Evidence for regulation of basic fibroblast growth factor gene expression by photoperiod and melatonin in the ovine pars tuberalis

In the ovine pituitary the in vivo expression of the bFGF gene was studied using in situ hybridisation and Northern analysis. Expression of bFGF mRNA was highest in the pars tuberalis (PT) and zona tuberalis (ZT) and this exp ression was higher in the pituitaries of animals acclimited to long days th an in those from short day housed animals. Expression in the pars intermedi a (PI) was also detectable but the pars distalis (PD) showed negligible exp ression compared with the PT. Regulation of bFGF gene was investigated in p rimary cultured PT cells. Both forskolin and PMA increased bFGF mRNA expres sion significantly and melatonin was able to inhibit these effects partiall y, however there was no independent effect of melatonin on bFGF mRNA levels . Despite the inducibility of the bFGF gene, bFGF protein levels in PT cult ure media were insensitive to the same stimuli and detectable bFGF protein declined with time. Exogenous bFGF had no effect on c-fos mRNA levels and d id not increase prolactin secretion from ovine lactotrophs. In contrast c-f os mRNA was induced in GH3 cells by bFGF. These data suggest that although basic fibroblast growth factor (bFGF) mRNA expression in the ovine PT is ph otoperiodically-sensitive, it is not directly involved in the seasonal regu lation of lactotrophic activity. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.