The regulation of interferon-tau production and uterine hormone receptors during early pregnancy

During early pregnancy the bovine embryo must produce a protein called interferon tau which inhibits the development of the luteolytic mechanism. Failure to inhibit luteolysis is the major cause of pregnancy loss in cows. The embryo must produce sufficient quantities of interferon tau by about day 16 to prevent luteolysis. Its ability to achieve this is largely dependent on the pattern of maternal progesterone production. A late rise in progesterone after ovulation or poor progesterone secretion during the luteal phase results in the development of poor embryos capable of producing little or no interferon tau at the critical time. The embryo inhibits luteolysis by preventing development of oxytocin receptors on the luminal epithelium of the uterine endometrium and thus oxytocin-induced secretion of PGF2 alpha and by the induction of a prostaglandin synthesis inhibitor within the endometrium. In sheep it has been hypothesised that interferon tau acts to inhibit endometrial oestrogen receptors and thus oestrogen-induced up-regulation of oxytocin receptors. In cows, the embryo inhibits the development of oxytocin receptors and the initiation of luteolysis without causing any change in uterine oestrogen receptors. Thus in the cow, the mechanism by which interferon tau inhibits oxytocin receptor development remains to be determined.

Expression of nitric oxide synthase isoforms in pregnant human myometrium

1. Endogenous nitric oxide has been proposed to play a role in the control of myometrial contractility in pregnancy. In this study, the expression, localisation and regulation of nitric oxide synthase (NOS) isoforms have been examined in human pregnant myometrium and cultured human myometrial smooth muscle cells, by immunoblotting, immunohistochemistry and reverse transcription-polymerase chain reaction. 2. Immunoblotting of extracts from freshly isolated myometrial tissue, affinity-enriched for NOS proteins by precipitation with ADP-sepharose, revealed expression of endothelial NOS (eNOS or NOS3) in tissues from preterm, term non-labour and active labour at term. Inducible NOS (iNOS or NOS2) and neuronal NOS (nNOS or NOS1) proteins were not detected at any stage of pregnancy. 3. Immunohistochemical detection showed that expression of eNOS protein was restricted to the endothelium of the myometrial vasculature, with no staining detected in myometrial smooth muscle cells. 4. Messenger RNA for all three NOS isoforms was detected, although iNOS and nNOS mRNAs were detectable only with high cycle number, implying a low copy number. 5. NOS isoforms were not detectable in human myometrial smooth muscle cells cultured from term non-labour pregnancies. Cytokine stimulation of cultured myometrial cells did not induce iNOS expression or nitrite accumulation in the culture medium, although both iNOS protein and nitrite release were detected in the human pulmonary epithelial cell line A549. 6. Levels of eNOS protein and of NOS mRNA expression were not correlated with gestational stage, suggesting that endogenously produced NO is not likely to be a modulator of myometrial tone during human pregnancy.

The role of luteal oxytocin in episodic secretion of prostaglandin F2alpha at luteolysis in the ewe

The role of luteal oxytocin in the generation of luteolytic episodes of prostaglandin F2alpha at luteolysis was investigated. On day 10 of the cycle Dorset ewes underwent either surgical removal of the corpora lutea (lutectomy; n = 4) or sham operation (sham; n = 4). Lutectomised ewes were then administered progesterone by twice daily i.m. injection in corn oil (20 mg/day) until day 14 when treatment was ceased to simulate luteolysis. The concentration of 13, 14 dihydro-15-keto prostaglandin F2alpha (PGFM) was measured in peripheral blood samples collected at 20-min intervals for 8 h on days 12-16 of the cycle. Progesterone and oestradiol concentrations were similar in the two groups over the whole experimental cycle while oxytocin fell dramatically following lutectomy. No prostaglandin F2alpha release episodes were seen on day 12 or 13, while from days 14-16 both groups exhibited a similar episode frequency (lutectomy 0.9/ewe/8 h; sham 0.8/ewe/8 h). Analysis of episode characteristics revealed lower episode amplitude (p<0.05) but longer episode duration (p<0.05) in the lutectomy group. The results demonstrate that a normal frequency of prostaglandin F2alpha release episodes occurs independently of luteal oxytocin secretion. However, luteal oxytocin is involved in regulating the pattern of release, perhaps causing the release of episodes of the magnitude required for the successful completion of luteolysis.

