THE DISTRIBUTION OF ADRENOCEPTORS AND OTHER DRUG RECEPTORS BETWEEN THE TWO ENDS OF THE RAT VAS DEFERENS AS REVEALED BY SELECTIVE AGONISTS AND ANTAGONISTS

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Abstract
1 The effects of adrenoceptor agonists and other agonists on the contractile responses of the prostatic and epididymal portions of the rat isolated vas deferens to single pulse field stimulation were investigated. 2 α-Adrenoceptor agonists produced prejunctional α2-mediated inhibition and post-junctional α1-mediated potentiation of the nerve-induced responses. Guanabenz and xylazine produced mainly inhibitory effects, xylazine being 10 times less potent. Clonidine and oxymetazoline produced inhibition with similar potency to guanabenz but at higher concentrations excitatory effects were present, particularly in the epididymal portion. Phenylephrine produced only potentiation of the nerve-induced response in both portions. Potentiation of nerve-induced responses was a more sensitive and quantitative index of excitation than was direct contraction of the tissue. 3 Isoprenaline and salbutamol both gave β2-mediated inhibition of the nerve-induced responses in both portions of tissue. At least part of the effect was post-junctional since phenylephrine contractions were inhibited. Isoprenaline also produced a post-junctional α1-mediated excitation. 4 Noradrenaline produced effects qualitatively similar to those of the other α-adrenoceptor agonists, inhibition and excitation predominating in the prostatic and epididymal ends respectively. 5 Morphine produced inhibition in the mouse but not in the rat vas deferens. In rat vas, however, enkephalin analogues produced pre-junctional inhibition of responses in both portions which could be partly reversed by naloxone; restoration of the adrenergic component was more complete. Rat anococcygeus showed no equivalent effect. 6 Adenosine 5′-triphosphate (ATP) inhibited nerve-induced responses in each portion with a greater effect on the prostatic portion.