scholarly journals Specific Inhibition of ADP-Induced Platelet Responses by 2-n-Amylthio Amp

1977 ◽  
Author(s):  
D. E. Maclntyre ◽  
J. L. Gordon ◽  
A. H. Drummond ◽  
M. Steer ◽  
E. W. Salzman
Keyword(s):  
Arachidonic Acid ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Potent Inhibitor ◽  
Shape Change ◽  
Inhibitory Effect ◽  
Specific Inhibition ◽  
Synthetic Analogues ◽  
Competitive Antagonist

“Primary” aggregation responses to ADP are blocked by 2-n-amylthio AMP (nAmSAMP)*, apparently competitively (Ki ≃ 10 μM). Shape change is inhibited by higher concentrations (> 0.1 mM). nAmSAMP has a modest inhibitory effect on platelet responses to ionophore Lilly A23187 and a greater effect on responses to collagen and blocks secretion and secondary aggregation induced by ADP, adrenaline, arachidonic acid, PGG2, and synthetic analogues of PGE2 and PGH2-nAmSAMP is a much less potent inhibitor than adenosine against all stimulants apart from ADP and is qualitatively unlike adenosine in the following respects:1. primary aggregation responses to the above agents (except ADP) and to serotonin and vasopressin are unaffected;2. inhibition is not increased by preincubation;3. inhibition is not decreased by an inhibitor of adenylate cyclase, SQ22536 (9-[tetrahydro-2-furyl]-adenine);4. basal levels of platelet cyclic AMP are unaffected. We conclude that, unlike adenosine, nAmSAMP does not inhibit platelet responses by stimulating adenylate cyclase. nAmSAMP appears to be a “specific” competitive antagonist of ADP and should therefore be useful in clarifying the role of ADP in platelet reactions.

scholarly journals Role of Cyclic Amp in Platelet Function : Evidence from Inhibition of Adenylate Cyclase in Intact Platelets by Adenosine Analogues

1977 ◽  
Author(s):  
R. J. Haslam ◽  
M. M. L. Davidson ◽  
J. V. Desjardins
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Platelet Function ◽  
Platelet Rich Plasma ◽  
Inhibitory Effects ◽  
Adenosine Analogues ◽  
Inhibitory Activities

Adenosine exerts independent stimulatory and inhibitory effects on the adenylate cyclase activity of platelet particulate fractions (Haslam & Lynham, 1972). Two adenosine analogues, 9-(tetrahydro-2-furyl) adenine (SQ 22536) and 2′, 5′-dideoxyadenosine (DDA) have now been found to show marked non-competitive inhibitory activities only. Basal and PGE1-stimulated adenylate cyclase activities were inhibited ~50% and ~70% respectively by 100 μM SQ 22536 and ~60% and ~80% respectively by 100 μM DDA. Both compounds also inhibited adenylate cyclase in intact platelets, when this was measured as the increase in cyclic [3H]AMP in platelets labelled with [3H] adenine and then incubated with papaverine. At the concentrations tested (10-500 μM), neither SQ 22536 nor DDA induced platelet aggregation or potentiated aggregation and release of [14C] 5-HT induced by suboptimal concentrations of ADP, Arg8-vasopressin, arachidonic acid or collagen added to heparinized or citrated platelet-rich plasma. However, both compounds partially blocked the inhibition by PGE1 or papaverine of aggregation induced by ADP or Arg8-vasopressin. From the concentrations exerting equal effects, DDA was ~3 times as potent in this regard as SQ 22536. Above 100 μM, the anti-inhibitory effects of both compounds decreased. The actions of these compounds in overcoming inhibition of aggregation by PGE1 were correlated with decreases in platelet cyclic [3H]AMP in platelets labelled with [3H] adenine. The results show that cyclic AMP plays no role in the responses of platelets to aggregating agents unless the platelet cyclic AMP level is elevated above the resting level and confirm that the effects of PGE1 on platelet function are mediated by cyclic AMP.

scholarly journals Regulation of platelet arachidonic acid oxygenation by cyclic AMP

Blood ◽  
1980 ◽  
Vol 56 (5) ◽  
pp. 853-858 ◽  
Author(s):  
AI Schafer ◽  
S Levine ◽  
RI Handin
Keyword(s):  
Arachidonic Acid ◽  
Cyclic Amp ◽  
Plasma Proteins ◽  
Inhibitory Effect ◽  
Albumin Concentration ◽  
Membrane Phospholipids ◽  
Conflicting Evidence ◽  
Induced Aggregation ◽  
Hydrolysis Of

