Effect of fetal adrenalectomy on catecholamine release and physiologic adaptation at birth in sheep.

Abstract

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.

Effects of labor contractions on catecholamine release and breathing frequency in newborn rats.

“…As compared with babies exposed to a trial of labor, babies delivered by elective cesarean section (even near term) show (a) an increased risk of respiratory morbidity (Cohen & Carson, 1985;Zanardo et al, 2004); (b) a fivefold increase in the likelihood of persistent pulmonary hypertension (Levine, Ghai, Barton, & Strom, 2001); (c) lower dynamic lung compliance (Faxelius, Hagnevik, Lagercrantz, Lundell, & Irestedt, 1983) and higher functional residual capacity, possibly as an adaptation to elevated lung water content (Hagnevik, Lagercrantz, & Sjoqvist, 1991); (d) increased incidence of postpartum respiratory distress (Irestedt, Lagercrantz, & Belfrage, 1984); (e) decreased protection from oxidative stress (Buhimschi, Buhimschi, Pupkin, & Weiner, 2003); and (f) delayed neurodevelopmental status (Otamiri, Berg, Ledin, Leijon, & Lagercrantz, 1991;Otamiri, Berg, Ledin, Leijon, & Nilsson, 1990). Animal studies of labor's effects on the fetus and newborn, conducted almost exclusively in the precocial sheep fetus, have revealed important roles of birth-related catecholamines, including stimulating lung liquid absorption (reviewed by Barker & Olver, 2002), sustaining metabolic and cardiac homeostasis (Padbury et al, 1987), and providing protection from hypoxia (C. T. Jones, 1980). Labor-induced catecholamine release may provide an important mechanism underlying the neonate's process of adapting to extrauterine conditions and the recruitment of vital postnatal behaviors (Ronca, Abel, & Alberts, 1996).…”

Role of the Alpha2-Adrenoceptors on the Pulmonary Circulation in the Ovine Fetus

“…Birth in-duces a marked surge in catecholamine secretion (12). Increased catecholamines at delivery promote lung fluid reabsorption, surfactant release, and systemic circulatory adaptation (13,14). However, the effects on the pulmonary circulation are uncertain.…”

In Utero Ventilation Augments the Left Ventricular Response to Isoproterenol and Volume Loading in Fetal Sheep

“…I). The order of oxygen ventilation and isoproterenol to simulate the important catecholamine surge at birth (28,37), and volume loading. We measured left ventricular output, vascular pressures, and heart rate, and determined the individual and combined effects of each intervention on these variables.…”

“…We have previously shown that oxygen ventilation in utero creates a central circulatory pattern that is identical to the immediate postnatal circulation (3). In addition, the newborn left ventricle functions under significant fJ-adrenergic stimulation (8,37), which is essential to the increase in output at birth (28), and at higher filling pressures (6, 11) than before birth, so we performed the studies during isoproterenol infusion and volume loading in addition to oxygen ventilation. We found that oxygen ventilation and isoproterenol increased left ventricular output, but not volume infusion, and that the effect of oxygen ventilation far exceeded that of isoproterenol.…”

“…In addition, many indices of systolic performance are increased in the newborn left ventricle relative to that of the adult (11, 12), so that myocardial immaturity may not necessarily be associated with impaired ventricular function. It is remarkable that both the prematurely born animal (26)(27)(28) and human (29), which have not been exposed to prenatal hormone surges and labor to accelerate myocardial maturation, are capable of greatly increasing left ventricular output in response to a patent ductus arteriosus. In addition, recent studies of fetal sheep undergoing oxygen ventilation in utero have shown a doubling of left ventricular output (3,30), and other determinants of output such as septal compliance (31) have been shown to change in the perinatal period.…”