Endotoxin dose-related leukocytosis in milk of guinea pigs

Objectives were to determine minimum and maximum doses of Escherichia coli endotoxin that would stimulate leukocytosis in the mammary gland of the guinea pig. Endotoxin concentrations of .005, .05, .5, 5.0, and 50.0 microgram/ml in 1 ml were used to stimulate migration of polymorphonuclear leukocytes in milk of guinea pigs at five times (2, 4, 6, 8, and 12 h postinjection with endotoxin). There were three animals in each experimental group per endotoxin concentration. Each animal served as its own control by having sterile saline injected into one mammary gland and endotoxin into the other. A control group of three animals had no saline or endotoxin injected. Guinea pigs were milked with a modified milking apparatus. Leukocyte numbers in the uninjected mammary gland did not differ from those in saline injected glands. The difference in mean leukocyte numbers between saline injected and .005 microgram/ml endotoxin injected glands approached significance at 5%. There was no difference between mean numbers recruited by the 5.0 and 50.0 microgram/ml endotoxin doses at 4, 6, 8, and 12 h. The chemotactic effect and, therefore, the rate of polymorphonuclear leukocyte recruitment was maximal at the 5 microgram/ml endotoxin dose.