ACUTE EFFECT OF ENDOGENOUS CALCITONIN ON RAT RENAL-FUNCTION

To evaluate the physiological role of calcitonin (CT) in the renal Ca transport, increasing Ca concentrations (0-7.5 mM) were administered t o thyroparathyroid-intact rats to provoke parathyroid hormone suppress ion and CT secretion. These groups of rats were compared to acutely th yroparathyroidectomized (TPTX) rats also infused with increasing Ca co ncentrations to produce comparable plasma Ca levels. A parathyroidecto mized group was also studied. The presence of a high CT level was asso ciated with a reduced fractional Ca excretion when compared to a TPTX group with a similar ultrafiltered Ca level (5.3 +/- 0.4 as compared w ith 10.6 +/- 0.4%; p < 0.01). The fractional Mg excretion was similarl y reduced by endogenous CT (26.8 +/- 0.9 as compared with 37.3 +/- 2.1 %; p < 0.01), The glomerular filtration rate was increased by CT, alth ough the filtration fraction was unchanged. Because of changes in filt ered Ca load due to an elevated glomerular filtration rate, comparison of TPTX and intact groups with comparable filtered Ca loads again dem onstrated greater absolute Ca and Mg reabsorption in the presence of C T. Therefore, these studies that evaluated the effect of endogenous se cretion of CT on nephron function confirm more recent studies using ex ogenous CT (human and salmon) that had suggested that CT is a renal Ca -conserving hormone like parathyroid hormone.