Ovarian superstimulation protocols modulate the morphological phenotypes in bovine oviduct

It has been shown that estradiol (E2) and progesterone (P4) have a significant influence on the alteration of morphological parameters in the oviduct of cattle. These morphological changes were demonstrated by comparing the effects of the different hormonal profiles between the hormonal phases of the estrous cycle or between the ipsi- and contralateral side of the preovulatory follicle/corpus luteum and even the size of the corpus luteum. In our previous study, we have shown that the ovarian superstimulation (OVS) protocol increases E2 levels in the bovine oviduct during the preovulatory phase. Therefore, we wanted to gain insight into the effects of OVS protocols on morphological parameters in the bovine oviduct. To this end, our study evaluated two OVS protocols, an FSH-only protocol and the FSH/eCG protocol, both of which were successfully standardized for Nelore cows (Bos taurusindicus). A third group was used as a control that was not superstimulated (synchronized estrus). The ampulla and isthmus segments of the oviduct were analyzed separately for morphometric analysis (hematoxylin and eosin staining - HE), quantification of total collagen (picrosirius red staining - PSR), analysis of fractal dimensions, and quantification of total mucin (staining with periodic acid-Schiffs/Alcian blue). Overall, both OVS protocols decreased mucosal height, epithelial area, and luminal area in the isthmus, while total collagen quantification increased. In contrast, cows subjected to the FSH/eCG protocol exhibited increased muscle layer area and mucosal height in the ampulla, while total collagen quantity decreased. Analysis of fractal dimensions showed that both OVS treatments increased cell organization in both isthmus and ampulla segments compared to the synchronized group when analyzing tissues stained with PSR. Finally, the FSH/eCG protocol increased the relative abundance of mucins in the isthmus and ampulla segments compared to the other groups. In conclusion, we have shown that cows subjected to OVS exhibit a different morphological phenotype in the bovine oviduct characterized by morphometric changes, collagen modulation, and histochemical alterations.