Reproduction Abstracts

Introduction: In dairy cows, post-partum endometritis caused by Gram negative bacteria (e.g. E. coli) adversely affects follicular function and is associated with subfertility. However, there is limited information of the effects of endometritis on the corpus luteum (CL). Recently, we showed that LPS dose-dependently decreased luteal endothelial cell (EC) network formation in vitro. The hypothesis tested was that CL from cows with endometritis would have reduced vascularisation and steroidogenic capacity.

Methods: Mid-luteal phase bovine ovaries were collected from cows with either no signs of endometritis (control, n=3) or presence of purulent endometrial discharge (n=3) confirmed macroscopically and histologically. Luteal sections were either snap frozen or fixed in Bouin’s. Ether-extracted progesterone content was determined by ELISA. Immunohistochemical analysis determined the degree of vascularisation (von Willebrand Factor) and pericyte coverage (smooth muscle actin SMA). Western blots assessed STAR, HSD3B, P450SCC and SMA protein expression (normalised to Histone H3). Groups were compared by t-tests.

Results and discussion: CL from cows with endometritis were slightly smaller (P<0.05) with reduced luteal progesterone content (1.2-fold, P<0.05). Control CL contained extensive vascularisation with steroidogenic cells largely adjacent to endothelial cells. This vascularisation (3-fold, P<0.01) and pericyte coverage (4-fold, P<0.001) was much lower in endometritic cows. Western blot confirmed that SMA protein expression was lower (6-fold, P<0.001). Quantification of Western blots clearly showed lower STAR (2-fold), HSD3B (8-fold) and P450SCC (3-fold) protein levels in cows with endometritis (all P<0.01). In summary, cows with endometritis had smaller CL with reduced progesterone content. This was associated with decreased expression of progesterone synthesis proteins. Dramatically attenuated luteal endothelial cell area and pericyte coverage suggest that the luteal vasculature might be particularly sensitive to uterine-derived bacterial endotoxins.