Responses of Isolated Feline and Human Cerebral Arteries to Prostacyclin and Some of its Metabolites

Abstract

The effects of prostacyclin (PGI₂) were studied in isolated cat basilar and middle cerebral arteries and in human pial arteries. In feline vessels with low resting tension, PGI₂had a contractile effect that reached a maximum of 132% (basilar artery) and 23% (middle cerebral artery) of the potassium-induced (127 m M) contraction. In potassium-contracted feline vessels, PGI₂caused a further contraction. When these vessels were contracted by PGF_2α, PGI₂induced relaxation, which was most marked in the middle cerebral artery. PGI₂consistently relaxed the middle cerebral artery contracted by the prostaglandin endoperoxide analogue U-44069, whereas the basilar artery was almost unaffected. In human pial arteries with low resting tension, PGI₂had no effects in concentrations below 10⁻⁶M, whereas higher concentrations induced contractions. In potassium-contracted (35 or 127 m M) preparations, PGI₂in concentrations below 10⁻⁶M produced relaxation; in higher concentrations further contraction was induced. Human pial arteries contracted by PGF_2α, U-44069, noradrenaline, or 5-hydroxytryptamine consistently relaxed in response to PGI₂(< 10⁻⁶M). The PGI₂metabolite 6-keto-PGE₁had effects similar to those of PGI₂, but proved to be less potent on human pial vessels. 6-Keto-PGF_1αwas ineffective, whereas 6, 15-diketo-PGF_1αhad minor relaxant effects. The results suggest that consideration must be given to regional as well as species differences concerning the cerebrovascular effects of PGI₂.