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Circulating vasoactive substances and hemodynamic adjustments at birth in lambs
1Department of Pediatrics, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|August 1, 1987
Summary
Angiotensin II (ANG II) formation supports the blood pressure and oxygenation increase after birth in lambs. High catecholamines may also aid postnatal circulation.
Area of Science:
- Physiology
- Neonatal Research
- Cardiovascular Studies
Background:
- Circulating vasoactive substances and hemodynamics are critical for neonatal adaptation.
- Cesarean section and spontaneous respiration trigger significant physiological changes in newborns.
Purpose of the Study:
- To investigate the roles of angiotensin II (ANG II) and catecholamines in postnatal circulatory adjustments.
- To examine the impact of ANG II inhibition on hemodynamics after birth.
Main Methods:
- Chronically instrumented, unanesthetized lambs underwent cesarean section.
- Infusions of saline, saralasin (ANG II inhibitor), or captopril (ACE inhibitor) were administered prenatally.
- Hemodynamics and plasma concentrations of renin activity, ANG II, and catecholamines were measured before, during, and after birth.
Main Results:
- Control lambs showed significant increases in plasma renin activity, ANG II, and catecholamines post-birth.
- Postnatal increases in systemic arterial pressure (Psa) and arterial O2 partial pressure (PaO2) were blunted in captopril and saralasin groups compared to controls.
- Intravenous ANG II infusion in control lambs demonstrated a systemic over pulmonary pressor response.
Conclusions:
- ANG II formation is crucial for the postnatal rise in Psa and PaO2.
- Elevated circulating catecholamines likely support postnatal cardiac output and Psa.