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Biomedical subjects

L Myatt

Publications and source records attributed to L Myatt.

At least 73 records · Page 4Linked to original sources
PubMed1990

Mechanisms of parturition: the transfer of prostaglandin E2 and 5-hydroxyeicosatetraenoic acid across fetal membranes.

Prostaglandin E2 production by amnion is thought to be an important event in the onset of human labor. It has been suggested that 5-hydroxyeicosatetraenoic acid, also produced in the amnion, may mediate prelabor contractions. For either of these compounds to play a paracrine role they need to cross the chorion, which has a high capacity to metabolize prostaglandins. With the use of an in vitro system we have shown that both prostaglandin E2 and 5-hydroxyeicosatetraenoic acid cross either amnion or intact amnion-chorion-decidua at a rate similar to that of an extracellular marker sucrose. Analysis by high performance liquid chromatography revealed that at physiologic concentrations neither prostaglandin E2 nor 5-hydroxyeicosatetraenoic acid were metabolized by amnion alone. Moreover, 100% of the 5-hydroxyeicosatetraenoic acid and 72% of the prostaglandin E2 remained in the active form after passage across intact amnion-chorion-decidua. There did not appear to be any difference in the rate of transfer or permeability of the membranes before or after spontaneous labor. We conclude that both 5-hydroxyeicosatetraenoic acid and prostaglandin E2 synthesised in the amnion can cross the membranes by diffusion through the extracellular space, remaining largely unmetabolized, and may play a role in the onset of human labor.

Biological Transport↗
PubMed1990

Production of prostaglandin E2 by human amnion in vitro in response to addition of media conditioned by microorganisms associated with chorioamnionitis and preterm labor.

To examine the potential role of bacterial infection in the cause of spontaneous preterm labor, human amnion cells in tissue culture were exposed to medium conditioned by culturing each of 21 microorganisms previously found in association with chorioamnionitis and preterm labor. At a final concentration of 0.1% bacterial conditioned medium, a significant stimulation of prostaglandin E2 production from amnion cells was observed for this range of microorganisms. Conditioned medium obtained from culturing Bacteroides fragilis caused a dose-related increase in prostaglandin production, final concentrations of 0.02% to 0.1% being stimulatory but greater concentrations (0.1% to 10%) causing a progressive inhibition of prostaglandin synthesis. A similar concentration-related response in which stimulation was followed by inhibition occurred on addition of increasing concentrations of phospholipase A2 to amnion cells. These data suggest that bacterial phospholipase may release arachidonic acid from amnion leading to prostaglandin E2 synthesis, but excessive addition of phospholipase and consequent increased arachidonic acid availability may give rise to substrate inhibition of cyclooxygenase enzyme and inhibit prostaglandin E2 synthesis. Overall it appears that a wide variety of microorganisms associated with preterm labor may secrete phospholipase, which liberates amnion arachidonic acid for conversion to the oxytocic agent prostaglandin E2.

Amnion↗
PubMed1990

Regulation of prostaglandin E2 synthesis in human amnion by protein kinase C.

A role for protein kinase C (PKC) in mediation of prostaglandin E2 synthesis in human amnion cells has been suggested. We have investigated the specificity of the stimulation of PGE2 synthesis by phorbol esters and employed putative PKC inhibitors to demonstrate the specificity of PKC stimulation. The three phorbol esters, tetradecanoyl phorbol-13-acetate, phorbol-12,13-dibutyrate and phorbol-12,13-didecanoate gave concentration-dependent (10(-10)-10(-7)M) increases in PGE2 synthesis when added to amnion cells in monolayer, however, no effect was seen with the structurally similar phorbols phorbol-12-13-diacetate, 4 alpha phorbol-12-13-didecanoate or phorbol base. The stimulatory effect of TPA (10(-8)M) on amnion PGE2 synthesis could be prevented by coincubation with the putative protein kinase C inhibitors 1-(5-isoquinoline sulphonyl) piperazine, 1-0-octadecyl-2-0-methyl-rac-glycero-3-phosphocholine, sphingosine and chlopromazine at concentrations of 10(-6)-10(-4)M. Addition of the transcription inhibitor actinomycin D at 10(-6)-10(-5)M prevented TPA (10(-8)M)-induced PGE2 synthesis. However, paradoxically, a further increase in PGE2 synthesis was seen when 10(-9)-10(-7)M actinomycin D was added together with TPA. The phospholipase A2 inhibitor quinacrine was able to prevent the TPA-induced increase in PGE2 synthesis even in the presence of exogenous arachidonic acid suggesting that phospholipase A2 may be a target for PKC action.

Amnion↗
PubMed1990

Pathways of arachidonic acid metabolism in human amnion cells at term.

