High voluntary alcohol consumption, in experimental liver cirrhosis is hardly responsive to opioid antagonist treatment

Rats with liver cirrhosis, evoked by chronic administration of thioacetamide (TAA), consumed voluntarily more alcohol than their healthy counterparts. Seeking the mechanisms underlying this phenomenon, the opioid system was screened for involvement and alterations. In vivo, the influence of chronically administered Naloxone and Naltrexone, non-specific opioid receptor antagonists, on alcohol intake was examined in free choice tests between 10% alcohol and tap water and ex vivo receptor binding studies were performed on cerebral membrane preparations.

TAA rats, selected for the study, had confirmed liver insufficiency: their plasma bilirubin concentrations were about 3 times higher, the prothrombin time was 50% longer and they consumed voluntarily 3 times more alcohol than the control animals. The drugs were given s.c. for five days, at the beginning of the dark phase of a 24h cycle, in a daily dose of 10 mg per kg body mass. Throughout the treatment, the rats were kept individually in metabolic cages with a free access to water, alcohol solution and food. Feed and fluid consumption, as well as the urine outputs, were recorded on the 2h, 4h, 6h and 24h after the drug administration. The mu opioid ligand - [(3)H]-(D-Ala(2), -N-MePhe(4), Glyol(5)) Enkephalin was used to obtain binding characteristics of the control and TAA rat brain membranes.

The drugs, if modified drinking behaviours, they did it transiently; alcohol, water and thus the total fluid intake by the cirrhotic and control rats was significantly less after 2h - 6h from either naloxone or naltrexone administration. Both drugs decreased general fluid consumption as such rather than the consumption of alcohol only, as observed from the recordings related to TAA rats. The binding data: K(d) of 2.62 +/- 0.98 nM and B(max) of 43.71 +/- 6.12 fmol/mg protein for cirrhotic rats, versus K(d) of 4.63 +/- 1.98 nM and B(max) 95.61 +/- 18.33 fmol/mg protein for the control ones, suggest that while the affinity of radioligand to cerebral mu receptors was similar for the two groups, there was a lower density of those receptors in the cirrhotic rats.

The results indicate some disturbances in the opioid system in cirrhotic rats. However, the low response to opioid therapy suggests that the opioid system may have only be partly involved in the development of the observed increased alcohol drinking in the rats with liver cirrhosis.