Transfer of Tilapia (Oreochromis niloticus) to a hyperosmotic environment is associated with sustained expression of prolactin receptor in intestine,gill, and kidney

Expression of the tilapia prolactin receptor (tiPRL-R) has been characteriz ed in the intestine of Oreochromis niloticus and the levels of both tiPRL-R transcripts and tiPRL binding sites have been further analyzed in this org an, as well as in gill and kidney, during adaptation of tilapia to a hypero smotic environment. A single high-affinity binding site for tilapia PRL-I ( tiPRL-I) was determined in full-length intestine by Scatchard analysis. A h eterogeneous distribution of tiPRL-R was detected in this organ, with the p osterior part always displaying a higher expression of both tiPRL-R transcr ipt and tiPRL binding sites than the anterior and medial parts. Transfer of tilapia to brackish water (BW) led to an apparent increase in the specific binding of tiPRLs in intestine and gill even for long-term-adapted fish, w hereas the high level of kidney tiPRL binding sites measured in control fis h reared in fresh water was still detected in BW-adapted tilapia. There was no overall significant modification of tiPRL-R transcript levels in any or gan during short-term or long-term adaptation, although a limited decrease occurred in the gill of BW-adapted fish, as shown earlier. Therefore, in O. niloticus adapted to BW, high and sustained levels of ti-PRL-R were observ ed in the three major osmoregulatory organs, gill, kidney, and intestine. ( C) 2001 Academic Press.