The effects of adenosine on receptor sensitivity in the rat vas deferens

Abstract

In the guinea-pig isolated vas deferens adenosine augments the contractile response to noradrenaline (NA). Adenosine also augments the contractile response to NA and phenylephrine in the prostatic portion of the transversely bisected rat vas deferens. However, adenosine appeared to neither augment nor diminish the responses to carbachol, 5HT or high K +. Repetitive exposure of the vas to various agonists induced a desensitisation specific to the particular agonist used. The rate of return of responsiveness (the rate of resensitisation) was investigated and, in particular, the effect of adenosine on that rate. In the rat vas deferens the rate of resensitisation of responses to NA was retarded by adenosine and this effect was abolished by 8-phenyltheophylline and by yohimbine, but not by atropine or propranolol. Neither 8-phenyltheophylline, yohimbine, propranolol nor atropine by themselves affected the rate of resensitisation of the rat α-adrenoceptor. Adenosine had no effect on the rate of resensitisation of responses to phenylephrine, 5HT, carbachol or high K +. It is considered that the potentiation of catecholamine responses by adenosine involves solely α 1-receptors but that the retardation of resensitisation may involve α 2-receptors which do not contribute directly to contraction.