Local regulatory mechanisms of ovarian function by a cross-talk between vascular endothelial cells and ovarian cells : a mechanism of ovulation and corpus luteum formation.

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In mammalian females, the ovary plays a central role as an endocrine gland as well as the site of germ cell production. This study focused on the paracrine/autocrine mechanisms for local regulation of ovulation and subsequent formation and regression of the corpus luteum (CL) in the cow and ewe For this purpose, a microdialysis system (MDS) was developed for follicle and the CL both in vivo and in vitro. This technique enables us to observe real-time changes in levels of intercellular transmitters in the ovary during a "death" and a "new formation" of follicle and the CL.In addition, the exposure of ovarian cells with bioactive molecules through MDS resulted in different responses seen in cell cultures, suggesting the importance of intact cell-to-cell contact. After the LH-surge, intrafollicular prostaglandin (PG) and angiotensin II (Ang II) production and secretion acutely increased, and ovulation occurred. During the early development of new CL after the ovulation, local PG and Ang II secretions are maintained at high levels, indicating a direct relationship between active secretion of these factors and a rapid angiogenesis in the CL.The results from in vitro studies led us to propose the concept that a local regulatory mechanism of angiogenesis also enhances the capacity of luteal cells to synthesize/secrete progesterone (P). The overall results of the study spotlight the impact of the cross-talk between vascular endothelial cells and ovarian steroidogenic cells via vasoactive peptides and PG at ovulation and CL formation/regression in the ovary.