alpha-Melanocyte stimulating hormone inhibits tumour necrosis factor-alpha stimulated intercellular adhesion molecule-1 expression in normal cutaneous human melanocytes and in melanoma cell lines

alpha-Melanocyte stimulating hormone (alpha-MSH) was found significantly to reduce tumour necrosis factor-alpha (TNF-alpha) stimulated upregulation of intercellular adhesion molecule-1 (ICAM-1) in normal adult cutaneous melanocytes. The maximum inhibitory response to alpha-MSH was obtained at around 10(-10) mol/L alpha-MSH when cells were coincubated with alpha-MSH and TNF-alpha for 24 h. alpha-MSH had little or no effect on basal ICAM-1 expression in melanocytes and the effects of alpha-MSH could be mimicked with 3-isobutyl-1-methylxanthine (IBMX). Preliminary data in three human melanoma cell lines also showed alpha-MSH and forskolin to be effective in significantly reducing TNF-alpha stimulated ICAM-1 expression over 24 h. The extent of the inhibition varied from cell line to cell line and was greatest in those cells with the highest number of alpha-MSH receptors. These data suggest that alpha-MSH has the ability to oppose the action of the pro-inflammatory cytokine TNF-alpha on melanocytes and melanoma cells.

Cloning of a human purinergic P2Y receptor coupled to phospholipase C and adenylyl cyclase

Clones encoding a new human P2Y receptor, provisionally called P2Y11, have been isolated from human placenta complementary DNA and genomic DNA libraries. The 1113-base pair open reading frame is interrupted by one intron. The P2Y11 receptor is characterized by considerably larger second and third extracellular loops than the subtypes described so far. The deduced amino acid sequence exhibits 33% amino acid identity with the P2Y1 receptor, its closest homolog. Northern blot analysis detected human P2Y11 receptor messenger RNA in spleen and HL-60 cells. The level of P2Y11 transcripts was strongly increased in these cells after granulocyte differentiation induced by retinoic acid or dimethyl sulfoxide. The new receptor was stably expressed in 1321N1 astrocytoma and CHO-K1 cells, where it couples to the stimulation of both the phosphoinositide and adenylyl cyclase pathways, a unique feature among the P2Y family. The rank order of agonists potency was: ATP > 2-methylthio-ATP >>> ADP, whereas UTP and UDP were inactive, indicating that it behaves as a selective purinoceptor.

Cloning of a human heptahelical receptor closely related to the P2Y5 receptor

The 6H1 receptor cloned from activated chicken T cells was initially considered an orphan G-coupled receptor, but was later included in the P2Y family of receptors for purine and pyrimidine nucleotides on the basis of a significant amino acid identity and was renamed P2Y5. Analysis of the expressed sequence tag database revealed the presence of a related sequence exhibiting 63% amino acid identity with this receptor. Starting from this partial sequence, we have isolated a complete clone and identified a 1113 base pair open reading frame encoding a new G-coupled receptor that we have called P2Y5-like. This sequence exhibits 61% identity with the chicken P2Y5 sequence and 30-33% with other P2Y subtypes. A construct encoding this P2Y5-like receptor was transfected into COS-7, 1321N1, and CHO-K1 cells, and expression was documented by Northern blotting. None of the 40 nucleotides and nucleosides tested was able to elicit a response in any of four functional assays: inositol phosphate formation, stimulation or inhibition of cAMP formation, and extracellular acidification measured with a microphysiometer. These results suggest either that the natural ligand of the P2Y5-like receptor is an uncommon nucleotide or alternatively that despite its structural similarity to the P2Y family it is not a nucleotide receptor.

Slow desensitization of the human P2Y6 receptor

The P2Y6 receptor is a recently cloned P2 receptor which displays a high sensitivity for diphosphonucleotides. In 1321N1 astrocytoma cells stably expressing this receptor, UDP induced a slow and sustained accumulation of inositol trisphosphate via a pertussis toxin-insensitive G-protein: the maximal level was only reached after 15 min and a significant response was maintained for at least 3 h. A full second response to UDP was obtained after the first 45-min stimulation, but was lost after 165 min. This slow and sustained time-course and the lack of desensitization was reproduced with ADP. UTP was unable to restimulate the P2Y4 receptor, another recently cloned P2 receptor with a preference for UTP, after the first 5-min stimulation. The P2Y4 receptor is thus rapidly desensitized whereas desensitization of the P2Y6 receptor is delayed. The rank order of potency of various diphosphonucleotides at the P2Y6 receptor was: UDP > TDP > IDP > GDP > ADP >> CDP. The activity of three non-specific antagonists of P2 receptors was characterized by the following rank order of potency: reactive blue 2 > pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) > suramin. In conclusion, the most impressive features of the human P2Y6 receptor revealed by this study are the slow and sustained time-course of its activation and its high resistance to desensitization.

