Effect of chronic lithium treatment on twenty four hour variation in plasma and red blood cell lithium and sodium concentrations, drinking behavior, body weight, kidney weight, and corticosterone levels

This study tested the hypothesis that lithium alters the phase relationships of various 24-hour rhythms. Six point 24-hour patterns were measured throughout a 12 hour light/12 hour dark cycle from separate groups of individually housed adult male wistar rats maintained for six weeks on ad lib water and either 1) Normal lab chow, 2) Lab chow supplemented with 50mM/KG of lithium chloride, or 3) Lab chow supplemented with 50mM/KG of sodium chloride. Plasma lithium levels were 0.7-1.0 mEq/1. The sodium diet had no effect on any of the variables measured relative to normal controls. Plasma but not red blood cell lithium levels demonstrated a 24-hour rhythm with higher levels during darkness. Serum and red blood cell sodium levels did not differ among the diets and showed no 24-hour variation. Lithium treated rats weighed significantly less than controls and had significantly heavier kidneys per 100 grams of body weight than controls. Resting plasma corticosterone levels demonstrated the expected 24-hour pattern in all groups, however, the lithium group evidenced higher levels during the middle of the dark hours than either control group. Water consumption also demonstrated a 24-hour rhythm. Lithium animals consumed far greater quantities of water than controls and this behaviour became increasingly exaggerated over the duration of the study. The data are interpreted as suggesting that lithium broadens the peak of twenty four hour rhythms such that normal elevation in these measures appear earlier and last longer.