Hypertension in rats with hereditary diabetes insipidus. The role of age.

The effect of age, sex and salt intake on the hypertension produced in homozygous (DI) and heterozygous (non-DI) Brattleboro rats and Long Evans rats was studied. The left kidney was removed at the age of 25, 35, 50 and 80 days (UNX 25, UNX 35, UNX 50, UNX 80), and 0.6% NaCl solution or water was offered as drinking fluid. In UNX DI rats drinking saline the mean value of blood pressure (BP) exceeded 150 torr. The highest values of BP were observed in DI UNX 25 females while no hypertension occurred in rats UNX 80. There was no correlation between individual values of BP and saline consumption in DI females with hypertension. However, individual BP values correlated with the urinary Na+/K+ ratio measured in the course of 24 h of water deprivation, due to age-dependent sodium excretion the values of which were highest in the UNX 25 group. Hydronephrosis was present in all DI rats with manifest hypertension. In hypertensive animals, BP values, Na+/K+ ratio and the frequency of hydronephrosis exhibited the same age dependence. The role of age and adaptability to the increased saline intake in the susceptibility of DI rats to experimental hypertension is discussed.