Renal action of progesterone: effect on calcium reabsorption

Recently, the kidney has been reported to be the site of receptors for progesterone. Although the exact segment of the nephron has not been precisely determined, the cortical collecting tubule was suspected, since the hormone displaces bound 3 H aldosterone. The aim of the present study was to investigate the effect of progesterone on calcium (Ca2+) transport by the renal luminal membranes and to determine the site and mechanisms of action. Incubation of proximal tubules from rabbit kidney with progesterone (lid not influence Ca2+ or Na+ transport by the luminal membranes. In the distal tubules (DT), a 5 min treatment with 10(-11) M of the hormone enhanced 0.5 MM Ca-45 uptake from 0.60+/-0.02 to 0.84+/-0.08 pmol/mug per 10 s (P < 0.05) in the absence of Na+ and from 0.26+/-0.02 to 0.41+/-0.02 pmol/mug per 10 s (P < 0.01) in the presence of 100 mM Na+. The dose-response curve showed a biphasic action with a peak at 10(-11) M. Ca2+ uptake by DT membranes presents dual kinetics. The hormone enhanced the Vmax value of the high affinity component from 0.41+/-0.05 to 0.57+/-0.06 pmol/mug per 10 s (P < 0.05). In contrast, incubation of DT with 10(-8) M progesterone decreased 1 mM Na+ uptake from 0.68+/-0.03 to 0.53+/-0.07 pmol/mug per 10 s (P < 0.05). Finally, 10(-11) M progesterone also enhanced Ca2+ uptake by the DT membranes through a direct nongenomic mechanism. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.