Plasma renin activity during lithium treatment of patients

Plasma renin activity (PRA) was determined in patients given lithium treatment. In a longitudinal study PRA was determined in 9 patients before the start of lithium treatment and at intervals during 3 months of treatment. The activity was increased significantly above pretreatment values on day 8 of the treatment; thereafter it fell to pretreatment values. In a transversal study 18 patients given lithium treatment for 2-20 years were compared with 11 control persons. PRA did not differ significantly between the two groups. The results indicate that PRA rises transiently shortly after start of lithium treatment and thereafter falls to pretreatment values where it remains even under prolonged lithium administration.