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Acute Effect of Endotoxin on Nucleic Acid Content of the Mammary Gland¹

Departments of Large Animal Surgery and Medicine Dairy and Panthology, Michigan State University, East Lansing 48823

ABSTRACT

Intramammary inoculation of endotoxin or physiological saline (0.85% NaCl) had little effect on the mammary deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) concentration of lactating guinea pigs killed three or six hours post-inoculation. Mammary DNA increased (P < 0.01) 12 and 24 hours after endotoxin treatment coincident with migration of leukocytes into the glandular parenchyma. There was also a slight increase in mammary DNA following saline treatment. Although endotoxin treatment increased mammary DNA concentration after 12 or 24 hours, RNA concentration of these glands was not significantly (P < 0.05) different from that of guinea pigs killed three or six hours post-treatment. Saline infusion increased (P < 0.01) mammary RNA concentrations after 12 and 24 hours. Endotoxin, but not saline, stimulated a decrease in mammary cell RNA of about the same magnitude as the increase in whole gland RNA resulting from leukocytic infiltration. This view is supported by a marked decrease in the RNA/DNA ratio 24 hours after endotoxin treatment. Relative to corresponding RNA/DNA ratios three hours post-treatment, endotoxin treatment resulted in a 60.4% decrease (P < 0.01) in RNA/DNA ratio after 24 hours. In contrast, the RNA/DNA ratio 24 hours after saline treatment was decreased 22.6% but not significantly (P < 0.05).

¹ Journal Article 5152 from the Michigan Agricultural Experiment Station. This investigation was supported, in part, by Michigan Agricultural Experiment Station Project 3058.