Background: Hormonal systems such as vasopressin (AVP) and the renin-angiotensin-aldosterone system (RAS) have been reported to become activated during anesthesia and surgery. The purpose of this study was to examine the relative importance of AVP and angiotensin II (AII) in blood pressure control during isoflurane anesthesia in rats.
Methods: Rats were given an AVP V1-receptor antagonist (AVP-a, 10 microg kg(-1)), the AII receptor antagonist saralasin (SAR, 20 microg kg(-1) min(-1)) and hexamethonium (HEX, 10 mg kg(-1)) intravenously in random order, awake or anesthetized with isoflurane.
Results: AVP-a had no effect on mean arterial pressure (MAP) in awake or anesthetized animals, but reduced MAP by 20.0+/-2.2% in the anesthetized rats which previously had been treated with SAR and/or HEX. SAR infusion had no effect on MAP when administered to conscious rats, but decreased MAP by 12.0+/-4.4% during anesthesia. Ganglionic blockade with HEX consistently lowered MAP in the conscious and anesthetized animals.
Conclusion: It is concluded that AVP contributes to the maintenance of blood pressure when the autonomic nervous system (ANS) and/or RAS are blocked during isoflurane anesthesia. SAR infusion leads to hypotension during anesthesia, but not in conscious rats. These findings indicate that AII is of importance for blood pressure maintenance during isoflurane anesthesia in rats, and that apparent pressor effects of AVP come into play when RAS and/or ANS are blocked.