We have compared the metabolism of (3H) arachidonic acid by monolayers of human amnion, cells obtained prior to or following labor at term. Radiolabel was either added exogenously or previously incorporated into cellular phospholipid pools to compare metabolism of arachidonic acid from different substrate sources. Cells obtained both prior to and following labor synthesized metabolites co-chromatographing on HPLC with di- and mono-HETEs and also a metabolite with polarity corresponding to a epoxyeicosatrienoic acid. Both types of cells were able to synthesize PGE2 when (3H) arachidonic acid was added exogenously. However, only those cells obtained following labor synthesized PGE2 from (3H) arachidonic acid incorporated into intracellular pools. These findings suggest that the cyclooxygenase and PGE2 isomerase enzymes are present in amnion prior to delivery but that exogenous arachidonic acid would be required for PGE2 synthesis at that time as the enzymes do not appear to be linked to a source of endogenous arachidonic acid. At the time of parturition, there may be a switching on of an enzyme system to generate arachidonic acid from intracellular pools specifically for PGE2 synthesis or alternatively coupling of such a system to a cyclooxygenase-PGE2 isomerase system resulting in PGE2 synthesis. These findings raise intriguing new possibilities for the regulation of eicosanoid synthesis in amnion which may include membrane topography, substrate pool-enzyme linking and regulation of specific phospholipase enzymes.

Amnion↗
PubMed1987

Preterm labor: stimulation of arachidonic acid metabolism in human amnion cells by bacterial products.

There is a strong association between preterm labor and infection. Some potentially pathogenic bacteria have phospholipase activity, and it has been suggested that release of phospholipase from these organisms may increase prostaglandin E2 synthesis in amnion cells and hence initiate preterm labor. In this study we established monolayer amnion cell cultures from tissue collected at elective cesarean section at term before labor. Cells were prelabeled with tritiated arachidonic acid and then further incubated after addition of 2%, 5%, or 10% (vol/vol) filtered medium in which either group B beta-hemolytic streptococcus, Streptococcus viridans, Escherichia coli, Bacteroides fragilis, or Lactobacillus had been growing. Tritiated arachidonic acid and its metabolites released by the amnion cells in these or control incubates were extracted from culture medium and separated by high-performance liquid chromatography. Addition of conditioned medium from each of the organisms with the exception of Lactobacillus caused an increase in overall arachidonic acid metabolism. There was an increase in the ratio of cyclooxygenase to lipoxgenase metabolism and in prostaglandin E2 production in particular when compared to controls. The profile of arachidonic acid metabolism in amnion cells following addition of filtered bacterial medium resembled that obtained from amnion cells cultured following spontaneous labor. We suggest that abnormal bacterial colonization of the genital tract may lead to an increase in arachidonic acid metabolism in amnion cells with an increase in prostaglandin E2 production and the consequent initiation of preterm labor.

Amnion↗
PubMed1987

The effects of lipoxygenase metabolites of arachidonic acid on human myometrial contractility.

The effects of the lipoxygenase products of arachidonic acid, 5- and 12-hydroxyeicosatetraenoic acid (5- and 12-HETE) and leukotriene B4 (LTB4), on the spontaneous contractility of lower uterine segment human myometrial strips obtained prior to labour have been studied in vitro. 5-HETE gave a dose- dependent (10-500ng) increase in both the rate of contractions and overall contractility of myometrial strips while 12-HETE and LTB4 had no effect at the same concentrations. Prostaglandin F2 alpha (50ng) contracted all myometrial strips in a similar pattern to 5-HETE but was approximately 10 times more potent. The effect of 5-HETE may be direct or perhaps indirect via interaction with the cyclo-oxygenase pathway. The findings do not disprove the contention that the onset of parturition may be characterised by a switch in arachidonic acid metabolism in intra-uterine tissues from lipoxygenase to cyclo-oxygenase products.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1987

Oestrogen receptor in the granulosa cell during postnatal development of the rat ovary.

Numbers of granulosa cells obtained from follicles of immature rats increased from 1.6 X 10(5) cells/ovary on day 8 to 7.1 X 10(6) cells/ovary on day 40 of age, the day of vaginal opening and first pro-oestrus. Very high levels of cytosol oestrogen receptor were found on day 8 (175,000 sites/cell) but by day 19 20,000 sites/cell were found. Nuclear receptor concentrations were highest on day 12 (5400 +/- 1470 (S.D.)sites/cell) and again on day 21 (5400 +/- 2300 sites/cell). After day 21 both cytosol and nuclear oestrogen receptor concentrations fell and remained low until nuclear concentrations rose at day 40. Two consecutive daily injections of FSH/LH (5 i.u.) increased cell number over control in animals killed on day 22, gave no significant alteration in animals killed on day 26 or 28 but decreased numbers in animals aged 32 and 35 days. Only on day 22 was the increase in cell number associated with an increase in nuclear oestrogen receptor concentrations. Indeed on days 32 and 35 increased nuclear receptor concentrations were associated with a decreased cell number.

