Neonatal adaptation: greater sympathoadrenal response in preterm than full-term fetal sheep at birth

Padbury, Jamés F.; Polk, D.; Newnham, John P.; Lam, Robert W.

doi:10.1152/ajpendo.1985.248.4.e443

Cited by 37 publications

(60 citation statements)

References 23 publications

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“…These preterm lambs, with PCO 2 values that averaged 95 mm Hg, had no changes in heart rate or blood pressure and cortisol levels did not change over 6 h. We did not measure catecholamines, although they would be expected to be very high after preterm delivery (32). A limitation of this study is that we did not evaluate cardiac output or other organ system function.…”

Section: Discussionmentioning

confidence: 95%

Effects of High Pco2 on Ventilated Preterm Lamb Lungs

2003

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High PCO 2 levels attenuate reperfusion injury and ventilationinduced injury in isolated and perfused lungs. We asked whether premature lambs could tolerate 6 h of ventilation with a PCO 2 Ͼ80 mm Hg and whether the high PCO 2 modulated the ventilatorinduced injury. Preterm surfactant-treated lambs were ventilated for 30 min with a high tidal volume (VT) to induce lung injury. The lambs then were ventilated for 5.5 h with a VT of 6 -9 mL/kg to achieve a PCO 2 of 40 -50 mm Hg in the control group. CO 2 was added to the ventilator circuit of a high PCO 2 group to maintain an average PCO 2 of 95 Ϯ 5 mm Hg. The high PCO 2 lambs had heart rates, blood pressures, plasma cortisol values, and oxygenation equivalent to the control lambs. The lungs of the high PCO 2 group had significantly higher gas volumes and had less lung injury by histopathology. Indicators of inflammation (white blood cells, hydrogen peroxide production, and IL-1␤ and IL-8 cytokine mRNA expression in cells from the alveolar wash) qualitatively indicated less injury in the high PCO 2 group, although the differences were not significant. Preterm lambs tolerated a very high PCO 2 without physiologic compromise for 6 h. The high PCO 2 may attenuate ventilator-induced lung injury in the preterm. BPD in preterm infants is highly associated with the use of mechanical ventilation and supplemental oxygen (1, 2). Efforts to decrease the incidence of BPD have included attempts to avoid mechanical ventilation with the use of continuous positive airway pressure (3), different techniques for mechanical ventilation such as high-frequency oscillatory ventilation (4), and lower VT ventilation resulting in higher PCO 2 values (5). In the mature lung, ventilator-mediated injury increases if the lung is inadequately inflated at end-expiration or overinflated at end-inspiration (6, 7). Attempts to decrease lung distention by decreasing VT will result in increases in PCO 2 , referred to as "permissive hypercapnia" (8). Laffey et al. (9) recently extended this concept to "therapeutic hypercapnia" by demonstrating that reperfusion injury of the lung can be prevented if the injury and reperfusion occur in the presence of a PCO 2 of 80 mm Hg. This work demonstrates that high PCO 2 can protect the lung from reperfusion injury, most likely via attenuation of free radical damage. This effect has also been reported for reperfusion injury of other organ systems, such as the brain and heart in adult and newborn animal models (10, 11). Broccard et al. (12) recently reported that high PCO 2 also minimized ventilatorinduced lung injury in isolated and perfused lungs. However, a protective effect of high PCO 2 values has not been demonstrated for ventilator-induced injury in vivo in animals or for the preterm lung. Therefore, we ventilated surfactant-treated preterm lambs to achieve normal PCO 2 values or equivalently ventilated other lambs with supplemental CO 2 to evaluate the tolerance of the preterm to high PCO 2 and the effect of the high PCO 2 on indicators of lung injury. MET...

