Effect of oestradiol on mRNA encoding GnRH receptor in pituitary tissue of orchidectomized sheep passively immunized against GnRH.

Abstract

The effect of oestradiol on tissue concentrations of GnRH receptor and mRNA encoding GnRH receptor was assessed in orchidectomized sheep (wethers) made deficient in GnRH by passive immunization. Wethers were assigned to one of four groups (n = 6 animals per group). Animals in groups 2 and 4 received ovine anti-GnRH sera (200 ml; i.v.) at passive immunization, while antisera against the carrier protein was administered to wethers in groups 1 and 3. Oestradiol was delivered as a continuous infusion (2 micrograms h-1) to wethers in groups 1 and 2. Animals in groups 3 and 4 were infused with vehicle alone. Anterior pituitary tissue was collected at the end of the 48 h infusion. Anti-GnRH sera induced a rapid reduction in the serum concentration of LH. Continuous delivery of oestradiol resulted in a twofold increase (P < 0.05) in tissue concentration of GnRH receptor. This oestradiol-induced response was manifest even in wethers in which endogenous GnRH had been neutralized by passive immunization. Conversely, infusion of oestradiol increased (P < 0.05), and intravenous administration of anti-GnRH sera decreased (P < 0.05), concentrations of mRNA encoding GnRH receptor in pituitary tissue. When delivered in combination, anti-GnRH sera reduced (P < 0.05), but did not eliminate, the oestradiol-induced augmentation of steady-state concentrations of mRNA encoding GnRH receptor. These data demonstrate that the basal concentration of mRNA encoding GnRH receptor is dependent on continued GnRH stimulation. In contrast, the oestradiol-induced increase in steady-state concentration of mRNA encoding GnRH receptor is manifest even in the absence of GnRH.