Studies on the composition and antibacterial activity of uterine fluid from mares

Forty uterine fluid samples were obtained during oestrus and dioestrus of successive cycles from 4 mares classified as resistant to bacterial infection of the uterus. The flushings were assayed for peroxidase activity and ability to influence phagocytosis by polymorphonuclear neutrophils. Uterine fluid volumes and protein concentrations and serum oestrogen values were similar during oestrus and dioestrus. Serum progesterone concentrations were depressed during oestrus. Equine neutrophils adherent to glass slides were exposed to a genital strain of Streptococcus zooepidemicus suspended in saline. Neutrophil phagocytosis was significantly higher when cells were incubated with oestrous uterine fluid than with dioestrous fluid. The addition of 5% serum to the incubation medium increased the rates of in-vitro phagocytosis, but these did not differ between oestrus and dioestrus. Rates of phagocytosis with and without serum were not correlated with serum oestrogens or progesterone, or with protein content of uterine fluid. Peroxidase activity of uterine fluid in the absence of infection was negligible throughout the oestrous cycle. There were no significant correlations between peroxidase levels and serum oestrogens or progesterone, but the correlation between peroxidase and protein concentration of uterine fluid was significant (r = 0 X 87). Bacterial or fungal infections led to increased protein content of uterine fluid, and usually marked increases in peroxidase, both probably derived from the visibly obvious populations of leucocytes.