In vitro effects of cortisol on the release and gene expression of prolactin and growth hormone in the tilapia, Oreochromis mossambicus

Exposure to cortisol inhibits prolactin (PRL) release from the tilapia pituitary within 10-20 min through a plasma membrane-associated, non-genomic pathway. In the present study, in vitro effects of cortisol on the release and mRNA levels of two PRLs (PRL188 and PRL177) and growth hormone (GH) were examined in the organ-cultured pituitary of the Mozambique tilapia, Oreochromis mossambicus. The PRL release was significantly greater in hyposmotic (300mOsmolal) than in hyperosmotic (350 mOsmolal) medium during the 2-8 h of incubation. The mRNA levels of two PRLs, as estimated by RNase protection assay, were increased after 8 h in hyposmotic medium. Cortisol (200 nM) inhibited the release of two PRLs under hyposmotic conditions within I h, and the inhibitory effects lasted for 24 h. Cortisol also reduced the gene transcription of both PRLs during 2-8 It of incubation but not after 24h. No effect of cortisol was observed on PRL release or on its mRNA levels under hyperosmotic condition. There was no significant effect of medium osmolality on the release or mRNA levels of GH during 8 h of incubation. However, GH release was significantly stimulated by cortisol after 4h, and the effect lasted for 24h under both hyposmotic and hyperosmotic conditions. Cortisol also caused a significant increase in GH mRNA levels at 8 and 24 h. These results suggest that cortisol inhibits PRL release from the tilapia pituitary through non-genomic and also through transcriptional pathways, while stimulating GH release through classical genomically mediated glucocorticoid actions. (C) 2003 Elsevier Inc. All rights reserved.