Transmembrane signalling mechanisms regulating expression of cationic amino acid transporters and inducible nitric oxide synthase in rat vascular smooth muscle cells

The signalling mechanisms involved in the induction of nitric oxide synthase and l-arginine transport were investigated in bacterial lipopolysaccharide (LPS)- and interferon-gamma (IFN-gamma)-stimulated rat cultured aortic smooth muscle cells (RASMCs). The expression profile of transcripts for cationic amino acid transporters (CATs) and their regulation by LPS and IFN-gamma were also examined. Control RASMCs expressed mRNA for CAT-1, CAT-2A and CAT-2B. Levels of all three transcripts were significantly elevated in activated cells. Stimulated CAT mRNA expression and l-arginine transport occurred independently of protein kinase C (PKC), protein tyrosine kinase (PTK) and p44/42 mitogen-activated kinases (MAPKs), but were inhibited by the p38 MAPK inhibitor SB203580, which at 3 microM caused maximum inhibition of both responses. Induction of NO synthesis was independent of p44/42 MAPK activation and only marginally dependent on PKC, but was attenuated markedly by the PTK inhibitors genistein and herbimycin A. SB203580 differentially regulated inducible NO synthase expression and NO production, potentiating both processes at low micromolar concentrations and inhibiting at concentrations of >/=1 microM. In conclusion, our results suggest that RASMCs constitutively express transcripts for CAT-1, CAT-2A and CAT-2B, and that expression of these transcripts is significantly enhanced by LPS and IFN-gamma. Moreover, stimulation of l-arginine transport and induction of NO synthesis by LPS and IFN-gamma appear to be under critical regulation by the p38 MAPK, since both processes were significantly modified by SB203580 at concentrations so far shown to have no effect on other signalling pathways. Thus, in RASMCs, the p38 MAPK cascade represents an important signalling mechanism, regulating both enhanced l-arginine transport and induced NO synthesis.

Induction of cyclooxygenase-2 expression in human myometrial smooth muscle cells by interleukin-1beta: involvement of p38 mitogen-activated protein kinase

1. Human myometrial smooth muscle cells (HMSMCs) in culture were exposed to recombinant human interleukin-1beta (IL-1beta, 10 ng ml-1) for 1 to 24 h. Cyclooxygenase-2 (COX-2) mRNA and protein were rapidly induced, with expression sustained at 24 h. 2. Cycloheximide (10 microg ml-1, 6 h) blocked IL-1beta-induced COX-2 protein expression and super-induced COX-2 mRNA expression. Induction of COX-2 mRNA and protein was blocked by dexamethasone (1 microm, 6 h). 3. IL-1beta-induced COX-2 expression was accompanied by a 3-fold increase of prostaglandin E2 release into the culture medium. 4. IL-1beta induced a transient (5-30 min) activation of p42/44 and p38 mitogen-activated protein kinase (MAPK) enzymes in HMSMCs. Activity of p38 MAPK was monitored by in-gel activity of its substrate MAP kinase-activated protein kinase-2 (MAPKAP kinase-2). Induction of MAPKAP kinase-2 activity was prevented by the p38 MAPK inhibitor SB 203580 (10 microm, 5-30 min). 5. COX-2 protein expression detected after 6 h IL-1beta stimulation was blocked by SB 203580 (10 microM). Exposure of HMSMCs to 10 ng ml-1 IL-1beta for only 30 min induced a level of COX-2 protein expression at 6 h culture similar to that detected in cells exposed to the cytokine for 6 h. 6. Exposure of cells to SB 203580 (10 microM during only the first 30 min of IL-1beta stimulation was effective in blocking COX-2 protein expression assayed after 6 h in culture. 7. This study has established that a transient activation of the p38 MAPK cascade is involved in IL-1beta-stimulated COX-2 expression in human myometrial smooth muscle cells. Induction of COX-2 by IL-1beta in HMSMCs provides support for the hypothesis that autocrine prostaglandin signalling in the myometrium, initiated by elevated intrauterine cytokine concentrations, plays a role in regulating myometrial contractility during labour.

