POSTNATAL-DEVELOPMENT OF LEYDIG-CELLS IN THE OPOSSUM (MONODELPHIS-DOMESTICA) - AN IMMUNOCYTOCHEMICAL AND ENDOCRINOLOGIC STUDY

This study involved characterization of Leydig celss of the opossum Mo nodelphis domestica, functionally by immunocytochemical identification of the enzyme 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and by measurement of testosterone levels using RIA. Immunostaining for 3 be ta-HSD was first detected in a few Leydig cells on Day 16, was increas ed by Day 24, reached a peak at 4 mo, and was present even in senescen t (3 yr) animals, Plasma testosterone was first measurable (0.35 no) a t prepuberty (3.5 mo), Prior to that, plasma testosterone concentratio ns were uniformly below the revel of detection (< 0.3 nM) in both sexe s from Day 5 to 2.5 mo. By 4 mo (puberty), plasma testosterone levels in males had risen significantly to 1.53 +/- 0.35 nM, continuing to in crease to 1.79 +/- 0.4 nM at 6 mo and peaking at 2.71 +/- 0.29 nM in t he adult (1-2 yr). Ovarian testosterone concentrations were consistent ly lower than those in the testis, as were those of adrenals of both s exes, Thus the testis would appear to be the major source of androgen production throughout life in this species, Our immunocytochemical stu dy suggests that in Monodelphis, puberty is reached at 4 mo, and this was further supported by a rise in circulating testosterone levels at this time.