Microvascular development and growth of uterine tissue during the estrous cycle in mares.

The study explores the activity of uterine tissue growth and microvascular (small blood vessels) development during the various stages of the estrous (reproductive) cycle in mares (female horses). No significant differences were observed in the vascular density of the uterine tissue between the follicular and luteal phase, regardless of the degree of fibrosis present in the tissue. However, several variations in the cellular content of endometrial cells were observed, suggesting a relationship between the development of vascular and non-vascular tissues. It also indicates a potential role of hormones such as estrogen and progesterone in regulating these processes.

Methods

• The researchers obtained uterine tissue from 30 mares during the breeding season from a slaughter facility.
• The stage of the estrous cycle for each mare was determined by observing the ovarian structures and plasma progesterone concentrations.
• They used light microscopy for characterizing the endometrium and histochemical techniques to mark the blood vessel walls.
• A computerized image analysis system was used to evaluate microvascular development.
• The growth of the uterine tissue was determined by analyzing the cellular content of DNA and RNA, and calculating the ratios of RNA:DNA and protein:DNA.

Results

• They observed no significant differences in vascular density (number of blood vessels) in the uterine tissue collected from mares either in the follicular or luteal phase of the estrous cycle.
• The classification of the degree of fibrosis (scarring or thickening of tissues due to excess fibrous connective tissue) in the endometrium did not affect these findings.
• There was a threefold increase in the amount of both DNA and RNA in the endometrial cells during the follicular phase compared to the myometrium (muscular layer of the uterus).
• The researchers detected hypertrophy (increase in the size of cells) of the endometrial tissue during the luteal phase, indicated by a significant increase in the cell protein content and the protein:DNA ratio.

Conclusions

• The study suggests that the growth of vascular tissues in the endometrium during the estrous cycle is synchronized with the development of non-vascular tissue.
• The results also indicate that hormones, specifically estrogen and progesterone, might have a role in regulating uterine growth and angiogenesis (formation of new blood vessels).