title: Role of sex steroid hormones in relative refractoriness to angiotensin II during pregnancy.
abstract: Normal human pregnancy is associated with significant vascular refractoriness to the pressor effects of infused angiotensin II, and in women destined to develop pregnancy-induced hypertension, this refractoriness is lost several weeks before the onset of hypertension. The plasma concentrations of sex steroid hormones gradually increase throughout pregnancy. In the present study, the effect of infusion of 17 beta-estradiol (E2), progesterone, or 5 alpha-dihydroprogesterone on the pressor response to infused angiotensin II (0.002 to 0.1 micrograms X min-1 X kg-1) was evaluated in eight unanesthetized and chronically instrumented nonpregnant ewes. Pressor response to infused angiotensin II (0.02 to 0.1 micrograms X min-1 X kg-1) was significantly suppressed by a 60-minute infusion of E2 (0.8 micrograms X kg-1), whereas infusion of progesterone (4 micrograms X min-1 X kg-1) or 5 alpha-dihydroprogesterone (0.8 micrograms X min-1 X kg-1) did not affect the pressor response. Neither the acid-base status, plasma renin activity, nor serum electrolytes were altered by the administration of E2 or progesterone. These results indicate that E2 may play an important role in the refractoriness to infused angiotensin II during pregnancy, and that this refractoriness by E2 is not mediated by changes in chemoreceptor reflex, renin-angiotensin system, or serum electrolytes, but more likely by the changes in the characteristics of the vascular wall.
mesh_terms: D043582:5-alpha-Dihydroprogesterone; D000804:Angiotensin II / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004341:Drug Evaluation; D004958:Estradiol / Q000494:pharmacology / Q000502:physiology; D005260:Female; D012739:Gonadal Steroid Hormones / Q000494:pharmacology* / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D011247:Pregnancy; D011277:Pregnanediones / Q000008:administration & dosage / Q000494:pharmacology; D011374:Progesterone / Q000494:pharmacology / Q000502:physiology; D012083:Renin / Q000097:blood; D012756:Sheep; D013997:Time Factors; D014655:Vascular Resistance / Q000187:drug effects
chemical_list: D012739:Gonadal Steroid Hormones; D011277:Pregnanediones; D000804:Angiotensin II; D011374:Progesterone; D004958:Estradiol; D043582:5-alpha-Dihydroprogesterone; D012083:Renin