Tetrachlorodibenzo-p-dioxin alters rat hypothalamic endorphin and mu opioid receptors

Abstract

The present study was undertaken to assess if hypothalamic [beta]-endorphin ([beta]E) and/or brain mu opioid receptors are associated with 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) (50 [mu]g/kg)-induced hypophagia and body weight decline in rats. Hypothalamic [beta]E concentrations were initially increased to 166% of controls on day 1, and then were depressed to 39% and 49% of control values on days 2 and 3, respectively. Brain mu opioid receptor number was increased 60% in TCDD-treated rats at day 3 without a change in the binding affinity. Food-restricted rats did not exhibit changes in hypothalamic [beta]E concentrations or brain mu opioid receptor number. These results indicate that TCDD causes early perturbations in hypothalamic [beta]E concentrations and brain mu receptor number, which may contribute to the mechanisms by which TCDD leads to decreased food intake and progressive weight loss.