TEMPORAL EFFECTS OF PARATHYROID HORMONE ON SERUM AND URINARY CALCIUM IN THE HAMSTER

Abstract

SUMMARY The temporal aspects of calcium addition to blood and renal conservation of calcium were compared in fasted, parathyroidectomized (PTX) hamsters after a single, intravenous injection of parathyroid hormone (PTH). Injection of 110 units of hormone rapidly stabilized urinary excretion of calcium at normal (sham-PTX) levels during a following 3-h period in contrast to the progressive and rapidly occurring hypercalciuria in animals without hormone replacement. Serum calcium concentrations increased rapidly after hormone replacement, rising 3 mg/100 ml within the first 2 h. No further increase was detected after 2 h with a significant decrease in concentration apparent between 3 and 4 h after injection of hormone. Nephrectomy, performed at intervals during the first 2-h period, resulted in significantly increased serum calcium concentrations by 4 h relative to animals with kidneys during the first 2-h period. The magnitude of this increase was directly related to the length of time kidneys were absent during the first 2 h after injection of hormone. These findings indicate that, in the hamster, the effects of PTH on the addition of calcium to blood and conservation of calcium by the kidney occur simultaneously and are both of very short duration (2 to 3 h). These short-lived effects of PTH in this species seem to be due, at least in part, to the participation of a renal influence.