AJP - Renal Physiology, Vol 244, Issue 4 432-F435, Copyright © 1983 by American Physiological Society
Effect of calcitonin on urine concentration in the rat
S. Carney, T. Morgan, C. Ray and L. Thompson
Because mammalian distal nephron segments with both calcitonin- and
antidiuretic hormone- (ADH) sensitive adenylate cyclase activity have been
described, in vivo and in vitro experiments were performed to study the
effect of calcitonin on rat distal nephron water permeability. Calcitonin 1
and 0.1 U/ml, but not 0.01 U/ml, significantly increased the diffusional
water permeability in the isolated papillary collecting duct by 15 and 11%,
respectively. However, this effect was small when compared with a 68%
increase with a supramaximal concentration of ADH (from 4.0 +/- 0.3 to 6.7
+/- 0.9 microns/s; n = 6, P less than 0.01). The normal increase in water
permeability with increasing concentration of ADH (0.02 and 0.2 mU/ml) was
depressed by the previous addition of calcitonin (1 U/ml) to the bath but
was unaltered with the supramaximal ADH concentration (2 mU/ml). Verapamil,
a compound that antagonizes cellular calcium entry, did not alter the
effect of calcitonin on diffusional water permeability. Calcitonin in
concentrations of 0.05, 0.5, and 5 U/ml produced a significant reduction in
urine flow and free water clearance. Pretreatment with calcitonin in these
concentrations inhibited the antidiuretic action of ADH. These studies
suggest that calcitonin acts as a partial agonist to ADH within the distal
nephron. It is unclear whether such an action represents a physiological or
a pharmacological effect.