Receptors responsive to extracellular pyrimidine nucleotides

Extracellular adenine nucleotides have long been known to mediate pharmacological responses via several subtypes of P2 purinoceptors. More recently, however, similar responses to uracil nucleotides have been demonstrated. Here, Didier Communi and Jean-Marie Boeynaems discuss the evidence to suggest that distinct pyrimidinoceptors do indeed exist, although they do not appear to constitute a separate receptor family of their own.

Pharmacological characterization of the human P2Y4 receptor

The P2Y4 receptor is a new member of the P2Y family which functionally behaves as a pyrimidinergic receptor. The pharmacological properties of the human P2Y4 receptor have been characterized following its stable expression in 1321N1 astrocytoma cells. UTP induced a biphasic accumulation of inositol trisphosphates, with an early peak at 30 s followed by a smaller but more sustained accumulation. ATP was a pure antagonist at early times and later behaved as a partial agonist. At 20 min, the rank order of potency of various nucleotides was the following: UTP > UDP = deoxy UTP > 5-bromo-UTP > ITP > ATP. Diadenosine polyphosphates also stimulated the production of inositol trisphosphates (after 20 min), more potently than ATP, but their maximal effect represented only 20-25% of that of UTP. Pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid inhibited strongly the UTP response, whereas suramin was inactive and reactive blue 2 had an intermediate effect. Pertussis toxin inhibited the response to UTP at early times (62 +/- 5% inhibition at 30 s), but its effect was no longer observed at 5 or 20 min. It is speculated that the P2Y4 receptor can exist in two distinct activation states differing in terms of time-course, specificity for uridine nucleotides and G-protein coupling.

Endothelial P2-purinoceptors: subtypes and signal transduction

1. Adenine nucleotides stimulate the synthesis and release of prostacyclin and nitric oxide (two potent platelet aggregation inhibitors) by endothelial cells from different origins. These responses are mediated by P2 purinergic receptors, coupled to the production of inositol (1,4,5)trisphosphate (InsP3) and to the increase of intracytoplasmic calcium concentration. 2. In bovine aortic endothelial cells (BAEC), both 2-MeSATP and UTP stimulate the production of InsP3. By experiments of additivity and cross desensitization, we have confirmed the expression of both P2Y/P2Y1 and P2U/P2Y2 receptors on these cells. Moreover, these receptors are not segregated on different subpopulations but are co-localized on the same cells. 3. The action of UTP on InsP3 production was inhibited by pertussis toxin and was unaffected by a pretreatment with phorbol 12-myristate, 13-acetate (PMA). On the other hand, the response induced by 2-MeSATP was inhibited by PMA but insensitive to pertussis toxin. These results suggest that P2Y/P2Y1 and P2U/P2Y2 receptors are respectively coupled to Gq/G11 and G1 proteins. 4. Northern blotting experiments revealed the expression of the P2Y1 (doublet of 2 and 2.2 kb) and of the P2Y2 (2.4 kb) receptor messengers in BAEC. A signal corresponding to the P2Y2 mRNA was also detectable in human umbilical vein endothelial cells. 5. These various results thus demonstrate the expression of the P2Y1 and P2Y2 receptors in vascular endothelial cells.

