The pattern of inhibin/activin alpha- and beta(B)-subunit messenger ribonucleic acid expression in rat testis after selective Leydig cell destructionby ethylene dimethane sulfonate

To further investigate the regulatory mechanisms responsible for the contro l of testicular inhibin/activin subunit gene expression, inhibin-alpha, -be ta(A), and -beta(B) messenger RNA(mRNA) levels were assessed after ethylene dimethane sulfonate (EDS)-induced destruction of Leydig cells (LC) in diff erent animal models: the intact rat, the rat treated with high doses of tes tosterone, and the unilaterally cryptorchid rat. In intact rats, EDS select ively eliminates the mature adult-type LCs, activating the proliferation an d differentiation of preexisting LC precursors into a new population of fun ctionally active LCs. In this model, a single dose of EDS (75 mg/kg BW, ip) induced a significant increase in testicular inhibin-alpha and -beta(B) mR NA levels 5 days after treatment (5.0- and 5.5-fold increases, respectively ), whereas inhibin-beta(A) mRNA remained undetectable upon Northern hybridi zation in control and EDS-treated testes. Moreover, in situ hybridization a nalysis demonstrated that the increased expression of inhibin-alpha and -be ta(B) mRNAs observed 5 days after EDS takes place mainly in Sertoli cells. Along with LC repopulation, the expression level of inhibin-alpha and -beta (B) messages declined, and inhibin-alpha mRNA returned to control values on day 40 after EDS. This treatment, however, failed to alter the pattern of testicular expression of FSH receptor and androgen-binding protein mRNAs, t hus suggesting selectivity for the above effects. In EDS-treated rats suppl emented with high doses of testosterone, the preexisting mature LCs are des troyed, but, due to elevated testosterone concentrations, disruption of spe rmatogenesis is attenuated, and the post-EDS rise in serum gonadotropins is blocked; the latter prevents LC regeneration. In this model, a 5.0-fold in crease in inhibin-alpha mRNA levels, similar to that found in intact animal s, was detected 5 days after EDS administration, but the rise in inhibin-be ta(B) levels was partially delayed. In addition, the blockade of LC repopul ation resulted in permanent elevation of inhibin-alpha and -beta(B) message s throughout the study period. In unilaterally cryptorchid rats, the abdomi nal testis shows disrupted spermatogenesis and altered paracrine environmen t that expedites LC repopulation after EDS treatment. In this model, the ab dominal testes showed a significant 2.5-fold increase in inhibin-cu mRNA le vels 5 days after EDS, but no effect was found in those of inhibin-beta(B). Further, the faster rate of LC repopulation resulted in precocious decline of inhibin-alpha mRNA levels. Finally, the expression of inhibin/activin s ubunit mRNAs was monitored during postnatal testicular development, specifi cally at the time of regression of fetal-type LCs and appearance of those o f the adult type. High levels of expression of inhibin-alpha and -beta(B) m RNAs were detected in neonatal and infantile testes, ii sharp decline in bo th messages took place between days 15-20, i.e. at the time when fetal-type Leydig cells are replaced by adult-type cells. From this time point onward , inhibin-alpha and -beta(B) mRNA levels remained low, ranging between 15-3 0% of the maximum. In conclusion, our results suggest that the adult-type L Cs differentially modulate the expression of inhibin/activin subunit genes and point to a major inhibitory role in this cell type on expression of the inhibin-alpha gene.