Acute effect of calcitonin on rat renal electrolyte transport

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Abstract
Renal clearance studies were performed on parathyroid-intact and acutely thyroparathyroidectomized (TPTX) rats to clarify calcitonin (CT) action on renal electrolyte transport. Althouth CT (0.15 U.cntdot.100 g body wt-1.cntdot.h-1) reduced fractional excretion of Ca and Mg by 72 and 46%, respectively, in TPTX rats without altering Na and PO4 excretion, a 10-fold increase in CT (1.5 U) caused a smaller reduction in Ca and Mg excretion and significantly increased Na and PO4 excretion. A higher CT dose (15 U) did not alter Ca excretion, increased Mg excretion, and caused an even greater increase in Na and PO4 excretion. Results in parathyroid-intact animals were similar. Despite the fall in plasma Ca following CT administration, the filtered Ca load was unaltered due to a concomitant increase in glomerular filtration rate. Ca infusion prior to CT (0.15 U) prevented a detectable fall in plasma Ca concentration. A 45% fall in fractional Ca excretion occurred despite the significant increase in filtered Ca. These data suggest that the physiological role of calcitonin on the nephron is to conserve Ca. Reports of increased electrolyte excretion presumably reflect a depressant effect of pharmacological doses of CT on nephron function.