Effect of lithium on the metabolic response to parathyroid hormone

Blood and urine samples were collected at timed intervals for up to 120 min after the start of a 30-min infusion of 30 IU bovine parathyroid hormone (PTH) into 6 normal male subjects. Infusions were performed before and after 7 days' treatment with lithium carbonate. A highly significant increase in the maximum renal tubular reabsorption capacity for calcium (TmCa/GFR) from 2.02 +/- 0.04 to 2.17 +/- 0.07 mmol/l (p less than 0.02) produced a significant rise in plasma calcium. Lithium had no effect on basal fasting PTH or nephrogenous cyclic AMP (cAMP). Changes in nephrogenous cAMP and TmP/GFR in response to PTH were not altered by lithium. The absorption of 47Ca following an oral calcium load was increased in 5 out of 6 subjects also treated for 1 week with lithium. These results suggest that lithium has a direct effect on calcium transport, both at the level of the renal tubule and the gut, which is not mediated by stimulation of parathyroid activity or via modification of PTH-stimulated adenylate cyclase.