The role of social isolation in the effects of alcohol on corticosterone and testosterone levels of alcohol-preferring and non-preferring rats

Aims: Alcohol has been reported to affect the hypothalamic-pituitary-gonadal axis (HPG-axis) and hypothalamic-pituitary-adrenal axis (HPA-axis) as expressed by increased or decreased corticosterone and testosterone levels. Both hormones have also been related to the aetiology of alcohol drinking and the development of alcoholism. Our aim has been to study these interrelations in animal models of alcohol drinking by using social isolation as a model of anxiety. Methods: The effects of alcohol on serum testosterone and corticosterone concentrations were investigated in alcohol-preferring (AA) and alcohol non-preferring (ANA) rat lines. Animals were tested in mornings and afternoons with 0.75 and 1.5 g alcohol/kg. Half of the animals were kept in single cages, while the control animals were housed in groups of four individuals. Results: The group-caged ANA rats displayed higher control corticosterone levels than the corresponding AA rats during morning sessions (P = 0.007). The AA rats displayed elevated corticosterone levels (am: P = 0.047) and the ANA rats displayed reduced control corticosterone levels (pm: P = 0.016) in the single cage situation compared with the group-cage situation. Corticosterone concentrations were not affected by low doses and increased (P < 0.05) by high doses of alcohol in all test groups except for isolated AA rats during afternoon sessions. In general, more significant reductions in testosterone levels following alcohol administration were found in the ANA line. In group-caged AA rats, alcohol reduced testosterone levels, while no such effect was observed in isolated AA rats. Conclusions: We suggest that social isolation, representing stress, may constitute a situation in which the HPA and HPG axes are connected together in promoting alcohol drinking.