Effects of prolonged vasopressin treatment in Brattleboro rats with diabetes insipidus.

Normal Long-Evans rats (LE) exhibited diurnal variations of plasma arginine vasopressin (AVP) concentrations with peak values at 10 A.M. and minimum values at 1 P.M. Brattleboro rats heterozygous for hypothalamic diabetes insipidus (DI) had significantly reduced plasma AVP concentrations and increased plasma osmolalities when compared with LE rats. By prolonged injection of 100 mU/day of vasopressin tannate (VPT) into Brattleboro rats homozygous for DI, plasma AVP concentrations close to those of LE rats were achieved. Potassium was retained for 7 days until escape of vasopressin-induced potassium retention occurred. When 500 mU VPT were injected into DI rats, high plasma AVP levels were induced. Potassium was retained for 2-3 days. After initial sodium retention, periods of natriuresis occurred. During treatment with 100 mU VPT/day most of the alterations present in DI rats were corrected, which included increased water turnover and external water loss, increased hematocrit and plasma sodium concentrations (but not increased plasma osmolalities), hypokalemia, increased activity of the renin-angiotensin system, and reduced adrenocortical function.