Inhibition of vasoconstrictor responses by prostacyclin (PGI2) in the feline mesenteric vascular bed.

The effects of infusion of prostacyclin, PGI2, on vasoconstrictor responses to sympathetic nerve stimulation, norepinephrine and angiotensin II were investigated in the mesenteric vascular bed of the cat. Stimulation of the sympathetic nerves and intra-arterial injections of norepinephrine and angiotensin increased mesenteric perfusion pressure in a frequency and dose-dependent manner. Responses to nerve stimulation and pressor hormones were reproducible and not altered by infusions of the Tris vehicle for PGI2 or the PGI2 breakdown product, 6-keto-PGF1 alpha. Infusions of PGI2, 1 and 0.3 micrograms/min, decreased mesenteric arterial perfusion pressure and, at the higher infusion rate, markedly reduced responses to nerve stimulation, norepinephrine and angiotensin. At the lower infusion rate PGI2 caused small but significant reductions in responses to norepinephrine and nerve stimulation but did not alter responses to angiotensin. Results of these studies demonstrate that PGI2 possesses the ability to inhibit vasoconstrictor responses in the feline intestinal vascular bed and suggest that this effect is postjunctional.