INTERRELATIONSHIP BETWEEN CALCITONIN AND PARATHYROID HORMONE IN INTACT, THYROIDECTOMIZED, PARATHYROIDECTOMIZED, AND THYROPARATHYROIDECTOMIZED RATS

ABSTRACT Calcitonin is capable of completely suppressing the hypercalcaemic effect of parathyroid hormone but not irreversibly. The parathyroid hormone extract used was the commercial preparation Para-Thor-Mone® (Lilly). When injected simultaneously, the parathyroid hormone had no influence on the hypocalcaemia induced by calcitonin one hour after the injection. The parathyroid hormone produced a hypercalcaemia of up to 42 h duration in rats without thyroids. If the thyroid gland was present the serum calcium did not exceed 5.5 mEq./l, probably because of an increased secretion of calcitonin. A transitory hypercalcaemia followed by a hypocalcaemia was seen in intact rats after an intraperitoneal calcium load. The hypocalcaemia could be explained by the counteracting secretion of calcitonin.