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Section: Discussionmentioning

confidence: 95%

Effects of High Pco2 on Ventilated Preterm Lamb Lungs

2003

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“…Lipolysis with resultant increase in FFA and glycerol is vit al to postnatal surviva l (38). The magnitude of this response is gr eater in mature newborn anima ls than in prematurel y delivered sheep (39). We anticipated that antenatal hormone treatment of these preterm animals might augme nt this adaptive response (40, 41).…”

Section: Ol---lij-----------------mentioning

confidence: 99%

Postnatal Cardiovascular and Metabolic Responses to a Single Intramuscular Dose of Betamethasone in Fetal Sheep Born Prematurely by Cesarean Section

et al. 1995

Pediatr Res

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Although the benefits of antenatal hormone treatment are well accepted, most studies have reported only pulmonary effects. There is evidence of beneficial cardiovascular and metabolic effects in studies using chronically catheterized animals; however because of the route of administration, the results are not directly applicable to clinical strategies. We previously demons trated sign ificant pulmonary effects in animals treated antenatally with a single, direct fetal, intramuscular injection of glucocorticoids . Th is study was performed to determine the effects of a single fetal injection of betamethasone (BETA) alone or in combination with thyroxine (T 4 ) on cardiovascular and metabolic respons es after preterm birth . Hemodynamic and metabolic response s at birth were determined in fetuses (126-d gestation; term = 150 d) treated with ultrasound-guided intramuscular injections of 0.5 mg/kg BETA (n = 7), BETA plus 60 g/kg T 4 (n = 7), or saline (SAL, n = 9). After 48 h, lambs were delivered by cesarean section and studied for 3 h. BETA treatment increased mean arterial blood pressure [56 ± 6 (SEM) versus 42 ± 3 mm Hg], heart rate (152 ± 5 versus 123 ± 4 beats/min), and cardiac Multiple studies have documented improved outcomes of preterm human infants born to mothers treated antenatally with glucocor ticoids. Most studies have focused primarily on pulmonary effects, although secondary outcome variables and retrospective metanalysis of clinical and other demographic data indicate beneficial effects in other organ systems (1, 2). Maternal corticosteroid treatment reduces nonrespiratory morbidities such as intraventricular hemorrhage, necrotizing enterocolitis, and patent ductus arteriosus. The mechanism(s) for these varied clinical outcomes is uncertain .In previous studies using chronically catheterized fetal sheep we demonstrated that antenatal corticosteroid infusion signifi- Responses of BETA + T 4 -treated animals were not different from animals treated with BETA alone. Glucose and FFA were simila r among all groups. The increase in catecholamine levels normally seen at birth was significantly attenuated in both the BETA and BETA + T 4 -treated animal s. A single, intramuscular injec tion of glucocorticoids 48 h before delive ry improves cardiovascular responses to preterm birth . This effect is not augmented by concomitant admi nistration of T4 ' (Pediatr Res 38: 709-715, 1995) Abbrev iations BETA, betamethasone T 4 , thyroxine T 3 , triiodothyronine SAL , saline TRH, thyrotropin-releasing hormone ANOVA, analysis of variance

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“…The surge in catecholamine that occurs at birth is associated with a rise in plasma FFA levels. It has been suggested by Padbury et al (35,36) that this is the primary signal for the initiation of nonshivering thermogenesis. In previous studies (8,23), the initial surge in plasma catecholamines after cooling without ventilation or cord snare was not accompanied by nonshivering thermogenesis.…”

Section: Discussionmentioning

confidence: 97%

Reversible Umbilical Cord Occlusion: Effects on Thermogenesis In Utero

1991

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A rapid fall in environmental temperature accompanies the transition from intrauterine to extrauterine existence, and effective thermogenesis is essential to neonatal adaptation. Studies on temperature regulation have shown the importance of thermal homeostasis in reducing the mortality rate of low birth weight infants. The mortality in preterm infants subjected to cold stress is dependent upon the degree and duration of hypothermia (1, 2).The demand for heat production is often maximal at the moment of birth, and the brown adipose tissue thermogenic response to chilling in newborn infants and precocial species such as the lamb is mediated by the sympathetic nervous system. Norepinephrine may increase oxygen consumption and heat production more than 3-fold (3, 4). The mammalian fetal environment is relatively thermostable, and the fetus does not appear to regulate its temperature independently of the mother (5). We

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Neonatal adaptation: greater sympathoadrenal response in preterm than full-term fetal sheep at birth

Cited by 37 publications

References 23 publications

Effects of High Pco2 on Ventilated Preterm Lamb Lungs

Effects of High Pco2 on Ventilated Preterm Lamb Lungs

Postnatal Cardiovascular and Metabolic Responses to a Single Intramuscular Dose of Betamethasone in Fetal Sheep Born Prematurely by Cesarean Section

Reversible Umbilical Cord Occlusion: Effects on Thermogenesis In Utero

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