Age-dependence of the rat Leydig cell and Sertoli cell function. Development of the peripheral testosterone level and its relation to mitochondrial and microsomal cytochromes P-450 and to androgen-binding protein.

The first part of this study compares peripheral testosterone levels with intratesticular levels of the cytochromes P-450 of two key enzymes of androgen biosynthesis, i.e. mitochondrial cholesterol monooxygenase (P-450(cscc)) and microsomal steroid-17 alpha-monooxygenase (P-450(C17 alpha)) during puberty and early adulthood of male Wistar rats. From 4 to 10 weeks of age, the testosterone level increases 8.7-fold, the P-450(C17 alpha) level 8.3-fold, but the P-450(cscc) level 24.5-fold as an indication of specific induction of this protein. From 13 to 50 weeks of age, the testosterone level remains constant, the P-450(cscc) level increases continuously by a factor of 1.4, but 62% of the P-450(C17 alpha) content are lost. This discrepancy is explained by a divergent regulation of the cytochromes P-450 of the two steroid monooxygenases: a persisting induction of P-450(cscc) and a concurrent down-regulation of P-450(C17 alpha) that may be a consequence of the high rate of Leydig cell steroid hydroxylation after puberty. Overlapping of both processes may (probably besides other developmental factors) result in a constant testosterone concentration in blood. The second part of the study compares testicular and epididymal levels of androgen-binding protein (ABP) with the peripheral testosterone level. The peripubertal increase in testicular ABP content is shown to be related only to the increase in testicular mass, whereas a specific accumulation of ABP occurs in the epididymis from 4 to 13 weeks of age. This pattern indicates an increasing secretory activity of the Sertoli cells that remains high during adulthood up to the 50th week.(ABSTRACT TRUNCATED AT 250 WORDS)