Circadian variation of the Ca2+-PTH curve during hypercalcaemia in dogs.

摘要

To test the hypothesis that the parathyroid hormone (PTH) response to hypercalcaemia is influenced by circadian rhythms, the Ca2+-PTH curve was studied in six dogs after infusion of CaCl< sub>2 (0.66 mEq/kg/h) at daytime (09:00 h) and at night-time (21:00 h). Plasma Ca2+ and PTH values measured before or after CaCl< sub>2 infusion were not different at day and at night. However, in the recovery from hypercalcaemia, PTH concentrations were significantly lower (P<0.05) at 21:00 h (23+or-7.5 pg/ml at Ca2+=1.30 mM) than at 09:00 h (38.8+or-6.9 pg/ml at Ca2+=1.30 mM). In addition, the Ca2+-PTH curve showed hysteresis at daytime (for the same Ca2+ concentration, PTH values were higher during recovery than during induction of hypercalcaemia) but not at night-time (PTH values were lower during recovery than during induction of hypercalcaemia). In conclusion, a circadian variation in the PTH secretory pattern during recovery from hypercalcaemia has been identified in dogs.