INSULIN-LIKE GROWTH-FACTOR-I AND GROWTH-FACTOR-II IN FOLLICULAR AND OOCYTE MATURATION

Insulin-like growth factors I and II are synthesized from animal and human follicles. Their reproduction is FSH-, LH- and oestrogen-dependent. Growth hormone is also involved. IGF-I receptor numbers increase in the presence of FSH, while estradiol has a synergic effect. IGF-I and IGF-II stimulate growth of different follicular cell elements. TGF-alpha has the same activity but seems to be mediated by an increase in IGFs. Conversely, TGF beta and activin inhibit follicular growth accompanied by a reduction in IGFs. In contrast to TGF alpha, IGFs do not cause acquisition of meiotic competence. Injection of IGF-I into cultures of prepuberal splenic primary follicles reduced IGF-II production.