EFFECTS OF ACCLIMATION SALINITY AND IN-VITRO MEDIUM OSMOTIC-PRESSURE ON THE INCORPORATION OF H-3 LEUCINE INTO THE 2 PROLACTINS OF THE TILAPIA, OREOCHROMIS-MOSSAMBICUS

The control of synthesis of the two prolactins (tPRL(188) and tPRL(177 )) in the anterior-most portion of the pituitary, the rostral pars dis talis (RPD), was investigated in freshwater (FW)- and seawater (SW)-ac climated tilapia. Individual RPD of FW and SW male tilapia were incuba ted in either hyposmotic or hyperosmotic medium containing H-3-leucine for various intervals, up to 360 min. The total quantity of the two t PRLs in media and RPD was assessed by gel electrophoresis and scanning densitometry of the stained bands. Synthesis was characterized as the uptake of 3H-leucine into the tPRL molecules. Results showed greater synthesis and release of both H-3-tPRLs in the RPD from FW tilapia tha n in those from SW-acclimated tilapia. The in vitro synthesis of both prolactins tPRd(188) and tPRL(177) in RPD of FW tilapia and tPRL(177) in RPD of SW fish was also augmented by exposure to hyposmotic medium. The ratio of the appearance of newly synthesized H-3-tPRL(188):H-3-tP RL(177) was approximately 1.3 in FW tilapia RPD and approximately 0.5 in SW tilapia RPD. The delay between effect of osmotic pressure on tPR L release and its effect on tPRL synthesis suggests that the rapid eff ect of osmotic pressure upon PRL release is at least partially indepen dent of its effect upon tPRL synthesis. Moreover, the altered ratios o f tPRL(188) and tPRL(177) observed in our studies suggest that the syn thesis rates of the two tPRLs are differentially sensitive to environm ental salinity. (C) 1995 Wiley-Liss, Inc.