VENTILATORY AND METABOLIC EFFECTS OF HYPERCAPNIA IN CONSCIOUS RATS - AVP V-1 RECEPTOR BLOCK

In conscious dogs, arginine vasopressin (AVP) inhibits an angiotensin II drive to ventilation during air breathing and during acute hypercap nia. To determine whether AVP inhibits respiration in rats, as in dogs , respiration and metabolism were measured in six male Sprague-Dawley rats using a plethysmograph. Rats breathed air, followed by 5% and 6.5 % CO2 with or without AVP V-1 receptor block. In unblocked experiments , minute ventilation (V) over dot increased to a comparable level duri ng inhalation of both CO, gas mixtures, resulting in a flattening of t he ventilatory response to increased Pace,. However, oxygen consumptio n decreased during 6.5% CO2, compared with 5% CO,, so that the ventila tory equivalent for O-2 increased in a more linear manner with respect to Pace,. The main effect of AVP V, receptor block was to increase me an arterial blood pressure; there was no significant effect of AVP V, receptor block on respiratory responses. AVP does not inhibit respirat ion in conscious rats as it does in conscious dogs.