PROLACTIN RECEPTORS IN LIVER, KIDNEY, AND GILL OF THE TILAPIA (OREOCHROMIS-MOSSAMBICUS) - CHARACTERIZATION AND EFFECT OF SALINITY ON SPECIFIC BINDING OF IODINATED OVINE PROLACTIN

Specific binding of 125I-ovine prolactin (oPRL) to microsomal fractions from gill, kidney, and liver of adult tilapia was determined. Specific binding varied among tissues, the highest values being displayed by kidney membranes. In the liver, the binding of oPRL was not strongly displaced by tilapia prolactins (tPRL177 and tPRL188), although tPRL177 was six times more potent than tPRL188. On the other hand, in kidney and gill membranes, the two tPRLs were equipotent. Tilapia PRLs showed low potency in competing for oPRL-binding sites when pregnant rat liver membranes were utilized. Tilapia growth hormone (tGH) and human growth hormone (hGH) displaced 125I-oPRL from liver as well as did tPRL177 but were not recognized well by renal or branchial receptors. Two 125I-oPRL-binding sites were detected in every tissue tested. These binding sites are subject to physiological regulation since adaptation to seawater resulted in a significant decrease in specific binding. © 1990.