BIOSYNTHESIS OF TESTICULAR-STEROIDS IN THE IMMATURE, ADULT AND SENESCENT GUINEA-PIG

The potential biosynthetic capacity of testicular hormones was studied in immature, pubertal and aging guinea-pig. In their sexual development towards puberty, changes in the relationship of the steroids involved in the steroidogenic pathways were observed. The testosterone/androstenedione ratio changes markedly, showing an important increase with pubertal proximity. The testosterone half-arrow-right-over-half-arrow-left androstenedione sequence, reversibly catalyzed by 17-beta-hydroxysteroid oxidoreductase (17-beta-oxido-reductase), clearly shifted towards androstenedione in immature animals irrespective of the precursor utilized. Post-pubertal animals showed a greater enzymatic activity in the 5-ene and 4-ene testicular synthesis pathways, testosterone production being greatest. In the aging animal, hormonal biosynthetic capacity falls. Reversion of the 17-beta-oxido-reductase activity could be one of the mechanisms responsible for the decrease in testosterone, as in immature guinea-pigs. In order to investigate the in vitro steroidogenic capacity of glands at different ages, minces of testicular tissue were incubated with labelled precursors. The studies were conducted in triplicate at 35-degrees-C. For equal quantities of incubated tissue the non-metabolized amount of [H-3]pregnenolone and [C-14]progesterone, utilized as precursors, was different in post-pubertal and senescent animals: 55.7 +/- 3 vs 59.3 +/- 2.3% (P < 0.01) for pregnenolone, and 50.1 +/- 3.3 vs 56.3 +/- 2.9% (P < 0.01) for progesterone, respectively. Testosterone production was 12 +/- 2% in adult and 6.7 +/- 2.7% in senescent animals (P < 0.01). The testosterone/androstenedione ratio was not significantly different in post-pubertal and senescent animals: 2.8 +/- 0.5 vs 2.4 +/- 0.4, but consistently higher than found in immature animals: 0.3 +/- 0.1. The lesser potential capacity of the aging tissue to synthesize testosterone could be explained by a decline in the glands capacity to metabolize the hormonal precursors.