Effect of deprival of LH on Leydig cell proliferation: involvement of PCNA, cyclin D3 and IGF-1

The levels of proliferating cell nuclear antigen (PCNA) and cyclin D3 which are known markers of cellular proliferation were monitored by immunoblotti ng in progenitor Leydig cells (PLC), immature Leydig cells (ILC) and adult Leydig cells (ALC) isolated from 21, 35 and 90 day old rats, respectively w hich represent the Leydig cells at different stages of development. The lev els of PCNA and cyclin D3 were highest in PLC, intermediate in ILC and lowe st in ALC. Following administration of an antiserum to LH to deprive endoge nous LH in 21 day old rats, a significant decrease in the levels of PCNA an d Cyclin D3 were observed suggesting the involvement of Lutenizing hormone (LH) in PLC proliferation. In support of this observation, Bromodeoxyuridin e (BrdU) incorporation was highest in PLC when compared with ILC and ALC, a nd administration of LH antiserum to 21 day old rats led to a total absence of BrdU incorporation by the isolated PLC. Also, there was a decrease in t he level of IGF-1 and IGF-1 receptor mRNA levels by 55 and 35%, respectivel y as assessed by semi-quantitative RT-PCR. In addition, the PLC isolated fr om rats deprived of endogenous LH incorporated much less BrdU following add ition of IGF-1. These results, which are obtained using an in vivo model sy stem establish that LH has a very important role in Leydig cell proliferati on in immature rats. (C) 2000 Elsevier Science Ireland Ltd. All rights rese rved.