Time-Course of the Uterine Response to Estradiol-17ß in Ovariectomized Ewes: Uterine Growth and Microvascular Development¹

^a Department of Animal & Range Sciences, ^b and Cell Biology Center, Biotechnology Institute, North Dakota State University, Fargo, North Dakota 58105

The time-course of uterine growth, cell proliferation, and microvascular development was evaluated during the first 72 h after implanting estradiol-17ß (E₂) into ovariectomized (OVX) ewes. Uterine fresh weight increased 2.3-fold by 24 h and increased further (3.3-fold) by 48 h. The majority (~75%) of this growth response was associated with tissue growth rather than a change in the tissue dry weight:fresh weight ratio. Both uterine cell number (DNA content) and cell size (RNA:DNA ratio) increased from 0 to 24 h (1.8-fold and 1.7-fold, respectively). Cell proliferation also increased dramatically between 8 h and 24 h after E₂ implantation. Endometrial microvascular volume density (percentage of tissue volume occupied by microvessels) increased ~1.8-fold by 24 h and then remained constant or declined slightly through 72 h. The total endometrial microvascular volume, however, increased ~5-fold from 0 to 24 h and increased further by 72 h. Thus, treatment of OVX ewes with E₂ caused a dramatic increase in uterine fresh and dry weights by 24 h, due primarily to hyperplasia and hypertrophy, with only a relatively small change in tissue dry weight:fresh weight ratio. This dramatic uterine growth was associated with a profound increase in endometrial microvascular volume.

¹ A portion of the study described in this manuscript served as a Senior Thesis for D.L.K. in the undergraduate Biotechnology program at NDSU. A publication of the North Dakota Agric. Exp. Sta., Project 1795.

² Correspondence. FAX: (701) 231–7590; lreynold{at}prairie.nodak.edu

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