EFFECT OF DOPAMINE ON CAROTID CHEMORECEPTOR ACTIVITY IN NEWBORN KITTENS

In newborn kittens, intravenous bolus injections of dopamine may be in hibitory or excitatory to the carotid chemosensory activity. In order to further identify the role of dopaminergic mechanisms on the chemose nsory activity in the kitten, 10 anesthetized, paralyzed and artificia lly ventilated kittens aged from 1 to 21 days were studied. The activi ty of a few chemoafferent fibers from one carotid sinus nerve was reco rded at three levels of Fi(O2), in N-2, 21, 8 and 100%, before and dur ing a continuous dopamine infusion at a dose of 10 mu g/kg/min. The im mediate effect of dopamine usually was a transient inhibition of carot id chemosensory discharge. After 2 min of infusion, the activity had c onsistently increased from 4.5 +/- 0.8 to 8.8 +/- 1.4 impulses/s (mean +/- SEM, p < 0.05) in normoxia. Dopamine also significantly increased the steady state chemosensory response to hypoxia from 24.6 +/- 3.7 t o 33.4 +/- 5.3 impulses/s. Hence, continuous infusion of dopamine has a dual effect on carotid chemoreceptor activity: early inhibition foll owed by excitation. The excitatory effect enhances the response to hyp oxia. These data suggest that the dual effect of dopamine on carotid c hemosensory discharge may be related to dopamine concentration in the carotid body.