On the relation between contraction and prostaglandin release in rabbit mesenteric blood vessels

The rabbit superior mesenteric artery and portal vein were used for a study of the effects of noradrenaline, high potassium, angiotensin II and bradykinin on both the contraction development and PG synthesis (PGE2 and PGF2 alpha) in tissue. Noradrenaline induced contractions but no PG release, high potassium evoked contractions and PG release, angiotensin II elicited contractions and PG release in the mesenteric artery but only PG release in the portal vein, and bradykinin initiated PG release and a small decrease in basal tone. The stimulus-evoked PG release was Ca2+-dependent. It is concluded that, at least in some tissues, stimulus-evoked PG release is completely independent from the contractile mechanism. The variable pattern in contractile responses and stimulus-evoked PG release in various tissue may depend on variations of the stimulus-induced accessibility of Ca2+ ions to either phospholipase A2 or the contractile apparatus.