Adrenergic blockade does not change ventilatory response to CO2 in awake resting goats

Although adrenergic agonists increase resting ventilation and responsiveness to CO2, there are conflicting data about the effect of adrenergic blockade on ventilatory responses. In this study, we investigated the effect of alpha- or beta-adrenergic blockade on the response to hyperoxic CO2 rebreathing in awake goats. In 5 goats, studied before and after intravenous administration of phentolamine or propranolol, there was no difference (compared to control studies) in the mean slope, x-intercept, or ventilation at end-tidal PCO2 (PETCO2) = 70 torr for the CO2 response curves after either drug. When mean inspiratory flow rate (VT/Ti) was plotted against PETCO2, there was also no change in these measurements after propranolol. After phentolamine, there was a slight decrease in the slope and x-intercept, but no change in VT/Ti at PETCO2 = 70 torr. We conclude that acute administration of alpha- or beta-adrenergic blockers does not affect ventilatory response to CO2 inhalation in goats, and suggest that adrenergic activity is not an important modulating influence for CO2 responsiveness in this species.