Temporal changes in LHRH and alpha and LHbeta subunit messenger RNA levels in resp0onse to testosterone in castrated adult rats

To elucidate the temporal relationship between LHRH and LH gene expression in response to testosterone (T), LHRH mRNA in the hypothalamus, and α and LH β mRNA in the anterior pituitary were simultaneously determined. After Silastic capsules containing T were implanted subcutaneously to castrated (2 weeks) adult rats, LHRH, α and LH β mRNA levels were determined by RNA-blot hybridization assay and hypothalamic LHRH content and serum LH levels were measured by radioimmunoassays. T implant to castrated rats decreased α and LH β mRNA levels in time- and dose-dependent manners, which were accompanied by parallel change in serum LH levels. On the other hand, T implant did not significantly alter LHRH mRNA level, which was discordant with changes in α and LH β mRNA levels. The present study showed that T differentially regulates LHRH and LH mRNA levels, suggesting that the negative feedback action of T on LH gene expression may be mainly due to the direct action of T on pituitary gonadtropes.