The "multihormonal" control of reproductive function is primarily mediated by the action of hormones of the endocrine system. In the testis, spermatogenesis is under the dual control of pituitary gonadotropins, FSH, which acts directly on the seminiferous epithelium, and LH, which stimulates synthesis and secretion of the testicular androgen, testosterone. This latter hormone exerts paracrine effects on the seminiferous tubule. In recent years, increasing attention has been focused on the role of other factors produced by the testis that regulate the function of this organ. Interest in the possible existence of communication and feedback between the tubules and Leydig cells among the various cellular components of the seminiferous epithelium stems from the tremendous increase in the information available on the biology and metabolic activities of Sertoli, Leydig, myoid, and germ cells. It is currently believed that there is a variety of hormones produced within the testis that are responsible for the interactions between the principal cell-types. 1 •2

Many of the factors involved in these intratesticular regulatory mechanisms are believed to be peptides, although few have been characterized. Among the peptides which have been shown unequivocally to be produced by the testis are those derived from pro-opiomelanocortin (POMC). In addition to the testis, these peptides are also present in the male and female reproductive tracts. Following the immunocytochemical localization of several members of the family of POMC-derived peptides in the steroid-secreting cells of the gonads and the epithelial cells of the reproductive tract, 3 numerous studies were performed on the synthesis, regulation, and function of such peptides in reproduction. In this chapter, we will review the information available on the presence and possible function of POMC-derived peptides in the gonads and peripheral reproductive tissues.