288 EFFECTS OF OVARIAN HORMONES ON THE CARDIAC AFFERENT REFLEX

Abstract

Background: In disease states, such as hypertension and heart failure, the cardiac afferent reflex has been implicated in driving pathophysiological increases in sympathetic nerve activity (SNA). The current study set out to investigate the impact that ovarian hormones have on the cardiac afferent reflex. Methods: On the day of experiment blood pressure (BP), heart rate (HR) and renal SNA were recorded in chloralose-urethane anesthetized, open-chest and baroreceptor denervated female Wistar rats with ovaries-intact or -removed. The cardiac afferent reflex was investigated by placing capsaicin (1, 5 and 10 μg per 10 μl) via a piece of filter paper onto the anterior surface of the left ventricle for 40 seconds. Results: Removal of ovaries abolished the initial vagal mediated decrease in renal SNA that was observed in females with ovaries-intact at 4 seconds post capsaicin application. At 40 seconds post-capsaicin application the increase in renal SNA was significantly greater in ovary-removed females compared to ovary-intact females. The estrous cycle in ovary-intact females also significantly impacted on the cardiac afferent reflex; females in the proestrous phase displayed greater increases in renal SNA compared to females in the estrous/metestrous phase. Discussion: The current findings suggest that circulating ovarian hormones affect the cardiac afferent reflex, with removal of circulating ovarian hormones resulting in greater reflex sympathetic excitation. These findings provide evidence of a mechanism that may contribute to greater sympathetic excitation in cardiovascular disorders post-menopause, compared to pre-menopausal, which may relate to higher rates of morbidity and mortality in women following menopause.