Acute oral calcium load decreases parathyroid secretion and suppresses tubular phosphate loss in long-term renal transplant recipients.

Persistent hyperparathyroidism and impaired tubular reabsorption of phosphate (P) are common after kidney transplantation. In order to assess the suppressibility of these abnormalities, we studied the effects of a single oral calcium (Ca) load (1 g) in 7 healthy subjects (HS) and in 14 normocalcemic long-term renal transplant recipients with good renal function (RT). In HS and RT, serum and urinary Ca were similar at baseline, and increased (p < 0.001) to the same extent after Ca ingestion. Serum parathyroid hormone (PTH) and nephrogenic cAMP (NcAMP) levels were higher at baseline in RT than HS (mean +/- SEM; respectively, PTH 7.8 +/- 0.8 vs. 3.5 +/- 0.6 pmol/l, p < 0.001, and NcAMP 24.8 +/- 2.3 vs. 13.9 +/- 2.3 nmol/l GFR, p < 0.01). After Ca, PTH (p < 0.001) and NcAMP (p < 0.01) decreased markedly in both RT and HS. Maximal changes in PTH and NcAMP were larger in RT than HS (PTH - 3.3 +/- 0.4 vs. -2.1 +/- 0.03 pmol/l, p < 0.01, and NcAMP -18.2 +/- 3.3 vs. -8.1 +/- 2.6 nmol/l GFR, p < 0.05). Although PTH levels remained significantly higher in RT than HS from baseline to the end of the study (p < 0.001), PTH decreased to the normal range in RT after Ca load. Moreover, NcAMP reached similar values in RT and HS after Ca (16.0 +/- 3.3 vs. 13.2 +/- 2.8 nmol/l GFR at the end of the survey, NS).(ABSTRACT TRUNCATED AT 250 WORDS)