Impaired baroreflex changes in muscle sympathetic nerve activity in adolescents who have a family history of essential hypertension.

To evaluate the baroreflex changes and basal sympathetic vasomotor tone among three groups of adolescent normotensives or borderline hypertensives with and normotensives without a family history of hypertension, we continuously recorded muscle sympathetic nerve activity, arterial pressure and heart interval. Baroreflex slopes were calculated either by plotting the heart interval against the preceding peak systolic arterial pressure, or by relating the percentage changes in muscle sympathetic nerve activity to the mean changes in systolic arterial pressure produced by intravenous phenylephrine. The baroreflex slopes for the heart interval were significantly smaller in borderline hypertensive offspring (14 +/- 2 ms/mmHg) than in control normotensives (23 +/- 2 ms/mmHg) or normotensive offspring (19 +/- 3 ms/mmHg), whereas those for muscle sympathetic nerve activity were significantly smaller both in normotensive offspring (-8.3 +/- 1.0%/mmHg) and borderline hypertensive offspring (-7.9 +/- 0.5%/mmHg) than in control normotensives (-16.3 +/- 1.4%/mmHg). Baseline muscle sympathetic nerve activity was higher in borderline hypertensive offspring (20.1 +/- 3.0 bursts/min) than in control normotensives (10.1 +/- 1.2 bursts/min) or normotensive offspring (12.8 +/- 1.4 bursts/min), and also the depressor responses to trimethaphan were significantly enhanced in borderline hypertensive offspring [-19.2 +/- 2 versus 14 +/- 1 (normotensive offspring) or 12 +/- 2 (control normotensives)]. These results indicate that baroreflex inhibition of muscle sympathetic nerve activity was reduced in adolescents with a family history of hypertension even when they were normotensive. This reduced reflex sympatho-inhibition could lead to the development of hypertension by increasing sympathetic vasomotor tone.