FOLLICLE-STIMULATING-HORMONE REGULATION OF INHIBIN ALPHA-SUBUNIT MESSENGER-RNA IN STAGED RAT SEMINIFEROUS TUBULES

Steady-state levels of inhibin-alpha and -beta(B) mRNAs are higher in stages II-VI of the seminiferous epithelial cycle than in stages VII-V III. We investigated follicle-stimulating hormone (FSH) regulation of inhibin alpha-subunit mRNA in stages II-VI and VII-VIII to study wheth er the stage specificity is due to differential hormonal regulation by FSH. Follicle-stimulating hormone caused a significant increase of in hibin-alpha mRNA levels in both stages during a 20-h incubation. The m echanism of the FSH effect was studied further in stages VII-VIII. Max imal stimulation of the inhibin-alpha mRNA level was achieved with 100 mu g/l FSH, dibutyryl-3',5'-cyclic adenosine monophosphate (db-cAMP, 0.2 mmol/l) and Sp-adenosine-3', 5'-monophosphothionate (Sp-cAMPS, 10 mu mol/l) (a cAMP agonist). The presence of Rp-cAMPS (200 mu mol/l) (a cAMP antagonist) abolished the stimulation, Rp-cAMPS alone had no eff ect. Inhibin-beta(B) mRNA levels in stages VII-VIII were not affected by FSH, db-cAMP, Sp-cAMPS or Rp-cAMPS. Phorbol 12-myristate 13-acetate (100 nmol/l) had no effect on inhibin-alpha or -beta B mRNA levels. A ctinomycin D abolished the stimulatory effect of FSH on inhibin-alpha mRNA expression. In conclusion, FSH stimulated inhibin-alpha mRNA expr ession similarly both in stages II-VI and VII-VIII of the seminiferous epithelial cycle and the stimulation in stages VII-VIII was cAMP-medi ated.