Abstract.We studied the secretory function of the corpus luteum (CL) in cows following different estrus synchronization protocols. Estrus was synchronized using one (n=4) or two injections (n=5) of prostaglandin F2α (PGF2α; dinoprost), two injections of different analogues of PGF2α (aPGF2α), luprostiol (n=5) and cloprostenol (n=5), at eleven-day intervals, a gestagen implant (norgestomet, n=5, for 10 days) or norgestomet together with a subsequent dinoprost injection on the day of implant removal (n=5). CL samples were collected by ovariectomy on Day 7-8 of the estrous cycle. Luteal strips were stimulated with LH (100 ng/ml) or prostaglandin E2 (PGE2, 10 -6 M) for 24 h in culture media. The progesterone (P4) and PGE2 concentrations in the media were measured by enzyme immunoassay. In the control CL (spontaneous estrus; n=5), LH and PGE2 stimulated P4 and PGE2 (P<0.001). The effects of both factors on P4 were reduced in the CL following dinoprost-and cloprostenol-synchronized estrus (P<0.05) and were absent in the luprostiol-synchronized CL (P>0.05). In the norgestomet-synchronized CL, the stimulatory effects of LH and PGE2 were higher compared with the CL synchronized by aPGF2α (P<0.05). Pharmacological manipulation of the estrous cycle using aPGF2α may cause lower P4 secretion. Estrus synchronization inhibited CL sensitivity to luteotropic factors. Therefore, attention should be focused on the estrous synchronization method in both in vivo and in vitro studies of CL functions in cattle. Key words: Cattle, Corpus luteum (CL), Estrus synchronization, Progesterone, Prostaglandin E2 (PGE2), Prostaglandin F2α (PGF2α) analogue (J. Reprod. Dev. 55: [170][171][172][173][174][175][176] 2009) he physiological processes of corpus luteum (CL) formation, growth and maintenance might be regulated by many different factors including luteinizing hormone (LH) and prostaglandin (PG)s [1,2]. After ovulation, as the CL forms from the wall of the ruptured follicle, it grows and rapidly vascularizes [3]. The CL is a complex tissue composed of parenchymal (steroidogenic) and nonparenchymal (fibroblast, vascular smooth muscle, pericyte and endothelial) cells [3,4]. Disturbances in physiological conditions and pharmacological manipulations during follicle growth and maturation, ovulation and as well during early CL formation influence the future secretory function of this new formed endocrine gland.The main function of the CL is secretion of progesterone (P4), an important hormone for the establishment and maintenance of a successful pregnancy [1,2,5]. In domestic animals, LH, which is released in a pulsatile fashion from the anterior pituitary, is one of the most potent regulators of P4 production [6]. LH stimulates basal P4 production in small luteal cells via the LH receptor. In addition to pituitary LH, intraluteal substances produced by the component cells of the CL play important roles in regulating P4 production during the luteal stages and pregnancy [1,2,7]. Arachidonic acid metabolites, such as PGE2 and PGI2, have been prop...

Interleukin-1 (IL1) has been shown to be a potent stimulator of prostaglandin (PG) production in bovine endometrium. The aim of the present study was to determine the cell types in the endometrium (epithelial or stromal cells) responsible for the secretion of PGE2 and PGF2a in response to IL1A, and the intracellular mechanisms of IL1A action. Cultured bovine epithelial and stromal cells were exposed to IL1A or IL1B (0 . 006-3 . 0 nM) for 24 h. IL1A and IL1B dose-dependently stimulated PGE2 and PGF2a production in the stromal cells, but not in the epithelial cells. The stimulatory effect of IL1A (0 . 06-3 . 0 nM) on PG production was greater than that of IL1B.The stimulatory actions of IL1A on PG production was augmented by supplementing arachidonic acid (AA). When the stromal cells were incubated with IL1A and inhibitors of phospholipase (PL) C or PLA2 (1 mM; anthranilic acid), only PLA2 inhibitor completely stopped the stimulatory action of IL1A on PG production. Moreover, a specific cyclooxygenase-2 (COX2) inhibitor blocked the stimulatory effect of IL1A on PG production. IL1A (0 . 06 nM) promoted COX2 and microsomal PGE synthase-1 (PGES1) gene and its protein expression. The expression of COX1, PGES2, PGES3, and PGF synthase (PGFS) mRNA was not affected by IL1A in the stromal cells. The overall results indicate that 1) the target of IL1A and IL1B for stimulating both PGE2 and PGF2a production is the stromal cells, 2) IL1A is a far more potent stimulator than IL1B on PG production in stromal cells, 3) the stimulatory effect of IL1A on PG production is mediated via the activation of PLA2 and COX2, and (4) IL1A induced PG production by increasing expressions of COX2 and PGES1 mRNAs and their proteins in bovine stromal cells.

