Testicular response to hCG in the immature lamb

Abstract

Previous studies have shown of an early postnatal activation of the hypothalamic-pituitary-gonadal axis (HPGA) in the male lamb, suggesting its usefulness in the study of this phenomenon in man. To define the time sequence in the appearance of this activity, the “in vivo” and “in vitro” testicular responsiveness to hCG of the immature lamb as compared to the adult ram was studied. One, 3,7,14, 21 and 28 day old lambs and 1 year old rams were hemicastrated and the second testis removed 2h after hCG (500 IU/kg). Plasma testosterone (T) was low from 1 to 28 days (<.3ng/ml), the highest levels being found at 28 days. Plasma T increment (Δ) after hCG rose progressively from 1 to 14 days (0.26±0.01 to 0.95±0.16ng/ml), decreased at 21 days (0.64±0.06) to rise again at 28 days (0.84±0.11ng/ml). The Δ T post hCG in adult rams was 8.3±0.66ng/ml. In general maximal Δ T levels were reached within 1h post hCG. Δ of T, 17-OH-progesterone, dehydroepiandrosterone and Δ4-androstenedione increased from 1 to 14 days. Testicular 17-20 lyase activity rose with age without influence of hCG. T production by isolated interstitial cells in basal and stimulated conditions (hCG, db cAMP, choleratoxin) was higher at 3 and 7 days. These data suggest that the lamb testis has the capacity to respond to hCG “in vivo” and to various stimuli “in vitro” from the first day of life.