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

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 F2-alpha-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-mu-g kg-1 bodyweight of Escherichia coli endotoxin as an intrauterine infusion and one hour later received an intravenous injection of lipid X (5-mu-g 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 1 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.