Intracellular cyclic adenosine monophosate (AMP) levels regulate the generation of thromboxane by platelets by inhibiting the hydrolysis of arachidonic acid from membrane phospholipids. However, there is conflicting evidence regarding the role of cyclic AMP in the control of the subsequent oxygenation of arachidonic acid by cyclooxygenase. We studoed the regulation of cyclooxygenase activity by agents that elevate platelet cyclic AMP (dibutyryl cyclic AMP and prostaglandins), measuring arachidonate-induced aggregation, O2 consumption, and malonaldehyde formation. In platelet-rich cyclic AMP. This inhibitory effect of cyclic AMP was absent in gel-filtered platelets suspended in buffer containing 0.5% albumin, and was progressively restored as plasma was added in increasing concentrations. Increasing the albumin concentration in platelet buffer suspensions likewise increased the ability of cyclic AMP to block the arachidonate-induced O2 burst and MDA production. We conclude that (1) the presence of plasma proteins is important in investigating platelet plasma milieu or at least in the presence of physiologic albumin concentrations.

scholarly journals Regulation of platelet arachidonic acid oxygenation by cyclic AMP

Blood ◽  
1980 ◽  
Vol 56 (5) ◽  
pp. 853-858 ◽  
Author(s):  
AI Schafer ◽  
S Levine ◽  
RI Handin
Keyword(s):  
Arachidonic Acid ◽  
Cyclic Amp ◽  
Plasma Proteins ◽  
Inhibitory Effect ◽  
Albumin Concentration ◽  
Membrane Phospholipids ◽  
Conflicting Evidence ◽  
Induced Aggregation ◽  
Hydrolysis Of

Abstract Intracellular cyclic adenosine monophosate (AMP) levels regulate the generation of thromboxane by platelets by inhibiting the hydrolysis of arachidonic acid from membrane phospholipids. However, there is conflicting evidence regarding the role of cyclic AMP in the control of the subsequent oxygenation of arachidonic acid by cyclooxygenase. We studoed the regulation of cyclooxygenase activity by agents that elevate platelet cyclic AMP (dibutyryl cyclic AMP and prostaglandins), measuring arachidonate-induced aggregation, O2 consumption, and malonaldehyde formation. In platelet-rich cyclic AMP. This inhibitory effect of cyclic AMP was absent in gel-filtered platelets suspended in buffer containing 0.5% albumin, and was progressively restored as plasma was added in increasing concentrations. Increasing the albumin concentration in platelet buffer suspensions likewise increased the ability of cyclic AMP to block the arachidonate-induced O2 burst and MDA production. We conclude that (1) the presence of plasma proteins is important in investigating platelet plasma milieu or at least in the presence of physiologic albumin concentrations.

scholarly journals High concentrations of exogenous arachidonate inhibit calcium mobilization in platelets by stimulation of adenylate cyclase

1988 ◽  
Vol 253 (1) ◽  
pp. 255-262 ◽  
Author(s):  
M A Kowalska ◽  
A K Rao ◽  
J Disa
Keyword(s):  
Arachidonic Acid ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Inhibitory Effect ◽  
Irreversible Damage ◽  
Fura 2 ◽  
Messenger Molecules ◽  
Thromboxane Production ◽  
High Concentrations ◽  
Stimulation Of

1. Exposure of platelets to exogenous arachidonic acid results in aggregation and secretion, which are inhibited at high arachidonate concentrations. The mechanisms for this have not been elucidated fully. In our studies in platelet suspensions, peak aggregation and secretion occurred at 2-5 microM-sodium arachidonate, with complete inhibition around 25 microM. 2. In platelets loaded with quin2 or fura-2, the cytoplasmic Ca2+ concentration, [Ca2+]i, rose in the presence of 1 mM-CaCl2 from 60-80 nM to 300-500 nM at 2-5 microM-arachidonate, followed by inhibition to basal values at 25-50 microM. Thromboxane production was not inhibited at 25 microM-arachidonate. Cyclic AMP increased in the presence of theophylline, from 3.5 pmol/10(8) platelets in unexposed platelets to 8 pmol/10(8) platelets at 50 microM-arachidonate; all platelet responses were inhibited with doubling of cyclic AMP contents. 3. The adenylate cyclase inhibitor 2′,5′-dideoxyadenosine attenuated the inhibitory effect of arachidonate, suggesting that it is mediated by increased platelet cyclic AMP and that it is unlikely to be due to irreversible damage to platelets. 4. Aspirin or the combined lipoxygenase/cyclo-oxygenase inhibitor BW 755C did not prevent the inhibition by arachidonate of either [Ca2+]i signals or aggregation induced by U46619. 5. Thus high arachidonate concentrations inhibit Ca2+ mobilization in platelets, and this is mediated by stimulation of adenylate cyclase. High arachidonate concentrations influence platelet responses by modulating intracellular concentrations of two key messenger molecules, cyclic AMP and Ca2+.

scholarly journals Oscillations of cyclic nucleotide concentrations in relation to the excitability of Dictyostelium cells