Induction of antioxidant stress proteins in vascular endothelial and smooth muscle cells: protective action of vitamin C against atherogenic lipoproteins

Elevated levels of lipid peroxidation and increased formation of reactive oxygen species within the vascular wall in atherosclerosis can overwhelm cellular antioxidant defence mechanisms. Accumulating evidence implicates oxidatively modified low density lipoproteins (LDL) in vascular dysfunction in atherosclerosis and oxidized LDL have been localized with in atherosclerotic lesions. We here report that human oxidatively modified LDL induce expression of 'antioxidant-like' stress proteins in vascular cells, involving increases in the activity of L-cystine transport, glutathione synthesis, heme oxygenase-1 and the murine stress protein MSP23. Moreover, treatment of human arterial smooth muscle cells with the dietary antioxidant vitamin C markedly attenuates adaptive increases in endogenous antioxidant gene expression and affords protection against smooth muscle cell apoptosis induced by moderately oxidized LDL. As vascular cell death is a key feature of atherosclerotic lesions and may contribute to the plaque 'necrotic' core, cap rupture and thrombosis, our findings suggest that the cytoprotective actions of vitamin C could limit plaque instability in advanced atherosclerosis.

Vitamin C protects human vascular smooth muscle cells against apoptosis induced by moderately oxidized LDL containing high levels of lipid hydroperoxides

Vascular cell death is a key feature of atherosclerotic lesions and may contribute to the plaque "necrotic" core, cap rupture, and thrombosis. Oxidatively modified low-density lipoproteins (LDLs) are implicated in the pathogenesis of atherosclerosis, and dietary antioxidants are thought to protect the vasculature against LDL-induced cytotoxicity. Because LDL oxidative modification may vary within atherosclerotic lesions, we examined the effects of defined, oxidatively modified LDL species on human arterial smooth muscle cell apoptosis and the cytoprotective effects of vitamin C. Moderately oxidized LDL (0 to 300 microg protein/mL), which has the highest content of lipid hydroperoxides, induced smooth muscle cell apoptosis within 6 hours, whereas native LDL and mildly and highly oxidized LDL had no effect. Moderately oxidized LDL increased cellular DNA fragmentation, release of fragmented DNA into the culture medium, and annexin V binding and decreased mitochondrial dehydrogenase activity and expression of the antiapoptotic mediator Bcl-x(L). Treatment of cells with native LDL together with the lipid hydroperoxide 13(S)-hydroperoxyoctadeca-9Z,11E-dienoic acid (HPODE, 200 micromol/L, 6 to 24 hours) also induced apoptotic cell death. Pretreatment of smooth muscle cells with vitamin C (0 to 100 micromol/L, 24 hours) attenuated the cytotoxicity and apoptosis induced by both moderately oxidized LDL and HPODE. Our findings suggest that moderately oxidized LDL, with its high lipid hydroperoxide content, rather than mildly or highly oxidized LDL, causes apoptosis of human smooth muscle cells and that vitamin C supplementation may provide protection against plaque instability in advanced atherosclerosis.

Acute activation of Maxi-K channels (hSlo) by estradiol binding to the beta subunit

Maxi-K channels consist of a pore-forming alpha subunit and a regulatory beta subunit, which confers the channel with a higher Ca(2+) sensitivity. Estradiol bound to the beta subunit and activated the Maxi-K channel (hSlo) only when both alpha and beta subunits were present. This activation was independent of the generation of intracellular signals and could be triggered by estradiol conjugated to a membrane-impenetrable carrier protein. This study documents the direct interaction of a hormone with a voltage-gated channel subunit and provides the molecular mechanism for the modulation of vascular smooth muscle Maxi-K channels by estrogens.

Identification of system y+L as the high-affinity transporter for L-arginine in human platelets: up-regulation of L-arginine influx in uraemia

Kinetic studies of L-arginine transport in human platelets have identified a high-affinity, low-capacity transport system [Michaelis-Menten constant (K(m)) about 10 microM] for cationic amino acids that also transports neutral amino acids with high affinity in the presence of Na+ but not K+. These characteristics, together with our kinetic cis-inhibition studies, indicate that saturable L-arginine transport in human platelets is mediated via the system y+L and not the classic cationic transporter system y+. We present here the first evidence that L-arginine transport via system y+L is increased twofold in platelets from patients with chronic renal failure. System y+L has been described in human erythrocytes, peripheral blood mononuclear cells and placenta, and up-regulation of system y+L activity in human platelets could explain the paradox of increased nitric oxide (NO) production by uraemic platelets under conditions of decreased plasma L-arginine and elevated NG-monomethyl-L-arginine (L-NMMA) concentrations.

