THE IGF FAMILY AND FOLLICULOGENESIS

The process of ovarian follicular development is a long and arduous on e, marked by dramatic proliferation and differentiation of both the so matic and germ cell elements. To a large extent, this explosive agenda is under the control of conventional endocrine principles, involving hormones such as pituitary gonadotropins and ovarian steroids. Importa ntly, it has become increasingly apparent that several phenomena centr al to ovarian physiology are not fully accounted for by conventional e ndocrine principles. As an example, consideration must be given to the process of follicular selection whereby a predetennined number of fol licle(s) is recruited, selected, allowed to assert dominance? and ulti mately ovulate despite the fact that all follicles are afforded compar able gonadotropic stimulation. These observations have given rise to t he suggestion that the regulation of ovarian function may be under the control of yet another group of modulatory principles known under the general term 'putative intra-ovarian regulators'. It is generally env isioned that the exquisitely-timed and highly-regionalized expression of these locally-derived, often peptidergic, principles may finally ac count for those aspects of the ovarian life cycle which at this time d efy conventional explanation. It has been hypothesized that the role o f IGF-1 in the context of ovarian physiology is to serve as an amplifi er of gonadotropin hormonal action. At this time, significant support for this hypothesis can be documented. More speculative is the notion that IGF-I may partake in intrafollicular intercompartmental coordinat ion, a concept presupposing enhanced more coordinated follicular devel opment, due to granulosa-theca-interstitial cell cross-talk and improv ed coupling. Entirely in the speculative realm is the proposition that IGF-1 may in fact partake in the process of follicular selection, a n otion for which relatively limited support can be: derived at this tim e. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.