Baroreflex function and pressor responsiveness in normotensive young subjects with a family history of hypertension.

Baroreflex control of heart rate, pressor responses to alpha agonist (phenylephrine) and isometric exercise before and during salt loading were compared between 13 normotensive subjects with hypertensive relatives (group A) and 9 normotensive subjects with no family history of hypertension (group B). Baroreflex slope was significantly lower in group A than in group B (9.6 +/- 1.6 vs 17.6 +/- 1.9 msec/mmHg; p less than 0.01), although blood pressure, heart rate and aortic distensibility were not different between two groups. Pressor responses to phenylephrine and isometric exercise were identical for both groups. During salt loading, pressor responses to phenylephrine and isometric exercise were significantly greater in group A than in group B. Baroreflex slope was not affected by salt loading in the two groups. These results suggest that baroreflex control of heart rate is impaired in normotensive young subjects with hypertensive relatives and this defect may be inherited rather than the result of elevated arterial pressure and decreased aortic distensibility. Pressor responses to alpha agonist and isometric exercise during high-sodium diet were augmented in subjects with a family history of hypertension.