Molecular determinants of a competent bovine corpus luteum: first- vs final-wave dominant follicles.

Reproductive management in cattle requires the synchrony of follicle development and oestrus before insemination. However, ovulation of follicles that have not undergone normal physiological maturation can lead to suboptimal luteal function. Here, we investigated the expression of a targeted set of 47 genes in (a) a first-wave vs final-wave dominant follicle (DF; the latter destined to ovulate spontaneously) and (b) 6-day-old corpora lutea (CLs) following either spontaneous ovulation or induced ovulation of a first-wave DF to ascertain their functional significance for competent CL development.

A PPAR-independent pathway to PUFA-induced COX-2 expression.

Polyunsaturated fatty acids (PUFAs) induce COX-2 in bovine endometrial stromal cells through activation of peroxisome-proliferator-activated receptor alpha (PPARalpha). We have investigated alternative (PPAR-independent) pathways to COX-2 induction using a reporter construct driven by a COX-2 gene promoter sequence lacking a PPAR response element. This construct was induced by PUFAs, but not by PPAR agonists.

Control of cyclic AMP concentration in bovine endometrial stromal cells by arachidonic acid.

Second messenger signalling through cyclic AMP (cAMP) plays an important role in the response of the endometrium to prostaglandin (PG) E(2) during early pregnancy. Arachidonic acid, which is a by-product of the luteolytic cascade in ruminants, is a potential paracrine signal from the epithelium to the stroma. We investigated the effects of arachidonic acid on the response of the stroma to PGE(2).

Peroxisome-proliferator-activated receptors and the control of levels of prostaglandin-endoperoxide synthase 2 by arachidonic acid in the bovine uterus.

Arachidonic acid is a potential paracrine agent released by the uterine endometrial epithelium to induce PTGS2 [PG (prostaglandin)-endoperoxide synthase 2] in the stroma. In the present study, bovine endometrial stromal cells were used to determine whether PTGS2 is induced by arachidonic acid in stromal cells, and to investigate the potential role of PPARs (peroxisome-proliferator-activated receptors) in this effect. Arachidonic acid increased PTGS2 levels up to 7.

Ligand-independent activation of steroid receptors.

In several transformed cell lines, the growth factors IGF-I and epidermal growth factor (EGF) activate second messenger systems that cause the phosphorylation of the estrogen receptor (ER). One kinase catalysing receptor phosphorylation is mitogen activated protein (MAP) kinase, and the result of phosphorylation is an increase in receptor transactivation function. EGF and IGF-I, secreted locally and systemically, are involved in uterine-conceptus interactions in early pregnancy, and therefore it is of interest to determine whether these growth factors affect ER function in the uterus.

The effects of lipopolysaccharide and interleukins-1alpha, -2 and -6 on oxytocin receptor expression and prostaglandin production in bovine endometrium.

Up-regulation of endometrial oxytocin receptor (OTR) expression followed by an increase in pulsatile endometrial prostaglandin (PG) F(2alpha) secretion causes luteolysis in cattle. Inhibition of luteolysis is essential for the maternal recognition of pregnancy but also occurs in association with endometritis. The factors regulating OTR expression at this time are unclear.

Acute effects of interferon on estrogen receptor function do not involve the extracellular signal-regulated kinases p42mapk and p44mapk.

Exposure to type I interferons (IFN) increased estrogen receptor (ER) ligand binding and induced protein kinase C (PKC) translocation within 30 min but had no effect on net incorporation of [32P] into ER in Madin Darby bovine kidney (MDBK) cells. Ligand binding was also increased within 30 min by phorbol ester and the protein phosphatase inhibitor okadaic acid. Mitogen-activated protein (MAP) kinase phosphorylation was initially inhibited between 2 and 30 min and subsequently activated between 30 and 60 min after treatment with IFN.

Structure of an ovine interferon receptor and its expression in endometrium.

A sheep type I interferon receptor (oIFNAR1) cDNA was isolated from a lambda-ZAP library using a reverse transcription (RT)-PCR product probe generated from oestrous endometrial RNA. The oIFNAR1 cDNA was 79, 66 and 95% homologous to human, murine and bovine IFNAR1 cDNAs respectively. The encoded receptor was a 560-amino acid transmembrane protein 80, 66 and 95% similar to human, murine and bovine IFNAR1 respectively.

