BAROREFLEX CONTROL OF MUSCLE SYMPATHETIC-NERVE ACTIVITY IN MILD HYPERTENSION

The importance of the arterial baroreflex control of muscle sympatheti c nerve activity (MSNA) has been investigated in physiological conditi ons and in cardiovascular dysfunctions. However, there is no consensus about the role played by the MSNA in hypertensive states, probably du e to the diversity of the methods used to study the arterial barorefle x control of MSNA. In the present study we evaluated the reflex change s in MSNA by increasing and decreasing the mean arterial pressure (MAP ) through 1 min intravenous infusion of phenylephrine (1 mu g/kg) and sodium nitroprusside (1 mu g/kg), respectively, in eight normotensive and eight mild hypertensive subjects. Both MAP and MSNA were significa ntly higher in hypertensive (117 +/- 2 mm Hg and 30 +/- 3 bursts/min) than in normotensive (96 +/- 4 mm Hg and 20 +/- 3 bursts/min) subjects . The reflex gain was calculated by the ratio percent of changes in MS NA/percent changes in MAP. The maximal reflex gain was statistically s imilar in normotensive and hypertensive groups during phenylephrine (5 .1 +/- 1.4 v 4.3 +/- 0.4 bursts/mm Hg, respectively) and nitroprusside (10.7 +/- 2.3 v 8.1 +/- 1.3 bursts/mm Hg, respectively) infusion. The present data showing that arterial baroreflex control of MSNA is not depressed in hypertensive subjects indicate that the elevated basal MS NA and the mild hypertension in human beings is not a consequence of b aroreflex control of MSNA dysfunction. (C) 1997 American Journal of Hy pertension, Ltd.