Lithium in pigmented eye rats: Effects of dose and time of day on drinking, body weight, retinal and blood distribution

Abstract

Lithium has been implicated in chronobiology (Seggie, et al., 1982, 1983). Previous work was done in Wistar rats, an Albino species, which lack the enzyme for synthesis of eye pigment. This pigment is important in regulation of light cued rhythms. The present project extends observations to Long Evans rats, a strain which has a pigmented eye. Groups of adult male rats were fed one of three diets: (1) normal laboratory chow; (2) a low lithium diet: lab chow supplemented with 30 mM/kg lithium chloride; and (3) a high lithium diet: lab chow supplemented with 50 mM/kg lithium chloride. Adult male rats were housed individually with free access to diet and water under a 12 hour light/12 hour dark schedule. After six weeks on the diets, body weight, water intake, plasma, red blood cell and retinal lithium and retinal weight were measured every 4 hours throughout the 24 hour cycle following sacrifice by rapid decapitation. Plasma lithium levels on the high diet were 0.57 ± 0.02 mEq/1 and did not evidence a diurnal rhythm. Plasma lithium levels on the low diet were 0.35 ± 0.01 mEq/1 and evidenced a small, but significant diurnal rhythm with levels lowest just before darkness and normal food intake. Red blood cell lithium levels were significantly higher than plasma levels at 0.83 ± 0.02 and 0.52 ± 0.02 mEq/1 for the high and low diets. Low diet, but not high diet red blood cells lithium levels evidenced a significant rhythm with a pattern similar to that seen in plasma lithium levels. Retinal lithium levels evidenced no diurnal change on either diet and were 0.82 ± 0.05 mEq/ kg and 0.55 ± 0.02 mEq/kg for the high and low diet. Retinal weight was 15.5 ± 2.0 mg for controls and was not affected by lithium in the diet. Body weight did not Evidence diurnal change on any of the diets: however, both the high and the low lithium diet groups weighed significantly less than controls (354 ± 4.8 g and 411 ± 7.4 g vs. 437 ± 7.8 g respectively). Water intake evidenced a significant diurnal rhythm with maximum intake during dark hours and was significantly elevated on the high, but no on the low diet at all time points. in pigmented eye compared to Albino rats, the 50 mM/kg dose lithium diet resulted in lower, but less variable plasma and red blood cell lithium levels, but equivalent effects on body weight and drinking (Seggie et al, 1982). The low dose lithium diet gave mixed results. Pigmented eye retinal weight was unaffected by lithium: however, lithium content of retina suggested that this tissue handles lithium in a manner similar to brain (Bond, 1975). These data suggest strain and possible species differences in the metabolism of lithium as it relates to chronobiology.