Reduction of specific arginine-vasopressin binding sites of renal medulla membranes in lithium treated rats.

To elucidate the early effects of lithium treatment on the kidney, arginine-vasopressin (AVP) binding sites in the renal medulla were measured by radiolabeled receptor assay (RRA) in rats injected intraperitoneally with lithium chloride (4 mmol/kg body weight) for 7 days. After the 8th day, urine volume of rats injected lithium (Li group) increased and was significantly larger than that of the control rats that were injected physiological saline (control group). On the same day, the AVP binding capacities of renal medulla membranes of the Li group (Bmax = 28.9 +/- 7.2 fmol/100 micrograms protein) were significantly lower than that of the control group (Bmax = 50.0 +/- 6.3 fmol/100 micrograms protein), but there was no difference in the dissociation constant between the two groups. Our findings suggested that lithium-induced diabetes insipidus was due to a reduction in the number of AVP binding sites in the kidney.