Seasonal expression of LHβ and FSHβ in the male newt pituitary gonadotrophs

Seasonal changes in LHβ and FSHβ mRNA levels were examined in the pituitary gland of the adult male newt, Cynops pyrrhogaster, using in situ hybridization histochemistry and a quantitative real-time RT-PCR method. The annual fluctuation of LHβ mRNA and FSHβ mRNA levels in the pituitary gland displayed a close relationship with seasonal changes in testicular function. The values obtained by both methods showed similar fluctuation. The levels of LHβ mRNA were always exceeded those of FSHβ. The present immunoelectron microscopic observations support the data on the gene expression levels of the β-subunits of LH and FSH. Gonadectomy in the summer increased the LHβ and FSHβ mRNA levels. Testosterone replacement inhibited the expression of LHβ mRNA, but not of FSHβ mRNA, suggesting that the expression of FSHβ is regulated by some non-steroid factor, probably inhibin. In the case of gonadectomy during any other season, the LHβ mRNA level increased, but not to the same extent as in summer, and androgen concentrations decreased to the minimum of the year. This finding provides new information about the regulation of annual changes in LHβ and FSHβ expression in the pituitary gonadotrophs.