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-estradiol in the modulation of baroreflex
sensitivity in male rats
Department of Anatomy and Physiology, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island, Canada C1A 4P3
Female mammals have an enhanced baroreflex
sensitivity compared with their male counterparts, leading researchers
to speculate that estrogen modulates autonomic tone. Therefore, this
study tests the hypothesis that exogenous estrogen can enhance the
baroreflex sensitivity of male rats. Male Sprague-Dawley rats
anesthetized with thiobutabarbitol sodium (50 mg/kg) were instrumented
to measure blood pressure and heart rate and for the intravenous
injection of drugs. The baroreflex was tested using intravenous
injections of phenylephrine (0.025, 0.05, and 0.1 mg/kg), and the
cardiovascular responses were plotted to obtain a measure of the
sensitivity of the cardiac baroreflex. Intravenous injection of
estrogen produced dose-related increases in the baroreflex sensitivity
due to an increase in the magnitude of the reflex bradycardia. In a
separate group of animals, stimulation of the vagus nerve for 2 h
resulted in a decrease in baroreflex sensitivity. This effect was
blocked when estrogen (1 × 10
2 mg/kg) was administered
immediately before the end of stimulation. In conclusion, intravenous
injection of estrogen in male rats significantly enhanced baroreflex
sensitivity and blocked the attenuation in the baroreflex sensitivity
observed after vagal stimulation.
visceral afferents; sympathetic; parasympathetic; ICI-182,780
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