Regulation of parathyroid hormone and vitamin D in essential hypertension

Patients with essential hypertension have been reported to have a higher serum concentration of parathyroid hormone (PTH) than normotensive individuals although this finding is not universal among studies. To further characterize the status of the calcium regulating hormones in essential hypertension, we measured the parathyroid gland response to acute EDTA-induced hypocalcemia and the renal response of 1,25(OH)2-vitamin D to dietary calcium deprivation in 16 hypertensive (H) and 15 normotensive (N) men. The average mean arterial blood pressure once all antihypertensive medications were discontinued was 108 +/- 7 mm Hg for the hypertensive group and 89 +/- 4 mm Hg for the normotensive group (P < .01). There were no group differences in baseline serum concentrations of ionized calcium, creatinine, intact PTH, and 1,25(OH)2-vitamin D, urinary calcium excretion, and creatinine clearance. After a 1-h infusion of EDTA at 12.5 mg/kg/h, the serum concentration of ionized calcium fell (H: 1.25 +/- .03 to 1.17 +/- .04 mmol/L, N: 1.26 +/- .04 to 1.18 +/- .04 mmol/L, P = NS) and PTH increased (H: 36 +/- 9 to 91 +/- 30 pg/mL, N: 40 +/- 14 to 85 +/- 28 pg/mL, P = NS). With an additional hour of EDTA at a dose of 25 mg/kg/h, serum ionized calcium concentration fell further (H: 1.01 +/- .05 mmol/L, N: 1.03 +/- .06 mmol/L, P = NS) and PTH increased to 150 +/- 58 pg/ml in patients and 130 +/- 32 pg/ml in controls (P < .001). The response suggested an increased maximal parathyroid gland secretory capacity in the hypertensive patients relative to the controls. There was no group difference in the serum concentration of 1,25(OH)2-vitamin D at baseline (H: 32 +/- 6 pg/ml, N: 32 +/- 8 pg/ml, P < .90) and following dietary calcium deprivation for three days (H 50 +/- 12, N 48 +/- 14 P < 0.76). The maximal stimulated PTH level was significantly higher in hypertensive than normotensive subjects in the absence of measured differences in serum ionized calcium concentration, serum 1,25(OH)2-vitamin D concentration, and creatinine clearance. These findings suggest an intrinsic alteration of PTH regulation in patients with essential hypertension, manifest as increased parathyroid gland secretory capacity.