Urinary dopamine response to angiotensin II is not abnormal in type 1 (insulin-dependent) diabetes mellitus

To examine the interaction between angiotensin II (ANGII) and dopamine in type I diabetes mellitus, urinary dopamine excretion was examined during ANGII infusion in 15 diabetic patients and 10 control subjects after pretreatment with lithium 750 mg and placebo. The antinatriuretic response and the urinary dopamine response to ANGII did not differ within or between the two groups on each study day. No correlation was observed between the decrements in urinary sodium excretion and urinary dopamine output during ANGII infusion in either group. The effect of insulin on urinary dopamine excretion was studied separately in seven non-diabetic subjects; sodium and potassium retention occurred during a hyperinsulinaemic euglycaemic clamp, but urinary dopamine did not change. The data suggest that the relationship between urinary sodium excretion and tubular dopamine synthesis remains normal in early type 1 diabetes mellitus both at baseline and during the antinatriuresis induced by angiotensin II. The cause of the reduction in urinary dopamine during ANGII infusion is unclear, but is probably not mediated directly by changes in proximal tubular sodium transport.