Bovine viral diarrhea virus: its effects on estradiol, progesterone and prostaglandin secretion in the cow

Bovine viral diarrhea virus (BVDV) is a major cattle pathogen responsible for a spectrum of symptoms, including reproductive failure. This study was designed to establish the effects of BVDV infection on estradiol, progesterone and PGF2alpha secretion in the cow. Seven BVDV-free cows were challenged with non-cytopathogenic BVDV (strain Pe 515: 5x10(6) tissue culture infected dose50) so that peak viremia occurred during the initial phase of luteal development in a synchronized estrous cycle. Ovulation was also synchronized in 7 sham-infected animals. Within 2 wk of inoculation, viremia, leukopenia and serum neutralizing antibodies were recorded in all of the BVDV-infected cows but not the sham-infected animals. Between Day 4 and Day 9 post estrus the BVDV-infected cows had significantly (P<0.01) lower plasma estradiol levels than the sham-infected animals. However, the BVDV infection did not alter rectal temperatures, plasma progesterone concentrations or PGF2alpha secretion 17, 18 and 19 d post estrus. These data highlight a potential causal link between BVDV viremia, endocrine dysfunction and poor fertility in the cow.

Acute oxidative stress modulates secretion and repetitive Ca2+ spiking in rat exocrine pancreas

The effects of the oxidant tert-butylhydroperoxide (t-buOOH) on carbachol-stimulated pancreatic secretion in the vascularly perfused rat pancreas have been studied in parallel with [Ca2+]i signalling and amylase output in perifused rat pancreatic acinar cells. Perfusion of the pancreas with t-buOOH (0.1-1 mM) caused a rapid and irreversible inhibition of carbachol-stimulated (3x10-7 M) amylase and fluid secretion. Pre-perfusion of the pancreas with vitamin C and dithiothreitol or a cocktail of GSH and GSH-precursor amino acids provided only marginal protection against the deleterious effects of t-buOOH, even though GSH levels were elevated significantly. In perifused pancreatic acini, repetitive [Ca2+]i spikes evoked by carbachol (3x10-7 M) were sustained for 40 min. t-buOOH (1 mM) acutely increased the amplitude and duration of Ca2+ spikes, then attenuated Ca2+ spiking and subsequently caused a marked and sustained rise in [Ca2+]i. t-buOOH-induced alterations in carbachol-stimulated [Ca2+]i signalling and amylase release in perifused pancreatic acini were prevented by vitamin C. Although vitamin C restored impaired Ca2+ signalling and maintained amylase output in pancreatic acini, it seems likely that oxidative stress inhibits fluid secretion irreversibly in the intact pancreas, resulting in a loss of amylase output. Thus, perturbations in [Ca2+]i signalling may not fully explain the secretory block caused by oxidative stress in acute pancreatitis.

Ovarian and hormonal responses of cows to treatment with an analogue of gonadotrophin releasing hormone and prostaglandin F2 alpha

Blood samples were taken from 11 cows and their ovaries were scanned by ultrasound at least daily. Around day 5 of an induced cycle, they were injected with 10 micrograms buserelin, an analogue of gonadotrophin releasing hormone, and on day 12 they received 0.5 mg cloprostenol, an analogue of prostaglandin F2 alpha (PGF2 alpha). Two days later six of the cows (the treated group) received a second injection of 10 micrograms buserelin, but the remaining five received no further treatment (control group). The dominant, that is, the largest follicle in each cow disappeared after the first buserelin injection and was replaced by a new one which grew synchronously in all the cows until after the treatment with PGF2 alpha. Ovulation occurred significantly earlier after PGF2 alpha in the treated group than in the control group (72 to 96 hours v 96 to 120 hours; P < 0.05). Plasma progesterone concentrations then increased more rapidly in the treated group than in the control group and were significantly higher on days 3 and 4 after ovulation (P < 0.05).

Heme oxygenase-carbon monoxide signalling pathway in atherosclerosis: anti-atherogenic actions of bilirubin and carbon monoxide?

Atherosclerosis is a major contributor to cardiovascular disease, and genetic disorders of lipoprotein metabolism are recognized risk factors in atherogenesis. The gaseous monoxides nitric oxide (NO) and carbon monoxide (CO), generated within the blood vessel wall, have been identified as important cellular messengers involved in the regulation of vascular smooth muscle tone. Microsomal heme oxygenases degrade heme to biliverdin and CO, and the cytosolic enzyme biliverdin reductase then catalyzes reduction of biliverdin to bilirubin, both powerful chain-breaking antioxidants. Two principal isozymes of heme oxygenase have been identified, a constitutive isoform HO-2 (M(r) approximately 34,000) and an inducible isoform HO-1 (M(r) approximately 32,000), which is expressed at a low basal level in vascular endothelial and smooth muscle cells and is induced by heavy metals, oxidative stress, inflammatory mediators and oxidized low density lipoproteins. Although NO and CO modulate intracellular cGMP levels, platelet aggregation and smooth muscle relaxation, CO has a much lower affinity for soluble guanylyl cyclase than NO. Decreased production or sensitivity to NO in atherosclerosis may be compensated for by an induction of HO-1, with bilirubin acting as a cellular antioxidant and CO as a vasodilator. This review examines the evidence that oxidized low density lipoproteins (LDL), hypoxia and pro-inflammatory cytokines induce HO-1 expression and activity in vascular endothelial and smooth muscle cells, and evaluates the anti-atherogenic potential of the heme oxygenase signalling pathway.

