RECEPTORS for dopamine have been classified into two functional types, D₁ and D₂ (refs 1,2). They belong to the family of receptors acting through G (or guanine nucleotide-binding) proteins³. D₂ receptors inhibit adenylyl cyclase, but D₁ receptors stimulate adenylyl cyclase and activate cyclic AMP-dependent protein kinases^4,5. Dopamine D₁ and D₂ receptors are targets of drug therapy in many psychomotor disorders, including Parkinson's disease and schizophrenia^6,7, and may also have a role in drug addiction and alchoholism⁸. D₁ receptors regulate neuron growth and differentiation⁹, influence behaviour and modify dopamine D₂ receptor-mediated events^10,11. We report here the cloning of the D₁ receptor gene, which resides on an intronless region on the long arm of chromosome 5, near two other members of the G-linked receptor family. The expressed protein, encoded by 446 amino acids, binds drugs with affinities identical to the native human D₁ receptor. The presence of a D₁ receptor gene restriction fragment length polymorphism will be helpful for future disease linkage studies.

Immunization of mice with acetaldehyde conjugated to human plasma proteins resulted in the production of polyclonal antibodies that reacted with erythrocyte protein-acetaldehyde conjugates, but not with control erythrocyte proteins. Such antibodies recognized erythrocyte protein-acetaldehyde conjugates prepared with 20-100 microM acetaldehyde, concentrations that exist in the blood of alcoholics. The antibodies also recognized acetaldehyde condensation products with synthetic poly-(L-lysine). Immunization with keyhole limpet hemocyanin-acetaldehyde conjugates resulted in antibodies against both plasma protein-acetaldehyde and erythrocyte protein-acetaldehyde conjugates, which did not cross-react with the respective unmodified carrier proteins. Immunization with human erythrocyte protein-acetaldehyde condensates led to the production of antibodies against both the protein moiety as well as the condensate. Monoclonal antibodies with affinities 50 times greater for the condensate than for the carrier protein were produced by hybridization of spleen cells from the immunized mice. Chronic alcohol administration to mice for 45-50 days led to the generation of antibodies that reacted against protein-acetaldehyde conjugates, suggesting that such adducts are formed in vivo and can act as neoantigens. Antibodies against acetaldehyde adducts should be of value in the identification of alcohol consumption and in the study of the biology of the adducts in relation to organ pathology.

In a study involving 68 ambulatory patients with known alcohol problems and 68 social drinkers matched for age and sex, a questionnaire about the patients' history of trauma identified 7 out of 10 subjects with drinking problems. In contrast, abnormal values for gamma-glutamyl transferase, mean corpuscular volume, or high-density lipoproteins had only moderate sensitivity (26% to 40%) for identifying alcohol problems but excellent specificity (88% to 99%) for ruling out cases. Similar rates of sensitivity and specificity were found among 61 family practice patients. Diagnostic accuracy was improved by combining tests results, using computer-based logistic regression analysis. This study suggests that a brief questionnaire on history of trauma is valuable for the earlier detection of problem drinking in ambulatory populations, in contrast to laboratory tests, which appear to have high sensitivity only with more chronic alcoholics.

We have previously reported that a hypermetabolic state, resembling that produced by thryoid hormones, exists in the livers of animals treated chronically with ethanol. We propose that this alteration produces a relative hypoxia in the centrilobular zone of the liver which, if severe enough, leads to cellular death and to the production of hepatitis. Rats consuming ethanol for 30 days, given with a nutritionally adequate diet, and exposed to reduced oxygen tensions for only 6 hr, developed histological and biochemical evidence of hepatocellular necrosis and inflammatory lesions confined to the centrilobular zone. The severity was proportional to the degree of hypoxia. Pair-fed (nonalcohol) controls showed no such lesions. Treatment of the animals with propylthiouracil for 3-10 days abolished the hypermetabolic state of the liver in ethanol-consuming animals, and drastically reduced the histological and biochemical effects of hypoxia in them. These findings may have implications for pathogenesis and treatment of alcoholic hepatitis in man.

The effect of acute ethanol administration on rates of synthesis and utilization of hepatic glutathione (GSH) was studied in rats after a pulse of [35S]cysteine. A 35% decrease in hepatic GSH content 5h after administration of 4 g of ethanol/kg body wt. was accompanied by a 33% increase in the rate of GSH utilization. The decrease occurred without increases in hepatic oxidized glutathione (GSSG) or in the GSH/GSSG ratio. The rate of non-enzymic condensation of GSH with acetaldehyde could account for only 6% of the rate of hepatic GSH disappearance. The increased loss of [35S]GSH induced by ethanol was not accompanied by an increased turnover; rather, a 30% inhibition of GSH synthesis balanced the increased rate of loss, leaving the turnover rate unchanged. The rate of acetaldehyde condensation with cysteine in vitro occurred at about one-third of the rate of GSH loss in ethanol-treated animals. However, ethanol induced only a minor decrease in liver cysteine content, which did not precede, but followed, the decrease in GSH. The characteristics of 2-methylthiazolidine-4-carboxylic acid, the condensation product between acetaldehyde and cysteine, were studied and methodologies were developed to determine its presence in tissues. It was not found in the liver of ethanol-treated animals. Ethanol administration led to a marked increase (47%) in plasma GSH in the post-hepatic inferior vena cava, but not in its pre-hepatic segment. Data suggest that an increased loss of GSH from the liver constitutes an important mechanism for the decrease in GSH induced by ethanol. In addition, an inhibition of GSH synthesis is observed.

Propylthiouracil has been shown experimentally to protect against alcohol-induced hepatocellular necrosis in hypoxic conditions. An earlier, short-term study of patients with alcoholism and liver disease indicated clinical improvement with propylthiouracil, but the effect on mortality could not be assessed. In the present study, we investigated the effect of propylthiouracil on mortality in patients with alcoholic liver disease in a long-term, double-blind, randomized clinical trial involving 310 compliant patients who received propylthiouracil (n = 157) or placebo (n = 153) for a maximum of two years.