A comparison of pre- and post-junctional potencies of several alpha-adrenoceptor agonists in the cardiovascular system and anococcygeus muscle of the rat. Evidence for two types of post-junctional alpha-adrenoceptor.

摘要: The pre- and post-junctional effects of five α-adrenoceptor agonist drugs were examined in the pithed rat. On pre-junctional receptors on cardioac-celerator nerves, oxymetazoline, guanabenz xylazine had which qualitatively similar to established clonidine; phenylephrine not. These could be antagonised by yohimbine. Post-junctional agonists, assessed as diastolic arterial pressor response or contraction anococcygeus, showed an unexpected pattern. almost abolished prazosin (1 mg/kg) whereas other four clonidine, only moderately antagonised, being particularly resistant; this resulted order potency for “prazosin-resistant” responses was that agonism cardiac vas deferens sympathetic nerves. Yohimbine produced greater antagonism than did prazosin. It is postulated at least two types α-adrenoceptors exist rat tissues, one α1-adrenoceptors previously demonstrated another has similarities prejunctional α2-adrenoceptors. Noradrenaline released from vasopressor nerves administered intravenously shown produce partly resistant prazosin, suggesting a physiological role each these α-adrenoceptors.