IN VIVO AND IN VITRO EFFECTS OF ESTRADIOL ON CARDIOVASCULAR VARIABLES IN THE GUINEA PIG (ESTROGENS, BLOOD PRESSURE, NOREPINEPHRINE, VASCULAR SMOOTH MUSCLE)
Abstract
Four experiments were conducted to gather information concerning the effects of estrogens on blood pressure (BP) and cardiovascular responsiveness (CR) in guinea pigs (GPs). In Experiment 1, ovariectomized female GPs were instrumented with chronic carotid artery and jugular vein catheters to allow simultaneous measurement of resting BP plus CR to intravenous infusions of norepinephrine (NE). Additional measurements were made on several metabolic variables, including food intake and water intake. Compared to subjects treated with control injections of the oil vehicle alone, injections of 3 or 30 ug estradiol benzoate (EB) for 4 days significantly reduced resting BP and CR to NE. Concurrent reductions were also noted in food and water intake. In order to assess whether such reductions in mineral and fluid intake may in themselves be responsible for the observed cardiovascular changes, similar reductions in availability of food and water were imposed on a group of subjects. These restrictions did not produce any significant changes in the cardiovascular variables. Experiment 2 examined the effectiveness of estradiol treatment on male guinea pigs. Compared to effects of control treatment, injections of 3 ug of EB for 4 days significantly reduced BP and CR to NE in both intact and castrated male GPs. Experiment 3 was designed to assess the short-term effects of ovariectomy on several metabolic and cardiovascular variables. When compared to sham-operated intact guinea pigs 13-15 days post-surgery, ovariectomy was found to have little differential effect on the variables monitored. However, comparison of results after realignment of data by vaginal estrus in the intact females indicated that the surgical and experimental procedures in this study were sufficiently disruptive to at least partially abolish the expected endocrine differences between the intact and ovariectomized groups. Experiment 4 involved the in vitro analysis of norepinephrine-induced contractions in vascular smooth muscle collected from ovariectomized GPs pretreated with either EB or the oil vehicle. Significantly smaller contractions to NE were found in tissue from EB treated subjects. In combination, results of these experiments indicate that estrogen treatments can reduce BP and CR in GPs, and that these effects may involve direct actions of this hormone on vascular smooth muscle.
Degree
Ph.D.
Subject Area
Psychobiology
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