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Biomedical subjects

J Jeremy

Publications and source records attributed to J Jeremy.

11 recordsLinked to original sources
PubMed1994

Alteration in vascular reactivity in isolated aortic rings from portal vein-constricted rats.

It has been suggested that increased production of nitric oxide by an inducible nitric oxide synthase isoenzyme is important in the pathogenesis of the vascular abnormalities seen in human beings and animals with portal hypertension. We investigated this hypothesis by studying the in vitro vascular reactivity of isolated aortic rings from portal vein-constricted and sham-operated rats. Aortic rings from portal vein-constricted rats exhibited significantly impaired contractility to phenylephrine and potassium chloride compared with control rats. Preincubation with the nitric oxide synthase inhibitor nitro-L-arginine methyl ester significantly increased contractility to phenylephrine and potassium chloride in both portal-hypertensive and control tissues, with greater effect in the portal-hypertensive rings. Despite nitro-L-arginine methyl ester, maximal contractions were still significantly smaller in the portal-hypertensive tissues. Vascular relaxation evoked by acetylcholine, but not by the endothelium-independent vasodilator glyceryl trinitrate, was significantly impaired in the portal-hypertensive group. Our results demonstrate significant impairment in vascular function in aortic rings in this model of portal hypertension. The addition of a nitric oxide synthase inhibitor partly corrected these changes, suggesting that although nitric oxide is likely an important mediator, other factors may also be involved in the pathogenesis of these alterations in vascular function.

Acetylcholine↗
PubMed1991

Comparison of prostanoid synthesis in cultured human vascular endothelial cells derived from omentum and umbilical vein.

Endothelial seeding of vascular grafts may reduce thrombogenicity and significantly improve graft patency. For clinical studies endothelial cells derived from human omentum may be the ideal source of cells as they are obtainable in large numbers. This study was designed to assess their ability to produce the antithrombogenic substance prostacyclin (PGI2). Human omental microvascular endothelial cells (HOTMECs) were grown and their ability to produce prostacyclin (PGI2), PGE2, PGF2 alpha and thromboxane A2 (TXA2) in response to a range of agonists was measured by radioimmunoassay. Control experiments were performed using human umbilical vein endothelial cells (HUVECs). Both HUVECs and HOTMECs synthesised similar quantities of PGI2 basally and both increased production after adding A23187 (calcium ionophore), arachidonic acid, sodium fluoride and phorbol ester. In contrast, both thrombin and histamine were potent stimulators of PGI2 release in HUVECs but were without effect on HOTMECs. In both cell types serotonin, carbachol and noradrenaline were without effect. The pattern of release of PGE2, PGF2 alpha and TXA2 were identical to those of PGI2 in both cell types but the quantities released were lower. These results show that HOTMECs can produce the antithrombogenic agent PGI2 in significant quantities and that they do so by mechanisms similar to those of large vessel endothelium. This supports the proposal that they would be a suitable cell source for vascular graft seeding.

Cells, Cultured↗
PubMed1989

ATP-evoked Ca2+ mobilisation and prostanoid release from astrocytes: P2-purinergic receptors linked to phosphoinositide hydrolysis.

Astrocyte cultures prelabelled with either [3H]inositol or 45Ca2+ were exposed to ATP and its hydrolysis products. ATP and ADP, but not AMP and adenosine, produced increases in the accumulation of intracellular 3H-labelled inositol phosphates (IP), efflux of 45Ca2+, and release of thromboxane A2 (TXA2). Whereas ATP-stimulated 3H-IP accumulation was unaffected, its ability to promote TXA2 release was markedly reduced by mepacrine, an inhibitor of phospholipase A2 (PLA2). ATP-evoked 3H-IP production was also spared following treatment with the cyclooxygenase inhibitor, indomethacin. We conclude that ATP-induced phosphoinositide (PPI) breakdown and 45 Ca2+ mobilisation occurred in parallel with, if not preceded, the release of TXA2. Following depletion of intracellular Ca2+ with a brief preexposure to ATP in the absence of extracellular Ca2+, the release of TXA2 in response to a subsequent ATP challenge was greatly reduced when compared with control. These results suggest that mobilisation of cytosolic Ca2+ may be the stimulus for PLA2 activation and, thus, TXA2 release. Stimulation of alpha 1-adrenoceptors also caused PPI breakdown and 45 Ca2+ efflux but not TXA2 release. The effects of ATP and noradrenaline (NA) on 3H-IP accumulation were additive, but their combined ability to increase 45Ca2+ efflux was not. Interestingly, in the presence of NA, ATP-stimulated TXA2 release was reduced. Our data provide evidence that functional P2-purinergic receptors are present on astrocytes and that ATP is the first physiologically relevant stimulus found to initiate prostanoid release from these cells.

