Dose response dependency in regulation of acute PTH (1-84) release and suppression in normal humans: a citrate and calcium infusion study.

The aim of the present study was to investigate the possible dose response dependency of the very early changes in intact parathyroid hormone concentrations (PTH) on different rates of blood ionized calcium (B-Ca2+) lowering and raising. On 8 different days, four healthy volunteers received trisodium-citrate infusions at five different rates and calcium chloride infusions at three different rates, all of 10 min duration. S-PTH and B-Ca2+ were measured twice before each infusion and after 1, 2, 3, 4, 5, 7, and 10 min of infusion. The decrements of B-Ca2+ expressed as area under the curve (AUC) correlated with the rate of trisodium-citrate infusions (r = 0.97, p < 0.001) and furthermore, these B-Ca2+ decrements were matched by S-PTH increments expressed as AUC (r = 0.96, p < 0001). Multigroup comparisons on the results of protocol A showed statistical significant (p < 0.02). The increments of B-Ca2+ expressed as AUC correlated with the rate of calcium chloride infusions (r = 0.92, p < 0.001) and furthermore, these B-Ca2+ increments were matched by S-PTH decrements measured as AUC (r = 0.95, p > 0.001). Multigroup comparisons on the results of protocol B showed statistical significant (p < 0.05). In conclusion, acute B-Ca2+ lowering and raising at different rates promotes stimulation and inhibition of the acute PTH release in rate dependent manner. For this mechanism being distinctly different from the steady state control of PTH secretion, we suggest the term 'delta regulation' (delta, i.e. the sign for change).