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

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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 PGF2α, 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 PGF2α, 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-PGF1αwas ineffective, whereas 6, 15-diketo-PGF1αhad minor relaxant effects. The results suggest that consideration must be given to regional as well as species differences concerning the cerebrovascular effects of PGI2.