Effect of ovarian hormones on the phagocytic response of ovariectomized mares.

The research examines the influence of ovarian hormones on the immune response to uterine infection in mares, specifically focusing on how the hormones estrogen and progesterone affect the process of phagocytosis, the mechanism of the body’s immune response to bacterial infection.

Experiment Design and Procedure

• The experiment was conducted on three groups of mares, each group consisting of six members, who had been ovariectomized (their ovaries surgically removed).
• Group 1 served as the control group, designated as ‘anoestrus’, without any hormone injection.
• Group 2 were given estrogen injections, labelled as ‘oestrus’, for a span of five weeks.
• Group 3 received progesterone injections, marked as ‘dioestrus’, over the same duration.
• All horses were artificially infected intrauterine with the bacterium Streptococcus zooepidemicus one week after the commencement of hormone treatment.
• The experimental outcomes were then evaluated weekly, using swabs and endometrial biopsies.

Results and Observations

• By the end of the first week, the estrogen-treated Group 2 did not exhibit any presence of the bacteria.
• Group 1, the control group, were clear of the bacteria after two weeks.
• Group 3, those treated with progesterone, remained infected throughout the observational period.
• The process of bacterial consumption by the immune system, known as phagocytosis, was measured by chemiluminescence, a process that measures light emitted during the chemical reaction of phagocytosis.
• Prior to infection, all groups showed no significant difference in the levels of phagocytosis. Bacterial cultures for all groups were also negative pre-infection.
• However, 48 hours post-infection, a marked increase in phagocytosis was observed in Group 2, the estrogen-treated mares, and a noticeable suppression was observed in Group 3, the progesterone-treated mares.
• The observed patterns of bacterial removal from the uterus closely followed the changes in the chemiluminescence response triggered by phagocytosis.

Conclusions

• The findings indicate that the hormonal status of the ovaries can indeed have an impact on the phagocytic response of the immune system, specifically in the case of streptococcal-induced endometritis in mares.
• More specifically, estrogen seemed to boost immune response and promote the elimination of the bacteria, while progesterone appeared to inhibit the process, leading to a prolonged infection.