Absence of the oxytocin-induced prostaglandin F2 alpha secretory response in uterus from ovariectomized ewes and activation of the response in vitro.

Oxytocin-induced prostaglandin F2 alpha (PGF2 alpha) responses were measured in explants of uterus from ovariectomized ewes on the day of tissue collection or after culture for 72 h in the presence or absence of oestradiol-17 beta (100 nmol/l). Oxytocin receptor binding activity was 210 +/- 47 fmol [3H]oxytocin bound per mg protein in fresh tissue and 89 +/- 24 and 90 +/- 17 fmol/mg in tissue cultured with control medium or with oestradiol respectively (means +/- S.E.

Role of protein kinase C in the inhibitory action of trophoblast interferons on expression of the oxytocin receptor in sheep endometrium.

PhosphoIipid/Ca(2+) -dependent protein kinase C (PKC) and oxytocin receptor were measured in sheep endometrial explants after culture for up to 96 h. Oxytocin receptor binding and PKC activity were reduced by up to 90% in explants exposed to recombinant ovine trophoblast interferon (rolFN-τ), recombinant bovine IFN-α(1) or ovine conceptus secretory proteins (a source of IFN-τ). Inhibition occurred in both caruncular and intercaruncular endometrium taken between days 7 and 10 of the oestrous cycle and in intercaruncular (but not caruncular) endometrium on day 6.

Oxytocin receptor binding activity in cultured ovine endometrium.

Oxytocin receptor binding activity in explants of caruncular and intercaruncular endometrium collected from luteal phase ewes increased during culture. An initial rise in binding activity occurred during the first 24 h of culture in both tissues; binding activity in intercaruncular endometrium continued to increase until day 6, remained unchanged on day 8 and had decreased by day 10 of culture. The maximum concentration of receptors in caruncular endometrium was significantly lower than that in intercaruncular endometrium (P < 0.

Effect of ovarian hormones on oxytocin receptor concentrations in explants of uterus from ovariectomized ewes.

The effects of oestradiol, progesterone, oxytocin and combinations of these hormones on oxytocin receptor binding in explants of uteri from ovariectomized ewes were determined. Receptor binding remained unchanged after 96 h in culture in control medium. Oestradiol at concentrations of 1 pmol-10 mumol l-1 did not alter receptor binding activity in tissue cultured for 96 h, but at 100 mumol l-1 oestradiol significantly reduced (P < 0.

Effect of continuous infusion of oxytocin on ovarian function and uterine oxytocin receptor concentration in the cyclic ewe.

Intact cyclic ewes have been used in experiments designed to examine the mechanism by which uterine oxytocin receptor synthesis is controlled during the oestrous cyclic. Previous experiments have shown that the prostaglandin F2 alpha analogue cloprostenol is luteolytic in ewes receiving oxytocin by continuous intra-venous infusion. When ewes receiving oxytocin are given cloprostenol uterine oxytocin receptor concentrations are raised, whereas in animals receiving oxytocin alone, they remain low.

Oxytocin delays oestradiol-induced luteolysis but does not affect oestradiol-induced luteinizing hormone secretion in the ewe.

Circulating concentrations of progesterone, the prostaglandin F2 alpha (PGF2 alpha), metabolite 13,14-dihydro-15-keto PGF2 alpha (DHKF2 alpha) and luteinizing hormone (LH) have been measured in cyclic ewes receiving a continuous infusion of oxytocin, in order to investigate the effect of maintained concentrations of circulating oxytocin on the luteolytic action of oestradiol-17 beta. Oxytocin (3 nmol h-1 intravenously) was given from Day 7 until Day 17 after oestrus with oestradiol-17 beta (2.76 mumol, intramuscularly in sesame oil, 0.

Prostaglandin-induced secretion of oxytocin and prolactin in red (Cervus elaphus) and Pere David's (Elaphurus davidianus) deer hinds: evidence for oxytocin of luteal origin.

Peripheral plasma concentrations of oxytocin in female red deer during the luteal phase of the oestrous cycle (9.3 +/- 2.1 fmol/ml) exceeded those in the follicular phase (3.

