Investigation of the Relationship between Endometrial MMP Activities and Sex Hormones in Mature Bitches

Endometrial matrix metalloproteinases (MMPs) are extensively studied in humans. However, owing to the distinct differences of the estrous cycle of bitches, the expression and activities of endometrial MMPs regulated by sex hormones should be significantly different. To understand the effect of sex hormones on the activity of MMPs, this study investigates the activities of endometrial MMP-2 and MMP-9 during different phases of the estrous cycle in bitches through the use of gelatine zymography. Estradiol and progesterone concentrations were also determined using enzyme-linked fluorescent assay. The activities of the latent forms of both MMP-2 and -9 were significantly higher in metestrus (MP) and late diestrus phases (L-DP) than in anestrus (AP) and proestrus/estrus phases (EP) (p<0.05). Similarly, the activities of the active forms of both MMPs in L-DP were significantly higher than in the other phases of the estrous cycle (p<0.05). Significant correlations were found between progesterone and the activities of latent and active forms of MMP-9 during MP (r= -0.83, p<0.05 and r= 0.94, p<0.01, respectively). Considering our results, together with that of previous studies on the role of MMPs in the reproductive system, we hypothesize that endometrial MMP-2 and MMP-9 play a key role in successful fertilization.