EFFECT OF SOMATOLACTIN AND RELATED HORMONES ON PHOSPHATE-TRANSPORT BY FLOUNDER RENAL TUBULE PRIMARY CULTURES

Winter flounder renal proximal tubule primary monolayer cultures mounted in Ussing chambers were used to determine the effect of salmon somatolactin (sSL) on transepithelial P-i and Ca2+ transport. sSL stimulated P-i reabsorption in a dose-dependent manner at physiological levels of the hormone (12.5 ng/ml). Net P-i transport was significantly altered by sSL (200 ng/ml) within 2 h after the initial exposure. Ca2+ fluxes were unchanged by the addition of 200 ng/ml sSL. The sSL-induced P-i reabsorption was abolished by 10 mu M H-89, a highly specific protein kinase A inhibitor. Moreover the production and release of adenosine 3',5'-cyclic monophosphate were significantly increased after 1 and 2 h of exposure to sSL. The data indicate that sSL directly stimulates net renal P-i reabsorption by an adenosine 3',5'-cyclic monophosphate-dependent pathway. In addition to sSL, flounder SL and rat prolactin greatly, and salmon growth hormone (2.3 mu g/ml) slightly, increased net P-i reabsorptive flux, whereas salmon prolactin had no effect.