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

Objective-To document uterine growth and microvascular development in the e ndometrium of uteri with differing degrees of fibrosis as well as uterine g rowth throughout the estrous cycle of mares. Animals-30 mares. Procedure-Uterine tissue was obtained during the breeding season from a sla ughter facility. Stage of estrous cycle of the mares was assessed on the ba sis of ovarian structures and plasma progesterone concentrations. Endometri um was characterized by use of light microscopy, and blood vessel walls wer e marked by histochemical techniques. Microvascular development was evaluat ed by a computerized image analysis system. Growth of uterine tissue was ba sed on cellular content of DNA and RNA, RNA:DNA, and protein:DNA. Results-Significant differences in vascular density were not observed in th e endometrium of uteri obtained from mares euthanatized during the follicul ar or luteal phase of the estrous cycle, regardless of whether endometrial classification of degree of fibrosis was considered. There was a 3-fold inc rease in amount of DNA and RNA of endometrial cells in the follicular phase when compared to myometrium. Hypertrophy of endometrial tissue during the luteal phase was reflected by a significant increase in cell protein conten t and protein:DNA. Conclusions and Clinical Relevance-Endometrial growth of vascular tissues d uring the estrous cycle may be coordinated with development of nonvascular tissue. Estrogen and progesterone may play a role in regulation of uterine growth and angiogenesis.