Regulation of Corpus Luteum Function in Cattle – an Overview

Abstract

The corpus luteum (CL) is a transient reproductive gland that produces progesterone (P), required for the establishment and maintenance of pregnancy. Although the regulation of bovine luteal function has been studied for several decades, many of the regulatory mechanisms involved are incompletely understood. We are far from understanding how these complex mechanisms function in unison. The purpose of this overview is to stress important steps of regulation during the lifetime of CL. In the first part, the importance and regulation of angiogenesis and blood flow during CL formation is described. The results underline the importance of growth factors especially of vascular endothelial growth factor A (VEGF A) and basic fibroblast growth factor (FGF-2) for development and completion of a dense network of capillaries. In the second part, the regulation of function by endocrine/paracrine- and autocrine-acting regulators is discussed. There is now more evidence that besides the main endocrine hormones LH and GH local regulators as growth factors, peptides, steroids and prostaglandins are important modulators of luteal function. During early CL development until mid-luteal stage oxytocin, prostaglandins and P itself stimulate luteal cell proliferation and function supported by the luteotropic action of a number of growth factors. The still high mRNA expression, protein concentration and localization of growth factors [VEGF, FGF-1, FGF-2, insulin-like growth factors (IGFs)] in the cytoplasm of luteal cells during mid-luteal stage suggest maintenance (survival) functions for growth factors. In the absence of pregnancy regression (luteolysis) of CL occurs. Progesterone itself regulates the length of the oestrous cycle by influencing the timing of the luteolytic signal prostaglandin F2alpha (PGF2alpha) from the endometrium. The cascade of mediators afterwards is very complex and still not well-elucidated. Evidence is given for participation of blood flow, inflammatory cytokines, vasoactive peptides (angiotensin II and endothelin-1), reactive oxygen species, angiogenic growth factors (VEGFs, FGFs, IGFs) and decrease of the classical luteotropic components as LH-R, GH-R, P450(scc) and 3beta-HSD. Despite of differences in methodology and interpretations, progress has been made and will continue to be made.

AKT-independent Phosphorylation of TSC2 and Activation of mTOR and Ribosomal Protein S6 Kinase Signaling by Prostaglandin F2α

“…However, luteal cells, in the course of cellular differentiation in vivo and in vitro, undergo a progressive hypertrophy (4,45,46). Given the selective induction of the FP receptor in ovarian cells following ovulation and the high levels of prostaglandins present during early CL development (1,2,47), it is plausible that mTOR/4EBP1/S6K1 signaling participates in the hypertrophy/differentiation of the luteal cell. In keeping with this theme, Alam et al (48) recently suggested that gonadotropin stimulated mTOR signaling may play a role in the differentiation of rat granulosa cells to the large luteal cell type.…”

“…In the event of pregnancy, the CL retains its role in progesterone synthesis in support of early pregnancy. In the absence of pregnancy luteolysis or corpus luteum regression occurs, a physiologic process associated with a reduction in progesterone secretion (functional regression) followed by death of endothelial and steroidogenic cells (structural regression) (1)(2)(3)(4). Prostaglandin F2␣ (PGF2␣) was identified as a luteolytic factor over 35 years ago (5,6).…”

“…The corpus luteum (CL) 2 is a transient endocrine gland derived from an ovulated follicle within the ovary. The steroidogenic cells of the CL produce progesterone, a prerequisite for normal maintenance of pregnancy in mammals.…”

Five different phenotypes of endothelial cell cultures from the bovine corpus luteum: Present outcome and role of potential dendritic cells in luteolysis

“…The in vitro cross-talk between two vascular cell types might give insight into the molecular demands for arteriole formation, maintenance and function. The aspect could become important when studying vasoconstriction in CL arterioles at the onset of luteolysis (Schams and Berisha, 2004). Given as marginal note, seldom occurring helical tubules in type 1 cultures are indicative of co-cultivation with vascular smooth muscle cells.…”

63 Effect of Endometrial Biopsy on Uterine Health of Tropically Adapted Beef Cattle

“…The corpus luteum (CL) is a temporary gland that secretes progesterone (P4), which is essential to regulation of the oestrous cycle, providing a uterine environment for establishment and maintenance of pregnancy (Schams and Berisha, 2004). CL function is assessed by the measurement of P4 in systemic blood or milk.…”