Systemic and uterine blood flow distribution during prolonged infusion of 17beta-estradiol

Abstract

Prolonged 17beta-estradiol (E2beta) infusion decreases mean arterial pressure (MAP) and systemic vascular resistance (SVR) while increasing heart rate (HR) and cardiac output (CO). It is unclear, however, which systemic vascular beds show increases in perfusion. The purpose of this study was to determine which reproductive and nonreproductive vascular beds exhibit alterations in vascular resistance and blood flow during prolonged E2beta infusion. Nonpregnant, ovariectomized sheep received either vehicle (n = 6) or E2beta (5 microg/kg iv bolus followed by 6 microg/kg over 24 h for 10 days; n = 9), and blood flow distribution was evaluated using radiolabeled microspheres at control and 120 min and 3, 6, 8, and 10 days of infusion. During E2beta infusion MAP (87 +/- 5 mmHg; mean +/- SE) decreased 3-9% and HR (83 +/- 5 beats/min) increased 4-31%. The combined baseline (control) perfusion to the uterus, broad ligament, oviducts, cervix, vagina, and mammary gland (reproductive blood flows) was 49 +/- 9 ml/min; at 120 min, E2beta increased flow (P < 0.001) to 605 +/- 74 ml/min (1,263%) and it remained elevated, but at a reduced rate, on day 3 (218 +/- 44 ml/min; 399%), day 6 (144 +/- 23; 217%), day 8 (181 +/- 19; 321%), and day 10 (204 +/- 48; 454%), accounting for only 3-17% of the E2beta-induced increase in CO. During this E2beta treatment, there also were significant decreases in vascular resistances leading to increases (P < 0.05) in blood flows to several nonreproductive (systemic) vascular beds including skin (32-113%), coronary (32-190%), skeletal muscle (25-133%), brain (21-292%), bladder (128-524%), spleen (87-180%), and pancreas (35-137%) vascular beds. Responses of these combined nonreproductive blood flows represent the major percentage (21-67%) of the E2beta-induced increase in CO. Vehicle infusion was without effect. We conclude that prolonged E2beta infusion increases reproductive and nonreproductive tissue blood flows. The latter appears to principally be responsible for the observed rise in CO and decrease in SVR.