Abstract. To determine whether glucocorticoids affect the function of the bovine corpus luteum (CL) during the estrous cycle and early pregnancy, we examined the effects of exogenous cortisol or reduced endogenous cortisol on the secretion of progesterone (P4) and on pregnancy rate. In preliminary experiments, doses of cortisol and metyrapone (an inhibitor of cortisol synthesis) were established (n=33). Cortisol in effective doses of 10 mg blocked tumor necrosis factor-induced prostaglandin F 2α secretion as measured by its metabolite (PGFM) concentrations in the blood. Metyrapone in effective doses of 500 mg increased the P4 concentration. Thus, both reagents were then intravaginally applied in the chosen doses daily from Day 15 to 18 after estrus (Day 0) in noninseminated heifers (n=18) or after artificial insemination (n=36). Pregnancy was confirmed by transrectal ultrasonography between Days 28-30 after insemination. Plasma concentrations of P4 were lower in cortisol-treated heifers than in control heifers on Days 17 and 18 of the estrous cycle (P<0.05). However, the interestrus intervals were not different between control and cortisol-treated animals (P>0.05). Moreover, metyrapone increased P4 and prolonged the CL lifespan in comparison to control animals (P<0.05). Interestingly, in inseminated heifers, cortisol increased the pregnancy rate (75%) compared with control animals (58%), whereas metyrapone reduced the pregnancy rate to 16.7% (P<0.05). The overall results suggest that cortisol, depending on the physiological status of heifers (pregnant vs. nonpregnant), modulates CL function by influencing P4 secretion. Cortisol may have a positive influence on CL function during early pregnancy, leading to support of embryo implantation and resulting in higher rates of pregnancy in heifers. Key words: Cattle, Cortisol, Early pregnancy, Estrous cycle, Progesterone (J. Reprod. Dev. 58: [223][224][225][226][227][228][229][230] 2012) G lucocorticoids (GCs) are involved in many physiological processes [1,2], including female reproductive functions [3] in rabbits [4], ewes [5] and humans [6]. Cortisol, an active GC, is an anti-inflammatory agent that acts to modulate the production and action of cytokines and prostaglandins required for ovulation, luteolysis, embryo implantation, fetal growth and placental development [3,7]. It is synthesized from cholesterol in the adrenal cortex and is locally regulated by 11β-hydroxysteroid dehydrogenases (11β-HSDs) [8]. The biological action of GCs is mediated through the activation of intracellular GR receptors (GC-R). Two isoforms of GC-R, GC-Rα and GC-Rβ, have been identified [9,10]. Access of GCs to GC receptors in target tissues is regulated by two 11β-HSDs, bidirectional 11β-HSD type 1 (11β-HSD1) that mainly converts cortisone to active cortisol [11] and 11β-HSD type 2 (11β-HSD2) that inactivates cortisol to cortisone [12]. Although both 11β-HSDs and GC receptors are expressed in the bovine corpus luteum (CL) [13,14] and endometrium [8] throughout the estrous cycle and ea...