Cardiovascular interactions between vasopressin, angiotensin and noradrenaline in the Brattleboro rat

1. The cardiovascular effects of bolus intravenous injections of vasopressin, angiotensin II and noradrenaline were studied in 6-hydroxydopamine pretreated, anaesthetized Brattleboro rats with hereditary diabetes insipidus and normal rats of the parent Long Evans strain. 2. Pretreatment with 6-hydroxydopamine did not significantly affect control values for mean arterial blood pressure, cardiac output or total peripheral resistance in either Brattleboro or Long Evans rats but the pressor response to haemorrhage was reduced in both strains compared to the control animals. 3. The pressor responses of the untreated Brattleboro rats to 250 mu kg-1 vasopressin were significantly greater and more prolonged than in control rats of the Long Evans strain. 4. Pretreatment with 6-hydroxydopamine significantly enhanced the peak pressor response to vasopressin, but not to angiotensin II (1 microgram kg-1), in Brattleboro and Long Evans rats. 5. Pretreatment with 6-hydroxydopamine resulted in an enhanced pressor response to 1 microgram kg-1 noradrenaline in both Brattleboro and Long Evans rats, but the effect was significantly greater in the vasopressin-deficient animals. 6. These results indicate differences in the pressor responsiveness of Brattleboro rats to vasopressin and noradrenaline, but not to angiotensin II, compared with control Long Evans rats and provide evidence for important interactions between the sympathetic nervous system and these pressor hormones.