Sex differences in the content of beta-endorphin and enkephalin-like peptides in the pituitary of obese (ob/ob) mice.

The beta-endorphin content in pituitary extracts of male and female obese (ob/ob) and lean (+/?) mice was determined by radioimmunoassay. The amount of beta-endorphin-like material contained in the pituitary of 3-month-old ob/ob male mice is similar to that of lean male mice. In contrast, the pituitary glands of female ob/ob mice have a greater amount of beta-endorphin-like material than lean female mice. To determine with greater precision the molecular nature of the polypeptide that accounts for the increase in beta-endorphin immunoreactivity, the various molecular forms of beta-endorphin immunoreactivity were resolved by Biogel P-30 column chromatography. At least four peaks of immunoreactive material were detected. The first peak elutes in the void volume, and the second and the third peaks appear in the elution volumes of beta-lipotropin and beta-endorphin, respectively. That the material present in the void volume might be proopiocortin is supported by adrenocorticotropic hormone radioimmunoassay. The increased total beta-endorphin immunoreactivity in pituitary glands of ob/ob mice is accounted for mainly by beta-endorphin. The beta-endorphin content of various brain structures of ob/ob mice is similar to that of lean littermates.