W.D. Schultze

Plasma Corticosteroid, Circulating Leukocyte and Milk Somatic Cell Responses to Escherichia coli Endotoxin-Induced Mastitis

Summary A mammary quarter in each of 4 cows was infused with 0.5 mg E. coli endotoxin to determine its effect on plasma corticosteroids, circulating leukocytes and milk somatic cells. At 1.5 hr following endotoxin infusion, segmented neutrophils decreased 23%, and by 5 hr dropped 93%. A shift left in the differential circulating leukocyte count began at 2.5 hr and reached maximum proportions between 18-24 hr postendotoxin infusion. Circulating lymphocytes, monocytes and eosinophils were all depressed in response to endotoxin. Plasma corticosteroid concentrations increased (P < 0.01) 2 hr following endotoxin infusion, reached maximum concentrations at 4 hr, then returned to prein-fusion concentrations by 12 hr. The initial decrease in circulating lymphocytes at 2.5 hr was not attributed to the lytic effect of the plasma corticosteroids, since depressions in circulating lymphocytes occurred too soon (0.5 hr) after the increase in plasma corticosteroids. The high plasma corticosteroid concentration appeared to have little effect at restoring leukocyte equilibrium, since the concentration of neutrophils and total leukocytes continued to decline up to 4 hr past the initiation of the plasma corticosteroid response. Serum glucose concentrations coincided with peak plasma corticosteroid concentration and appeared to be one of the primary physiological effects mediated by elevated plasma corticosteroid concentrations. Three hours following endotoxin infusion or 1.5 hr after the noted depression in segmented neutrophils, the concentration of milk somatic cells increased from 5.7 × 104 cells/ml milk at 0 hr to 37.5 × 104 cells/ml. However swelling of infused quarters was detected as early as 2 hr postinfusion and was attributed to diapedesis and lysis of neutrophils. Total milk somatic cell concentrations reached maximum proportions at 18 hr, averaging 54 × 106 cells/ml milk. The authors thank Miss Barbara A. Becker, Mr. D. Carroll, Mr. S. T. Kirk, and Mr. A. J. Kral for their excellent technical assistance.