gonadotropins and testoste­rone. These hormones exert an indi­rect effect on spermatogenetic cells by locally produced autocrine, para-crine and juxtacrine regulations of tes-ticular functions. They mediate inter­actions between Leydig cells, peritubular myoid cells, Sertoli cells and spermatogenetic cells as a pre requisite of maintenance and control of Spermatogenesis. The physiologi­cal role of these factors in the testis and their regulatory function remain to be studied in detail (Glander et al., 1996).
One of the molecules that are be­lieved to be involved in the develop­ment of germ cells are insulin like gro- •
wth factor-l (IGF-I) (Spiteri Greech &Nieschlage, 1992; Loir &Le Gac, 1994), which is found in plasma and tissue fluids. Probably, the tissue IGF-I from paracrine / autocrine sources is more important than those from circu­lation (Lin, 1995).
IGF-I exerts a direct as well as an indirect influence on steriodogenesis (Lin et al., 1986; Saez et al., 1989). metabolism (Oonk et a!., 1989), cell proliferation and differentiation (Borland et al., 1984; Soder et al., 1992) and is modified in its action by growth hormone (Lin, 1995). Testicu-lar IGF-I is mainly produced in Sertoli cells (Ritzen, 1983) by stimulation of follicle stimulating hormone (Cailleau etal.,1990).