Influences of female reproductive hormones on sympathetic control of the circulation in humans

The significant increase in cardiovascular disease risk with the loss of es trogen and progesterone at menopause has lead to increasing interest in the cardiovascular influences of female reproductive hormones. In addition to direct influences of estrogen to promote endothelium-dependent vasodilation , recent evidence demonstrates important influences of both estrogen and pr ogesterone on the neural control of the peripheral circulation. These influ ences have been studied in two general contexts. First, the effects of thes e hormones on the sympathetic control of the cutaneous circulation have rec eived substantial attention. The control of neurogenic vasodilation in the skin in response to hyperthermia is shifted to higher and lower internal te mperatures by progesterone and estrogen, respectively. Reflex vasoconstrict or control of skin blood flow is shifted to higher internal temperatures wh en the hormones are elevated. Second, reproductive hormones have recently b een shown to significantly alter sympathetic neural control of the skeletal muscle circulation. Sympathetic neural control of the skeletal muscle circ ulation (measured directly as muscle sympathetic nerve activity [MSNA]) is altered by hormone status such that resting MSNA is decreased by estrogen, as is the MSNA response to exercise. Furthermore, the baroreflex control of MSNA is significantly modified by estrogen and progesterone. Therefore, fe male reproductive hormones have widespread influences on the sympathetic co ntrol of the circulation in humans. The individual influences of estrogen a nd progesterone often antagonize one another, and when both hormone concent rations are increased, the net effect probably depends on their relative co ncentrations and bioactivity. The mechanisms responsible for these influenc es and their health-related implications deserve further attention.