Elevated serum dopamine-beta-hydroxylase activity in rats with inherited diabetes insipidus

The activity of dopamine-beta-hydroxylase, the enzyme that catalyzes the conversion of dopamine to norepinephrine, was measured in the serum of a strain of Wistar rats homozygous and heterozygous for a genetic form of hypothalamic diabetes insipidus and in Wistar control rats. Serum dopamine-beta-hydroxylase activity and water intake was highest in the homozygous affected rats and lowest in normal controls. Treatment with pitressin tannate reduced serum enzyme activity and water intake in rats with diabetes insipidus to levels which did not differ from controls. Thus serum dopamine-beta-hydroxylase activity appeared to vary directly with changes in sympathetic nerve activity in response to intravascular volume depletion and repletion.