The effect of pregnancy on the expression of uterine oxytocin, oestrogen and progesterone receptors during early pregnancy in the cow

The expression of oxytocin receptor (OTR) in the uterine endometrium plays an important role in the initiation of luteolysis. During early pregnancy, the conceptus secretes interferon tau (IFN|gt) which inhibits OTR up-regulation and luteolysis. In this study, uterine horn cross sections were collected on day 16 from 15 pregnant cows (PREG), 9 uninseminated controls and 5 inseminated cows with no embryo present. The latter two groups had similar results and were combined to form a single non-pregnant (NP) group. The animals were given an oxytocin challenge shortly before tissue collection to assess prostaglandin F2alpha (PGF2alpha) release through the measurement of the metabolite 13,14-dihydro-15-keto PGF2alpha (PGFM). The mRNAs for OTR, oestrogen receptor (ER) and progesterone receptor (PR) were localised by in situ hybridisation. The results were quantified by optical density (OD) measurements from autoradiographs using image analysis. OTR protein was measured by autoradiography with iodinated oxytocin antagonist and ER and PR protein was detected by immunocytochemistry. The release of PGFM after the oxytocin challenge was significantly higher in the 14 NP cows (187%+/-15%) compared with the PREG group (131%+/-11%) (P<0.01). Low concentrations of OTR mRNA were localised to the luminal epithelium (LE) in 6 out of the 14 NP cows, of which 2 also expressed OTR protein, while OTR mRNA and protein were undetectable in all the pregnant animals. These results indicated that the sampling time coincided with the onset of the luteolytic mechanism in the NP cows. On day 16 ER mRNA was detectable in both the LE and glands of both PREG and NP animals. There were no differences in either ER mRNA or protein between NP and PREG samples. PR mRNA was moderately expressed in the caruncular stroma, with lower levels in the dense caruncular-like stroma and glands. There were no differences between PREG and NP animals. The expression of PR mRNA and protein in the deep glands was variable between animals. These results suggested that, in cows, the presence of an embryo suppressed the expression of OTR, but had no effect on the expression of the transcriptionally regulated ER on day 16.

Induction of cystine transport via system x-c and maintenance of intracellular glutathione levels in pancreatic acinar and islet cell lines

The relationship between l-cystine transport and intracellular glutathione (GSH) levels was investigated in cultured pancreatic AR42J acinar and betaTC3 islet cells exposed to diethylmaleate, an electrophilic agent known to activate cellular antioxidant responses. Cystine transport was mediated predominantly by the Na+-independent anionic amino acid transport system x-c, with influx inhibited potently by glutamate and homocysteate but unaffected by cationic or neutral amino acids. Saturable cystine transport was 10-fold higher in AR42J (531 pmol (mg protein)-1 min-1) than in betaTC3 (49 pmol (mg protein)-1 min-1) cells, and GSH levels were higher in AR42J cells. Treatment with 2-mercaptoethanol increased GSH levels in betaTC3 cells from 7.5 to 36 nmol (mg protein)-1, whilst the GSH content in AR42J cells (64 nmol (mg protein)-1) was not altered significantly. Incubation of AR42J or betaTC3 cells with homocysteate (2.5 mM, 0-48 h), a competitive inhibitor of cystine transport via system x-c, reduced intracellular GSH levels and resulted in a time-dependent (6-24 h) induction of system x-c transport activity. Treatment of AR42J cells with diethylmaleate (100 microM, 0-48 h) resulted in a time- (5-10 h) and protein synthesis-dependent induction of cystine transport, with intracellular GSH levels initially decreasing and then increasing 2-fold above control levels after 24 h. Diethylmaleate also depressed GSH levels in betaTC3 cells, but cystine transport was not elevated significantly. In both AR42J and betaTC3 cells, inhibition of gamma-glutamyl cysteine synthetase by buthionine sulphoximine (100 microM, 24 h) reduced GSH levels but had no effect on cystine transport. The present findings establish that induction of system x-c leads to changes in GSH levels in pancreatic AR42J acinar and betaTC3 islet cells, with changes in the intracellular redox state stimulating transporter expression. Induction of activity of system x-c, together with adaptive increases in GSH synthesis in response to oxidative stress, may contribute to cellular antioxidant defences in pancreatic disease.

