Fibroblast Growth Factors as Local Mediators of Gonadal Function

Abstract

Although the presence and effects of many growth factors in gonadal tissues has been established by several investigators (1–4), their physiological function remains, to a large extent, speculative. The main reason behind this problem is the fact that in in vitro assays, growth factors have a tremendous number of biological activities. A case in point is basic fibroblast growth factor, basic FGF (3,4). This mitogen is characterized by its ability to elicit a neovascular response in in vivo assays of angiogenesis (5) and is thought to participate in these processes in the reproductive system (3). Yet these growth factors are also characterized by their capacity to modulate the growth and function of a wide number of cells (6,7). These include granulosa, adrenocortical, endothelial and smooth muscle cells, chondrocytes and fibroblasts, just to name a few. In some instances, basic FGF has no effect on cell proliferation, but only affects differentiated function (8–10). In other cases, its mitogenic activity appears to be the predominant activity (6,7). With the structural characterization of basic FGF, it has become of paramount importance to establish its possible physiological function(s) in tissues where it has been identified. At first glance, its pleiotropic activities might seem to preclude determining a specific function for this molecule; however, the discovery that it is widely distributed and found in almost all tissues suggests that its biological activities are local and thus potentially highly specific for any given environment. On this basis, it seems unlikely that an adrenal-derived FGF plays the function of a wound healing and/or angiogenic factor. More likely it is involved in adrenocortical homeostasis, an activity of the molecule in vitro (11).