1. Disturbances of calcium metabolism, mimicking mild, compensated secondary hyperparathyroidism, accompany essential hypertension, but it is not known whether these alterations are primary or only secondary to the elevated blood pressure.
2. Indices of systemic calcium metabolism were followed prospectively during 6 months' treatment with either propranolol, bendroflumethiazide or verapamil in 35 patients with essential hypertension. Multivariate statistical methods were employed to study the effects of blood pressure reduction upon the metabolic indices with adjustment for the effects of the different antihypertensive agents.
3. Propranolol treatment increased the plasma ionized calcium and serum phosphate concentrations, and reduced the serum levels of parathyroid hormone, free fatty acids and glycerol. Neither the total nor the total albumin-modified serum calcium concentration was significantly affected. Thus, presumably the decrease in free fatty acids reduced the calcium complex and the calcium binding to albumin, and consequently increased the plasma ionized calcium, thereby suppressing the secretion of parathyroid hormone.
4. Bendroflumethiazide caused a reduction of the fasting renal calcium excretion to half the pretreatment level, but produced no other significant changes in the various indices of calcium metabolism.
5. During verapamil treatment, the fasting renal excretion of calcium and magnesium increased, whereas the free fatty acids and glycerol concentrations in serum were reduced. These two changes presumably balanced each other, as the plasma ionized calcium and serum parathyroid hormone concentrations were not significantly altered.
6. There were no consistent relationships between the decrease in blood pressure and the changes in the metabolic indices, either in the total sample or within any subgroup. These findings indicate that disturbances of calcium metabolism in essential hypertension are primary to, and not induced by, the elevated blood pressure per se.