Intragonadal control mechanisms.

On the weight of the evidence presented above, it is concluded that regulation at a local, intragonadal level is an integral part of the overall regulation of gonadal function in both sexes. The interaction between cells within a gonad extends beyond the same cell type to include germ cell-somatic cell interactions as well. We believe this local interaction between cell types facilitates the differing requirements of the various developmental stages of germ cells within the gonad, which would not be possible by simply varying the afferent pituitary hormone supply. We re-emphasize that the local factors responsible for these interactions are acting in conjunction with the pituitary hormones, and, in some cases, may be their proximate regulators. A more controversial phenomenon is the possibility of an interaction between the gonads which does not involve the hypothalamic-pituitary axis. The little evidence which is available to support this hypothesis comes mainly from studies on ovarian function, particularly recruitment and selection of follicles. More research on this phenomenon is warranted. Not surprisingly there are many parallels between the testes and ovaries with respect to the nature and action of local regulators. For example, the intragonadal action of steroids, the local modulation of the response of target cells to FSH, the influence of macrophages on steroidogenesis and the presence of mitotic and meiotic regulators are common to both sexes. It would not be surprising if the chemical nature of these factors in the ovary and testes are similar. If the ever-increasing list of factors and activities being discovered in the gonads is any guide, the phenomena outlined in this review are just the beginning of an extensive list of cell-cell interactions occurring within and between the gonads. No doubt the gonads will share with other organs the same interactions between cells which are required for normal cellular function. The uniqueness of the gonads lies in their protection and production of germ cells. The challenge of the future for reproductive biologists will be to discover and describe the interactions within and between germ cells which are obligatory for normal reproductive function, and to apply that information to devising ways of overcoming infertility and regulating fertility.