Evidence for physiological importance of calcitonin in the regulation of plasma calcium in rats.

Abstract

A B S T R A C T To determine the physiological importance of calcitonin in the regulation of plasma calcium, studies were carried out in fasting animals to (a) assess the acute effects of thyroparathyroidectomy (TPTX) and thyroidectomy (TX) on plasma and urinary calcium; (b) investigate whether the changes in plasma calcium produced by removal of the glands were dependent on the presence of the kidney; and (c) determine if the effect of TPTX on plasma calcium is affected by age. Except where otherwise indicated, all studies were carried out on fasting male Wistar rats weighing over 300 g. The following observations were made. (a) TPTX and TX caused an increase in plasma calcium in nephrectomized animals. (b) This increase was not dependent on nephrectomy since in intact animals bearing autoparathyroid transplants TX also caused a significant rise in the mean plasma calcium level (0.37 mg/100 ml at 1i h). (c) Urinary calcium increased twofold in the 3-h period immediately after TX. (d) In unnephrectomized immature (50-g) rats, TPTX caused a progressive decrease in plasma calcium in contrast to old (360-g) rats, where a significant fall observed at 6 h was preceded by an increase in plasma calcium (0.5 mg/100 ml at 11 h). From these observations we conclude that: (a) calcitonin must play an important physiological role in the regulation of plasma calcium since the termination of its basal secretion caused an immediate but transient increase in plasma calcium in old unfed rats; (b) the relative importance of calcitonin and parathyroid hormone in the acute regulation of plasma calcium is agerelated; and (c) the action of parathyroid hormone on bone may be modified by changes in ambient calcitonin concentration.

Role of calcitonin in the rapid minute‐to‐minute regulation of plasma Ca2+ homeostasis in the rat

“…Consequently, feeding indirectly stimulates the secretion of CT by enhancing the secretion of gastrointestinal hormones, such as gastrin, glucagon, cholecystokinin and secretin, which in turn stimulate CT secretion. The resulting inhibition of the Ca 2+ transport from bone into the extracellular fluid prevents an excessive increase in plasma Ca 2+ [20][21][22][23]. It seems that the present data obtained in fasting rats support this hypothesis, as the degree of hypercalcaemia resulting from TPTX and TX in fasting rats was clearly diminished.…”

A transient increase in renal clearance of phosphate in response to continuous infusion of salmon calcitonin in rats.

“…However, we could show at least in intact rats that the direction of the change in Cca depended on the dosage of calcitonin; lower doses (0.01-2 MRC U) of calcitonin caused a decrease in Cca, while higher doses (3 MRC U) produced a rise in Cca. That calcitonin in physiological doses causes a diminution of urinary Ca in rats was suggested by a recent report of Kalu et al (1975).…”

Biochemical Changes in Blood Components after Lethal Doses of Radiation.

“…This raises the possibility that elevated gastrin Aay be a response to radiation-induced gastric stasis. Calcitonin is an important regulator of plasma calcium (43), and the reduction of calcium by calcitonin can decrease calcium-dependent secretory mechanisms such as gastrin secretion.…”