SUMMARY Sixteen healthy, normotensive husband-wife pairs participated in a study to investigate the effect of reduction of dietary sodium intake (goal ^ 60 mEq/day) on blood pressure. Sodium excretion decreased from a control average of 152.7 ± 10.1 (SE) mEq/day to 69.5 ± 4.5 mEq/day (p < 0.001). Results indicated significant decreases in both systolic (p < 0.001) and diastolic (p < 0.001) blood pressure after a period of sodium restriction. In the entire group, there was no significant change in potassium excretion (58.4 ± 3.2 vs 54.6 ± 3.5 mEq/day) or body weight (76.0 ± 2.8 vs 75.3 ± 2.7 kg). Although there was variability in the blood pressure response, the decrease in blood pressure was significantly correlated with the magnitude of sodium restriction (r = 0.36, p < 0.03). These results indicate that the blood pressure response to sodium restriction may not be limited to individuals with hypertension and that the response is heterogeneous in normotensive subjects. (Hypertension 5: 790-795, 1983

SUMMARY To assess the influence of heredity on factors that help regulate the arterial blood pressure in man, we conducted sodium-loading and depletion studies in monozygotic and dizygotic twins, normotensive first-degree relatives of essential hypertensives, and in nonnotenslve control subjects matched for age, sex, and race. Following sodium-loading, we found evidence for the influence of genetic variance on the natriuretic responses, plasma renin activity (PRA), plasma aldosterone concentrations (PA), and plasma and urinary norepinephrine. Relatives of hypertensives differed from controls in that they had higher blood pressures, greater renin values, and relatively sluggish natriuretic responses. Since renin and fractional sodium excretion values were inversely correlated in all subject groups, it is possible that the heritable influences we observed on sodium excretion were mediated by the renin-angiotensin-aldosterone system. 79 the nature of these influences has not been defined clearly. To examine inherited mechanisms that may contribute to the development of essential hypertension in some individuals, or the resistance to hypertension in others, we conducted detailed studies of monozygotic and dizygotic normotensive twins, normotensive firstdegree relatives of essential hypertensives, and large numbers of normotensive white and black subjects by means of a standardized protocol incorporating both sodium-loading and depletion. "14 In these studies we examined electrolyte balance, components of the renin-angiotensin-aldosterone system, and humoral indicators of sympathetic nervous system activity. The studies in twins 1-34fluences in each of these areas. The studies in normotensive, first-degree relatives of essential hypertensives indicated the existence of important differences in electrolyte excretion and peripheral renin values that may contribute to the susceptibility to hypertension of this high-risk group." We present these findings in light of their bearing on the importance of heredity in regulating blood pressure in man. Methods Studies in TwinsData from monozygotic (MZ) and dizygotic (DZ) twins provide a unique opportunity to test for the existence of genetic variation in traits. Since MZ twins are genetically identical and DZ twins are related as full siblings, a given trait would be expected to exhibit smaller twin-pair differences for MZ than DZ twins if genetic influences are present. On the other hand, if the trait is only influenced by environmental variability, the MZ and DZ twin-pair differences should be approximately equal.The statistical methods involved in the analysis of MZ and DZ twin data have been recently reviewed by Christian. 16 We chose the comparison of MZ and DZ twins as the most efficient method for the initial investigation of heritable components in quantitative by guest on May 11, 2018 http://hyper.ahajournals.org/ Downloaded from

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