The role of vasopressin in blood pressure maintenance in diabetic orthostatic hypotension.

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Abstract
The purpose of these studies was to assess the role of vasopressin in maintaining supine and upright blood pressures in hypertensive diabetic subjects. Patients with (n = 6) or without (n = 10) evidence of autonomic insufficiency had blood pressure and heart rate monitored before and after receiving an intravenous injection of 0.5 mg of a V1 vasopressin inhibitor. None of the patients had supine changes in blood pressure or heart rate. However, upon assuming the erect position, the six patients with preexisting orthostatic hypotension had an average blood pressure fall of 44 mm Hg after vasopressin inhibition (as opposed to 20 mm Hg before), accompanied by a modest rise in heart rate of 20 beats/min. Those without autonomic dysfunction were separated into two subgroups. Four developed an average fall in orthostatic blood pressure of 18 mm Hg after vasopressin inhibition, whereas the remaining six had no change. There were no distinguishing hormonal characteristics (vasopressin, renin, and catecholamine levels) between the groups, but in the patients with autonomic dysfunction, the renin level failed to rise when upright. We conclude that vasopressin plays an important role in preventing or minimizing orthostatic hypotension in diabetic patients. Its pressor contribution is crucial in those with autonomic insufficiency and impaired renin and sympathetic responses, in whom the pressor effectiveness of vasopressin is greatly enhanced.