Testicular steroidogenesis can be divided during the life span of mammals into two distinctive phases, one occurring during the early stage of life, in the fetal and neonatal period, and the other after puberty and for the rest of adult life. The early testicular steroidogenic activity is due to a special fetal population of Leydig cells that are steroido-genically very active and differ morphologically and functionally from adult Leydig cells. LH is responsible for the regulation of steroidogenesis in adult Leydig cells, but there is information suggesting that initiation of steroidogenesis by fetal Leydig cells is independent of gonadotropic stimulation. cialis professional
The importance of paracrine interactions between the testicular cell compartments, including effects of locally produced testicular factors on Leydig cell steroidogenesis, has been stressed in several recent investigations.
Some of these factors may have specific functions in the fetal testis.
Vasoactive intestinal peptide (VIP), a 28-amino acid molecule, was first isolated from porcine duodenum and was considered to be a vasodilatory gut hormone. It was later identified in endocrine cells , as well as in the nervous system . Both VIP and VIPergic fibers are distributed widely throughout the reproductive tract of males and females. In males, most of the VIPergic fibers are found in the prostate, seminal vesicles, and vas deferens, but some innervation is also present in the testicular stroma. During fetal life in rodents, VIP has recently been shown to regulate growth during the early postimplantation period . In cultured whole mouse embryo at embryonic day (E) 9.5, VIP dramatically accelerates embryonic growth . Treatment with VIP resulted in doubling of the DNA content and stimulated mitosis. Most of the studies on VIP have concentrated on its role as a central nervous system neurotransmitter and neuromodulator with neurotropic properties . Less attention has been paid to its endocrine actions during fetal life.