Immunohistochemical analysis of androgen effects on androgen receptor expression in developing Leydig and Sertoli...

Leydig and Sertoli cells are both targets of androgen action in the testis. Androgen exerts contrasting effects on the two cell types partially inhibiting steroidogenesis in adult Leydig cell and stimulating adult Sertoli cell functions required to support spermatogenesis. The developmental changes in the messenger RNA (mRNA) levels of androgen receptor (AR) also differ between Leydig and Sertoli cells, with Leydig cell AR mRNA being highest on day 35 postpartum, whereas Sertoli cell AR mRNA levels are highest on day 90. The purpose of the present study was to determine if the concentrations of AR in Leydig and Sertoli cells are differentially regulated during development using quantitative immunostaining. AR protein levels were measured in rat testes after hormonal treatments at three developmental stages: on days 21, 35, and 90 postpartum. At each age, five groups of animals were treated for 4 days with: 1) vehicle; 2) LHRH antagonist (NalGlu, 0.3 mg/kg BW.day) to suppress endogenous levels of androgen that accompany inhibition of LH and FSH secretion; 3) NalGlu + LH (0.2 mg/kg BW.day); 4) NalGlu + testosterone (T, at 7.5 mg/kg BW.day); and 5) NalGlu + MENT (a potent synthetic androgen, 7 alpha-methyl-19-nortestosterone, 0.7 mg/kg BW.day). AR protein was visualized by immunohistochemistry and measured by computer-assisted image analysis in Leydig and Sertoli cells using frozen sections of tests. After NalGlu treatment, AR levels in Leydig cells declined sharply to 42% and 31% of vehicle control (P < 0.01) in the 21 and 35 days postpartum age groups, respectively, but in 90-day-old rats there was no change. AR levels were partially maintained by exogenous LH, and completely maintained by exogenous androgen treatments in Leydig cells from 21- and 35-day-old rats, whereas in Leydig cells from 90-day-old rats, AR levels were unaffected in all treatment groups. In contrast, after NalGlu treatment, the AR concentration in Sertoli cells from 90-day-old rats were reduced to 32% of control (P < 0.01). Moreover, in Sertoli cells from 90-day-old rats, AR levels were partially maintained by LH and completely maintained by androgens. A similar trend was observed on day 35. On day 21, however, AR levels in immature Sertoli cells were unaffected in all treatment groups. These results indicate that androgen maximally stimulates AR levels in immature Leydig cells but is without significant effect in adult Leydig cells. In contrast, AR levels in Sertoli cells are more sensitive to androgen regulation in adult compared with immature animals. These findings indicate that there are distinct mechanisms controlling AR concentrations in Leydig and Sertoli cells during the development of the testis.