1979 ◽  
Vol 81 (1) ◽  
pp. 33-47 ◽  
Author(s):  
G. Gerisch ◽  
D. Malchow ◽  
W. Roos ◽  
U. Wick
Keyword(s):  
Signal Processing ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Inhibitory Effect ◽  
Camp Concentration ◽  
Surface Receptors ◽  
Camp Generation ◽  
Adenylate Cyclase Activation ◽  
Signal Input ◽  
Extracellular Camp

Aggregating cells of Dictyostelium discoideum are able to release cyclic AMP periodically. The oscillations of cAMP generation are associated with changes in adenylate cyclase activity. Cyclic AMP receptors on the cell surface are functionally coupled to the oscillating system as evidenced by phase shifts that are induced by small pulses of extracellular cAMP. An important element of the oscillating system is the signal processing from surface receptors to the adenylate cyclase. This pathway exhibits adaptation resulting in the suppression of responses to constant, elevated concentrations of cAMP. The signal input for adenylate cyclase activation is, therefore, a change in the extracellular cAMP concentration with time. Oscillations in the absence of detectable changes of intra- or extracellular cAMP concentrations suggest the possibility that there is a metabolic network in D. discoideum cells that undergoes oscillations without coupling to adenylate cyclase. Cyclic GMP concentrations oscillate with a slight phase difference in advance of that of cAMP, suggesting that the two nucleotide cyclases might not be activated by the same mechanism. Elevation of extracellular calcium exerts an inhibitory effect on the accumulation of cAMP and on the second of the two cGMP peaks.

Roles of Cyclic Nucleotides in the Inhibition of Platelet Function by Physiolocic and Pharmacological Agents

1979 ◽  
Author(s):  
R.J. Haslam
Keyword(s):  
Platelet Aggregation ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Platelet Function ◽  
Inhibitory Effects ◽  
Pharmacological Agents ◽  
Arterial Blood ◽  
Cyclic Cmp ◽  
Amp Inhibition

Cyclic AMP mediates the inhibitions of platelet aggregation caused by PCI2, PGE1 and PGD2. Thus, these compounds activate platelet adenylate cyclase and Increase platelet cyclic AMP; their inhibitory effects are blockod by inhibitor? of adenylate cyclase, are potentiated by inhibitors of cyclic AKP phosphodiesterase and are mimicked hy N6 ,2'-0-dibutyryl cyclic AMP. Inhibition of adenylate cyclase does not potentiate platelet aggregation in the absence of inhibitory prostaglandins, indicating that platelet cyclic AMP is too low to affect aggregation under these conditions. To determine whether platelets in the circulation are exposed to agents that increase platelet cyclic AMP, washed rabbi platelets labelled with [3H] adenine were incubated with rabbit arterial blood under various conditions; any increases in cyclic [3H]AMP were measured. These experiments showed that freshly taken rabbit arterial blood does not normally contain any factors that can increase platelet cyclic AMP sufficiently to affect platelet function; specifically, circulating PGI2 was less than 0.1 pmol/ml of blood. It follows that increases in cyclic AMP in circulating rabbit platelets must occur only locally or under special conditions. The role of the moderate increases in platelet cyclic CMP caused by aggregating agents remains uncertain, but the inhibition of aggregation by compounds such as sodium nitroprusside that increase cyclic CMP up to 100-fold suggests that cyclic CMP may, like cyclic AMP, be an inhibitory mediator.

scholarly journals Role of diamine oxidase during the treatment of tumour-bearing mice with combinations of polyamine anti-metabolites

1983 ◽  
Vol 212 (3) ◽  
pp. 895-898 ◽  
Author(s):  
A Kallio ◽  
J Jänne
Keyword(s):  
Diamine Oxidase ◽  
Potent Inhibitor ◽  
Specific Inhibitor ◽  
Inhibitory Effect ◽  
Tumour Cells ◽  
Adenosylmethionine Decarboxylase ◽  
Growth Inhibitory ◽  
Sequential Combination ◽  
Marked Accumulation

Treatment of mice bearing L1210 leukaemia with 2-difluoromethylornithine, a specific inhibitor of ornithine decarboxylase (EC 4.1.1.17), produced a profound depletion of putrescine and spermidine in the tumour cells. Sequential combination of methylglyoxal bis(guanylhydrazone), an inhibitor of adenosylmethionine decarboxylase (EC 4.1.1.50), with difluoromethylornithine largely reversed the polyamine depletion and led to a marked accumulation of cadaverine in the tumour cells. Experiments carried out with the combination of difluoromethylornithine and aminoguanidine, a potent inhibitor of diamine oxidase (EC 1.4.3.6), indicated that the methylglyoxal bis(guanylhydrazone)-induced reversal of polyamine depletion was mediated by the known inhibition of diamine oxidase by the diguanidine. In spite of the normalization of the tumour cell polyamine pattern upon administration of methylglyoxal bis(guanylhydrazone) to difluoromethylornithine-treated animals, the combination of these two drugs produced a growth-inhibitory effect not achievable with either of the compounds alone.

