EFFECTS OF EPINEPHRINE ON THE CARDIORESPIRATORY RESPONSE TO HYPOXIA IN SEDATED NEWBORN PIGLETS WITH INTACT AND DENERVATED CAROTID-BODIES

In order to evaluate the effects of epinephrine on the cardiorespirato ry response to hypoxia in the neonate, 35 sedated, spontaneously breat hing newborn piglets (($) over bar X +/- SD, age 5 +/- 0.8 days; weigh t 1.6 +/- 0.3 kg) with intact (ICE) or denervated (DCB) carotid bodies were studied before and during an infusion of saline or epinephrine ( 2.2 +/- 1.0 mu g/kg/min, i.v.). Cardiorespiratory measurements were pe rformed while the animals breathed room air and after 10 min of hypoxi a (FiO(2) 0.10) during saline or epinephrine infusion. During epinephr ine infusion, the ICE animals had a sustained increase in minute venti lation during hypoxia while the control group showed a biphasic ventil atory response with depression during sustained hypoxia. After the che modenervation, the ventilatory response to hypoxia was completely blun ted in saline and epinephrine animals. In the ICE and DCB animals, the arterial blood pressure decreased significantly with hypoxia during e pinephrine infusion, while cardiac output increased significantly in a ll ICE and DCB saline animals. The oxygen consumption (VO2) decreased significantly after 10 min of hypoxia in all groups except in the ICE epinephrine animals, in whom the VO2 did not change with hypoxia. In c onclusion, the administration of epinephrine to newborn piglets revers es the depressed ventilatory response to hypoxia and this effect requi res the activity of the peripheral chemoreceptors.