The evaluation of the novel pressor activity of gamma-piperidinobutyramide (WY 20051, DF480).

1 gamma-Piperidinobutyramide (Wy 20051, DF480) injected intravenously evoked pressor responses in the anaesthetized ganglion blocked rat preparation over the dose range 2.4 x 10(-6)-3.0 x 10(-4) mol/kg. 2 High doses (greater than 3.8 x 10(-5) mol/kg) or even repeated submaximal doses (1.9 x 10(-5) mol/kg) of Wy 20051 caused tachyphylaxis of this pressor response. 3 The noradrenaline pressor-response curve was shifted significantly to the right of the control curve following a dose of Wy 20051 (1.5 x 10(-4) mol/kg cumulative). 4 The dose-response curve for the pressor action of Wy 20051 was potentiated in reserpine-treated anaesthetized rats. In contrast, tyramine-induced pressor responses were abolished. 5 Wy 20051 contracted the guinea-pig isolated aortic spiral preparation (3.8 x 10(-5)-6.0 x 10(-4) mol) and evoked constrictor responses in the perfused mesenteric vasculature preparation of the rat (5.9 x 10(-7)-1.2 x 10(-5) mol). At higher doses the responses were reduced. 6 Wy 20051-induced constrictor responses of the perfused mesentery were unaffected by blockade of alpha-adrenoceptors or by tachyphylaxis of 5-hydroxytryptamine receptors. 7 The time for abolition of Wy 20051-induced constrictor responses of the mesentery in a calcium-free medium was not significantly different from that required for noradrenaline, but was significantly greater than that for KCl (P less than 0.001). 8 Wy 20051 and noradrenaline, but not KCl, evoked constrictor responses in the depolarized rat mesenteric vasculature. 9 The results indicate that Wy 20051 evokes pressor responses which have some of the characteristics of those of noradrenaline. However, the responses are not elicited by an alpha-adrenoceptor mechanism.