Responses of the guinea-pig vas deferens and urinary bladder to hypogastric nerve stimulation in vivo

Frusemide potentiates acetylcholine and carbachol in contracting the rat urinary bladder

The interaction between acetylcholine and carbachol, and frusemide, a loop diuretic, have been studied on the rat isolated urinary bladder strip preparation. Acetylcholine (4.36 x 10(-8) - 1.3 x 10(-6) M) and carbachol (5.5 x 10(-8) - 6.9 x 10(-6) M) induced contractions and these were significantly potentiated by frusemide (3.02 x 10(-6) M). The ratio of EC50 in the absence of frusemide to EC50 in the presence of frusemide was 1.58 +/- 0.03 (s.e.m.) for acetylcholine and 1.86 +/- 0.14 for carbachol. Potentiation of acetylcholine and carbachol contractions by frusemide was not observed in tissues treated with hexamethonium (2.5 x 10(-5) M). Rhythmic contractions induced by frusemide alone were markedly reduced by hexamethonium (2.5 x 10(-5) M) and tetrodotoxin (10(-6) M) but they were not significantly reduced by atropine (1.7 x 10(-6) M). The result suggests that frusemide increases the sensitivity of the bladder to acetylcholine and carbachol, and that it may have a nicotinic stimulant effect on the bladder. This extra-renal action may contribute to its prompt diuretic property.

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.

Effects of five alpha-blockers on the hypogastric nerve stimulation of the canine lower urinary tract

Electrical stimulation of the hypogastric nerve increased both urethral and bladder pressures of anaesthetized male dogs, without affecting cardiovascular parameters. Intravenous injections of prazosin, phentolamine, thymoxamine, phenoxybenzamine and yohimbine inhibited the urethral pressure increase in a dose-dependent manner, but the increase in bladder pressure was not modified by these alpha-blockers.

Comments on the atropine resistance of the neurogenic contractile response of the rat detrusor muscle

The resistance to atropine or scopolamine of the neurogenic contractile response to field stimulation of intramural nerves of the rat detrusor was studied during the early phase of Wallerian degeneration in vitro and in vivo. The neurogenic contractile response to low frequency stimulation of control bladders was completely resistant to atropine or scopolamine in vitro. As a matter of fact the response was enchanced by the drugs. In vivo a transient shortening of the response could be seen. 26-34 h after bilateral extirpation of the pelvic ganglia there was prominent degeneration activity in the bladders in vitro as well as in vivo. Atropine or scopolamine inhibited this activity in vivo but enhanced it in vitro. The neurogenic contractile response to field stimulation of the bladder nerves was blocked in vivo but not in vitro by the antimuscarinic drugs 26-34 h after neurectomy. The results support the concept that the excitatory neurotransmission in the detrusor is essentially cholinergic. An explanation of the difference between the in vivo and the in vitro results based on differences in degree of blockade of pre- and post-junctional muscarinic receptors and diffusion of the antimuscarinics in the tissue is proposed.

Reserpine-induced detrusor hyperreflexia: an in vivo model for studying smooth muscle relaxants at urinary bladder level

A new in vivo model for studying the effects of smooth muscle relaxant drugs at urinary bladder level has been developed. This involves the determination of a cystometrogram at a physiological filling rate in urethane anesthetized rats. The amount of infused saline required to elicit TTX-sensitive rhythmic contractions (micturition reflex) of urinary bladder was choosen as end point to evaluate the effect of test substances. Reserpine pretreatment significantly reduced the volume of saline required to elicit the micturition reflex. The effect of reserpine can be reproduced by intravenous prazosin, but not by propranolol or yohimbine, in control rats. Intravenous, but not topical, hexamethonium reversed the effects of reserpine pretreatment on the amount of infused saline required to elicit rhythmic contractions. The nature of rhythmic contractions produced by saline filling of the urinary bladder in these experimental conditions, as well as the potential mechanism(s) involved in the effects of reserpine, are discussed in view of the existing literature on the physiology and pharmacology of the micturition reflex. The effects of various drugs commonly used to produce a relaxation of bladder muscle suggest that this model might be useful for detecting substances of potential therapeutic usefulness in the treatment of bladder hypermotility disorders.

Responsiveness of the guinea-pig vas deferens to phenylephrine and norepinephrine in vivo

A method is described for the study of guinea-pig vas deferens in vivo response to phenylephrine and norepinephrine. Tissue sensitivity to both agonists did not differ in vivo but the maximum response to phenylephrine was smaller. Responsiveness to norepinephrine was depressed in vitro after in vivo experiments. No such effect was observed for phenylephrine. This method allowed the comparison of the responsiveness of the guinea-pig vas deferens to adrenoceptor agonists in vivo and in vitro.

Stimulation of adrenergic nerve fibres to the urinary bladder of the rat

The contraction of the rat detrusor muscle caused by electrical stimulation of the hypogastric or pelvic nerves was followed by relaxation when the nerves were stimulated for a short period. The relaxation was more pronounced when the initial contraction was reduced by atropine. It was found to be mediated by adrenergic fibres acting on inhibitory beta2-receptors. Stimulation of the hypogastric or pelvic nerves at high frequencies increased the contractile response probably via adrenergic fibres activating excitatory alpha-receptors.

Adrenergic and cholinergic innervation of the rag urinary bladder

The autonimic innervation of the rat urinary bladder was studied using histochemical methods and nerve stimulations. A sparse adrenergic innervation of the detrusor muscle was found. It was supposed to originate from long adrenergic neurones. The trigonum area had a rich ssupply of adrenergic fibres, probably derived from short adrenergic neurones. A uniformly rich supply of acetylcholine-esterase (AChE)-positive nerves was found in the WHOLE BLADDER. Postganglionic sympathetic denervation caused no detectable change of adrenergic or AChE-positive nerves in the bladder, while parasympathetic decentralization or denervation produced a total disappearance of adrenergic fibres. The AChE-positive nerves were appreciably reduced in number after parasympathetic decentralization and not detectable after postganglionic denervation. Neither adrenergic nor AChE-positive ganglion cells could be demonstrated in the bladder wall. Electrical stimulation of the hypogastric nerves or the pelvic nerves distal to the pelvic ganglia elictied contraction of the detrusor muscle. The responses were not affected by hexamethonium, dihydroergotamine or proparanolol but were slightly reduced by guanethidine, reduced to about 40% by atropine and potentiated by eserine. Stimulation of the pelvic nerve proximal to the pelvic ganglion was partially blocked by hexamethonium. It si concluded that the urinary bladder of the rat is supplied by postganglionic adrenergic fibres mainly via the pelvic nerves and only to a lesser extent via the hypogastric nerves. Probably cholinergic fibres pass to the bladder mainly via the pelvic nerves but also via the hypogastric nerves, having their cellbodies outside the bladder wall, partly proximal to the pelvic ganglia.