Animals↗
PubMed1986

Characterisation of non-activated and activated estrogen- and antiestrogen-receptor complexes by high performance ion exchange chromatography.

The ionic species of cytosol estrogen receptors from mature rat uteri have been compared by HPIEC on a SynChrom AX-1000 column when complexed with either [125I]iodoestradiol, [3H]estradiol or [3H]4-hydroxy tamoxifen. Three species of receptors (isoforms) each suppressible by excess competitor were fractionated at identical salt concentrations regardless of ligand employed. One species eluted in the column void volume (10 mM) and the others at congruent to 90 mM and congruent to 155 mM phosphate. Activation of receptor complexes by increasing time of incubation with ligand from 1 to 24 h at 4 degrees C or addition of 10 mM GTP increased the proportion of the congruent to 90 mM species for all 3 ligands. The addition of 10 mM molybdate to homogenization and HPIEC buffers resulted in only two species being resolved at 10 and 110 mM phosphate. These species were again identical regardless of ligand employed. Increasing concentrations of estradiol (1-40 nM) tamoxifen (20 nM-4 microM) and 4-hydroxy tamoxifen (2-400 nM) were able to compete for binding of [125I]iodoestradiol to each of the three ionic species. Binding to each species was inhibited equally by each concentration of competitor. There was no preferential or unique association of estrogen or antiestrogen with any of the ionic species and all ligands gave identical ionic species of non-activated and activated receptor complexes.

Animals↗
PubMed1986

Uptake, transfer and metabolism of prostaglandin E2 in the isolated perfused human placental cotyledon.

(3H) PGE2 uptake and transfer in the isolated perfused human placental cotyledon was assessed by a single pass paired isotope dilution technique utilising (14C) sucrose as an extracellular marker. Metabolism of (3H) PGE2 was measured by analysing maternal and fetal effluents from perfused human placental cotyledons after bolus injection of (3H) PGE2 into either the maternal or fetal sides. Maximal uptake of (3H) PGE2 was greater on the maternal (81 +/- 8%) than the fetal sides (42 +/- 12%) and showed saturation with increasing concentrations of PGE2 only on the fetal side with an apparent Km of 12 +/- 4.9 nmol/l and vmax of 1.5 +/- 0.2 pmol/min/g. Total recoveries of (3H) PGE2 were 84.6 +/- 11.8% and 32.6 +/- 6.3% of the injected dose after injection on the fetal and maternal sides respectively. Transfer of (3H) PGE2 was the same in both directions being 6.4 +/- 1.2% of the injected dose in the fetal-maternal direction and 5.8 +/- 2.7% of the injected dose in the maternal-fetal direction. Metabolism was greater on the maternal side (35% of injected (3H) PGE2) than the fetal side (18% of injected (3H) PGE2) and was principally to the 13,14-dihydro-15-keto-PGE2 metabolite. Metabolism of (3H) PGE2 after passage across the placenta was the same in both directions and was of the order of approximately 60%.

Biological Transport↗
PubMed1986

The actions of prostaglandins and their interactions with angiotensin II in the isolated perfused human placental cotyledon.

The prostaglandins PGE1, PGE2, PGD2, PGF2 alpha, U46619 and 6 beta-PGI1 were administered as bolus injections both separately and in combination with angiotensin II into the fetal circulation of isolated human placental cotyledons perfused in vitro. PGF2 alpha and PGD2 caused small dose-dependent increases in fetal perfusion pressure when compared with U46619 which acted as an extremely potent vasoconstrictor of the fetal-placental vasculature. PGE1 caused very small dose-dependent decreases in fetal perfusion pressure when injected on its own. In combination with angiotensin II, PGE1, PGD2 and 6 beta-PGI1 caused significant, dose-related attenuations of the angiotensin II vasoconstrictive response whereas PGE2, PGF2 alpha and U46619 potentiated the response. Injections of angiotensin II after the infusion of indomethacin into the fetal circulation resulted in a potentiation of angiotensin II induced vasoconstriction. The results indicate that prostaglandins exert their effects on the fetal-placental circulation by modulating the actions of angiotensin II.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1985

Activation of oestrogen receptor complexes: evidence for the distinct regulation of ligand and oligonucleotide binding sites.

