Plasma phosphate and the hypocalcemic response of intact, parathyroidectomized and nephrectomized rats to thyrocalcitonin.

Abstract

The purpose of these experiments was to study the effect of the administration of rat thyrocalcitonin (RTCT) to intact, parathyroidectomized (PTX) and nephrectomized (Nephx) rats up to 24 hr after bilateral nephrectomy. The work was instigated because of our recent reports suggesting that, under various physiological conditions, there was a marked difference in the ΔCa:ΔPO4 produced by either TCT or ultimobranchial calcitonin administration. For these experiments all rats were injected with 25 MRC mU of a crude extract of RTCT. Comparative studies were made in both parathyroid intact and PTX animals before and at various intervals following nephrectomy. These studies indicated that the plasma phosphate drop following TCT was surprisingly constant both before and after nephrectomy, despite the rising plasma phosphates caused by kidney removal. The hypocalcemic effect of the hormone was enhanced, however, by the high phosphate level. In fact, the drop in plasma calcium level produced was proportional to sta...