The mediating role of the parathyroid gland in the effect of low calcium intake on blood pressure in the rat.

Recent reports suggest an inverse relationship between calcium intake and blood pressure. This effect could be mediated by parathormone (PTH), since a low calcium intake leads to an increase in PTH and this hormone produces an increase in intracellular calcium, raising the excitability of the muscle arteriolar cells. Wistar female rats, 56 days old, were submitted to a parathyroidectomy or to a sham operation. After that, they were placed on a normal or on a calcium-free diet during 10 weeks. Four groups of nine rats were studied: parathyroidectomized animals on a normal calcium diet, parathyroidectomized ones on a calcium-free diet, controls (sham operation) on a normal calcium diet, and controls (sham operation) on a calcium-free diet. The control calcium-free diet showed a significant increase in blood pressure values over the treatment period. The parathyroidectomized calcium-free diet group did not show any increase. The difference between these two groups regarding change in blood pressure was statistically significant. The parathyroidectomized-calcium-free group showed no weight increase during the study, while rats in the other three groups significantly increased their weight. PTH could be the mediator of the blood pressure rise observed in the calcium-deprived rats in spite of the possible confounding effect of the poor weight increase detected in the parathyroidectomized-calcium deprived animals. These results warrant future studies since the role of PTH in the regulation of blood pressure needs to be confirmed. This possibility, therefore, opens a new area of research in the study of the pathophysiology of hypertension.