Regulation of Testicular Inhibin Subunit Messenger Ribonucleic Acid Levelsin Vivo: Effects of Hypophysectomy and Selective Follicle-Stimulating Hormone Replacement*

Abstract

To examine the pretranslational regulation of inhibin subunits in the rat testis by FSH, we studied the effects of hypophysectomy with or without selective FSH replacement on testicular inhibin subunit mRNA levels in immature and adult animals. In the first experiment (Exp I), sexually immature (20-23 days old) intact and hypophysectomized male rats were killed 1, 3, and 7 days after surgery, and the testicular content of inhibin subunit mRNAs was determined by filter hybridization. A second group of immature, intact, or hypophysectomized rats was treated with saline or FSH for 7 days as follows: I) intact, saline; II) hypophysectomized, saline; III) hypophysectomized, FSH [0.05 microgram/100 g BW, sc, twice daily (BID)]; IV) hypophysectomized, FSH (0.50 microgram/100 g BW, sc, BID); V) hypophysectomized, FSH (5.0 micrograms/100 g BW, sc, BID); and VI) hypophysectomized, FSH (50.0 micrograms/100 g BW, sc, BID). In the second experiment (Exp II), adult (60 days old) intact or hypophysectomized animals were treated with saline, FSH, and/or testosterone for 7 days as follows: I) intact, saline; II) hypophysectomized; saline; III) hypophysectomized, 22-mm testosterone implant; IV) hypophysectomized, FSH (50.0 micrograms/100 g BW, sc, BID; and V) hypophysectomized, 22-mm testosterone implant plus FSH (50.0 micrograms/100 g BW, sc, BID. The effects of FSH and testosterone on testicular inhibin subunit mRNA levels were measured by filter hybridization. In Exp I, the level of inhibin alpha-subunit mRNA per testis was significantly lower in hypophysectomized rats than in intact controls at all time points after surgery. Replacement of FSH to hypophysectomized immature rats led to a dose-dependent increase in alpha-subunit mRNA per testis. However, hypophysectomy and FSH replacement had no significant effect on beta-B-subunit mRNA. In adult rats (Exp II), hypophysectomy significantly lowered and FSH replacement increased testicular inhibin alpha-subunit mRNA levels. Replacement of testosterone to adult animals, either alone or in combination with FSH, had no effect on expression of inhibin alpha-subunit mRNA. beta-B mRNA levels in adult testis were not significantly altered by any of the treatments. beta-A-Subunit mRNA levels were below the detection threshold of filter hybridization in both Exp I and II. Collectively, these data demonstrate that FSH regulates alpha- but not beta-B-subunit mRNA in the testis of both immature and adult rats in vivo. Differential regulation of inhibin subunits may provide a mechanism for creation and regulation of functional diversity of inhibin-related peptides in the testis.