The regulation of oxytocin gene expression in early bovine luteal cells
Abstract
The oxytocin gene is maximally expressed in the cells of the early bovine corpus luteum (1–5 days post-ovulation) and provides an excellent marker for luteinization, having been up-regulated in vivo at ovulation. However, it is down-regulated again later in the luteal phase. To help understand the mechanisms involved in regulating this gene, and hence differentiation in the early bovine corpus luteum, oxytocin secretion into the medium as well as oxytocin mRNA were measured in serum-free cultures of early luteal cells in the presence or absence of various effectors. Insulin-like growth factor I (IGF-I) deferred the endogenous down-regulation of the gene and hence increased oxytocin peptide secretion in the first days of culture. Prostaglandin F2α had no influence on oxytocin mRNA levels but reduced the stimulatory effect of IGF-I on peptide secretion, indicating an effect at the post-transcriptional level. Oestradiol had no effect either on oxytocin mRNA levels or on oxytocin secretion.
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Cited by (21)
Influence of noradrenaline on progesterone synthesis and post- translational processing of oxytocin synthesis in the bovine corpus luteum
1999, TheriogenologyNoradrenaline (NA) influences secretory function of the bovine corpus luteum (CL), stimulating secretion of progesterone and ovarian oxytocin (OT). To study whether NA is able to stimulate progesterone synthesis and to affect post-translational OT processing, different doses of NA alone or in combination with different doses of OT were added to bovine CL slices from 8 to 13 d of the estrous cycle. To determine which receptors NA affects, and if dopamine (DA) also affects CL function, we used NA or DA combined with a β-antagonist (propranolol). The results indicated that NA stimulates both luteal progesterone and OT content; furthermore, it increased the activity of 3β-hydroxysteroid dehydrogenase (3β-HSD) and peptidyl glycine-a-amidating mono-oxygenase (PGA), terminal enzymes in synthesis of these 2 hormones. The stimulating effect of NA was inhibited by propranolol and by pre-treatment of CL slices with high OT doses. Post-translational processing of OT synthesis by PGA activation was also stimulated by DA, but this effect was inhibited by 0-receptor blocker. Thus DA acts in CL as a NA precursor. In conclusion, it can be assumed that the noradrenergic system affects CL secretory function on different levels of regulation. Furthermore, a high concentration of OT in CL prevents NA from activating PGA and thus decreases post-translational OT synthesis.
The role of sex steroids in the oxytocin hormone system
1999, Molecular and Cellular EndocrinologyThe sex steroids and the peptide hormone oxytocin are both ancient modulators of the reproductive system of most metazoan species responsible for tissue differentiation and acute events respectively. In vivo experimentation implies estrogenic control of both the oxytocin (OT) gene and that for its receptor (OTR). Yet neither gene promoter appears able to bind classic estrogen-dependent nuclear receptors (ER) in vitro. The literature is confused by some transfected cell culture experiments which suggest that the human and rat OT gene promoter can be regulated by both ERα and ERß through a major hormone response element at −160 bp upstream of the transcription start site. These findings depended, however, upon the presence of a high molar excess of the nuclear estrogen receptor. The current consensus suggests that the sex steroids are acting indirectly on both the OT and OTR genes, possibly involving intermediate transcription factors or cofactors. They may also act upon the OTR at the cell membrane, though more study is needed before the few current observations can be generalized. Due to the OT system being so ancient and fundamental to all aspects of reproduction, it is likely that the mechanisms by which the sex steroids influence this system are going to be of general importance to many other basic aspects of reproductive control.
Oxytocin secretion by cells from bovine corpora lutea destined to be normal or short-lived
1996, Animal Reproduction ScienceThe working hypothesis for this study was that oxytocin (OT) production is greater in bovine luteal cells destined to be short-lived compared with cells from corpora lutea (CL) of a normal estrous cycle, and that OT secretion is dependent on the lipoprotein environment. Cultures of luteal cells were established from CL obtained on Day 4 or 10 of a normal estrous cycle (Day 0, day of behavioral estrus), and from CL destined to be short-lived, 4 days after ovulation induction. Mixed luteal cells and enriched cultures of large luteal cells (LLC) were incubated in control medium or medium containing (1) low-density lipoproteins (LDL), (2) high-density lipoproteins (HDL), or (3) both LDL and HDL. Addition of lipoproteins had no effect on OT secretion, regardless of stage of estrous cycle or cell type. Mixed luteal cell cultures obtained from Day 4 short-lived and Day 4 normal CL secreted similar quantities of OT, and both secreted less (P < 0.01) OT than mixed luteal cells from Day 10 normal CL. At 48 h in culture, Day 10 mixed luteal cells secreted more (P < 0.01) OT than Day 4 mixed cells from both short-lived and normal CL. Similarly, enriched cultures of LLC obtained from Day 4 normal CL secreted less (P < 0.01) OT than enriched cultures of LLC from Day 10 normal CL. Accumulation of OT at 48 h was greater (P < 0.01) from Day 10 than from Day 4 enriched cultures of LLC; however, Day 4 large cells secreted more OT late in the culture period (day × time, P < 0.001). The similar secretion profiles exhibited by mixed luteal cells obtained from short-lived and normal CL provide evidence that increased basal oxytocin secretion in vitro is not associated with CL destined to be short-lived; however, an increased capacity to secrete oxytocin by Day 4 enriched cultures of LLC late in the culture period suggests involvement of OT in the luteinization process.
