Observations on an isolated preparation of guinea-pig urinary bladder stimulated through the hypogastric nerves

Phosphodiesterase-linked inhibition of nonmicturition activity in the isolated bladder

OBJECTIVE

To explore the influence of intracellular cAMP on phasic activity in the isolated bladder (phasic rises in intravesical pressure associated with waves of contraction and local stretches that can be activated by muscarinic or nicotinic agonists), as it has been argued that this activity underlies nonmicturition contractions, and that it contributes to the generation and modulation of afferent nerve activity.

MATERIALS AND METHODS

Isolated whole bladders from female guinea pigs (270-300 g) were cannulated via the urethra and suspended in a chamber containing oxygenated Tyrode solution at 33-35 degrees C. Bladder pressure was recorded and pharmacological agents added to the solution bathing the abluminal surface of the bladder.

RESULTS

Forskolin (1-3 micro mol/L), an activator of adenyl cyclase, reduced the frequency and amplitude of the phasic activity induced by the muscarinic agonist arecaidine (300 nmol/L). There were similar changes in frequency and amplitude in bladders exposed to the nonspecific phosphodiesterase (PDE) inhibitor iso-butyl-methyl-xanthene (IBMX). The actions of specific PDE inhibitors were explored to assess which isoenzymes might be responsible for regulating phasic activity. ENHA (PDE-2), zaprinast (PDE-5, -6, -8, -9 and -11) and siguazodan (PDE-3) had no effect. Zardavarine (PDE-3, -4) and Ro 20-1724 (PDE-4) reduced both the frequency and amplitude of the phasic activity. Nerve-mediated rises in intravesical pressure were also inhibited by Ro 20-1724, and the inhibition was more pronounced at 6.5 Hz than at 30 Hz stimulation. Ro 20-1724 inhibited nerve-mediated fluctuations induced by prolonged (200 s) stimulation at 6.5 Hz.

CONCLUSION

The mechanisms influencing the frequency of agonist-induced phasic activity in the isolated bladder are slowed by cAMP. Degradation of intracellular cAMP in the cells responsible for phasic activity appears to involve primarily PDE-4. The importance of these observations in relation to the overall physiological regulation of the bladder are discussed, and the possible importance of these findings in the development of pharmacological strategies to modulated bladder activity reviewed.

Effects of selective cholinergic antagonists and alpha,beta-methylene ATP on guinea-pig urinary bladder contractions in vivo following pelvic nerve stimulation

1. An in vivo preparation measuring functional detrusor muscle strength in terms of intravesical bladder pressure (Pves) following in situ pelvic nerve stimulation has been developed in urethane-anaesthetized guinea pigs. 2. The increase in bladder pressure following pelvic nerve stimulation was abolished by topical lidocaine or tetrodotoxin, suggesting a neurogenic origin for the in vivo contractile response. 3. Cholinergic antagonists (i.v.) decreased the amplitude of the peak pressure response by about 50% at both high (30 Hz) and low (5 Hz) stimulation rates, with a rank order of potency of atropine greater than propantheline greater than oxybutynin greater than hexahydrosiladifenidol greater than pirenzepine greater than methoctramine. 4. The P2 purine receptor antagonist, alpha,beta-methylene ATP (i.v.), antagonized pelvic nerve-stimulated bladder contractions differentially at 5 and 30 Hz. At low frequencies, alpha, beta-methylene ATP was both more potent (2.5-fold) and more efficacious (-77 compared to -55% delta) than at 30 Hz. Atropine and alpha,beta-methylene ATP together completely inhibited the contractile response. 5. Together, the findings indicate that in guinea pigs, urinary bladder contractions induced by pelvic nerve stimulation in vivo may be mediated by both muscarinic and purinergic receptors and that these bladder contractions may be mediated by the M2 beta subtype rather than by M1 or M2 alpha muscarinic receptors.

The neural and non-neural mechanisms involved in urethral activity in rabbits

The effects of electrical and chemical stimulation on the mechanical or electrical properties of the circular smooth muscle cells of the bladder neck, and proximal urethra of the male rabbit were investigated by means of micro-electrode, double-sucrose-gap and tension-recording methods. In the bladder neck, application of short current pulses (50 microseconds) produced an initial excitatory junction potential (e.j.p.) with a superimposed spike, followed by a late depolarization, and these electrical events evoked contraction. The initial e.j.p. was unaffected by guanethidine, phentolamine, methysergide or mepyramine, indicating the initial e.j.p. is not mediated by activation of adrenergic, tryptaminergic or histaminergic receptors. The late depolarization was enhanced by pre-treatment with neostigmine (10(-7) M) and abolished by atropine (10(-6) M). In the proximal urethra, electrical-field stimulation evoked phasic contraction which was followed by relaxation, associated with initial e.j.p.s, late depolarization and inhibitory junction potentials (i.j.p.s). Guanethidine (10(-5) M) or phentolamine (10(-6) M) reduced the size of the initial e.j.p. to 40-50% of the control value and combined application of guanethidine and atropine further reduced the amplitude of the e.j.p. to 20-30%. There was a parallel reduction in the mechanical response. The late depolarization was enhanced by neostigmine and abolished by atropine. The i.j.p. and muscle relaxation were not affected by propranolol, phentolamine, guanethidine or atropine. These results indicate that the proximal urethral smooth muscle cells are innervated by adrenergic and cholinergic excitatory, and by non-cholinergic non-adrenergic inhibitory nerve fibres. In the prostatic urethra, field stimulations also evoked twitch contractions with or without following phasic contraction and relaxation. The twitch contractions were abolished by d-tubocurarine (10(-6) M), suggesting that they arise from striated muscle. Exogenously applied prostaglandin (PG) E1, PGE2 or PGF2 alpha (greater than 10(-10) M) evoked sustained increase in the muscle tone in the presence or absence of indomethacin, and enhanced the amplitude of muscle relaxation evoked by the field stimulation without affecting the resting membrane potential. Indomethacin (10(-6)-10(-5) M) gradually reduced the muscle tone of the proximal urethra with no change in the resting membrane potential. At the reduced muscle tone, electrical-field stimulation did not evoke muscle relaxation. Thus, the amplitude of muscle relaxation evoked by field stimulation was dependent on the level of muscle tone of the circular muscle strips.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of the hypogastric nerve in bladder and urethral activity of the dog

1. Stimulation of the hypogastric nerves increased the pressure in both the bladder and urethra of anaesthetized female dogs. 2. The responses were reduced but not abolished by the alpha-adrenoceptor antagonist phentolamine, whereas the beta-adrenoceptor antagonist propranolol was either without effect or increased the responses. Atropine, methysergide and hexamethonium were without effect. 3. Close arterial injection of phenylephrine increased and isoprenaline decreased urethral pressure but both produced only a slight increase in bladder pressure. 4. Hypogastric nerve stimulation reduced subsequent responses of the bladder and urethra to pelvic nerve stimulation or to close arterial injection of acetylcholine. Isoprenaline, but not phenylephrine, also had an inhibitory action and 5-hydroxytryptamine enhanced the responses. 5. In the presence of hexamethonium the inhibitory action of isoprenaline still occurred but 5-hydroxytryptamine no longer enhanced the responses, suggesting that 5-hydroxytryptamine acts on the ganglia and isoprenaline acts, at least partially, on smooth muscle. 6. These results suggest that the role of the hypogastric nerves may be to modify inputs to the bladder and urethra as well as to act directly on the smooth muscle.