title: Endogenous angiotensins and catecholamines do not reduce skin blood flow or prevent hypotension in preterm piglets.
abstract: Endocrine control of cardiovascular function is probably immature in the preterm infant; thus, it may contribute to the relative ineffectiveness of current adrenergic treatments for preterm cardiovascular compromise. This study aimed to determine the cardiovascular and hormonal responses to stress in the preterm piglet. Piglets were delivered by cesarean section either preterm (97 of 115 days) or at term (113 days). An additional group of preterm piglets received maternal glucocorticoids as used clinically. Piglets were sedated and underwent hypoxia (4% FiO2 for 20 min) to stimulate a cardiovascular response. Arterial blood pressure, skin blood flow, heart rate and plasma levels of epinephrine, norepinephrine, angiotensin II (Ang II), angiotensin-(1-7) (Ang-(1-7)), and cortisol were measured. Term piglets responded to hypoxia with vasoconstriction; preterm piglets had a lesser response. Preterm piglets had lower blood pressures throughout, with a delayed blood pressure response to the hypoxic stress compared with term piglets. This immature response occurred despite similar high levels of circulating catecholamines, and higher levels of Ang II compared with term animals. Prenatal exposure to glucocorticoids increased the ratio of Ang-(1-7):Ang II. Preterm piglets, in contrast to term piglets, had no increase in cortisol levels in response to hypoxia. Preterm piglets have immature physiological responses to a hypoxic stress but no deficit of circulating catecholamines. Reduced vasoconstriction in preterm piglets could result from vasodilator actions of Ang II. In glucocorticoid exposed preterm piglets, further inhibition of vasoconstriction may occur because of an increased conversion of Ang II to Ang-(1-7).
authors.affiliation: UQ Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Yvonne A
authors.initials: YA
authors.lastname: Eiby
authors.affiliation: UQ Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia School of Biomedical Sciences and Pharmacy, University of Newcastle, Newcastle, New South Wales, Australia.
authors.forename: Eugenie R
authors.initials: ER
authors.lastname: Lumbers
authors.affiliation: UQ Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Staunton
authors.affiliation: UQ Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Layne L
authors.initials: LL
authors.lastname: Wright
authors.affiliation: UQ Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Paul B
authors.initials: PB
authors.lastname: Colditz
authors.affiliation: School of Biomedical Sciences and Pharmacy, University of Newcastle, Newcastle, New South Wales, Australia Graduate School of Medicine and Illawarra Health and Medical Research Institute, University of Wollongong, Wollongong, New South Wales, Australia.
authors.forename: Ian M R
authors.initials: IM
authors.lastname: Wright
authors.affiliation: UQ Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia.
authors.forename: Barbara E
authors.initials: BE
authors.lastname: Lingwood
keywords: Blood pressure; cardiovascular; glucocorticoids; neonatal; skin blood flow