Opiate receptors and beta-endorphin levels in brain areas of dogs with portal-systemic encephalopathy.

ABSTRACT

Clinical observation has indicated a supersensitivity to morphine in patients with hepatic encephalopathy. With the aim of clarifying the issue, radioreceptor binding studies of opiate receptors were performed in frontal cortex and hypothalamus of 6 dogs with mild portal-systemic encephalopathy induced by chronic treatment with dimethylnitrosamine followed by porto-caval shunt end-to-side. beta-Endorphin assays were performed in the same areas with radioimmunoassay. Opiate receptors labeled with [3H]naloxone in both areas showed a significant increase in the receptor densities (Bmax) without changes in the dissociation constant (KD). In parallel beta-endorphin levels showed a decline during the development of encephalopathy in both areas. The increased densities of opiate receptors in the mild stage of encephalopathy may explain the supersensitivity to morphine in patients with liver diseases.