Vitamin C protects human arterial smooth muscle cells against atherogenic lipoproteins: effects of antioxidant vitamins C and E on oxidized LDL-induced adaptive increases in cystine transport and glutathione

Glutathione (GSH) plays a key role in cellular antioxidant defenses by scavenging reactive oxygen species and reducing lipid peroxides. Intracellular GSH levels are regulated by transport of its precursor L-cystine via system xc-, which can be induced by oxidant stress. As oxidatively modified low density lipoproteins (LDLs) contribute to impaired vascular reactivity and the formation of atherosclerotic lesions, we have examined the effects of oxidized LDL and the antioxidant vitamins C and E on the L-cystine-GSH pathway in human umbilical artery smooth muscle cells (HUASMCs). Oxidized LDL, but not native LDL, elevated intracellular GSH levels and L-cystine transport via system xc- in a time-dependent (up to 24 hours) and dose-dependent (10 to 100 microg x mL-1) manner. These increases were dependent on protein synthesis and the extent of LDL oxidation, but the induction of L-cystine transport activity was independent of GSH synthesis. Pretreatment of HUASMCs for 24 hours with vitamin E (100 micromol/L) attenuated oxidized LDL-mediated increases in GSH, whereas pretreatment with vitamin C depressed basal levels and abolished oxidized LDL-induced increases in GSH and L-cystine transport in a time-dependent (3 to 24 hours) and dose-dependent (10 to 100 micromol/L) manner. Pretreatment of cells with dehydroascorbate had no effect on oxidized LDL-mediated increases in L-cystine transport and only marginally attenuated increases in GSH. Our findings provide the first evidence that vitamin C spares endogenous adaptive antioxidant responses in human vascular smooth muscle cells exposed to atherogenic oxidized LDL.

Role of early luteal phase progesterone in control of the timing of the luteolytic signal in cows

The effects of the pattern and concentration of early luteal phase progesterone on subsequent prostaglandin F2 alpha release in response to exogenous oxytocin was investigated during simulated luteal phases in ovariectomized cows treated with progesterone and oestradiol in patterns designed to simulate the range of luteal phase concentrations that occur naturally. In the first experiment, three groups of four cows received different concentrations of early luteal phase progesterone to determine the effective concentration in terms of cycle control. The results show that a plasma progesterone concentration early in the luteal phase as low as 0.6 ng ml-1 was sufficient to affect the timing of the subsequent luteolytic signal. In the second experiment, an early (day 1), a normal (day 4) or a late (day 7) postovulatory increase in progesterone was recreated in three groups of four cows. Responsiveness to oxytocin in the early progesterone group developed 3 days earlier than in the normal progesterone group, demonstrating the ability of early progesterone to advance the luteolytic signal. However, in the late progesterone group, there was no delay in the development of responsiveness to oxytocin compared with the normal progesterone group, demonstrating that the luteolytic signal is programmed to occur by a given time, irrespective of the early progesterone pattern. This demonstrates that a factor other than the timing of the early luteal phase progesterone increase ultimately must control the timing of luteolysis in cows.

Environmental estrogenic pollutants induce acute vascular relaxation by inhibiting L-type Ca2+ channels in smooth muscle cells

There is an ongoing scientific debate concerning the potential threat of environmental estrogenic pollutants to animal and human health (1-5). Pollutants including the detergents 4-octylphenol and p-nonylphenol and chlorinated insecticides have recently been reported to modulate sexual differentiation by interacting with nuclear steroid receptors (6-8). So far, the focus has been on reproductive organs, but sex steroids have far more widespread actions. The lower incidence of cardiovascular disease in women has been attributed to estrogens (9-14), yet no information is available on the vascular actions of environmental estrogenic pollutants. In the present study we have investigated the effects of acute exposure to 17beta-estradiol, the antiestrogen ICI 182,780, and estrogenic pollutants on coronary vascular tone as well as on intracellular Ca2+ levels ([Ca2+]i) and Ca2+ and K+ channel activity in vascular smooth muscle cells. We report here that 4-octylphenol, p-nonylphenol, o.p'-DDT, and the antiestrogen ICI 182,780 inhibit L-type Ca2+ channels in vascular smooth muscle cells and evoke a rapid and endothelium-independent relaxation of the coronary vasculature similar to that induced by 17beta-estradiol. Thus, inhibition of Ca2+ influx via L-type Ca2+ channels in vascular smooth muscle cells may explain the acute, nongenomic vasodilator actions of environmental estrogenic pollutants.

