Alteration in the reactivity of hamster cheek pouch arterioles to prostaglandin E2 and noradrenaline during pregnancy or sex steroid treatment.
Dioestrous and pregnant, or ovariectomized hamsters treated with sunflower oil, oestradiol or progesterone were anesthetized with pentobarbital and the arterioles of the cheek pouch membrane were prepared for microcirculatory study. Prostaglandin E2 (PGE2) or noradrenaline (NA) were topically applied and changes of the arteriolar diameter were measured on the screen of a closed-circuit television. PGE2 induced arteriolar dilatation in dioestrous or ovariectomized hamsters, but induced vasoconstriction in pregnant or in oestrogen-treated animals. Vasoconstriction induced by PGE2 in oestrogen-treated animals disappeared after administration of alpha-adrenergic blockers. In this situation, PGE2 induced vasodilatation once again. NA elicited arteriolar constriction in each experimental group. In ovariectomized hamsters treated with oestrogen the constriction was more pronounced than in progesterone treated animals. In pregnant animals it was significantly greater on day 14 than in dioestrous animals. Progesterone treatment blunted the vascular effect of both PGE2 and NA. It was concluded that the reverse effect of PGE2 and the increased sensitivity to NA induced by high oestradiol levels may have roles in the regulation of local blood flow during the ovarian cycle and pregnancy.