Calcitonin diuretic effect in the rabbit.

In an attempt to study the renal effects of Calcitonin (porcine CT) in the rabbit, the excreted fractions of filtered water, osmolality, sodium, potassium and chloride, and the calcium and phosphorus urinary excretions were studied during isotonic (ISD) and hypertonic (HSD) saline diuresis. Four doses (0.1, 0.8, 4 and 20 IU MRC/kg were perfused during one hour in I.S.D.; 4 and 20 IU MRC/kg in HSD. During ISD, Calcitonin at doses of 4 and 20 IU MRC/kg/hr significantly increased the diuresis and the Na+, Cl-, K+, PO4 3-, Ca2+ excreted fractions. This effect was also observed, to a lesser extent, at a dose of 0.8 IU MRC/kg/hr, whereas 0.1 IU MRC/kg/hr produced no significant effect. During ISD, a log dose related effect of CT appeared to exist with all studied parameters. Moreover, a biphasic pattern of free-water clearance was observed during ISD: this parameter increased during the first half hour of CT perfusion, and then decreased dramatically. During HSD, CT perfusion induced a decrease of free-water reabsorption and urinary osmolality/plasma osmolality ratio. These results suggest that the diuretic effect and saliuretic effect of CT (in the rabbit) are mainly the consequence of the decrease of the proximal reabsorption of sodium. The possibility of a second site of action is discussed. The diuretic effects of CT are compared to data observed with the well-known diuretic drugs.