Response of GH, ACTH, TSH and IGF-I to Gonadotropin Releasing Hormone Stimulation in Ovariohysterectomized Rats

Abstract

GnRH is not only a primary regulator of gonadal function but also a possible factor which affects other pituitary cells out of gonadotrophs. Recently, it has been reported that GnRH might induce the release of GH, but the effects on GH and other pituitary hormones of GnRH still remained controversial. In this study, OHE was performed in 30-week-old female Sprague Dawley rats as experimental groups. Intact female rats were taken as control group. GnRH stimulation at different weeks (20, 24, and 30) after OHE was examined in all rats. Evaluation of the circulating GH, IGF-I, ACTH, TSH concentrations at different time points with commercial ELISA kits was carried out. Results indicated that the GH levels after stimulation in all OHE groups tended to be lower than the control group but without significant difference. In all groups, the IGF-I levels at 30 min after GnRH stimulation were significantly lower than the basal IGF-I levels. The levels of ACTH at 30 min after GnRH administration were significantly higher (p<0.05) than the basal ACTH levels in all groups. Furthermore, both the basal and stimulated ACTH levels in all OHE groups were significantly higher (p<0.05) than the control ones. The TSH levels after GnRH stimulation in all OHE groups tended to be higher than the control ones but without significant difference. Thus, GnRH administration could induce GH, ACTH and TSH secretion but reduce IGF-I levels in ovariohysterectomized rats. The body weight increment after neutralization in female rats is probably accomplished with the elevation of IGF-I and ACTH.