IMMUNOHISTOCHEMICAL ANALYSIS OF ANDROGEN EFFECTS ON ANDROGEN RECEPTOREXPRESSION IN DEVELOPING LEYDIG AND SERTOLI CELLS

Leydig and Sertoli cells are both targets of androgen action in the te stis. Androgen exerts contrasting effects on the two cell types: parti ally inhibiting steroidogenesis in adult Leydig cell and stimulating a dult Sertoli cell functions required to support spermatogenesis. The d evelopmental changes in the messenger RNA (mRNA) levels of androgen re ceptor (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 ce lls are differentially regulated during development using quantitative immunostaining. AR protein levels were measured in rat testes after h ormonal 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 o f LH and FSK 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 po tent synthetic androgen, 7 alpha-methyl-19-nortestosterone, 0.7 mg/kg BW . day). AR protein was visualized by immunohistochemistry and measu red by computer-assisted image analysis in Leydig and Sertoli cells us ing frozen sections of testes. After NalGlu treatment, AR levels in Le ydig cells declined sharply to 42% and 31% of vehicle control (P < 0.0 1) in the 21 and 35 days postpartum age groups, respectively, but in 9 0-day-old rats there was no change. AR levels were partially maintaine d by exogenous LH, and completely maintained by exogenous androgen tre atments in Leydig cells from 21- and 35-day-old rats, whereas in Leydi g cells from 90-day-old rats, AR levels were unaffected in all treatme nt groups. In contrast, after NalGlu treatment, the AR concentration i n 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 w ere 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. Th ese results indicate that androgen maximally stimulates AR levels in i mmature 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 fin dings indicate that there are distinct mechanisms controlling AR conce ntrations in Leydig and Sertoli cells during the development of the te stis.