Microcirculatory effects of prostacyclin (PGI2) in the hamster cheek pouch.

The effects of prostacyclin (PGI₂) on small blood vessels in the hamster cheek pouch microcirculation were studied microscopically. Prostacyclin applied systemically or locally caused an increase in the diameter of precapillary arterioles (10–50 μm diameter) with inherent or induced tone. It was more potent prostaglandin PGE₁, PGE₂, or bradykinin. In animals treated with indomethacin (4 mg/kg po), the relative vasodilator potency of prostacyclin to PGE₁ and PGE₂ was increased. The cyclic endoperoxide precursor of prostaglandins, PGH₂, and the stable chemical breakdown product of prostacyclin, 6-oxo-PGF_1α, were also dilators but were less potent than prostacyclin itself. In some experiments, responses of arterioles to PGH₂ were biphasic, a long-lasting dilatation being preceded by a short-lasting vasoconstriction. The postcapillary venules (20–50 μm diameter) in this preparation were inactive and did not respond by dilatation or constriction to PGI₂, PGE₁, PGE₂, PGH₂, 6-oxo-PGF_1α, bradykinin, or noradrenaline.