Sympathetic pressor responses to glutamate nanoinjections in the rostral ventrolateral medulla are influenced by ovarian hormones in active but not sedentary female rats

Abstract

Cardiovascular disease (CVD) is the leading cause of death worldwide. One of the leading risk factors for CVD is hypertension. The incidence of hypertension in females increases drastically after the onset of menopause, suggesting female reproductive hormones have cardioprotective effects. However, the interaction between female reproductive hormones and blood pressure-lowering effects of regular physical activity are poorly understood. Blood pressure is controlled by a region of the brainstem known as the rostral ventrolateral medulla (RVLM). Previously, we reported that female rats had lower resting blood pressure than male rats, but had higher sympathoexcitatory responses to direct activation of the RVLM, as did sedentary animals from both sexes. Therefore, the purpose of our study was to examine the interaction between ovarian hormones and sedentary and active conditions. We hypothesized that during low or high hormone stages, sedentary female rats would have higher blood pressure responses to activation of the RVLM compared to the physically active female rats. In addition, we hypothesized that ovariectomy (OVX) would reduce the ability of exercise to blunt pressor responses to RVLM activation. OVX or sham surgeries were performed at four weeks of age and groups were split into active (running wheels) or sedentary conditions (no running wheels) for 12 weeks. At 16 weeks of age, vaginal lavages were collected under Isoflurane anesthesia to categorize stages of the estrous cycle and all rats received glutamate nanoinjections (1, 10, & 100 mM; 30 nl ea.) into the RVLM, under Inactin anesthesia. Sedentary versus active conditions promoted significantly greater pressor responses to nanoinjections of glutamate (100 mM) in the RVLM in both the high hormone (proestrus/estrus; 25±2 vs 14±3 mmHg, p<0.001) and low hormone (diestrus/metestrus; 21±2 vs 14±2 mmHg, p=0.007) groups. In OVX rats, the beneficial effects of exercise appeared to be lost as pressor responses to 100 mM of glutamate were similar in sedentary versus active rats (20±2 vs 25±6 mmHg, resp., p>0.05). Our results indicate that the absence of ovarian hormones offset the decreased pressor responses originating from the RVLM in active but not sedentary animals and could help explain the increased risk for CVD in females after menopause. They also demonstrate the increased risks of CVD and hypertension associated with a sedentary lifestyle as a result of this greater sensitivity to sympathoexcitation. 1R01-HL161233 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.