Angiogenesis, changes in blood flow, and extracellularmatrix remodeling are the processes associated with the development and demise of the bovine corpus luteum(CL) during the estrous cycle. APJ (putative receptor protein related to angiotensin type 1 receptor) is a G-proteincoupled receptor, and its ligand, apelin, has been identified as a novel regulator of blood pressure and as an angiogenic factor. We hypothesized that the apelin–APJ system is involved in luteal function. This study investigated whether apelin–APJ exists in bovine CL and determined their expression profiles and localization during luteal phase and prostaglandin F2a (PGF2a)-induced luteolysis. During the luteal phase, apelin mRNA expression increased fromearly to late CL and decreased in regressed CL. APJmRNA expression increased from early to mid-CL and remained elevated in late and regressed CL. Apelin and APJ proteins were immunohistochemically detected only in the smooth muscle cells of intraluteal arterioles during the luteal phase. PGF2α stimulated apelin and APJmRNA expression at 0.5–2 and 2 h respectively, and then themRNA expression of apelin–APJwas inhibited from4 h duringPGF2α-induced luteolysis. Additionally, apelinmRNA and protein were stimulated at 1 h after PGF2α injection only in the periphery of mid- but not early CL. The present study indicated that the apelin–APJ was localized in the smooth muscle cells of intraluteal arterioles, and responded to PGF2a at the periphery of mid-CL in the cow. Thus, the apelin–APJ system may be involved in the maturation of CL and the luteolytic cascade as a regulator of intraluteal arterioles in cow.    «

Angiogenesis, changes in blood flow, and extracellularmatrix remodeling are the processes associated with the development and demise of the bovine corpus luteum(CL) during the estrous cycle. APJ (putative receptor protein related to angiotensin type 1 receptor) is a G-proteincoupled receptor, and its ligand, apelin, has been identified as a novel regulator of blood pressure and as an angiogenic factor. We hypothesized that the apelin–APJ system is involved in luteal function. This study invest...    »