TESTICULAR MATURATION IN THE RAT - INVIVO EFFECT OF GONADOTROPINS ON STEROIDOGENIC ENZYMES IN THE HYPOPHYSECTOMIZED IMMATURE RAT

Hypophysectomized immature rats were treated with LH or FSH to assess the role of these hormones on the activity of testicular steroidogenic enzymes during sexual maturation. Rats were hypophysectomized on Day 21 and hormone treatment was initiated on Day 27 and continued for 5 or 10 days. A 10,000 x g supernatant of testicular homogenates was assayed for 17β-hydroxysteroid dehydrogenase, Δ5-3β-hydroxysteroid dehydrogenase-isomerase, 5α-reductase and 5α-androstane-3α+3β-hydroxysteroid dehydrogenase activities. All enzyme activities decreased after hypophysectomy. Treatment with LH for 10 days stimulated 5α-reductase by 6-fold, Δ5-3β-hydroxysteroid dehydrogenase by 4-fold, 5α-androstane-3α+3β-hydroxysteroid dehydrogenase by 2-fold and 17β-hydroxysteroid dehydrogenase by only 50%. In constrast, treatment with FSH for 10 days stimulated 17β-hydroxysteroid dehydrogenase more than 2-fold. Although FSH treatment for 5 days significantly increased Δ5-3β-hydroxysteroid dehydrogenase-isomerase activity (56%) and 5α-androstane-3α+3β-hydroxysteroid dehydrogenase activity (30%), these increases were not maintained for the 10 day treatment period. FSH treatment had neither a maintenance nor a stimulatory effect on 5α-reductase activity. The demonstration that FSH treatment increased 17β-hydroxysteroid dehydrogenase activity is consistent with our previous hypothesis that the increase in 17β-hydroxysteroid dehydrogenase activity during sexual maturation may be regulated by FSH and that this may be one mechanism by which FSH increases testicular responsiveness to LH.