scholarly journals Prostacyclin as a potent effector of adipose-cell differentiation

1989 ◽  
Vol 257 (2) ◽  
pp. 399-405 ◽  
Author(s):  
R Négrel ◽  
D Gaillard ◽  
G Ailhaud
Keyword(s):  
Arachidonic Acid ◽  
Cyclic Amp ◽  
Critical Role ◽  
Terminal Differentiation ◽  
Prostaglandin F2 Alpha ◽  
Adipogenic Effect ◽  
Adipose Cells

The terminal differentiation of Ob1771 pre-adipose cells induced by arachidonic acid in serum-free hormone-supplemented medium containing insulin, transferrin, growth hormone, tri-iodothyronine and fetuin (5F medium) was strongly diminished in the presence of inhibitors of prostaglandin synthesis, namely aspirin or indomethacin. Carbaprostacyclin, a stable analogue of prostacyclin (prostaglandin I2) known to be synthesized by pre-adipocytes and adipocytes, behaved as an efficient activator of cyclic AMP production and was able, when added to 5F medium, to mimic the adipogenic effect of arachidonic acid. Prostaglandins E2, F2 alpha and D2, unable to affect the cyclic AMP production, failed to substitute for carbaprostacyclin. However, prostaglandin F2 alpha, which is another metabolite of arachidonic acid in pre-adipose and adipose cells, able to promote inositol phospholipid breakdown and protein kinase C activation, potentiated the adipogenic effect of carbaprostacyclin. In addition, carbaprostacyclin enhanced both a limited proliferation and terminal differentiation of adipose precursor cells isolated from rodent and human adipose tissues maintained in primary culture. These results demonstrate the critical role of prostacyclin and prostaglandin F2 alpha on adipose conversion in vitro and suggest a paracrine/autocrine role of both prostanoids in the development of adipose tissue in vivo.

ADRENALINE (ADR) INTERACTIONS WITH THROMBIN AND COLLAGEN -EFFECTS ON PLATELET ARACHIDONATE RELEASE AND 5HT SECRETION AND ROLE OF ENDOGENOUSLY FORMED THROMBOXANE A2 (TxA2)

1987 ◽  
Author(s):  
Y Patel ◽  
S Krishnamurthi ◽  
V V Kakkar
Keyword(s):  
Arachidonic Acid ◽  
Platelet Aggregation ◽  
Adenylate Cyclase ◽  
Synergistic Effects ◽  
Thromboxane A2 ◽  
Human Platelets ◽  
Presence And Absence ◽  
Pre Treatment ◽  
Arachidonate Release

We have examined the effect of combinations of ADR + thrombin (T) and ADR + collagen (C) on platelet arachidonate release and 5HT secretion, and assessed the role of endogenously formed TxA2 on these responses using indomethacin (I). Washed, human platelets prelabelled with [3H]-arachidonic acid (AA) or [14C]-5HT were used, ADR was added 10 sec before T or C and the reaction was terminated 3 min later. In the range 1-100μM, ADR induced no detectable aggregation or 5HT secretion but potentiated platelet aggregation when added with sub-threshold concentrations of T or C, which on their own induced no aggregation. At 2-4 fold higher concentrations of T and C (threshold for 5HT secretion), 5HT secretion and AA/TXB2 release were also potentiated by ADR (1-10μM) by 30-50%. Pre-treatment of platelets with I (10μM) abolished threshold T and C-induced 5HT secretion, as well as its potentiation by ADR. However, approximately 2-fold and 5-fold higher concentrations of T and C respectively were able to induce 'I-insensitive'secretion, which was further potentiated by ADR. In I-treated platelets, C-induced AA release and its potentiation by ADR were also abolished suggesting a role for endogenously formed TxA2 This was confirmed by addition of the TxA2 mimetic, U46619 (0.3μM), which potentiated C-induced AA release in the presence and absence of ADR, even though it induced no AA release on its own or, in combination with ADR alone in the absence of collagen. The latter suggests agonist specificity regarding the ability of TxA2 to synergistically stimulate AA release. Finally, unstirred platelets in PRP pre-incubated with ADR (10μM) for 120 min lost their responsiveness to ADR, when eventually stirred; however, these 'ADR-desensitised' platelets when washed and resuspended, were able to demonstrate synergistic effects on secretion when stimulated with ADR+T or ADR+C. This is analogous to the previously demonstrated ability of ADR to inhibit adenylate cyclase even in 'ADR-desensitised' platelets and re-inforces the separation regarding the mechanisms underlying the various effects of ADR on platelets.

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