Elevation of blood pressure in young rats fed a low calcium diet. Effects of nifedipine and captopril.

Hypertension was developed in 5-week-old male rats fed a low calcium diet, which evokes hypocalcemia and nutritional hyperparathyroidism, for 2 weeks. Blood pressure returned to normal after changing to a normal calcium diet. These changes of blood pressure were preceded by changes of calcium levels in plasma. In parathyroidectomized rats receiving a normal calcium diet, blood pressure did not rise, though the plasma calcium level decreased to a similar extent as in rats fed the low calcium diet. These findings seem to indicate that hyperparathyroidism, not hypocalcemia, is involved in the elevation of blood pressure in rats fed a low calcium diet. The elevated blood pressure was reduced by a calcium antagonist, nifedipine, but not by an inhibitor of angiotensin-converting enzyme, captopril. This may indicate that hypertension due to nutritional hyperparathyroidism responds to the calcium antagonist nifedipine and calcium supplementation, and is not dependent on renin.