Physiological responses and expression of arginine vasotocin receptor, prolactin and prolactin receptor mRNA in olive flounder Paralichthys olivaceus during osmotic stress

Abstract

We cloned complementary DNA (cDNA) encoding the arginine vasotocin receptor (AVT-R) from the kidney of olive flounder (Paralichthys olivaceus). Olive flounder AVT-R cDNA consists of 1155 bp, and encodes a protein of 384 amino acids. To investigate the stress responses and osmoregulatory abilities of olive flounder in changing salinities (35, 17.5, 8.75, 4, and 0 psu), we examined the expression of AVT-R, prolactin (PRL), and PRL receptor (PRL-R) messenger RNA (mRNA) in osmoregulatory organs using quantitative real time PCR (QPCR). AVT-R and PRL-R were expressed in the gill, kidney, and intestine, whereas PRL mRNA was expressed only in the pituitary gland. In addition, we measured the levels of plasma glucose, cortisol, aspartate aminotransferase (AST), and alanine aminotransferase (ALT). The mRNA expression and plasma parameters increased in hypoosmotic environments. Furthermore, osmolality decreased significantly according to salinity concentration decreased. These results suggest that AVT-R, PRL, and PRL-R mRNA play important roles in the hormonal regulation of osmoregulatory organs, thereby improving the osmoregulatory ability of olive flounder in hypoosmotic environments.