NORMOTENSIVE BLACKS HAVE HEIGHTENED SYMPATHETIC RESPONSE TO CORD PRESSER TEST

The purpose of this study was to compare sympathetic nerve activity re sponses to the cold presser test in black and white normotensive subje cts. We recorded muscle sympathetic nerve activity (microneurography o f the peroneal nerve), arterial blood pressure, and heart rate in 9 no rmotensive American blacks (24+/-2 years, mean+/-SEM) and 10 normotens ive American whites (28+/-2 years) at rest and during hand immersion i n ice water (cold presser test). Body weight was not different in the two groups (72.4+/-3.7 versus 74.1+/-3.8 kg, black versus white subjec ts). During supine rest, mean arterial pressure (92+/-2 versus 93+/-3 mm Hg, black versus white), heart rate (66+/-4 versus 62+/-3 beats per minute, black versus white), and muscle sympathetic nerve burst frequ ency (12+/-2 versus 17+/-3 bursts per minute, black versus white) were not different in the two groups. During the cold presser test, mean a rterial pressure, heart rate, and muscle sympathetic nerve activity in creased from supine rest in both groups. The magnitudes of increases i n mean arterial pressure and total minute muscle sympathetic nerve act ivity were significantly greater in blacks than whites (33.5+/-3 versu s 22.4+/-3 mm Hg and 416+/-24% versus 243+/-31% of control, respective ly, black versus white, P<.05). The increases in heart rate were not s ignificantly different for the two groups. These data suggest that the enhanced presser response to cold stress observed in normotensive bla cks is attributable to greater increases in peripheral sympathetic ner ve activity. This heightened sympathetic response to stress may predis pose blacks to the development of hypertension.