Plasma vasopressin during insulin withdrawal in insulin-dependent diabetes.

Plasma vasopressin was measured in seven insulin-treated diabetics during 24 h of insulin withdrawal to determine: 1) if abnormalities of the neurohypophysial-renal axis contribute to the dehydration of uncontrolled diabetes mellitus; and 2) the factors causing elevated levels of vasopressin in diabetic ketoacidosis. During the 24 h period of insulin withdrawal, blood glucose rose from 6.7 +/- 1.0 to 20.7 +/- 2.4 mmol/l, whereas plasma vasopressin was 3.6 +/- 0.5 pg/ml initially and in four patients showed little change. Markedly elevated levels of plasma vasopressin (17.8, 19.8 and 26.6 pg/ml) were observed in three patients following the onset of hypovolaemia, nausea and/or vomiting which are known to stimulate vasopressin release. Free water clearance was negative throughout the study in all patients. Thirst was not noted despite marked hyperglycaemia (16.9 +/- 2.5 mmol/l) until a significant fall in body weight of 0.9 +/- 0.2 kg had occurred (p less than 0.005). We concluded that marked elevation of vasopressin results from non-osmotic stimulation and that the mechanisms of body water conservation are overridden by the glycosuric diuresis.