Adenine Nucleotides↗
PubMed1988

Astrocytes as eicosanoid-producing cells.

A variety of prostaglandins and leukotrienes, together with thromboxane and prostacyclin metabolites, can be detected in central nervous tissues and in cerebrospinal fluid. Defined cultures of astrocytes have revealed these cells to be a major source of eicosanoids. In common with other eicosanoid-producing cells, agents such as calcium ionophores and phorbol esters are potent stimuli for promoting release. While in other tissues agonists for receptors linked to calcium mobilisation prompt eicosanoid release, this does not seem to be the case in astrocytes, though a range of such receptors are present. The notable exceptions to this observation are adenosine triphosphate and adenosine diphosphate, presumably acting through P2 purinergic receptors. Many cell types in the CNS are targets for eicosanoids, possessing receptors linked to adenylate cyclase or phospholipase C. An appreciation of the functional significance of activation of these receptors is just now beginning. Eicosanoids have effects in the CNS that involve not only the vascular supply but also synaptic modulation and immune regulation.

Animals↗
PubMed1988

Effect of vitamin E supplementation on platelet thromboxane A2 production in type I diabetic patients. Double-blind crossover trial.

Vitamin E deficiency is associated with increased platelet aggregation, which can be normalized through vitamin E supplementation. In diabetes, increased platelet thromboxane A2 (TXA2) production is correlated with decreased platelet vitamin E content. We therefore investigated the effect of 400 mg DL-alpha-tocopherol acetate daily for 4 wk on ADP- and collagen-induced platelet aggregation and platelet TXA2 production in 22 type I (insulin-dependent) diabetic patients without macroangiopathy and with no or only minimal microangiopathy by a double-blind placebo-controlled crossover study. Platelet aggregation was induced in platelet-rich plasma by two or three different concentrations of ADP and collagen. TXA2 was measured by the stable spontaneous breakdown product thromboxane B2 by a specific radioimmunoassay. Whereas metabolic control remained unchanged during the study period, platelet TXA2 production was significantly (P less than .05 and P less than .01) reduced at each ADP concentration and at two of three collagen concentrations. Because increased TXA2 production of diabetic platelets is thought to play an important pathogenetic role in diabetic angiopathy, we conclude that vitamin E treatment could be beneficial with respect to platelet-vessel-wall interaction and thus might be promising for the prevention of diabetic angiopathy.

Adenosine Diphosphate↗
PubMed1987

Phorbol ester stimulation of prostanoid synthesis by cultured astrocytes.

The role of protein kinase C in mediating the synthesis and release of various prostanoids (prostaglandins E2, I2, F2 alpha and thromboxane A2) from astroglial cells derived from neonatal rat cerebrum and maintained in primary culture was investigated using phorbol ester. Phorbol myristate acetate stimulated the release of arachidonic acid from prelabelled cells and all 4 prostanoids in a dose-dependent manner (EC50 = 300 nM). This effect was inhibited by the protein kinase inhibitor 1-(-5-isoquinolinylsulfonyl)-2-methylpiperizine (IC50 = 25 microM) and the phospholipase A2 inhibitor, mepacrine (IC50 = 5 microM). In addition, the stimulatory effect of the phorbol ester was not apparent in cells which had been depleted specifically of protein kinase C. In the presence of the calcium ionophore A23187, phorbol ester-stimulated prostanoid release was enhanced. In the absence of extracellular calcium, there was no prostanoid-stimulation by phorbol ester, but the calcium channel blocker verapamil did not mimic this effect. We conclude that stimulation of protein kinase C by phorbol ester elicits prostanoid synthesis and release by a process that involves calcium influx and the activation of phospholipase A2.