The activation of the rat uterine oestrogen receptor has been measured in vitro by its binding to oligodeoxythymidylate cellulose (oligo(dT] and was found to be sensitive to the time and temperature of prior incubation of cytosol with oestradiol. The presence of 20 mM dithiothreitol promoted receptor activation and was partially inhibited by 10 mM molybdate; molybdate also inhibited the time- and temperature-dependent activation of receptor. The nucleotides GTP, ATP, ADP, CTP and UTP all promoted receptor activation; the effect of GTP was significantly greater than that of ATP. It is unlikely that phosphate donation is involved in receptor activation as the effects of GTP could be reproduced by p[NH]ppG (guanosine 5'-[beta, gamma-imido]triphosphate), while PPi was also effective in activating receptor. The results provide evidence for the distinct regulation of the oligonucleotide- and ligand-binding domains, since manipulations which promoted binding to oligo(dT) did not affect either ligand binding capacity or the rate constant and composition the biphasic dissociation of the ligand receptor complex.

Animals↗
PubMed1985

Prostaglandin production and stimulation by angiotensin II in the isolated perfused human placental cotyledon.

Levels of prostaglandins E and F2 alpha, thromboxane B2, and 6-oxo-prostaglandin F1 alpha were measured by radioimmunoassay in the maternal and fetal effluents of isolated human placental cotyledons perfused in vitro. All prostaglandins measured were released in greater amounts by the maternal side than by the fetal side of the perfused cotyledon although there were no consistent concentration gradients between the two sides. The approximate rank order of prostaglandin release into the maternal side was thromboxane B2 greater than prostaglandin F2 alpha congruent to prostaglandin E congruent to 6-oxo-prostaglandin F1 alpha, and that into the fetal side was thromboxane B2 congruent to prostaglandin F2 alpha congruent to prostaglandin E congruent to 6-oxo-prostaglandin F1 alpha. Injection of angiotensin II (0.5 microgram) into the fetal circulation stimulated prostaglandin E and 6-oxo-prostaglandin F1 alpha but not thromboxane B2 and prostaglandin F2 alpha release into the fetal circulation and had no effect on maternal release. Angiotensin II (0.5 microgram) had no effect on either side of the perfused cotyledon when injected into the maternal circulation. It is proposed that prostaglandin release into both maternal and fetal circulations may be flow-dependent and that the angiotensin II-stimulated release of prostaglandin E and 6-oxo-prostaglandin F1 alpha may serve to modulate the vasoactive actions of angiotensin II on the fetal vasculature.

6-Ketoprostaglandin F1 alpha↗
PubMed1984

The effects of the components of the renin-angiotensin system on the isolated perfused human placental cotyledon.

Angiotensins I, II, and III, renin substrate, and des-Asp1-angiotensin I were injected as a bolus into either the maternal or fetal circulation of human placental cotyledons perfused in vitro. All drugs tested produced dose-related increments in fetal perfusion pressure when injected into the fetal circulation, with the order of potency being angiotensin I approximately equal to angiotensin II approximately equal to angiotensin III greater than or equal to des-Asp1-angiotensin I greater than or equal to renin substrate. The responses to all the drugs could be blocked by the competitive inhibitor of angiotensin II, (Sar1, Ala8)-angiotensin II, but only the actions of angiotensin I, renin substrate, and des-Asp1-angiotensin I could be blocked by angiotensin converting enzyme inhibitor. When the agents were injected into the maternal circulation, only angiotensins II and III caused dose-related increments in fetal perfusion pressure. Possibly, the placenta may be the main site of conversion of angiotensin I to angiotensin II in the fetoplacental unit, and angiotensin II produced by the placenta could act locally to control fetoplacental blood flow.

Angiotensins↗
PubMed1984

Activated oestrogen receptors in breast cancer and response to endocrine therapy.

The status of oestrogen and progesterone receptors has been measured in 147 primary breast tumours. In addition to the measurement of cytoplasmic oestrogen receptors, the ability of these receptors to bind to oligo(dT)-cellulose has been assessed. This indicates the capability for activation of cytoplasmic receptors to a form able to bind in the nuclear compartment in vivo and thus be part of a functional receptor pathway. All the receptor concentrations measured were increased in the postmenopausal group of patients. All nuclear oestrogen receptors in this group were available for labelling at 4 degrees C, in contrast to the premenopausal group. The apparent functionality of the oestrogen receptor pathway could be equally assessed either by the co-presence of cytosol progesterone receptor with nuclear oestrogen receptor (30 or 4 degrees C) or with activated cytosol oestrogen receptor. The presence of activated cytosol oestrogen receptor was as reliable (80%) as the presence of either nuclear oestrogen receptor at 30 (83%) or 4 degrees C (81%) in predicting the response of breast tumours to endocrine therapy.

Adult↗