CONTROL OF SODIUM-EXCRETION IN PATIENTS WITH CRANIAL DIABETES-INSIPIDUS MAINTAINED ON DESAMINO-[8-D-ARGININE]VASOPRESSIN

1. We have studied the response of six patients with cranial diabetes insipidus and six age-matched control subjects to dietary sodium restr iction during constant administration of the synthetic vasopressin ana logue desamino-[8-D-arginine]vasopressin. 2. Urine flow increased on t he first low salt day in the normal control subjects but not in the pa tients with cranial diabetes insipidus. Body weight fell 1.35 kg in th e control subjects but was constant in the patients with cranial diabe tes insipidus. 3. Urinary sodium excretion fell at the same rate in bo th groups. Diurnal variation of urinary sodium excretion and creatinin e clearance was present in the control subjects but not in the patient s with cranial diabetes insipidus. 4. Changes in plasma sodium concent ration and osmolality were similar. Plasma protein concentration incre ased more in the control subjects (from 69.1+/-1.5 to 73+/-1.2 versus from 71.7+/-1 to 73.2+/-1.1 g/l). The responses of plasma atrial natri uretic peptide, plasma renin activity and salivary aldosterone concent ration were similar between the two groups. Salivary aldosterone conce ntration levels were consistently higher in the patients with cranial diabetes insipidus. 5. We confirm that the low salt diuresis is trigge red by release from the antidiuretic activity of arginine vasopressin. In the patients with cranial diabetes insipidus extracellular fluid o smoregulation appeared to be achieved by the movement of water out of and sodium into the extracellular fluid. 6. Absent posterior pituitary function and hypothalamic disturbances did not alter renal sodium con servation. Total extracellular fluid sodium appeared to be lower in th e patients with cranial diabetes insipidus than in the control subject s. Disturbances of hypothalamic and pituitary function may have caused resetting of overall sodium balance and altered diurnal cycles of uri nary sodium excretion and creatinine clearance.