Effect of continuous infusion of oxytocin on prostaglandin F2 alpha secretion and luteolysis in the cyclic ewe.

Circulating concentrations of 13,14-dihydro-15-keto PGF2 alpha (DHKF2 alpha), luteinizing hormone (LH) and prolactin (PRL) have been measured in cyclic ewes treated with continuous infusions of oxytocin, in order to investigate the mechanism by which the treatment delays luteal regression. Continuous infusion of oxytocin reduced prostaglandin F2 alpha (PGF2 alpha) secretion but had no detectable direct effect on LH or PRL. Oxytocin (3 nmol h-1 i.

Post-translational processing of oxytocin-neurophysin prohormone in the ovine corpus luteum: activity of peptidyl glycine alpha-amidating mono-oxygenase and concentrations of its cofactor, ascorbic acid.

Peptidyl glycine alpha-amidating mono-oxygenase (PGA), the terminal enzyme in the pathway of oxytocin synthesis, was measured in extracts of ovine corpora lutea throughout the oestrous cycle. Activity of PGA was low early in the cycle but increased between days 2 and 10 (from 2.3 to 9.

Mesotocin and luteal function in macropodid marsupials.

Pituitary glands and corpora lutea collected at various stages of the reproductive cycle of the tammar wallaby (Macropus eugenii), were extracted and fractionated by high-performance liquid chromatography, and specific radioimmunoassays were used to measure mesotocin ([Ile8]-oxytocin) and oxytocin. Mesotocin, but not oxytocin, was identified in extracts of pituitary; the mean concentration of mesotocin in this tissue was 0.75 nmol/g wet weight.

Stimulation of phosphoinositide hydrolysis by oxytocin and the mechanism by which oxytocin controls prostaglandin synthesis in the ovine endometrium.

Slices of caruncular endometrium from steroid-treated ovariectomized sheep were incubated with myo-[2-3H]inositol to label tissue phosphatidylinositol. Effects of oxytocin were determined on the rate of incorporation of radioactivity into phosphatidylinositol and on the hydrolysis of phosphoinositides to inositol phosphates and diacylglycerol. Incorporation of radioactivity into phosphatidylinositol was linear during 2 h incubations; 10(-7) M (100 nM)-oxytocin caused a 2.

Transient uterine refractoriness after oxytocin administration in ewes.

Steroid-primed, ovariectomized ewes were treated intravenously with 2 doses of 1 microgram oxytocin at intervals of 1, 2, 4 or 6 h. The initial dose resulted in increases in 13,14-dihydro-15-keto-PGF-2 alpha in the peripheral circulation from 173 to 667 pg/ml within 5 min; subsequent doses caused responses of 23 +/- 1, 23 +/- 6, 54 +/- 12 and 62 +/- 10% respectively of the initial dose. Concentrations of oxytocin receptor in myometrium, caruncular endometrium and intercaruncular endometrium were, respectively, 185 +/- 33, 128 +/- 7 and 105 +/- 14 fmol/mg protein at 2 h after saline injection and 147 +/- 27, 195 +/- 52 and 170 +/- 50 fmol/mg protein at 2 h after administration of 1 microgram oxytocin.

Ovarian oxytocin and the maternal recognition of pregnancy.

The secretion of oxytocin by the corpus luteum is thought to stimulate the episodic release of PGF-2 alpha from the uterus, thereby contributing to luteolysis. In pregnancy corpus luteum function is maintained, and secretion of oxytocin, or its actions on the uterus, appear to be inconsistent with the successful establishment of gestation. Protection against the effects of oxytocin is ensured by a number of mechanisms, including the cessation of luteal oxytocin secretion, which is evident by Day 20 after mating in sheep, and the maintenance of low levels of the oxytocin receptor in the uterus.

Ovarian peptides: role of luteal oxytocin in the control of estrous cyclicity in ruminants.

The peptide hormone oxytocin has long been known to affect the life-span of the corpus luteum on administration. There is now a good deal of evidence to suggest that endogenous oxytocin may also be involved in this process, probably through a stimulatory action on uterine prostaglandin synthesis. Recently the role of oxytocin in controlling estrous cyclicity has been given added prominence by the discovery that oxytocin is secreted by the ruminant corpus luteum.