Responsiveness of parathyroid hormone secretion to a phosphate load in hypertensive patients with non insulin dependent diabetes mellitus

Abstract

Introduction: Abnormalities in calcium phosphate (Ca-P) metabolism and Ca-P related hormones are well documented in patients with essential hypertension (EH), but less in patients with non insulin dependent diabetes mellitus (NIDDM). The present study was designed to assess the responsiveness of parathormone (PTH) secretion to an oral phosphate (Pi) load (100 mmol) in patients with EH - NTS and hypertensive patients with NIDDM - CNT.
Material and methods: In 29 patients in NTS group (45.6 ± 1.3 y), 32 in CNT group (48.4 ± 0.9 y) and in 23 healthy subjects-GK (42.7 ± 2.7 y) - 25-OH-D₃, intact PTH, ionized (Ca²⁺) and phosphate (P) were estimated in blood serum before and PTH in 4, 8, 12, 18 and 24 hours, Ca²⁺ and P in 2, 4, 6, 8, 10, 12, 18 and 24 hours after an oral administration of Pi. Urinary excretion of calcium and phosphate were also estimated on day before and at the day of an oral Pi load.
Results: In NTS group lower basal 25-OH-D₃ serum levels (22.9 ± 1.7 vs. 30.9 ± 2 ng/ml; p = 0.02), while in CNT group higher PTH (22.7 ± ± 2.2 vs. 15.6 ± 1.9 pg/ml; p < 0.05) levels were found. Both NTS and CNT patients showed an exaggerated response of PTH secretion to the Pi load (as expressed as the AUC) as compared with GK [757 ± 51.7 vs. 790 ± 53.8 vs. 600 ± 39 (pg/ml)*24 h]. In addition patients in groups NTS and CNT showed a higher calciuria than GK (2.48 ± 0.2 and 2.42 ± 0,2 vs. 1.77 ± 0.2 mmol/d.) and a delayed normalization of plasma P at the day of the Pi load.
Conclusions:
1. Both NTS and CNT groups are characterized by an abnormal calcium and phosphate metabolism and exaggerated response of PTH secretion to an oral phosphate load as compared with GK controls.
2. Probably hypertension and not NIDDM seems to be the leading cause of calcium-phosphate abnormalities in hypertensive diabetic patients.