A sex difference in the cardiac afferent reflex control of renal sympathetic nerve activity

Both the perception of cardiac pain and susceptibility to sudden cardiac death following myocardial infarction differs between men and women. A potential pathway which could mediate these sex differences is the cardiac afferent reflex. The aim of this project was to characterize cardiac afferent reflex control of renal sympathetic nerve activity (RSNA) in females in the different phases of the estrous cycle and in males. Arterial pressure (AP), heart rate (HR) and RSNA were recorded in anesthetized, open chest, sinoaortic denervated male and female rats. Capsaicin (1–10 μg per 10 μl) was applied to the surface of the left ventricle. In males RSNA steadily increased post capsaicin application, reaching a maximum at 40 seconds (male maximum RSNA increase 93 ± 5%). In contrast to males, females reached maximum RSNA increases at 10 seconds post capsaicin application and varied significantly with the estrous cycle; maximum RSNA increase during estrous was 10 ± 6% vs. 60 ± 10% in proestrous. The maximum RSNA response in males was significantly greater than in any of the female groups. Changes to HR and BP mimicked the changes to RSNA. These results suggest the sex hormones modulate the cardiac afferent reflex. The reduced sympathetic activation via the cardiac afferent reflex seen in the females could explain why females are at less risk of sudden cardiac death. Funded by Auckland Medical Research Foundation and Lotteries Health.