Mechanisms of acute vasodilator response to bacterial lipopolysaccharide in the rat coronary microcirculation

1. In this study the mechanisms of the acute vasodilator action of bacterial lipopolysaccharide (LPS) were investigated in the rat Langendorff perfused heart. 2. Infusion of LPS (5 microg ml(-1)) caused a rapid and sustained fall in coronary perfusion pressure (PP) of 59 +/- 4 mmHg (n = 12) and a biphasic increase in NO levels determined in the coronary effluent by chemiluminescent detection. Both the fall in PP and the increase in NO release were completely abolished (n = 3) by pretreatment of hearts with the NO synthase inhibitor L-NAME (50 microM). 3. LPS-induced vasodilatation was markedly attenuated to 5 +/- 4 mmHg (n 3) by pretreatment of hearts with the B2 kinin receptor antagonist Hoe-140 (100 nM). 4. Vasodilator responses to LPS were also blocked by brief pretreatment with mepacrine (0.5 microM, n = 3) or nordihydroguaiaretic acid (0.1 microM, n = 4) and markedly attenuated by WEB 2086 (3 microM, n = 4). 5. Thirty minutes pretreatment of hearts with dexamethasone (1 nM), but not progesterone (1 microM), significantly modified responses to LPS. The action of dexamethasone was time-dependent, having no effect when applied either simultaneously with or pre-perfused for 5 min before the administration of LPS but inhibiting the response to LPS by 91 +/- 1% (n = 4) when pre-perfused for 15 min. The inhibition caused by dexamethasone was blocked by 15 min pretreatment with the glucocorticoid receptor antagonist RU-486 (100 nM) or by 2 min pre-perfusion of a 1:200 dilution of LCPS1, a selective antilipocortin 1 (LC1) neutralizing antibody. 6. Treatment with the protein synthesis inhibitor, cycloheximide (10 microM, for 15 min) selectively blunted LPS-induced vasodilatation, reducing the latter to 3 +/- 5 mmHg (n = 3), while having no effect on vasodilator responses to either bradykinin or sodium nitroprusside. 7. These results indicate that LPS-induced vasodilatation in the rat heart is dependent on activation of kinin B2 receptors and synthesis of NO. In addition, phospholipase A2 (PLA2) is activated by LPS resulting in the release of platelet-activating factor (PAF) and lipoxygenase but not cyclo-oxygenase products. These effects are dependent on de novo synthesis of an intermediate protein which remains to be identified.

Increased L-arginine transport in human erythrocytes in chronic heart failure

1. Transport of L-arginine was investigated under zero-trans conditions in human erythrocytes from healthy donors and patients with heart failure. 2. Saturable influx of L-arginine was mediated by the classical cationic amino acid transport systems y+ and y+L. 3. The Vmax for L-arginine transport via system y+ increased from 292 to 490 mumol h-1 l-1 of cells in heart failure. 4. With system y+ inhibited by N-ethylmaleimide (0.2 mmol/l), the Vmax for the transport of L-arginine via system y+L was unaffected in erythrocytes from patients with heart failure. 5. The inhibition of L-arginine and L-leucine influx by NG-monomethyl-L-arginine was similar in erythrocytes from control and heart failure patients. 6. Plasma L-arginine levels were reduced in patients with heart failure (59 mumol/l) compared with controls (125 mumol/l). Plasma from patients with heart failure also contained the endogenous L-arginine analogue NG-monomethyl-L-arginine, which was undetectable in plasma from controls. 7. Intracellular concentrations of L-arginine and NG-monomethyl-L-arginine were significantly elevated in erythrocytes from patients with heart failure compared with controls, consistent with an increased transport capacity for L-arginine and NG-monomethyl-L-arginine. 8. The present study provides the first evidence that system y+ mediates the increased transport of L-arginine in human erythrocytes from patients with chronic heart failure. These findings are similar to our previous results obtained in patients with chronic renal failure. Since both pathologies seem to present with an increased synthesis of nitric oxide, studies of L-arginine transport in erythrocytes may provide a valuable paradigm to study abnormalities of the L-arginine-nitric oxide signalling pathway.

