Naloxone, adrenalectomy, and steroid replacement: evidence against a role for circulating beta-endorphin in food intake.

Naloxone has a dose-dependent, significant anorectic effect when administered to normal rats, consistent with an antagonism of central or peripheral enkephalinergic or endorphinergic mechanisms. Mean levels of circulating immunoreactive beta-endorphin were similar in intact rats (0.5 ng/ml) and dexamethasone-treated adrenalectomized rats (0.5 ng/ml). In contrast, plasma levels were high in adrenalectomized rats with no replacement steroid (1.3 ng/ml) and in adrenalectomized rats given the mineralocorticoid deoxycorticosterone (0.9 ng/ml). In sharp distinction to the clear changes in circulating immunoreactive beta-endorphin produced by adrenalectomy and selective steroid replacement, no differences were seen in baseline food intake or anorectic response to naloxone. We conclude that a physiological role for circulating beta-endorphin in the regulation of food intake appears unlikely.