Prostaglandin F<inf>2α</inf>, progesterone and oxytocin production by cultured bovine luteal cells treated with prostaglandin E<inf>2</inf> and pregnancy-specific protein B
1995, ProstaglandinsThe objectives of this experiment were to study the effects of pregnancy-specific protein B (PSPB) and prostaglandin E2 (PGE2) on bovine luteal cell progesterone (P4), prostaglandin F2α (PGF2α) and oxytocin production. Corpora lutea were collected during the mid- (days 10–12; n = 5) or late-luteal (days 17–18; n = 5) stages of the estrous cycle. Luteal cells were dispersed and accessory cells removed. Luteal cells (1.5 × 105) were incubated in a 3 × 3 factorial arrangement and treated with PSPB (0, 2.5, or 5.0 μg) and PGE2 (0, 100, or 200 ng) in 500 μL of Ham's F-12 medium. All cells were incubated for 18 h before adding treatments. Samples were then collected at 6 h and 12 h. During the 18 h pretreatment period, P4, PGF2α, and oxytocin production was similar between the prospective treatment groups. The PSPB failed to increase P4 production. The PGE2 × time interaction showed that P4 increased in response to PGE2 treatment at 6 h (P < 0.001) and 12 h (P < 0.03). Also, the stage × time interaction indicated that mid-stage cells produced more (P < .001) P4 than late-stage cells during the pretreatment period at 6 h and 12 h. The PSPB did not alter PGF2α production by mid-stage cells, but increased (P < .05) PGF2α by late-stage cells. Also, PGE2 stimulated (P < 0.001) PGF2α secretion by both mid- and late-stage cells; luteal cells treated with 200 ng of PGE2 produced more (P < 0.001) PGF2α than 100 ng of PGE2. Oxytocin secretion was not changed by treatment with PGE2 or PSPB. Oxytocin production was greater (P < 0.001) by mid-stage than late-stage cells during the pretreatment period at 6 h and 12 h. Oxytocin production was similar between the 6h and 12 h culture times within stage of the cycle. These data indicate that PSPB does bot change bovine luteal cell P4 or oxytocin production, but elevates PGF2α in late-stage cells. The PGF2 increases both P4 and PGF2α, but does not alter oxytocin production. Lastly, PSPB and PGE2 do not interact to promote P4, PGF2α, or oxytocin production by cultured bovine luteal cells.
The regulation of neurohypophyseal peptide gene expression in gonadal tissues
1993, Regulatory PeptidesEffects of gonadotropins, insulin and insulin-like growth factor I on ovarian oxytocin and progesterone production
1991, Molecular and Cellular EndocrinologyOxytocin is produced in the granulosa-derived cells of the ruminant corpus luteum where its gene is dramatically up-regulated within days of ovulation. Regulation of these processes is poorly understood but oxytocin release can be increased by insulin, insulin-like growth factor I (IGF-I), and gonadotropins. Here we have assessed interactions between these regulatory systems. Follicle-stimulating hormone (FSH), luteinizing hormone (LH) and human chorionic gonadotropin (hCG) caused dose-dependent release of oxytocin from bovine granulosa cells cultured in medium containing 100 ng/ml insulin. The gonadotropins also increased oxytocin mRNA levels and their effects were mimicked by forskolin. The effects of these stimuli on oxytocin and progesterone release were synergistically increased by insulin or IGF-I. Binding studies revealed separate binding sites with characteristics of insulin and IGF-I receptors. Insulin potentiated the effects of hCG and forskolin on oxytocin mRNA levels and release of oxytocin and progesterone in cells from follicles containing > 50 ng/ml estradiol. In cells from follicles containing < 5 ng/ml estradiol these stimuli had little effect on oxytocin release although progesterone release was synergistically increased by insulin and forskolin. The data suggest that gonadotropins regulate oxytocin synthesis and release and that these effects are amplified by insulin or IGF-I acting via their own receptors. Changes associated with maturation of the target cells in vitro appear prerequisite for oxytocin production in response to increased cAMP levels in the presence of insulin or IGF-I.