Biosynthesis and metabolism of 2-iodohexadecanal in cultured dog thyroid cells

2-Iodohexadecanal (2-IHDA) is a major thyroid iodolipid. It mimics the main regulatory effects of iodide on thyroid metabolism: inhibition of H2O2 production and of adenylyl cyclase. The biosynthesis of 2-IHDA and its metabolism have been investigated in cultured dog thyroid cells maintained in a differentiated state by forskolin. Incubation of these cells with [9,10-3H]hexadecan-1-ol or [9,10-3H]palmitic acid labeled several phospholipids, but [9, 10-3H]hexadecan-1-ol was selectively incorporated into plasmenylethanolamine. In the presence of an exogenous H2O2 generating system (glucose oxidase), iodide induced the production of [9,10-3H]2-IHDA from [9,10-3H]hexadecan-1-ol-labeled cells but not from [9,10-3H]palmitic acid-labeled cells. 2-IHDA was also generated during the lactoperoxidase-catalyzed iodination of brain and heart plasmalogens, and of ethyl hexadec-1-enyl ether, a synthetic vinyl ether-containing compound. Taken together, these results show that thyroid 2-IHDA is derived from plasmenylethanolamine via an attack of reactive iodine on the vinyl ether group. 2-Iodohexadecan-1-ol (2-IHDO) was also detected in these studies; it was formed later than 2-IHDA, and thyroid cells converted exogenous 2-IHDA into 2-IHDO in a time-dependent way. The ratio of 2-IHDO/2-IHDA increased with H2O2 production and decreased as a function of iodide concentration. An aldehyde-reducing activity was detected in subcellular fractions of the horse thyroid. No formation of 2-iodohexadecanoic acid could be detected. Reduction into the biologically inactive 2-IHDO is thus a major metabolic pathway of 2-IHDA in dog thyrocytes.

[Cardiovascular diseases: toward an optimal use of clinical biological laboratories]

Cardiovascular diseases are a frequent cause of morbidity and mortality in our country. The early detection of risk factors by laboratory tests and the subsequent preventive treatment may have a substantial beneficial effect on public health. However, since these tests are performed on large populations, they must be chosen with caution, in order to optimise their cost/ effectiveness ratio. Savings obtained by the judicious use of the clinical lab could allow, already in 1996, the reimbursement of some new informative tests, like the plasma homocysteine and the LDL-cholesterol, and later, of the lipoprotein (a), all tests which are presently at the charge of the patient.

Evidence that most high-affinity ATP binding sites on aortic endothelial cells and membranes do not correspond to P2 receptors

It has recently been demonstrated that two types of ATP receptors, the P2Y and P2U receptors, are coexpressed on bovine aortic endothelial cells. The aim of the present study was to characterize directly P2Y and P2U subtypes on intact bovine aortic endothelial cells and on membranes prepared from these cells using adenosine 5'-0-(3-thio[35S]triphosphate) ([35S]ATP gamma S), [alpha-32P]ATP and [alpha-32P]UTP as radioligands. [35S]ATP gamma S binding to bovine aortic endothelial cell membranes was saturable and apparently involved a single class of high-affinity binding sites (Kd: 14 +/- 11 nM. Bmax 1.6 +/- 0.7 pmol/mg protein; mean +/- S.D.). A similar class of high-affinity binding sites was identified with [alpha-32P]ATP (Kd: 14 +/- 9 nM; Bmax: 1.7 +/- 1.1 pmol/mg protein; mean +/- S.D.). Competition experiments showed that only one third of these sites bound 2-methylthio-ATP (2-MeSATP) with high affinity (Ki: 21 +/- 5 and 14 +/- 10 nM, mean +/- S.D., for [35S]ATP gamma S and [alpha-32P]ATP, respectively) and might therefore represent the P2Y receptors. UTP did not compete with [35S]ATP gamma S or [alpha-32P]ATP for binding at the remaining sites, indicating that they are not the P2U receptors. No high-affinity UTP binding sites could be detected using [alpha-32P]UTP. [35S]ATP gamma S binding to intact bovine aortic endothelial cells was competed by ATP gamma S (Kd: 1.0 +/- 0.5 microM; mean +/- S.D.), but not by 2-MeSATP and UTP, indicating that these binding sites are neither the P2Y nor the P2U receptors.

Cloning, functional expression and tissue distribution of the human P2Y6 receptor

In order to isolate new subtypes of P2Y purinoceptors, a human placenta cDNA library was screened at middle stringency with a P2Y4 probe. The purification and the sequencing of several clones led us to identify a 984 base pair open reading frame encoding a new human P2Y receptor. It appeared later that this sequence corresponds to the human ortholog (88% amino acid identity) of the rat receptor recently cloned by Chang et al (J. Biol. Chem. 270, 26152-26158, 1995) and called P2Y6. Northern blot analysis detected human P2Y6 receptor messenger RNA in human spleen, placenta, thymus, intestine, and blood leukocytes. In 1321N1 cells stably expressing the human P2Y6 receptor, the formation of IP3 was stimulated by nucleotides with the following order of potency: UDP > 5-bromo-UPT > UTP > ADP > 2-methylthio-ATP >> ATP. The P2Y6 receptor, together with the previously cloned P2Y4 subtype (Communi et al., J. Biol. Chem., 270, 30849-30852, 1995), belongs thus to a subfamily of pyrimidinoceptors inside the P2Y family.

