MODULATION OF RESPIRATORY RHYTHM BY ALPHA(2)-ADRENOCEPTORS IN AWAKE AND ANESTHETIZED GOATS

The purpose of this study was to examine the effects of alpha(2)-adren oceptor agonists in the control of breathing with goats that were eith er awake (n = 7) or anesthetized and artificially ventilated (n = 11). Awake goats infused intravenously with either of the alpha(2)-agonist s clonidine (1.0-6.0 mu g/kg) or guanabenz (15.0-63.0 mu g/kg) exhibit ed two distinct ventilatory patterns. One pattern was characterized by tachypnea in which respiratory frequency and minute ventilation incre ased to similar to 50% above control values. A second ventilatory patt ern consisted of slow breathing with reductions of respiratory frequen cy and minute ventilation and highly variable expiratory duration inte rvals. These two patterns were unaffected by bilateral carotid body de nervation. In anesthetized goats, alpha(2)-agonists also caused an arr hythmia in phrenic nerve activity that was similar to the slow breathi ng pattern seen in awake goats. Respiratory disturbances were abolishe d by the selective cu,-receptor antagonist SKF-86466 (100-500 mu g/kg) , indicating that the effects are mediated by alpha-receptors. The res ults suggest that stimulation of alpha(2)-adrenoceptors generally has an inhibitory effect on breathing in goats. The disruption of ventilat ion with clonidine or guanabenz suggests that alpha(2)-adrenoceptors m ay play an important role in the control of central respiratory rhythm .