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1 Endocrine Research Laboratory, St. Luke's Medical Center, Milwaukee, WI, USA
2 Department of Pediatrics, Medical College of Wisconsin, Milwaukee, WI, USA; Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, WI, USA
3 Endocrine Research Laboratory, St. Luke's Medical Center, Milwaukee, WI, USA; Department of Medicine, Medical College of Wisconsin, Milwaukee, WI, USA
* To whom correspondence should be addressed. E-mail: hraff{at}mcw.edu.
The nursing rat pup exposed to hypoxia from birth exhibits ACTH-independent increases in corticosterone and renin/angiotensin II-independent increases in aldosterone. These increases are accompanied by significant elevation of plasma lipid concentrations in the hypoxic neonates. The purpose of the present study was to compare changes in the concentrations of specific fatty acid metabolites and lipid classes in serum and adrenal tissue from normoxic and hypoxic rat pups. We hypothesize that lipid alterations due to hypoxia may partly explain increases in steroidogenesis. Rats were exposed to normoxia or hypoxia from birth, and pooled serum and adrenal tissue from 7-day-old pups were subjected to metabolomic analyses. Hypoxia resulted in specific and significant changes in a number of fatty acid metabolites in both serum and the adrenal. Hypoxia increased the concentrations of oleic (18:1n9), eicosapentaenoic (EPA; 20:5n3), and arachidonic (20:4n6) acids in the triacylglyceride fraction of serum and decreased oleic and EPA concentrations in the cholesterol ester fraction. In the adrenal, hypoxia caused an increase in several n6 fatty acids in the triacylglyceride fraction, including linoleic (18:2n6) and arachidonic acid. There was also an increase in the concentration of alpha-linolenic acid (18:3n3) in the triacylglyceride fraction of the hypoxic adrenal, along with an increase in linoleic acid concentration in the diacylglyceride fraction. We propose that specific changes in lipid metabolism in the adrenal, as a result of hypoxia, may partly explain the increased steroidogenesis previously observed. The mechanism responsible may involve alterations in cellular signaling and/or mitochondrial function. These cellular changes may be a mechanism by which the neonate can increase circulating adrenal steroids necessary for survival, therefore bypassing a relative insensitivity to normal stimuli.
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