Cloning and tissue distribution of the human P2Y1 receptor

Sets of degenerate oligonucleotide primers synthesized on the basis of the best conserved regions of the chick brain P2Y/P2Y1 and the murine neuroblastoma P2U/P2Y2 receptors were used in polymerase chain reaction experiments on human genomic DNA. An amplified fragment of 712 base pairs was then used as a probe to screen a human genomic DNA library. Several clones were isolated and sequencing revealed an intronless 1122 base pair open reading frame. The corresponding amino acid sequence revealed 83% identity with the chick brain P2Y1 receptor and 34% with the murine neuroblastoma P2Y2 receptor. In COS-7 cells transfected with the coding sequence inserted into the pcDNA3 expression vector, 2-methylthioATP and ATP produced a strong stimulation of inositol phosphates, a typical response of a P2Y1 receptor. Northern blot analysis detected a 6.7 kilobase messenger RNA in most human tissues, the strongest signals being observed in prostate and ovary.

Action of cAMP on expression and release of adhesion molecules in human endothelial cells

The expression of E-selectin induced by tumor necrosis factor (TNF) on the surface of human umbilical vein endothelial cells (HUVEC) was partially inhibited by an increase in the level of adenosine 3',5'-cyclic monophosphate (cAMP), produced by forskolin or cholera toxin combined with the type IV phosphodiesterase inhibitor rolipram and the protein kinase A agonist phosphorothioate analogue of cAMP SpcAMPS. The same agents had no significant effect on the constitutive and TNF-stimulated expression of intercellular adhesion molecule 1 (ICAM-1), whereas the effect on vascular cell adhesion molecule 1 (VCAM-1) expression was variable depending on cell culture conditions. The stimulatory effects of phorbol 12-myristate 13-acetate and bacterial lipopolysaccharide (LPS) on E-selectin expression were also downregulated by the forskolin-rolipram combination and by SpcAMPS. Inhibition of the surface expression of E-selectin was associated with a decrease of the total amount of the protein in the cell lysate and a reduced mRNA level, with no significant effect on mRNA stability. In anesthetized rats, the terbutaline-rolipram combination reduced the rolling of leukocytes induced by LPS in the mesenteric microcirculation. In addition to their partial inhibitory effect on the TNF-induced surface expression of E-selectin on HUVEC, the forskolin-rolipram combination and SpcAMPS strongly inhibited the release of soluble E-selectin from these cells; the release of soluble ICAM-1 and VCAM-1 was unaffected by these agents. Isoproterenol reduced the release of soluble E-selectin, whereas it had no significant effect on the cell surface expression of the protein. This study underscores the potential anti-inflammatory effect of a rise in the endothelial cAMP level.

Cloning and functional expression of a human uridine nucleotide receptor

In order to isolate new subtypes of P2 purinoceptors, sets of degenerate oligonucleotide primers were synthesized on the basis of the best conserved segments in the published sequences of the chick brain P2Y/P2Y1 and murine neuroblastoma P2U/P2Y2 receptors. Their use in polymerase chain reaction (PCR) experiments on human genomic DNA amplified, among other things, a 712-base pair sequence, that was used as a probe to screen a human genomic DNA library. Several clones corresponding to a single locus were isolated, and the sequence analysis revealed an intronless 1095-base pair open reading frame. The deduced amino acid sequence is consistent with a G protein-coupled receptor and exhibits 51% identity with the human P2Y2 receptor and 35% with the chick P2Y1 receptor. A close comparison with the human P2Y2 sequence reveals the conservation of histidine 262, arginine 265, lysine 289, and arginine 292, which were reported to be involved in nucleotide binding (Erb, L., Garrad, R., Wang, Y., Quinn, T., Turner, J. T., and Weisman, G. A. (1995) J. Biol. Chem. 270, 4185-4188). Northern blot analysis detected a 1.8-kilobase messenger RNA in human placenta. The coding sequence was inserted in the pcDNA3 vector in order to transfect 1321N1 human astrocytoma cells. In cells stably expressing the receptor, UTP and UDP stimulated the formation of inositol phosphates with equivalent potency and maximal effect, ATP behaved as a partial agonist, and ADP was almost inactive. We have thus cloned a new member of the G protein-coupled P2 purinergic receptor family, which functionally behaves as a pyrimidinergic receptor.

