CHANGES IN RAT-BRAIN OPIATE RECEPTOR CONTENT UPON CASTRATION AND TESTOSTERONE REPLACEMENT

The saturable binding of naltrexone-3H in the brains of castrated male rats exceeds that found in intact animals by a factor of two. This increase is androgen dependent since testosterone replacement reduced the binding to control levels. Scatchard analysis of the saturation curves revealed that the change in binding reflects increased available binding sites and is not due to increased binding affinity. This relationship between testosterone and brain opiate receptors provides for the participation of endorphins in the regulation of pituitary gonadotropins by gonadal hormones. The increased content of opiate receptors in the brains of castrated rats correlates with the greater brain N-demethylation of morphine establishing a further link between this biotransformation and agonist action. © 1979.