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 immunoblotting in progenitor Leydig cells (PLC), immature Leydig cells (ILC) and adult Leydig cells (ALC) isolated from 21, 35 and 90 day old rats, respectively which represent the Leydig cells at different stages of development. The levels of PCNA and cyclin D3 were highest in PLC, intermediate in ILC and lowest in ALC. Following administration of an antiserum to LH to deprive endogenous LH in 21 day old rats, a significant decrease in the levels of PCNA and Cyclin D3 were observed suggesting the involvement of Lutenizing hormone (LH) in PLC proliferation. In support of this observation, Bromodeoxyuridine (BrdU) incorporation was highest in PLC when compared with ILC and ALC, and 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 the level of IGF-1 and IGF-1 receptor mRNA levels by 55 and 35%, respectively as assessed by semi-quantitative RT-PCR. In addition, the PLC isolated from rats deprived of endogenous LH incorporated much less BrdU following addition of IGF-1. These results, which are obtained using an in vivo model system establish that LH has a very important role in Leydig cell proliferation in immature rats.