Coexpression of P2Y and P2U receptors on aortic endothelial cells. Comparison of cell localization and signaling pathways

Depending on the vascular bed considered, the actions of ATP on the endothelium are mediated by either P2Y or P2U receptors. The two types of receptors seem to coexist on bovine aortic endothelial cells, where they are both coupled to phospholipase C. In this study, we have investigated whether they are truly coexpressed on the same cells and whether their signaling pathways diverge beyond phospholipase C activation. Measurements of [Ca2+]i in single cells showed that almost all bovine aortic endothelial cells are responsive to both 2-methylthio-ATP (2MeSATP), an agonist of P2Y receptors, and UTP, an agonist of P2U receptors. UTP stimulated the release of prostacyclin from freshly isolated bovine aortic endothelial cells, even when they were exposed to cycloheximide at the time of their collection: this indicates that P2U receptors must already be expressed on endothelial cells in situ and do not appear during cell culture. The time course of inositol phosphate (InsP) accumulation and the relative proportion of Ins(1,4,5)P3, Ins(1,3,4,5)P4, and Ins(1,3,4)P3 were similar in cells stimulated by 2MeSATP or UTP. UTP and 2MeSATP both stimulated the hydrolysis of phosphatidylcholine by phospholipase D, as reflected by the release of [3H]choline from prelabeled cells. The responses to both agents were blocked after downregulation of protein kinase C, resulting from a prolonged exposure to phorbol 12-myristate 13-acetate: this blockade occurred at a step distal to phospholipase C activation. A single difference between the two pathways has been identified: the effect of 2MeSATP on InsP3 was significantly more inhibited after a short exposure to phorbol 12-myristate 13-acetate than that of UTP.(ABSTRACT TRUNCATED AT 250 WORDS)

Involvement of multiple receptors in the actions of extracellular ATP: the example of vascular endothelial cells

The role of ATP and ADP as intercellular mediators is now well established. The presence of the nucleotides in extracellular fluids can result from several mechanisms: cell lysis, selective permeabilization of the plasma membrane and exocytosis of secretory vesicles, such as platelet dense bodies. Extracellular adenine nucleotides are rapidly degraded by ectonucleotidases expressed inter alia on the surface of endothelial cells. They act on cells via the family of P2 receptors which encompasses more than 5 subtypes, some of which have been cloned recently. The P2T, P2U and P2Y receptors belong to the superfamily of receptors coupled to G proteins, whereas the P2X receptor is a cation channel and the P2Z receptor a non-selective pore. ATP and ADP stimulate the endothelial production of prostacyclin (PGI2) and nitric oxide (NO), two vasodilators and inhibitors of platelet aggregation, via an increase in cytosolic Ca2+. This action of adenine nucleotides is believed to limit the extent of intravascular platelet aggregation and to help localize thrombus formation to areas of endothelial damage. The endothelial response to nucleotides is mediated by at least two distinct subtypes of P2 receptors, P2Y and P2U, both coupled to phospholipase C.

