Differential Production and Regulation of Inhibin Subunits in Rat Testicular Cell Types*

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Abstract
The distribution of the .alpha.-, .beta.A-, and .beta.B subunits of inhibin/activin polypeptides were studied in the testis of adult (60-day-old) and immature (12-day-old) krats. Immunohistochemical techniques using antisera selctive for each subunit were used to localize the polypeptide chains. In situ hybridization using radiolabeled complementary RNA probes enabled localizations of the messenger RNAs (mRNAs) encoding these subunits. In 12-day-old rats, immunostaining and mRNA signal for the .alpha.-subunit was found in Leydig cell clusters. The .beta.A- and .beta.B-subunit staining and .beta.A-subunit message were detectable in isolated interstitial cells, but the clusters appeared to lack these subunits. Positive immunostaining for each subunit was localized in a Sertoli cell-like pattern in seminiferous tubules, as was a positive mRNA signal for the .alpha.- and .beta.B-subuint over regions containing these cell types. Treatment with human CG (hCG) and PMSG greatly enhanced the production of the .alpha.-subunit in the Leydig cell clusters, but not within the tubules, of these young rats. In adult rats, .alpha.- and .beta.B-subunit staining, and .alpha.-subunit mRNA signal, was observed in the interstitial cells. As in the immature animals, all three subunits were localized in a Sertoli cell-like pattern in the tubules, and a positive mRNA signal for the .alpha.- and .beta.B-subunits was found over these cells. There was, however, no obvious change in the expression of the subunits in the testis of adult rats after gonadotropin treatment. The present findings suggest that: 1) in the rat testis, both Sertoli and interstitial cells produce inhibin/activin subunits; 2) the .alpha.- and .beta.-subunits are produced by different types of interstitial cells in immature rats; and 3) the production of the .alpha.-subunit in the Leydig cells of immature rats is regulated by LH-like hormones.