Exogenous ACTH stimulus during the preovulatory period alters patterns of leukocyte recruitment in the ovary of dairy cows.

Before ovulation, the ovary exhibits signs of local inflammation. However, the effects of adrenocorticotropin (ACTH) on the complexity of this inflammatory response are not yet well described. Thus, the aim of this study was to evaluate the effects of ACTH administered to dairy cows during the preovulatory period on the local distribution of different subsets of leukocytes infiltrated in the ovary, along with the gene expression of relevant chemokines (C-C motif chemokine ligand-2 (CCL2), C-X-C motif chemokine ligand-8 (CXCL8), CCL25 and CXCL1) involved in leukocyte chemotaxis and blood perfusion on the follicular wall of dominant follicles. Also, the direct effect of ACTH on chemokine gene expression was addressed in cultured antral follicular walls. For this purpose, both an in vivo and an in vitro experiment were performed. For the in vivo experiment, exogenous ACTH (100 IU) was administered intramuscularly to Holstein cows (n = 12) during proestrus every 12 h for four days before ovulation, when ovariectomy was performed (day 18). Daily ovarian Doppler ultrasonography was used to evaluate the percentage of irrigated area, the pulsatility index and the resistance index in the dominant follicles. The distribution of monocytes-macrophages (CD14), T- (CD2) and B-lymphocytes (CD79a) and granulocytes (CH138A) in the ovary was analyzed by immunohistochemistry. In follicular wall samples, gene expression of CCL2, CXCL8, CXCL1 and CCL25 was evaluated, whereas IL-17A expression was analyzed by Western blot. The total number of CD14, CD79a and CD2 infiltrated cells was lower in the ACTH-treated group than in the control group (p < 0.05). Chemokine gene expression showed lower mRNA of CCL2, CCL25 and CXCL1 (p < 0.05) in the ACTH-treated group. Meanwhile, IL-17A protein expression and hemodynamic parameters were similar between groups (p > 0.05). In the in vitro assay, antral follicular walls were stimulated with ACTH to corroborate the gene expression profile of chemokines. mRNA expression of CCL2 tended to be lower in the stimulated follicular walls (p = 0.092). Our results suggest that exogenous ACTH stimulus during the preovulatory period reduces the number of infiltrated leukocytes in the bovine ovary and this could be due to a lower chemotaxis capacity of the ovary.