Prostaglandin F₂_α Regulates the Nitric Oxide Generating System in Bovine Luteal Endothelial Cells

Abstract

Abstract. The objective of the present study was to elucidate whether luteolytic prostaglandin F2α (PGF) plays roles in regulating the nitric oxide (NO) generating system in luteal endothelial cells (LECs). Reverse transcriptase PCR, immunoblotting and immunostaining revealed the presence of PGF receptor mRNA (521 bp) and protein (64 kDa) in cultured LECs obtained from the mid-stage corpus luteum. When cultured LECs were exposed to 0.1 μM-10 μM PGF, NO production was significantly stimulated by PGF at 24 h. When LECs were exposed to 1 μM PGF for 2, 6 and 24 h, PGF did not affect the expressions of endothelial NO synthase (eNOS) mRNA and protein. On the other hand, PGF stimulated the expression of inducible NOS (iNOS) mRNA (P<0.05) and protein (P<0.05) at 2 h, but not at 6 and 24 h. By observing the conversion of [ 3 C]L-arginine to [ 3 C]L-citrulline, we found that PGF stimulated NOS activity in cultured LECs at 2 h (P<0.05). The overall findings indicate that bovine LECs are a target for PGF and that PGF stimulates iNOS expression and NOS activity in bovine LECs. Stimulation of the NO generating system and NOS activity by PGF may result in increasing local NO production followed by luteolysis. Key words: eNOS, iNOS, Luteal endothelial cell, Nitric oxide, Prostaglandin F2α (PGF2α) (J. Reprod. Dev. 55: [418][419][420][421][422][423][424] 2009) he corpus luteum (CL) is a transient endocrine gland essential for regulation of ovarian cycles as well as for establishment and maintenance of pregnancy. If pregnancy does not occur, the bovine corpus luteum starts to regress between days 17-19 after ovulation [1]. Functional and structural regression of the CL in mammals is induced by the pulsatile release of prostaglandin F2α(PGF) from the uterus and the ovary [2][3][4]. Although regarded as a physiological luteolysin in the cow, the local mechanism involved in the luteolytic action of PGF remains unclear.The actions of PGF are mediated by the PGF receptor (FPr) located in the plasma membrane. Bovine luteal cell membranes have the ability to bind PGF throughout the estrous cycle [5,6]. However, there is no consensus on the presence of FPr in the bovine luteal vasculature. Cavicchio et al. reported the absence of FPr mRNA in luteal endothelial cells (LECs) isolated from early pregnant cows [7]. More recent studies using endothelial cells (ECs) derived from cyclic bovine CLs have demonstrated that freshly isolated and cultured LECs express FPr mRNA [8,9]. Furthermore, FPr has been immunohistologically demonstrated to be expressed in luteal tissue including steroidogenic cells and large blood vessels in the peripheral region of the mature CL [10].Directly treating pure populations of luteal steroidogenic cells with PGF does not inhibit basal progesterone (P4) production [11,12], although intramuscular injections of PGF analogues induce a rapid decrease in P4 production [13]. Similarly, a decrease in P4 release has been observed when bovine luteal cells (LCs) were exposed to PGF in the presence of endothelin-1 (EDN1) [14,...

Role of Nitric Oxide in the Regulation of Superoxide Dismutase and Prostaglandin F2.ALPHA. Production in Bovine Luteal Endothelial Cells

“…The cultures and passages were repeated until a homogeneous population of pure LECs was obtained. The LECs isolated in the present study were confirmed by immunocytochemical staining for rabbit anti-human von Willebrand factor (factor-VIII, F3520; Sigma-Aldrich) and CD31 expression as reported previously [7,20,21]. The bovine LECs used in the present study correspond to type 1 according to the previous classification reported by Spanel-Borowski and Bosch [22].…”

“…PGF and NO may interact and activate LECs and non-LECs to initiate functional and structural luteolysis, as both are produced by LECs. Interestingly, PGF stimulates NO production in cultured bovine LECs [7]. On the other hand, NO increases PGF production in both LSCs [9] and LECs (the present study).…”

“…Therefore, the luteal microenvironment seems to be exposed to high oxygen conditions, especially during a short period of time (1-2 h) following PGF treatment. Interestingly, PGF stimulates the NO generating system by increasing inducible NO synthase (iNOS) mRNA and protein expression and NOS activity in cultured LECs [7]. These findings suggest that NO plays crucial roles in the local mechanism of CL regression.…”

“…Also, an increase in SOD activity and a decrease in catalase activity have been demonstrated during the loss of luteal function in mice [28]. Previous studies have shown that PGF stimulates NO synthesis in the bovine in vivo [13] and in LECs in vitro [7]. The above findings suggest that a local increase in NO production induced by PGF within the bovine CL affects the function of the CL and that the acute elevation of SOD represents a response of LECs to protect themselves against oxidative stress induced by PGF treatment at the beginning of functional luteolysis.…”

“…Previous studies have demonstrated that endothelial cells produce reactive oxygen species (ROS) [5] including nitric oxide (NO) [6,7] and that ROS inhibit P4 production [8,9] and induce apoptosis in bovine luteal steroidogenic cells (LSCs) [10,11]. Therefore, ROS including NO in the LEC may play an important role for elucidating the local mechanisms of functional and structural luteolysis in the bovine CL.…”