Inhibition of human thyroid adenylyl cyclase by 2-iodoaldehydes

2-Iodohexadecanal (IHDA), which can be formed upon addition of iodine to the vinyl ether group of plasmalogens, has been identified as a major thyroid iodolipid (Pereira et al. (1990) J. Biol. Chem. 265, 17018-17025). In this study, we have investigated the possibility that it would be a mediator of the inhibitory effect of iodide on thyroid adenylyl cyclase. In human thyroid membranes, IHDA inhibited the adenylyl cyclase activity stimulated by thyrotropin (TSH), GTP-gamma-S or forskolin (FSK), whereas it did not decrease the specific binding of TSH to its receptors. The inhibitory effect on the cyclase reached a maximum after a 1-h-pre-incubation of the membranes with IHDA at 30 degrees C and was poorly reversible. It was also observed following a 4-h incubation with IHDA at 4 degrees C, a condition in which adenylyl cyclase is protected against heat inactivation. IHDA decreased the Vmax of adenylyl cyclase, but had no effect on the Km for ATPMg2-.IHDA also inhibited the FSK-stimulated adenylyl cyclase activity in liver and kidney cortex membranes, but had no effect on the Mg(2+)-ATPase activity of thyroid membranes. The inhibitory effect of IHDA has also been demonstrated in intact cells. As in membranes, IHDA decreased the rise in cAMP induced by TSH in cultured dog thyroid cells and this inhibition was maintained following pretreatment of the cells with pertussis toxin. In order to evaluate the specificity of the IHDA action, various analogs have been synthesized. This study has permitted the identification of two major structural features required for the inhibition of human thyroid adenylyl cyclase; the terminal aldehyde function and an iodine atom at C2, other halogens being ineffective. In conclusion, we have shown that IHDA exerts a direct inhibitory effect at or near adenylyl cyclase; all the properties of this effect characterized so far are identical to those of the adenylyl cyclase inhibition obtained following the exposure of thyroid tissue to iodide.

Inhibition of H2O2 production by iodoaldehydes in cultured dog thyroid cells

2-Iodohexadecanal (IHDA) has been identified as a major thyroid iodolipid which can be formed upon addition of iodine to the vinyl ether group of plasmalogens (Pereira et al., 1990). In order to test whether IHDA plays a role in the thyroid autoregulation by iodide, we have investigated its effects on the production of H2O2 by cultured dog thyroid cells. IHDA inhibited the formation of H2O2 in dog thyroid cells stimulated by carbamylcholine (CCHOL). In the presence of BSA, which potentiated its action, the effect of IHDA was maximal after 2 h and had an IC50 around 5 microM. The effect of IHDA was not decreased by methimazole, which abolished the inhibition by iodide. IHDA also inhibited the stimulatory effect of bradykinin, but had only a marginal effect on the production of H2O2 induced by ionomycin or phorbol 12-myristate 13-acetate (PMA). The accumulation of inositol phosphates in CCHOL-stimulated thyroid cells was decreased by IHDA. As evaluated by measurements of 51Cr release and [3H]thymidine incorporation into DNA, IHDA had no adverse effect on thyroid cell viability. Several analogs of IHDA, of which the synthesis is described, have been tested for their inhibitory activity. This allowed the identification of two major structural features required for the biological activity: the carbonyl group at C1 and an halogen atom at C2, with iodine conferring a greater activity than bromine, while chlorine and fluorine were inactive. In conclusion, IHDA inhibits the production of H2O2 in CCHOL-stimulated dog thyroid cells by decreasing the phospholipase C cascade activity. This effect involves both the aldehyde function and the iodine atom. These results suggest that IHDA might be the mediator of some of the regulatory actions of iodide on the thyroid gland.

Inhibition of thyroid NADPH-oxidase by 2-iodohexadecanal in a cell-free system

The major nonpolar iodolipid formed in horse thyroid cells has recently been identified as 2-iodohexadecanal (2-IHDA). We have investigated in vitro the effect of 2-IHDA on the NADPH-oxidase, NADPH-cytochrome c reductase, and thyroid peroxidase (TPO) activities of a porcine thyroid plasma membrane preparation. 2-IHDA inhibited NADPH-oxidase activity, with half-inhibition at 3-5 microM, but it had no effect on NADPH-cytochrome c reductase. It inhibited the TPO-catalyzed iodination of protein, but not iodide oxidation. Hexadecanal also inhibited NADPH-oxidase. Inhibition by the non-iodinated lipid aldehydes depended on the length of their aliphatic chain: dodecanal and tridecanal gave maximal inhibition. Free iodide, 2-iodohexadecanol and palmitic acid all had no inhibitory effect. Washing treated membranes showed that the inhibition of NADPH-oxidase by hexadecanal was fully reversible, whereas that of 2-IHDA and other iodinated or brominated alkanals was irreversible. Thus the interaction between some residues of the thyroid NADPH-oxidase and the lipid aldehyde groups was favored or stabilized by the iodine atom. Modification of primary amine and thiol groups of NADPH-oxidase inhibited its activity. These groups could also be the target of lipid aldehydes. We suggest that 2-IHDA, because it inhibits TPO and more profoundly the H2O2-generating system in thyroid plasma membrane, modulates iodide metabolism in the thyrocyte and may mediate the Wolff-Chaikoff effect.

