Carotid sinus pressure, blood volume, and vasopressin in the anaesthetized rabbit

Experiments were carried out on anaesthetized rabbits to determine the influence of carotid sinus pressure (CSP) on the changes in the plasma concentration of arginine vasopressin (AVP) that occurred in response to changing blood volume. The aortic depressor nerves were sectioned in all experiments and the vagus nerves remained intact. Both carotid sinuses were perfused at constant controlled pressure. Blood volume was increased (n = 10) or decreased (n = 10) by 10 and 20% of the estimated blood volume. Plasma immunoreactive arginine vasopressin concentration (IR-AVP) was significantly higher at a CSP of 60 mmHg (1 mmHg = 133.322 Pa) than it was at a CSP of 120 mmHg in both groups of animals. Increasing blood volume did not cause any significant change in IR-AVP at either carotid sinus pressure. Haemorrhage of 10% of the blood volume did not change IR-AVP. Haemorrhage of 20% of the blood volume significantly increased IR-AVP at both CSPs; the magnitude of the increase in IR-AVP was not altered by changing the CSP. No interaction was demonstrated between the effects of CSP and blood volume on plasma IR-AVP.