Histochemical Studies on Hydroxysteroid Dehydrogenase Activity of Fetal Pig Testes1,2

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Abstract
Histochemical studies were undertaken for the detection and localization of Δ5-3β-hydroxysteroid dehydrogenases (HSD) and 17β-HSD in gonads of male pig fetuses of 1.5-29.0 cm crown-rump (C-R) length. The steroid substrates used for Δ5-3β-HSD were pregnenolone, dehydroepiandrosterone, and androstenediol, and for 17β-HSD the substrates were testosterone, estradiol-17β, and androstenediol. Considerable differences were found in both intensity and location of reactions within the gonads, depending on the age of fetus and the substrate used. Δ5-3β-HSD activity, which might be related to steroid hormone formation at a very early stage in fetal development, was seen clearly in gonads from fetuses of 1.5-cm C-R length. An increase was observed with pregnenolone, dehydroepiandrosterone, and androstenediol at 2.5-3.0-cm C-R stages. The histochemical demonstration of Δ5-3β-HSD activity in the 2.5-3.0-cm fetuses was remarkable in two ways. First, it appeared to be stronger before the early differentiation of the Leydig cells. Second, the HSD activity seemed to be confined to the forming sex cords, with no reaction for the added substrates in the mature and immature Leydig cells and in mesenchymal cells of the interstitium. Substrate utilization was low, or absent, in fetuses from midpregnancy for all steroids. HSD reactions were present again at the 19.0-cm C-R stage and activity increased toward the end of gestation for all substrates except testosterone. Estradiol was the best substrate in fetal testes in late pregnancy where its utilization was confined to the interstitial cells. These findings are discussed in relation to steroidogenesis in the fetal testes.

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