1. The cardiovascular effects of pressor doses of arginine vasopressin were examined in anaesthetized Brattleboro rats with hereditary diabetes insipidus (BDI) and normal rats of the parent Long Evans (LE) strain, either 37 or 85 days old.
2. Control mean arterial blood pressure and total peripheral resistance were similar in adult animals of the two strains but were significantly lower in the young BDI rats compared with the young LE rats.
3. The three doses of vasopressin produced greater pressor responses in the young, immature LE rats compared with the young BDI rats, whereas in the adult animals vasopressin had the greater pressor effect in the BDI rats compared with the LE rats of comparable age.
4. There was little effect of vasopressin on cardiac output after the initial decrease, particularly in the BDI rats whether immature or adult, despite more prolonged decreases in heart rate.
5. These studies indicate important age-related differences in the pressor response to vasopressin in anaesthetized rats, in addition to the clear differences in response between the animals with (LE) or without (BDI) the circulating endogenous peptide.