Acetyl-l-carnitine restores the daily pattern of hypothalamic β-endorphin in rats exposed to continuous light

With the aim of evaluating the effect of acetyl-l-carnitine (ALC) on the daily pattern of hypothalamic beta-endorphin (beta-EP), we studied the effect of chronic treatment with ALC on hypothalamic beta-EP contents after suppression of the dark-phase of the light-dark cycle in female rats. We evaluated the hypothalamic content of beta-EP immunoreactivity every 3 h for 24 h in: (1) female rats treated with ALC for 15 days; (2) female rats treated with ALC for 15 days and exposed to continuous light for 24 h. The concentration of beta-EP immunoreactivity in tissue extracts was measured by radioimmunoassay. The results demonstrate that concentrations of beta-EP immunoreactivity in the medial basal hypothalamus show a circadian rhythm, with beta-EP immunoreactivity levels being higher during the night than during the rest of the day. Exposure to continuous light for 24 h abolished the nocturnal increase in hypothalamic beta-EP immunoreactivity. Rats treated with ALC showed a daily pattern in the beta-EP content of the medial basal hypothalamus similar to that of control rats. These data emphasize the possible role of ALC in restoring or maintaining the endogenous rhythmicity of central beta-EP.