Acute Oral Calcium Load Decreases Parathyroid Secretion and Suppresses Tubular Phosphate Loss in Long-Term Renal Transplant Recipients

Abstract

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/lGFRp < 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 ± 3.2 vs. 13.2 ± 2.8 nmol/l GFR at the end of the survey, NS). At baseline, RT had higher phosphaturia than HS (246 ± 25 vs. 127 ± 19 µmol/l, p < 0.01), and Ca ingestion lowered phosphaturia to similar values in both RT and HS (116 ± 13 vs. 95 ± 7 µmol/l GFR, NS). Renal P threshold expressed as TmP/GFR and tubular reabsorption rate of P were lower in RT than HS at baseline, and resumed normal values after Ca. To summarize, in normocalcemic long-term kidney transplant recipients, a single oral Ca intake acutely blunted the excessive PTH secretion and increased tubular reabsorption of P up to a normal range. We conclude therefore, that PTH is a main factor of tubular P loss in these patients.

Asprosin, a Fasting-Induced Glucogenic Protein Hormone

“…In such mice plasma asprosin was found to be far lower than in mice with normal blood glucose (Figure S5F). Together, these in vitro and in vivo results are consistent with the notion that glucose serves as a negative influencer of plasma asprosin levels in a negative-feedback loop and is consistent with the regulation of other major hormones (for example, calcium suppresses parathyroid hormone secretion and glucose suppresses glucagon secretion) (Campbell and Drucker, 2015; Dumoulin et al, 1995). …”

Osseous Complications of Renal Transplantation

“…Normocalcemic transplant patients with increased PTH (subclinical hyperparathyroidism) may benefit from calcium supplementation. Calcium administration has been shown to normalize PTH and reduce phosphaturia in these patients (9).…”