EFFECTS OF ACUTE AND CHRONIC ESTROGENIC TREATMENT ON VASOMOTOR RESPONSES OF AORTIC RINGS FROM OVARIECTOMIZED RATS

The effects of either chronic or acute estrogenic treatment on the ''i n vitro'' vasomotor responses to phenylephrine (10(-9)-10(-5) M) and t o carbachol (10(-9)-10(-5) M) Of aortic rings excised from ovariectomi zed rats were analyzed. Chronic estrogenic treatment consisted in a si ngle subcutaneous dose of 1 mu mol estradiol 17-stearate. Effects of a cute estrogenic treatment were evaluated by recording the responses of aortic rings excised from untreated ovariectomized rats both before a nd after the addition of 17 beta-estradiol to the superfusing solution s. In order to identify the endothelium-dependent responses each exper iment was performed simultaneously on pairs of rings from the same aor ta, one with and the other without functional endothelium. The contrac tile responses to phenylephrine of endothelium-intact vessels were att enuated by chronic estrogenic treatment; this attenuation was further increased by preincubation of the vessels with indomethacin and was re verted by No-nitro-L-arginine methyl ester. Either chronic or acute es trogenic treatment enhanced the carbachol-induced endothelium dependen t relaxation of phenylephrine-precontracted rings. The results may be explained by assuming that estrogens increase the basal release of bot h nitric oxide and a cyclooxygenase-dependent vasoconstricting prostan oid as well as the receptor-mediated release of nitric oxide from the endothelium of the rat aorta.