Effect of estrogen and progesterone on the phagocytic response of ovariectomized mares infected in utero with β-hemolytic streptococci

Abstract

SUMMARY Eighteen ovariectomized mares inoculated in utero with Streptococcus zooepidemicus were placed in 3 groups to determine the effects of estrogen and progesterone on the kinetics of phagocytosis, streptocidal activity, and uterine clearance of streptococcal infection. Streptococcal phagocytosis was measured by chemiluminescence ( cl ) and streptocidal activity of peripheral blood leukocytes was measured by bactericidal assay. Clearance of streptococcal infection was determined by culture of the endometrium for evidence of streptococci. Measurements of phagocytosis and streptocidal activities were made before, and at 2 and 10 days after, the mares were inoculated. Endometrial bacterial cultures were examined before, and at 7 and 14 days after, infection. Before the inoculations were done, streptococcal phagocytosis and intracellular streptocidal activity were not significantly ( P > 0.05) different in the estrogen, progesterone, or nontreated groups of mares. Bacterial cultures for S zooepidemicus were negative for each group. At 2 days after infection, estrogen-treated mares showed a 3-fold increase in cl response over preinoculation values and did not have streptococcal colonies in cultures after 60 minutes’ incubation in streptocidal assay nor streptococcal colonies in cultures from the endometrium at 7 days. Progesterone-treated mares, after 2 days, did not have an increase in cl response over preinoculation value nor streptocidal activity in 60 minutes, but had colony counts of 5.7 x 10 10 streptococci from endometrial culture. At 10 days, estrogen-treated mares had returned to preinoculation values for cl and streptocidal assays. Streptococci were not cultured from the uterus at 14 days. Conversely, leukocytes from progesterone-treated mares at 10 days had a 3-fold increase in cl response and killed 10 3 streptococci in 60 minutes; endometrial bacterial colony counts in 4 mares were 5.1 x 10 10 streptococci, but none in 2 mares. Similar findings were obtained in cl response and intracellular streptocidal activity in each treatment group. These results closely paralleled the kinetics of streptococcal clearance from the uterus. The results obtained indicate an intimate association between phagocytic response and ovarian hormone influence on the uterus, which may be an important factor in experimentally induced endometritis.