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Des travauxin vitro suggerent que le VIP pourrait jouer un role important au niveau de la biosynthese de testosterone. Nous avons demontre que des Souris chez lesquelles le gene codant pour le VIP est supprime montrent des niveaux de testosterone seriques tres reduits compares aux animaux sauvages. Egalement, ces animaux transgeniques presentent une reduction des niveaux de FSH (Follicle-stimulating hormone) a l’âge de quatre mois. L’etude de la structure testiculaire a revele une legere augmentation du pourcentage de tubules degeneres chez les animaux VIP-/-compares aux animaux sauvages. Les animaux chez lesquels le gene codant pour le VIP a ete supprime, a l’âge de quinze mois, ont des niveaux de steroidogenese bas compares aux souris sauvages. De maniere interessante, la degenerescence testiculaire est moins severe chez les animaux VIP-/-comparee a celles des animaux sauvages. L’ensemble de ces resultats suggere que: 1) le VIP est un facteur important pour la regulation de la biosynthese de testosterone et la secretion de FSH et 2) VIP regule le vieillissement testiculaire.

1. The central nervous systems (CNS) of males and females differ in the control mechanisms for the release of gonadotropins from the anterior pituitary gland as well as the capacity to display sex specific behaviors. 2. In guinea pigs and monkeys, these differences are organized through the actions of prenatal androgens secreted by the fetal testes. In both males and females androgen receptors have been identified within the brain during the period in development in which organization of the CNS occurs. Sex differences between the ratio of cytosolic and nuclear androgen receptors are due to the amount of endogenous androgen present in the circulation of the developing fetus. Thus, at least part of the biochemical machinery necessary for androgen action resides in the CNS during the period of sexual differentiation. 3. In addition to the physiological differences that have been observed, morphological differences that are androgen dependent have been found in the medial preoptic nucleus and the bed nucleus of the stria terminalis of the guinea pig. The location of these sex differences in brain morphology coincides roughly with the location of steroid binding neurons. 4. In some species the in situ conversion of testosterone to dihydrotestosterone (DHT) by the 5 alpha-reductases or to estradiol-17 beta by cytochrome P450 aromatase mediates testosterone's action. The gonadotropin surge mechanism of adult guinea pigs exposed to a 5a-reductase inhibitor in utero during the critical period for sexual differentiation was unaffected in either males or females even though the development of the external organs of reproduction of males was feminized by the treatment. Likewise, the gonadotropin surge mechanism of subjects exposed to an aromatase inhibitor in utero during the critical period for sexual differentiation was unaffected by this treatment. 5. The mechanism controlling negative feedback, however, was affected in both males and females. Subjects that were exposed to an aromatase inhibitor while developing in utero could not respond to the negative feedback actions of estrogen on gonadotropin release in adulthood. 6. The surge mechanism for the control of gonadotropin secretion in nonhuman primates is not sexually differentiated as it is in rodents. Castrated male monkeys release surge amounts of LH in response to an estrogen challenge. Both infant and adult dimorphic behaviors of rhesus monkeys are organized by the prenatal actions of androgen.