Development of Δ⁵-3β hydroxysteroid dehydrogenase and glucose-6-phosphate dehydrogenase activity in Leydig cells of the fetal rat testis: A quantitative cytochemical study

Quantitative cytochemistry was used to follow changes in the activity of two enzymes essential for steroidogenesis. Δ⁵-3β hydroxysteroid dehydrogenase and glucose-6-phosphate dehydrogenase, during fetal development of the testis. The activity of these enzymes was measured by microdensitometry in individual Leydig cells in cryostat sections of testes from fetal rats from 17 to 21 days postconception. To quantify production of reducing equivalents generated by glucose-6-phosphate dehydrogenase and utilized via each of two pathways (Type I and Type II hydrogen), sections were incubated in medium with and without phenazine methosulphate, an artificial electron-transfer agent. Of these, Type I hydrogen is thought to be required for steroid hydroxylating reactions while Type II hydrogen is used for more generalized cellular biosynthesis. There was a significant increase in δ⁵-3β hydroxysteroid dehydrogenase activity between 17 and 18 days postconception, and again between 18 and 19 days. Maximum levels were reached by Day 19, followed by a decline over the following 2 days. Parallel changes were seen in the production of Type I reducing equivalents by glucose-6-phosphate dehydrogenase, with a peak in activity on Day 19 of gestation. In contrast, generation of Type II hydrogen was maximal on Day 17, declined to low levels on Days 18 and 19, and returned thereafter to values similar to those found for Type I hydrogen on Days 20 and 21. The parallel development of type I hydrogen generation and δ^b5-3β hydroxysteroid dehydrogenase activity confirms the suggestion that Type I hydrogen is related to steroidogenic activity. The pattern of changes in the activity of δ⁵-3β hydroxysteroid dehydrogenase and Type I hydrogen also provides additional support for the view that, in the rat fetus, androgen secretion by the testis is maximal around Days 18 and 19 postconception. The very different pattern of Type II hydrogen generation is probably related to the more generalized processes of Leydig cell growth and differentiation that take place earliere in fetal development.