QUANTITATIVE-ANALYSIS OF ANDROGEN RECEPTOR MESSENGER-RIBONUCLEIC-ACIDIN DEVELOPING LEYDIG-CELLS AND SERTOLI CELLS BY IN-SITU HYBRIDIZATION

Testosterone produced by Leydig cells is critical for the maintenance of spermatogenesis by Sertoli cells throughout adulthood in the rat. H owever, the presence of androgen receptors (AR) in Leydig cells in pre pubertal rats suggests additional roles for androgen in early Leydig c ell function and differentiation. In the present study, AR messenger R NA (mRNA) was directly measured by in situ hybridization in sections o f rat testes at three developmental stages: on day 21 postpartum, when Leydig cells exist as mesenchymal-libe progenitors; on day 35, when t hey are still immature, producing low amounts of testosterone; and on day 90, when they are fully functional in the sexually mature animal. Testicular AR mRNA was detected in Leydig cells, pericytes, peritubula r myoid cells, and Sertoli cells. On day 90, AR mRNA levels in Sertoli cells varied with the cycle of the seminiferous epithelium, achieving peak intensity at stages VII-VIII. Measurements were made by image an alysis and expressed as integrated signal intensities per unit labeled area (mean +/- SEM; n = 3 rats at each age). The results showed that levels of Leydig cell and Sertoli cell AR mRNA change significantly du ring development (P < 0.05). Leydig cell AR mRNA was intermediate on d ay 21 (at 17.3 +/- 0.7), highest on day 35 (at 26.9 +/- 1.6), and lowe st on day 90 (at 11.8 +/- 1.1). The trend for isolated Leydig cells fr om these three ages was identical. In contrast, Sertoli cell AR mRNA w as lowest on day 21 (at 19.3 +/- 1.0), intermediate on day 35 (at 24.5 +/- 1.4), and highest on day 90 (at 36.9 +/- 0.5). In Leydig cells, t he highest level of AR mRNA was present during puberty, whereas the gr eatest amount of AR mRNA in Sertoli cells was present on day 90. This indicates that Leydig cells and Sertoli cells use different mechanisms to maintain AR levels. We infer from these data that Leydig cells are maximally sensitive to androgen during puberty, which is consistent w ith our hypothesis that androgens facilitate their differentiation.