Daily variation in influence of lithium on serum calcium concentration: a preliminary report

1. One millilitre of 5% glucose (vehicle, n = 10) or 1 mL solution of lithium chloride (LiCl) (0.5 or 2.0 mmol/kg per day, n = 10 for each) was injected intraperitoneally in Wistar rats at 10:00 or 22:00 h for 6 days. Blood samples for ionized and total calcium were taken on day 7. 2. Mild elevations in ionized, but not non-ionized (total-ionized) calcium were observed following LiCl treatment in both administration times. 3. The increment in ionized calcium was greater when LiCl was injected at 22:00 h than when it was given at 10:00 h. 4. These data indicate that: (1) the influence of lithium on calcium metabolism varies with its administration time; and (2) mild hypercalcaemia induced by the agent mainly depends on the elevation in the ionized fraction of calcium.