Serum cortisol changes in heifers induced by lipid X: A monosaccharide precursor in the biosynthesis of Gram-negative endotoxin

Abstract

An experiment was conducted to measure the changes in serum cortisol and luteinising hormone ( LH) concentrations in heifers during the luteal phase of the oestrous cycle after the administration of lipid X and Gram-negative endotoxin. Nine heifers whose oestrous cycles were synchronised with prostaglandin F 2α. were assigned at random on day 10 after the second prostaglandin injection to one of the following groups. Group 1 heifers (n=3) received 5 μg kg −1 bodyweight of Escherichia coli endotoxin as an intrauterine infusion and one hour later received an intravenous injection of lipid X (5 μg kg −1 bodyweight). The treatment was reversed in group 2 heifers (n = 3), endotoxin was administered one hour after the lipid X treatment. Group 3 heifers (n=3) received endotoxin infusion and lipid X treatment at the same time. Similar dosages and routes of administration were used in all the groups for lipid X and endotoxin treatments. Blood samples were collected once every 15 minutes for seven hours, beginning one hour before and six hours after the initial treatment. In group I heifers there was a fourfold increase in serum cortisol concentrations within 30 minutes after both the treatments (from 6·5 to 24·6 ng ml −1 and from 7 · 3 to 29 · 5 ng ml −1 respectively). In group 2 heifers the cortisol concentrations increased from the baseline concentrations of 7·2 to 33·2 ng ml −1 within 30 minutes after lipid X treatment and remained at 22 · 5 ng ml −1 during endotoxin treatment. There was a further increase in cortisol concentrations (28·9 ng ml −1) after the endotoxin treatment. Serum cortisol concentrations reached baseline values within two hours after the treatment. In group 3 heifers there were no changes in serum cortisol concentrations. There were no changes in serum LH concentrations in any heifer. The results suggest that lipid X might have structural and functional similarities to E coli endotoxin.