Animals↗
PubMed1987

Inositol phospholipids are probably not the source of arachidonic acid for eicosanoid synthesis in astrocytes.

In astrocyte-enriched cultures of the rat cerebral cortex the Ca2+ ionophore A23187 provoked the breakdown of inositol phospholipids, the liberation of arachidonic acid and the release of prostaglandins E2, F2 alpha, I2 and thromboxane A2. However, agonists for receptors also coupled to inositol phospholipid metabolism in these cells failed to produce an increase in the release of both arachidonic acid and eicosanoids. Results suggest that the A23187-stimulated release of arachidonic acid and eicosanoids is caused by a phospholipase A2-mediated attack on lipids other than the inositol phospholipids. Moreover, receptors linked to inositol lipid turnover are not involved in the control of eicosanoid release from astrocytes.

Animals↗
PubMed1985

Eicosanoid synthesis and release from primary cultures of rat central nervous system astrocytes and meningeal cells.

Primary cultures of astrocytes and meningeal cells derived from neonatal rat brain synthesize and release thromboxane A2 and prostacyclin, respectively. Exogenously supplied arachidonic acid and the calcium ionophore, A23187, promote the release of eicosanoids; these effects are blocked by indomethacin and the calcium chelator, ethyleneglycoltetraacetic acid. The finding that astrocytes synthesize and release thromboxane A2 is discussed in the light of our recent findings of receptor-linked membrane phospholipid turnover in these cells.

Animals↗
PubMedDate not supplied

Signalling pathways activated by 5-HT(1B)/5-HT(1D) receptors in native smooth muscle and primary cultures of rabbit renal artery smooth muscle cells.

The potential of primary cultures of rabbit renal artery vascular smooth muscle cells (VSMCs) was assessed as a means to investigate the signalling pathways linked to 5-hydroxytryptamine (5-HT) 5-HT(1B)/5-HT(1D) receptors in native arteries. In renal artery segments denuded of endothelium, incubated with ketanserin and prazosin (each 1 microM), and prestimulated with 20 mM K(+) Krebs buffer, 5-HT and CP 93,129, a 5-HT(1B) receptor agonist, evoked concentration-dependent contractions. GR 127935, a 5-HT(1B)/5-HT(1D) receptor antagonist, significantly antagonised 5-HT-evoked contractions at nanomolar concentrations. Reverse transcription polymerase chain reaction (RT-PCR) of mRNA from smooth muscle cells from the isolated renal artery and from primary cultures of VSMCs from the same artery expressed mRNA transcripts for the 5-HT(1B) receptor and the 5-HT(1D) receptor in both preparations. The sequence of the PCR fragments corresponded to the known sequence for these receptors. Application of 5-HT evoked a concentration-dependent, pertussis toxin (PTx)-sensitive reduction in cyclic AMP in both cultured cells and intact artery (cyclic AMP concentration reduced by 65.53 +/- 3.33 and 52.65 +/- 5.34% from basal with 10 microM 5-HT, respectively). The effect of 10 microM 5-HT on cAMP was increased in the presence of 20 mM K(+) (reduced by 82.50 +/- 2.50 and 87.54 +/- 3.97%, respectively). In intact arteries, contraction through 5-HT(1B)/5-HT(1D) receptors was significantly attenuated by inhibitors of phosphatidylinositol 3-kinase (wortmannin) and activated mitogen-activated protein kinase (MAPK), MEK (U0126). In the cultured VSMCs, activated MAPK was identified by immunocytochemistry and immunoblotting after stimulation with 5-HT, but only if 20 mM K(+) was present at the onset of stimulation. These data provide the first direct evidence that 5-HT(1B)/5-HT(1B) receptors are linked to the activation of MAPK and indicate that primary cultures of renal VSMCs could provide a model system to study further the signalling pathways linked to these receptors.

Androstadienes↗