Effects of prostaglandins on baseline pressure and responses to noradrenaline in a perfused rat mesenteric artery preparation. PGE1 as an antagonist of PGE2.

Concentrations of PGE1, PGE2, PGA1, PGA2 and PGF2alpha ranging from 10 to 10(5) pg/ml (2.8 x 10(-11) to 2.8 x 10(-7)M) were perfused through a rat mesenteric vascular bed preparation and their effects on baseline pressure and responses to noradrenaline noted. PGs A2 and FEalpha elevated baseline pressure at concentrations of 100 pg/ml and above but the other three PGs had little or no effect. PGs E2, A1 and F2alpha markedly potentiated responses to noradrenaline at all concentrations studied. In contrast PGs E1 and A2 caused a clear potentiation at 10 pg/ml but at higher concentrations the effect disappeared and concentrations of above 10(4) pg/ml were actually inhibitiory. E1 could antagonize the vascular effects of E2. These results offer possible explanations for some of the confusing findings reported in the literature.