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Plasma catecholamine levels increase dramatically at birth. To determine the contribution of adrenal catecholamine secretion to the surge in catecholamines at birth and the role in newborn adaptation, we performed surgical adrenalectomy or sham operation on near-term ovine fetuses. After recovery in utero, the animals were delivered and supported by mechanical ventilation. Plasma catecholamine levels, heart rate, blood pressure, cardiac output, pulmonary function, surfactant secretion, and release of free fatty acids (FFA) and glucose were compared in control and adrenalectomized animals. Plasma epinephrine increased rapidly at birth in controls but was undetectable in adrenalectomized animals. Norepinephrine levels were not statistically different. Heart rate, blood pressure, cardiac output and contractility increased abruptly after cord cutting in controls but did not increase in adrenalectomized animals. Lung compliance, pulmonary function, surfactant pool size, glucose and FFA levels were significantly decreased in adrenalectomized animals. These results suggest that adrenal epinephrine secretion is vital to many of the adaptive events at birth.

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To examine the serial changes of left ventricular output and regional blood flow distribution during the early neonatal period, we measured blood flow volume in the ascending aorta, middle cerebral artery, celiac artery, superior mesenteric artery, and renal artery in 23 normal term infants at 1, 4-8, 24, and 96 h after birth. The blood flow volume in each vessel was measured by the pulsed Doppler technique. In the middle cerebral artery, celiac artery, and superior mesenteric artery, the blood flow volume at 1 and 4-8 h of age was significantly lower than after 24 h of age. In contrast, renal artery blood flow volume did not change significantly throughout the study period. The reduced organ blood flow volume soon after birth was related to a low diastolic blood flow in the major vessels, and the percent diastolic integral of blood flow velocity in each vessel showed an inverse linear correlation with the diameter of the ductus arteriosus. The left ventricular output 1 h after birth was 365 +/- 69 mL/kg/min, which was significantly higher than after 4-8 h of age. Left ventricular output gradually declined to 301 +/- 63 mL/kg/min at 4-8 h of age (p < 0.05 versus 96 h), 272 +/- 48 mL/kg/min at 24 h, and 258 +/- 54 mL/kg/min at 96 h. There was a significant positive correlation between left ventricular output and the ductus arteriosus diameter.(ABSTRACT TRUNCATED AT 250 WORDS)

ABSTRACT. A marked increase in plasma catecholamines at birth has been described in animals and man. Because the factors that regulate catecholamine secretion are incompletely understood and because it has recently been suggested-that endogenous opiates are important in the regulation of catecholamine secretion, we designed studies to2etermine the influence of opiate receptor blockade prior to delivery on the increase in plasma catecholamines at birth. Term fetal sheep were delivered by cesarean section and randomly assigned to receive naloxone or vehicle. Naloxone was given just prior to umbilical cord cutting as a 2 mg/kg bolus followed by 2 mg/kg/h. Naloxone administration resulted in significantly greater peak levels of plasma norepinephrine (peak levels of 1.5 f 0.4 versus 0.9 f 0.1 ng/ml) and epinephrine (peak levels of 1.4 f 0.7 versus 0.9 f 0.3 ng/ml) and higher norepinephrine values throughout the study period. Naloxone administration was associated with significantly elevated heart rate (peak 184 f 12 versus 207 f 13 beats per min) and blood pressure (peak 95 f 6 versus 88 f 2 mm Hg). These studies demonstrate that opiate receptor blockade from birth markedly augments the neonatal sympathoadrenal response in the term newborn lamb. Fetal and newborn animals secrete catecholamines in response to a variety of stimuli including hypoxia (I), hemorrhage (2), hypothermia (3), labor (4), and delivery (5). The marked increase in catecholamine secretion at birth is particularly important because of the wide range of physiological changes which occur at birth and the importance of the sympathoadrenal system in modulating these changes. In the chronically catheterized fetal sheep, plasma catecholamines begin to rise in the last 3 h of Received September 30, 1986; accepted January 9, 1987 spontaneous labor prior to delivery (4). There is then a further augmentation in plasma levels of both NE and E following delivery and cord cutting (6). We were interested to extend our observations to study the factors that regulate catecholamine release at birth.Two levels of control of catecholamine release have been recognized, including oc 2 receptor-mediated presynaptic inhibition of NE release and inhibition by endogenous opiate peptides. BEND is secreted in response to stress (7) and degrees of hypoxia in fetal sheep known to produce marked catecholamine secretion result in markedly increased levels of circulating BEND (8).Catecholamines and ENK are costored and secreted by the adrenal medulla in response to cholinergic or splanchnic nerve stimulation (9-12). Opiate peptides inhibit catecholamine release by inhibition of neurotransmission in sympathetic ganglia (13,14) and inhibition of adrenal medullary catecholamine secretion (1 5). The physiological significance of these observations in vivo is unclear. In the present study, in order to investigate the role of endogenous opiates in vivo as modulators of sympathoadrenal activity at birth, we compared plasma catecholamine levels with and without continuous opiate receptor...

In order to assess the possible influence of differences in delivery mode on cardiovascular adaptation at birth, we measured left ventricular output and its regional distribution in the major organs sequentially using an echographic technique during the first 96 h of life. We studied 27 normal newborns, of whom 15 were delivered vaginally and 12 by cesarean section. We also measured umbilical arterial and venous catecholamine concentrations. The umbilical arterial epinephrine and norepinephrine concentrations in the infants delivered vaginally were significantly greater than those in the infants delivered by cesarean section (epinephrine 1,195 ± 208 vs. 565 ± 81 pg/ml p < 0.05; norepinephrine 11,832 ± 3,819 vs. 5,153 ± 1,400 pg/ml, p < 0.05). The left ventricular output and its regional distribution showed a similar pattern in the two groups, and there were no significant differences between them. These results indicate that the capacity of infants delivered by cesarean section to tolerate cardiovascular changes during the early neonatal period is comparable to that in infants delivered vaginally, even though there are significant differences in the catecholamine surge between these groups.

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