inf. indicates the start of infusion) before (A) and after (B) intravenous injection of 1 mg/kg atropine. (Sjogren 1976 a)
Fig. 3 Unanaesthetized rabbit. T i e intravesical pressure during the last portion of the infusion. TP = micturition threshold pressure. MP = micturition pressure. R indicates the first distinct pressure rise. (Sjogren 1976 b)
yoL_!..I 72
CHRISTER SJOGREN
Imk, L
crn H20
20 0
,lrnin
,
t’
t
M
M
Fig. 4 Unanaesthetized rabbit. The intravesical pressure during infusion, before (A) and after (B) intravenous injection of 1 mg/kg atropine. (Sjogren 1976 b)
t
a f ropin e 12 mg/kg i a
Fig. 5 Electrically induced rabbit bladder contractions in vivo. Atropine 12 mg/kg given intraarterially has no apparent effect on the contractions. (Sjostrand ef at. 1972)
residual volume of 10-25 %. But, the fact that atropine (1 mg/kg i.v.) reduced the bladder capacity by 20-30 % and that no residual volume was left in the bladder were highly surprising observations (Fig. 4). This effect of atropine can probably b e ascribed to its central stimulating action (Winter 1941). It can be concluded that an intact CNS is crucial for the physiological bladder mechanisms and for yielding more reliable results in studies concerning the effects of drugs on the bladder. Purinergic transmission?
Fig. 6 Guinea-pig bladder in vifro. ATP (bath conc. lO--’M) added at the arrows. (Sjogren, unpublished results)
also tested and was found to increase the bladder capacity, threshold pressure and residual volume and to decrease the micturition pressure. In order t o eliminate the disadvantages associated with the recordings in anaesthetized animals, we carried out a similar experiment in unanaesthetized rabbits. The bladder capacity (45 ml), threshold pressure (17 cm H20), and micturition pressure (35 c m H2O) substantially exceeded those found in anaesthetized animals and the bladder did not contain any residual volume after micturition (Fig. 3). Anticholinergics, for example emeprone, increased the bladder capacity by only 5 - 10 %, decreased the micturition pressure by 15-40 % and caused a
However, the question can be raised whether cholinergic mechanisms alone are essential for the bladder emptying. If the bladder is stimulated electrically via pelvic nerves o r transmurally a forceful contraction is elicited. In most animal species this contraction can be inhibited by atropine, but only to a maximal extent of 20-30 % (Fig. 5). (Ambache and Zar 1970; Sjostrand e t al., 1972). The cause of this atropine resistance has been the subject of several discussions. Burnstock (1972) has contributed with an interesting explanation for the phenomenon. H e postulates the existence of a nerve type which he terms purinergic nerves and which might have ATP as transmitter. ATP evokes a detrusor contraction both in vivo and in viiro (Fig. 6). The evidence presented by Burnstock for a purinergic transmission in the urinary bladder is summarized below.
URINARY BLADDER AND ANTICHOLINERGICS
I . A T P is taken u p and stored in terminal axons. 2 . Large opaque vesicles are present in terminal axons. 3. ATP produces bladder contraction in vivo and in v i t r o . 4. Both ATP- and nerve-mediated contractions can be blocked by quinidine. 5. Tetrodotoxin does not influence the A T P contraction.
6. Tachyphylaxis caused by high doses of A T P reduces the nerve mediated contraction.
7 . Inactivating enzymes exist. There are also arguments against a purinergic transmission. Anyhow, it is an interesting aspect, which might explain observations disaccordant with the established concept of the autonomic nervous system.
References Ambache, N. And M.A. Zar: Non-cholinergic nature of the postganglionic motor neurones in guinea-pig bladder. J . Physiol. 1970,209, 10- 12. Barrington, F.J.F.: The effect of lesions of the hindand midbrain on micturition in the cat. Quart. J . Exp. Physiol. 1925,15,81- 102. Burnstock, G.: Purinergic nerves. Pharmacol. Rev. 1972,24, 509-581.
73
Edvardsen, P.: Nervous control of urinary bladder in cats. I. The collecting phase. Act0 physiol. scnnd. 1%8,72, 157-171. Elliott, T.R.: The innervation of the bladder and urethra. J . Physiol. (London), 1907,35,367-445. de Groat, W.C. and W.R. Saurn: Sympathetic inhibition of the urinary bladder and of pelvic ganglionic transmission in the cat. J . Physiol. 1972, 220, 297 - 3 14. de Groat, W.C.: Nervous control of the urinary bladder of the cat. Brain Research, 1975,87,201- 1 1 . Kuru, M.: Nervous control of micturition. Physic>/. Rev. 1%5,45,425-494. Sjogren, C.: The effects of some anticholinergic compounds on the infused urinary bladder of anaesthetized rabbits. Acta Pharmacol. et Toxicol. 1976 a, 39, 167-176. Sjogren, C.: The effects of some anticholinergic compounds on the infused urinary bladder of unanaesthetized rabbits. Acta pharmacol. et toxicol. 1976 b. 39, 177-185. Sjogren, C.: Unpublished results. Sjostrand, S.E., C. Sjogren and C.G. Schmiterlow: Responses of the rabbit and cat urinary bladders in situ to drugs and to nerve stimulation. Acta pharmacol. et toxicol. 1972,31p 241 -254. Tang, P.C.: Levels of brain stem and diencephalon controlling micturition reflex. J . Neurophysiol. 1955,18,583-595. Winter, I.C.: The pharmacology of micturition. The effect of drugs on the bladder and urethra with autonomic supply intact. J . Urol. 1941,46,925-980.
