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

1. The pressor responses produced by the intravenous administration of alpha,beta-methylene ATP were tachyphylactic. 2. alpha,beta-Methylene ATP can attenuate pressor responses to sympathetic nerve stimulation both in the presence and in the absence of alpha-adrenoceptor blocking agents. 3. alpha,beta-Methylene ATP has no effect on the pressor responses produced by bolus injections of noradrenaline. 4. In the presence of alpha-adrenoceptor blocking agents, alpha,beta-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 alpha-adrenergic and that this occurs as co-transmission. The same applies to rat vas deferens, confirming in vitro data. The pithed rabbit had an alpha-blocker-resistant vasopressor nerve-mediated response but this was resistant to alpha,beta-methylene ATP.