Cricadian variatons in hepatic glutathione content, γ-glutamylcysteine synthetase and γ-glutamyl transferase activities in mice

Abstract

Experiments were conducted to determine if the circadian variations previously observed in hepatic reduced glutathione (GSH) concentrations also occurred in the associated enzymatic activities involved in the synthesis (γ-glutamylcysteine synthetase) and degradation (γ-glutamyl transferase) of glutathione using male CF-1 mice. All parameters were measured at four hour intervals over a 24-h period under normal (L: 0600–1800 h) and reversed (L: 1800–0600 h) lighting schedules. Circadian rhythms were found in each parameter under both lighting schedules. With GSH content, the rhythms' peak occurred at 0200 h and the nadir at 1400 h under the normal lighting schedule and was reversed (peak: 1800 h; nadir; 0600 h) under reversed lighting. The enzymatic activities also varied in a circadian manner with a phase shift in the peak and nadir occurring with a change in lighting schedule. Liver weight varied in a circadian manner under both lighting schedules with greatest weights occurring at the end of the dark phase. These data show that not only does GSH content vary in a circadian manner but that associated enzyme activities do as well. However, the hepatic enzyme activities did not correlate well with the GSH rhythm and, thus, do not provide a mechanistic rationale for the GSH rhythm.