Testicular and serum levels of inhibin and expression of inhibin subunit mRNAs are differentially affected by hemicastration in rats of various ages

Abstract

Abstract Age-related short-term effects of hemicastration on testicular weight, serum FSH, immunoreactive inhibin, LH and testosterone, testicular levels of inhibin subunit mRNA expression, and bioactive and immunoreactive inhibin were studied in rats of 8, 15 and 22 days of age. Hemicastration led to an increased weight of the remaining testis after 24 h in 8- and 15-day-old rats, but not in 22-day-old rats. Serum FSH levels were elevated in all hemicastrated rats after 8 h. However, serum immunoreactive inhibin levels were decreased only after 72 h in 8-day-old rats and after 24 h in 15- and 22-day-old rats. Inhibin α-subunit mRNA expression was increased in the testes of hemicastrated rats of 8 and 15 days of age, whereas inhibin βB-subunit mRNA expression was elevated in the testes of 15-day-old rats but not in those of 8- and 22-day-old rats. The increase in α-subunit mRNA content per testis was caused by an increased concentration and increased testicular weight, whereas the increase in βB-subunit mRNA in the remaining testis parallelled the increased testicular weight, indicating that different mechanisms play a role in the regulation of these mRNAs. In 22-day-old rats, a transiently decreased expression of inhibin βB-subunit mRNA was observed 8 h after hemicastration. The increased inhibin α- and βB-subunit mRNA expression in 8- and 15-day-old rats did not result in increased testicular bioactive and immunoreactive inhibin content of the remaining testis, whereas in 22-dayold rats an increased immunoreactive inhibin content of the remaining testis was observed. These data indicate that efficiency of translation, post-translational modifications or transport from the testis play an important role in determining the final testicular content of inhibin. In conclusion, the response of the remaining testis and the role of inhibin in the regulation of the pituitary-testis axis after unilateral castration depend on the age at which the animals are hemiorchidectomized. Journal of Endocrinology (1994) 141, 143–151