Elevated D-glucose induces insulin insensitivity in human umbilical endothelial cells isolated from gestational diabetic pregnancies

1. The effects of human insulin and elevated D-glucose on L-arginine transport and synthesis of nitric oxide (NO) and prostacyclin (PGI2) have been investigated in human umbilical vein endothelial cells isolated from gestational diabetic pregnancies. 2. The increase in the Vmax for L-arginine transport (9.0 +/- 1.1) pmol (micrograms protein)-1 min-1) in diabetic endothelial cells cultured in 5 mM D-glucose was unaffected following 24 h exposure to 25 mM D-glucose. 3. Gestational diabetes-induced increases in basal intracellular cGMP and L-citrulline levels (inhibitable by L-NAME) and [Ca2+], were unaffected by elevated D-glucose. In contrast, PGI2 release was inhibited in diabetic cells exposed to either 5 or 25 mM D-glucose. 4. Elevated D-glucose attenuated histamine (10 microM, 5 min)-stimulated accumulation of cGMP and L-citrulline in endothelial cells isolated from gestational diabetic pregnancies. 5. The membrane hyperpolarization (-79 +/- 0.9 mV) sustained in diabetic endothelial cells in culture was insensitive to elevated D-glucose. 6. Elevated D-glucose abolished the stimulatory effect of human insulin (1 nM, 8 h) on L-[3H]leucine incorporation in diabetic endothelial cells cultured in 5 mM D-glucose. 7. Human insulin reduced the elevated rates of L-arginine transport and cGMP accumulation in diabetic cells cultured in 5 mM D-glucose but failed to reduce increased rates of transport or NO production in cells exposed to 25 mM D-glucose or cycloheximide. 8. Our findings demonstrate that hyperglycaemia impairs the actions of human insulin on umbilical vein endothelial cells isolated from gestational diabetic pregnancies. Changes in insulin sensitivity and/or its signalling cascade may be affected by hyperglycaemia associated with gestational diabetes, resulting in insulin resistance in endothelial cells derived from the fetal vasculature.

Transport of L-arginine and the nitric oxide inhibitor NG-monomethyl-L-arginine in human erythrocytes in chronic renal failure

1. Transport of L-arginine and the nitric oxide synthase inhibitors NG-monomethyl-L-arginine and NG-nitro-L-arginine was investigated in human erythrocytes from healthy donors and uraemic patients on haemodialysis. 2. Although K(m) values for total L-arginine influx were not significantly different in erythrocytes freshly isolated from controls or uraemic patients, uraemia was associated with an increase in the Vmax for transport (826 compared with 1176 mumol h-1 l-1 of cells) which was reduced to control values after dialysis. 3. Saturable influx of L-arginine was mediated by the classical cationic amino acid transport system y+ and system y+L, known to transport cationic and neutral amino acids with higher affinity. 4. Under zero-trans conditions, the Vmax for L-arginine transport via system y+increased from 271 to 700 mumol h-1 l-1 of cells in uraemia, while K(m) values increased from 44 to 94 mumol/l. Dialysis had no significant effect on the kinetic parameters altered by uraemia. 5. Under zero-trans conditions, and with system y+ inhibited by N-ethylmaleimide (0.2 mmol/l), transport of L-arginine via system y+L was unaffected by uraemia. 6. Saturable influx of NG-monomethyl-L-arginine was also mediated by systems y+ (K(m) = 56 mumol/l, Vmax = 353 mumol h-1 l-1 of cells) and y+L (K(m) = 17 mumol/l, Vmax = 51.3 mumol h-1 l-1 of cells) and, as with L-arginine, uraemia increased the transport capacity for NG-monomethyl-L-arginine. 7. Influx of the neutral nitric oxide synthase inhibitor NG-nitro-L-arginine was not readily saturable. 8. Intracellular concentrations of L-arginine and NG-monomethyl-L-arginine were significantly increased in erythrocytes from uraemic patients when compared with controls, consistent with an increased transport capacity for L-arginine and NG-monomethyl-L-arginine. 9. The present study provides evidence that system y+ mediates the increased transport of L-arginine and NG-monomethyl-L-arginine in human erythrocytes from patients with chronic renal failure. Our findings may have implications for the activity of the L-arginine-nitric oxide signalling pathway in vascular endothelial and smooth-muscle cells in uraemia.