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Renal vasoconstriction is increased and renin and aldosterone secretion is decreased in young persons at risk for hypertension. These findings support the hypothesis that alterations in renal hemodynamics occur at an early stage in the development of familial hypertension.

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Several disturbances in calcium metabolism have been reported in primary hypertensive subjects. It is, however, not clear whether these alterations predate the development of hypertension or occur as a consequence of high blood pressure. We studied indexes of calcium metabolism in three groups of normotensive children with different familial predispositions for hypertension, based on parental blood pressure levels, with two, one, or no hypertensive parents. Plasma intact parathyroid hormone pressure regulation. In some hypertensive subjects, urinary excretion of magnesium may be decreased and show an inverse relation with blood pressure.16 Serum phosphate concentration is reported to be lower in hypertension and negatively related to blood pressure. 17Besides changes in serum and urinary electrolytes, raised circulating parathyroid hormone (PTH) levels have been demonstrated in hypertensive individuals. 1318 We reported previously that plasma intact PTH is raised in young hypertensive subjects compared with normotensive subjects of similar age, suggesting that alterations in calcium metabolism may be important in the early phase of primary hypertension. 1920Discussion remains as to whether changes in calcium metabolism are causally related to the development of high blood pressure. 21 In genetically hypertensive rats, calcium supplementation during the developmental phase of hypertension diminished the blood pressure increase. 22 In another study, however, genetically hypertensive rats fed a calcium-deficient diet did not show an increased blood pressure rise compared with rats fed a normal diet. 23 Parathyroidectomy in young genetically hypertensive rats, while keeping a normal serum calcium level, delayed the rise in systolic blood pressure for 42 weeks. 24 In humans, information on the part played by changes in calcium metabolism in the development of high blood pressure may be gained from comparison of