Acute effect of human chorionic gonadotropin (hCG) on 17 alpha-hydroxylase and C17,20-lyase activity in neonatal or prepubertal rat testis

Developmental changes in testicular interstitial cell populations, LH receptors and in the response to hCG in the rat

High doses of hCG were administered to immature rats of different ages and the animals killed 48 h later. Serum testosterone increased 2 to 4-fold over control values 48 h after hCG. In-vitro androgen production showed different patterns according to age. Animals younger than 35 days, when treated with hCG, retained the ability to respond to in-vitro gonadotrophic stimulation. This ability was lost in testes from rats aged 45 days. The number of free LH-receptors 48 h after hCG diminished with increasing age to become non-detectable at 35 and 45 days. In control animals the proportion of differentiated Leydig cells in relation to their mesenchymal precursors increased progressively with age to reach highest values at 45 days. hCG administration induced a shift of the cellular composition of the interstitium toward the more mature cell types. hCG has a predominantly trophic action on mesenchymal precursors in young rats, promoting their differentiation. These effects are minimal in the differentiated Leydig cells in older animals. It is proposed that the observed biochemical responses are the result of the balance between the increase in LH receptors and steroidogenic enzymes in the developing new generation of young Leydig cells and the down-regulation of receptors and enzymatic lesions in fully differentiated Leydig cells.

Absence of development of late steroidogenic lesions in rat testis during the end of fetal life

In the rat during the last 4 days of fetal life, the production of testosterone by the testis does not increase, whereas the plasma level of biological LH-like activity rises sharply. The present study was designed to test whether this phenomenon is attributed to the development of defects in the activity of the enzyme 17 alpha-hydroxylase and C17,20-lyase (called late steroidogenic lesions) during the end of fetal life. As this occurrence would lead to an age-related decrease in the ratio testosterone/progesterone, the testicular productions of these two steroids were evaluated on 18.5, 20.5, and 21.5 days postconception. Three different measurements were performed: (a) the in vivo testicular contents; (b) the in vitro secretions during a 120-min incubation in the presence or in the absence of 100 ng/ml ovine LH; (c) the testicular contents after these incubations. These measurements never revealed a decrease in the ratio testosterone/progesterone as a function of fetal age. It would appear that late steroidogenic lesions do not develop during the end of fetal life in the rat.