A qualitative study of the autonomic receptors modulating the contractile activity of isolated ovine ureter

Abstract

The aim of the present study is to evaluate the role autonomic receptors in initiating neurogenic contractions and the role of post-synaptic alpha adrenergic receptors in controlling the contractility of the ovine ureter. Isolated sheep ureter strips were studied to clarify the autonomic receptor functions by investigating the actions of selective agonists and antagonists. Noradrenaline shows a well pronounced excitatory effect on uretero-pelvic and vesicular regions which can be blocked by phenoxybenzamine, a nonselective alpha adrenergic receptor blocker. Selective blockade of alpha-1 receptors with prazosin did not inhibit the action noradrenaline but yohimbine, a selective alpha-2 receptor blocker, abolished the effect of noradrenaline in pelvic, proximal and vesicular regions of the ureter. Selective blockade of alpha-1 receptors with prazosin inhibit the action of noradrenaline all regions of the ureter except pelvic, proximal and vesicular regions of the ureter. Clonidine, a selective alpha-2 agonist, produced a significant contractile effect on the ureter in the pelvic, proximal and vesicular regions but not significant effect on the rest of the regions of the ureter. Phenylephrine, a selective alpha-1 receptor agonist show remarkable contractile effect on all parts of the ureter except the pelvic, proximal and vesicular regions. High intensity, high frequency, short duration stimuli applied on spontaneously contracting ureteral segments show enhancement of contraction which can be blocked by pretreating the preparation with phenoxybenzamine and tetrodotoxin (TTX). This study suggests that post-synaptic receptors responsible for the mediation of the stimulatoiy action of noradrenaline are of the alpha-2 subtype in the pelvic, proximal and vesicular regions of the ureter and alpha-1 in the rest of the regions. © 2010 Asian Network for Scientific Information.

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