Activational and organizational actions of gonadal hormones and the sex-specific effects of prolactin on food intake by rats

Results of previous studies indicate that there is a sex-specific feeding response to prolactin (PRL) by rats: Only female mts significantly increase their food intake. The possible roles of the activational and/or organizational actions of the gonadal hormones in this sex difference were explored. In the first experiment, activational hormone exposure was manipulated in adult male and female rats. The results suggest that the activation of actions of estrogen are not necessary for, and that testosterone does not block, PRL-induced increases in food intake by female rats. In a second experiment, organizational hormone exposure was manipulated in male and female mts during the early postnatal period. Genetic male rats organized as females by postnatal Day-1 castration significantly increased their food intake, while genetic female rats organized as males by postnatal androgen treatment maintained baseline levels of food intake. Overall, these experiments suggest that organizational, but not activational, gonadal hormone exposure plays a critical role in the development of this sex-specific response to PRL. (C) 1999 John Wiley & Sons, Inc.