Factors affecting uterine clearance of inoculated materials in mares

Twelve acyclic mares of various ages (2-29 years) and parity (maiden-multiparous) were given oestradiol-17 beta i.m. (winter 1982) or progesterone i.m. (winter 1983) to induce changes in the endometrium consistent with oestrus and dioestrus, respectively. After hormone treatment, mares were inoculated intrauterine with 50 ml saline containing 5 X 10(5) Streptococcus zooepidemicus bacteria, 51Cr-labelled 15-micron microspheres, and 500 mg charcoal (Groups E + B and P + B) or microspheres and charcoal only (Groups EC and PC). At 5 h after inoculation uteri were flushed with 50 ml saline containing tracer amounts of 125I-labelled HSA. In Group E + B inoculated materials were cleared more rapidly in younger than in older mares, and there was a significant positive correlation between age and bacterial concentration, total numbers of bacteria, and amounts of microspheres and charcoal in the uterus and also between age and the WBC concentration and total numbers of WBC. In Group EC there was a significant positive correlation between age and the amounts of microspheres and charcoal remaining in the uterus, and between age and WBC concentration and total numbers of WBC. We suggest that in the oestrogen-dominated uterus physical drainage may be a factor in determining whether a mare is 'resistant' or 'susceptible' to bacterial challenge of the uterus. Physical clearance is increased in younger (resistant) mares in the presence and absence of an antigenic stimulus. In mares in Group P + B there was no correlation between age and the values measured.(ABSTRACT TRUNCATED AT 250 WORDS)