Estradiol reduces pituitary responsiveness to somatostatin (SRIF-14) and down-regulates the expression of sst2 in female goldfish pituitary

CÁRDENAS R; LIN X; CANOSA LF; ARAMBURO C; PETER RE

GENERAL AND COMPARATIVE ENDOCRINOLOGY

Año: 2003 vol. 132 p. 119 - 124

0016-6480

Sex steroid hormones have been shown to regulate somatostatin (SRIF) gene expression in goldfish brain, which in turn influencesthe regulation of GH secretion. In this study, the influences of sex steroids on pituitary responsiveness to SRIF-14 and thepituitary expression of a type two SRIF receptor (sst2) were examined. Results from in vitro perifusion of pituitary fragments showthat pituitaries from estradiol-primed sexually regressed female fish have significantly lower GH release responsiveness to pulseexposure to SRIF-14 than pituitaries from control or testosterone-treated sexually regressed females. Results from in vitro staticculture show that pituitaries from sexually mature female fish have lower GH release responsiveness to SRIF-14 than those fromsexually regressed females. In addition, the sst2 receptor mRNA levels in pituitaries from mature and recrudescent female fish aresignificantly lower than in sexually regressed female fish. Our results indicate that estradiol acts at the level of the pituitary toregulate GH secretion by influencing the responsiveness to SRIF-14. The underlying mechanism includes, in part, reduction of theexpression of sst2 receptors, presumably leading to the lower number of the receptors available for SRIF binding.