Influence of repeated administration of lithium on urinary excretion of prostaglandins in rats.

The present study was undertaken to examine whether urinary excretions of prostaglandins increase by repeated administration of a non-toxic dose of lithium. Our previous study demonstrated that 2 mEq/kg/day of lithium chloride (LiCl) is not a toxic dose; and therefore, this dose of LiCl in 1 ml vehicle (5% glucose solution) or 1 ml of vehicle alone was injected intraperitoneally for 7 days into Wistar rats. On day 7, 3% body weight of 1% NaCl solution was given orally; and urine for the determination of PGE2 and 6-keto-PGF1 alpha, a metabolite of PGI2, was collected for 6 hr after dosage. Thereafter, blood samples for measuring plasma renin activity (PRA) were obtained. The urinary amounts of PGE2 and 6-keto-PGF1 alpha in the Li-treated rats were significantly greater than those in the control animals. The values of PRA did not significantly differ between the two groups of rats. These findings indicate that the production of prostaglandins, including those of PGE2 and PGI2, are enhanced during repeated administration of a non-toxic dose of lithium. The enhanced production of prostaglandins might not be mediated through the activated renin-angiotensin system.