Is endotoxin-induced hypotension related to nitric oxide formation?

Nitric oxide (NO), an endothelium-derived relaxing factor (EDRF), is released by different types of cells under the influence of endotoxin and various cytokines: a causative role of endothelium-derived NO in the endotoxin-induced hypotension has thus been suggested. To test the hypothesis that NO may be involved in the acute hypotension following endotoxin challenge, we administered a competitive inhibitor of NO synthase, L-N-monomethylarginine (L-NMMA) to anesthetized dogs in the presence and absence of endotoxin. Dogs were randomly allocated to three groups. Group 1 (n = 3) was given Escherichia coli endotoxin (3 mg/kg, i.v.), group 2 (n = 3) was given L-NMMA (5 mg/kg, i.v. bolus) 15 min after endotoxin and group 3 (n = 3) was given L-NMMA only. One additional dog was given L-arginine (100 mg/kg, i.v. bolus) after L-NMMA and endotoxin to reverse the inhibition of NO synthase. In each animal, saline was infused intravenously throughout the experiment to restore and maintain pulmonary artery occluded pressure at baseline level. After L-NMMA, the increases in mean arterial pressure were similar in group 2 (from 55 +/- 18 to 75 +/- 15 mm Hg, p < 0.01) and in group 3 (from 107 +/- 27 to 128 +/- 24 mm Hg, p < 0.01). Systemic vascular resistance increased from 2,994 +/- 72 to 3,658 +/- 673 dyn.s.cm-5 (p < 0.01) in group 3. Group 1 had lower plasma lactate levels than group 2 (3.5 +/- 2.3 +/- vs. 2.0 +/- 1.6 mEq/l, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that ATP, ADP and AMP are not ligands of the striatal adenosine A2A receptors

It has been claimed recently that, in several cell types, ATP can induce a stimulation of cAMP production which is sensitive to methylxanthine inhibition and is not mediated by the ATP degradation product, adenosine. One explanation for these results would be direct activation of adenosine A2 receptors by ATP itself. We have therefore investigated whether adenine nucleotides are ligands of adenosine A2A receptors from bovine striatum. We show here that ATP, ADP, AMP and their phosphorothioates analogues (ATP gamma S, ADP beta S and AMP alpha S), at a 100 microM concentration, produced a 83-91% inhibition of the binding of [3H]CGS21680, an adenosine A2A receptor agonist, to striatum membranes. However, this action was inhibited by adenosine deaminase or by adenosine 5'-O-(alpha, beta-methylene)diphosphate (APCP), an inhibitor of 5'-nucleotidase-mediated AMP degradation. The effects of adenosine deaminase and APCP were dependent on their concentration. These results indicate that ATP, ADP and even AMP can exert an effect on the adenosine A2A receptors only through their breakdown into adenosine by ectonucleotidases.

Evidence that a form of ATP uncomplexed with divalent cations is the ligand of P2y and nucleotide/P2u receptors on aortic endothelial cells

1. The response of bovine aortic endothelial cells to adenosine 5'-triphosphate (ATP) is mediated by both P2y and nucleotide/P2u receptors. In order to determine which form of the nucleotide is the true ligand of these receptors, we have investigated the effects of divalent cations on ATP-, uridine 5'-triphosphate (UTP)- and 2 methylthioadenosine 5'-triphosphate (2MeSATP)-induced inositol phosphate accumulation in these cells. 2. Omisson of Mg2+ from a calcium-free incubation buffer caused a shift to the left of the ATP concentration-action curve. 3. In the presence of EDTA (1 mM), the basal level of inositol trisphosphate (InsP3) was markedly increased and the absolute maximal response to ATP was decreased; however, the response to low concentrations of ATP was enhanced. 4. When the results were plotted in terms of calculated ATP4- concentrations, the concentration-response curves obtained in the presence of 1.25 mM Mg2+ lay closer to the respective curves obtained when Mg2+ was omitted from the medium or when Mg2+ was omitted and EDTA (1 mM) was added. The curves became almost superimposable when the baseline value was subtracted. 5. A similar shift to the left of the concentrations-action curves was also observed with both UTP and 2MeSATP. 6. Our data provide evidence that a form of ATP uncomplexed with divalent cation is the preferential agonist of both the nucleotide/P2u and the P2y receptors expressed on bovine aortic endothelial cells.