URINE CALCIUM EXCRETION, NEPHROGENOUS CYCLIC-ADENOSINE MONOPHOSPHATE AND SERUM PARATHYROID-HORMONE LEVELS IN PATIENTS WITH ESSENTIAL-HYPERTENSION

To evaluate the role of calcium and the parathyroid gland in the pathophysiology of essential hypertension, creatinine clearance, urinary excretion of sodium, calcium and nephrogenous cyclic adenosine monophosphate (NcAMP) and serum parathyroid hormone (PTH) levels were measured in 25 newly diagnosed essentially hypertensive patients before institution of any treatment and in 25 age- and sex-matched normal volunteers. While no significant differences in creatinine clearance, serum total calcium levels of 24-hour sodium excretion existed between the two groups, hypertensives had a higher mean (+/- SD) 24-hour calcium excretion rate (199.0 +/- 44.7 vs. 152.8 +/- 33.6 mg, p < 0.001), a higher mean NcAMP excretion rate (2.54 +/- 0.8 vs. 1.87 +/- 0.5 nmol/100 ml glomerular filtrate, p < 0.001) and a higher mean serum PTH concentration (1.87 +/- 0.6 vs. 1.53 +/- 0.4 ng/ml, p < 0.001) than the normotensives. A significant positive correlation existed between calcium and sodium excretion in both hypertensives (r = 0.66, p < 0.001)) and normotensives (r = 0.67, p < 0.001), but given the same levels of creatinine clearance and sodium excretion, hypertensives excreted more calcium than normotensives (p < 0.001)). In both hypertensives and normotensives, serum PTH levels were positively correlated with NcAMP excretion (r = 0.42, p < 0.05, and r = 0.41, p < 0.05, respectively) and the ratio of urinary sodium to urinary calcium excretion (r = 0.59, p < 0.001, and r = 0.75, p < 0.001), respectively). The above results suggest that in essential hypertension, increased activity of parathyroid glands may occur as a consequence of increased urinary calcium losses which are presumably due to an intrinsic defect in renal calcium handling.