**3. Role in oviductal function**

In the oviduct, endocrine and paracrine factors induce morphological, biochemical, and physiological alterations in the infundibulum, ampulla, and isthmus to provide an ideal microenvironment for oocyte transport and maturation, sperm capacitation and transport, and fertilization and early embryonic development. Thus, the temporal and spatial organization of each of these events is fundamental to reproductive efficiency [6, 25]. It is known that some peptides are responsible for the orchestration of these processes, including angiotensin II (ANG II) [26, 27].

ANG II is the major bioactive peptide of the renin-angiotensin system. This vasoactive peptide is derived from angiotensinogen in a two-step process that first involves the renin-dependent conversion of angiotensinogen to angiotensin I (ANG I), followed by ANG I conversion to ANG II via angiotensin-converting enzyme I (ACE-I). The fact that ANG II has a reproductive role in the female mammal is demonstrated by the presence of ANG II receptors in reproductive tissues in several species. There are two types of ANG II receptors: type 1 (ANGR1) and type 2 (ANGR2) [28].

The oviductal cells are capable of producing ANG II [29]. It has been reported that the ACE-1 mRNA abundance is higher during the postovulatory phase and that ANG II released by oviductal tissues is greater in the follicular and postovulatory phases than the luteal phase of the bovine estrous cycle [29]. In women, ANG II concentration in the fallopian tubes is higher in the secretory phase of the menstrual cycle [30].

Both receptors are present in the oviduct. In the human fallopian tube, ANGR1 receptor is in the epithelial cells of the mucosa; there are higher levels in the ampulla than in the fimbria and isthmus [31, 32], and ANGR1 receptor concentration is higher in the proliferative phase than in the secretory phase. In the bovine oviduct, the presence of ANGR2 has been demonstrated in all oviducts during the pre-ovulatory period [33].

ANG II is involved in the ciliary beat frequency (CBF) of oviductal ciliary cells. ANG II stimulates the increase in CBF in the mucosa of human fallopian tubes acting on the ANGR1 [31, 32]. Additionally, elevated ANG II interacts with other contraction-release substances to activate oviductal smooth muscle contractions [29].The combination of the action of ANG II to activate CBF and muscle contraction during the peri-ovulatory phase suggests the important function of ANG II in the rapid transport of gametes to the fertilization site [29].

In addition, ANG II is involved in sperm survival. In the bovine oviduct, ANG II participates in the local immunological response of the oviduct against allogeneic sperm, modulating the phagocytic activity of neutrophils [34].
