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-hydroxylase activity
Testicular feminized (Tfm) mice are totally insensitive to androgen and may be used to study the role of the androgen receptor in normal development and function. We have examined testicular and Leydig cell steroidogenesis in Tfm mice. Serum bioactive LH was high in Tfm mice but serum testosterone was low and this was associated with a severe reduction in testicular testosterone production in vitro. Examination of [3H]pregnenolone metabolism by testes of Tfm mice indicated that progesterone, rather than testosterone, was the major steroid produced. Leydig cells were isolated from normal and Tfm mice and from normal mice in which testicular descent was surgically prevented before puberty. As in whole testes, androgen production in response to human chorionic gonadotrophin was severely reduced in Leydig cells from testes of Tfm mice compared with normal or cryptorchid groups. In contrast, progesterone production by Leydig cells from testes of Tfm mice was markedly increased in comparison with other groups. Total steroid production (progesterone plus androstenedione plus testosterone), however, was only 24% of normal in Leydig cells from Tfm mice. The pattern of steroid production by Leydig cells from cryptorchid testes was similar to control, although total steroid production was reduced to about 50% (this was significantly higher than the Tfm group, P<0·05). The high progesterone/androgen ratio in testes from Tfm mice suggested that 17
-hydroxylase was depleted in these animals. To confirm this, activity of the four major steroidogenic enzymes associated with the smooth endoplasmic reticulum was measured. Activities (per testis) of 3β-hydroxysteroid dehydrogenase and 5-reductase were normal in Tfm and cryptorchid mice but, as expected, 17-hydroxylase activity was only 2·4% of control and 4·5% of cryptorchid testes. 17-Ketosteroid reductase activity was markedly reduced in cryptorchid testes (14·4% of control) but there was a further reduction in testes from Tfm mice to 0·1% of control. Results show that the Tfm mutation is associated with marked loss of 17-hydroxylase and 17-ketosteroid reductase activities. This suggests that these enzymes may require receptor-mediated androgen stimulation during development to express normal activity.
Journal of Endocrinology (1991) 131, 443–449
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