Influence of prostaglandins E1 and F1alpha on K-induced responses in vascular smooth muscle.

The effects of PGE1 and PGF1alpha (1.4-8.4 X 10(-8)M) were studied on contractures induced by 10--60 mM KCl in the isolated rabbit aorta. The greatest PG-induced increases in the K-contractures were observed at the lower concentrations of KCl. Greater tension increases were noted, particularly at the higher K concentrations with the simultaneous addition of KCl and the PGs rather than with their sequential addition in which the PGs were added after KCl. For example, when the PGs were added to tissues contracted with 60 mM KCl, no additional tension increases occurred, while significant increases were observed when the PGs were added simultaneously with 50--60 mM KCl. Isobolic plots of the data indicate that PGE1 at lower concentrations and PGF1alpha at all concentrations interacted with KCl as competitive antagonists. At median doses PGE1 exhibited an additive effect with KCl, while higher doses interacted in a synergistic manner.