Blockade of vasopressor and vas deferens responses by , fB - methylene ATP in the pithed rat

1 The pressor responses produced by the intravenous administration of a,#-methylene ATP were tachyphylactic. 2 a,fi-Methylene ATP can attenuate pressor responses to sympathetic nerve stimulation both in the presence and in the absence of a-adrenoceptor blocking agents. 3 a,#-Methylene ATP has no effect on the pressor responses produced by bolus injections of noradrenaline. 4 In the presence of a-adrenoceptor blocking agents, a,x-methylene ATP further attenuates contractions of the vas deferens produced by nerve stimulation. 5 The results, together with previous data, suggest that the vasopressor response to stimulation of the sympathetic outflow in the rat is partly purinergic and partly a-adrenergic and that this occurs as co-transmission. The same applies to rat vas deferens, confirming in vitro data. The pithed rabbit had an a-blocker-resistant vasopressor nerve-mediated response but this was resistant to a,#methylene ATP.