EFFECT OF THEOPHYLLINE ON VENTILATORY ROLL-OFF DURING HYPOXIA IN GOATS

The increase in pulmonary ventilation (Vover dotE) during the first mi nutes of hypoxia is not sustained as after several minutes Vover dotE decreases or ''rolls-off'' toward control levels. We hypothesized that intravenous infusion of theophylline, by blocking the central inhibit ory effects on breathing of adenosine, would attenuate the hypoxic Vov er dotE roll-off. Twelve unanesthetized adult goats were exposed for 2 0 min to a 12% O-2-88% N-2 gas mixture. In some studies, theophylline was infused intravenously (IV) for 20 min before and during the hypoxi a. The highest infusion rate of 6.0-8.0 mg/min was sufficient to total ly prevent the arterial hypertension and bradycardia that occurred wit h IV infusion of 4 mg . min(-1) of adenosine. Nine of the 12 goats dem onstrated Vover dotE roll-off without the theophylline infusion. In go ats that demonstrated Vover dotE roll-off without theophylline, a sign ificant (P < 0.05) Vover dotE roll-off was observed even at the highes t theophylline infusion rate. We therefore conclude that the Vover dot E roll-off during hypoxia is not primarily or critically mediated by a denosine in awake, adult goats.