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Biomedical subjects

D Deykin

Publications and source records attributed to D Deykin.

At least 55 records · Page 3Linked to original sources
PubMed1987

Neointimal hyperplasia occurring after carotid endarterectomy in a canine model: effect of endothelial cell seeding vs. perioperative aspirin.

Neointimal hyperplasia of the arterial wall may occur after carotid endarterectomy. This proliferative lesion is a pathologic response of the injured arterial wall and may lead to progressive stenosis. We investigated the effect of endothelial cell seeding (ECS) or antiplatelet therapy with aspirin (ASA) on inhibition of this lesion in a canine model. Endarterectomies were performed in 160 carotid arteries; 46 endarterectomies were treated perioperatively with aspirin (325 mg per day), 34 were seeded with a high density (3 X 10(6)) of autogenous endothelial cells, and 80 were untreated control arteries. At selected time intervals, the patent arteries were perfusion-fixed and the cross-sectional area (measured in square millimeters) of neointimal hyperplasia was measured by means of digital planimetry. At 6 weeks, patency of the endarterectomized carotid artery was 88% in the ASA and ECS groups, in contrast to 35% in the control group (p less than 0.01). The cross-sectional area of neointimal hyperplasia was not significantly different in the ASA and the control groups at 6 weeks. However, the ECS group showed a marked reduction in neointimal hyperplasia at 6 weeks (p less than 0.01). This inhibition of neointimal hyperplasia after carotid endarterectomy by ECS may reflect accelerated luminal healing or a direct inhibition of smooth muscle cell proliferation in the injured arterial wall.

Animals↗
PubMed1986

Effects of insulin and prior exercise on prostaglandin release from perfused rat muscle. Evidence that prostaglandins do not mediate changes in glucose uptake.

Prostaglandin generation and its inter-relation to the metabolic effects of insulin and prior exercise were examined in perfused muscle of fed rats. During a 60 min perfusion of the rat hindquarter, a substantial release of the prostaglandins PGF2 alpha, PGE2 and 6-oxoPGF1 alpha was observed. Blood cells present in the perfusate released these substances in negligible amounts indicating the prostaglandins were produced by the hindquarter. Addition of insulin to the perfusate increased both glucose uptake and the generation of PGE2 and 6-oxoPGF1 alpha. At 30 min after intense treadmill exercise, glucose and alpha-aminoisobutyric acid (AIB) uptake by the hindquarter were increased in the absence of added insulin, but prostaglandin release was not increased. Insulin further increased glucose and AIB uptake; however, in contrast with its effects in non-exercised rats, insulin no longer stimulated prostaglandin generation. Indomethacin (10 microM) added to the perfusate inhibited the release of PGF2 alpha and PGE2 by 90% and the release of 6-oxoPGF1 alpha by 54%. It had no effect on the stimulation of glucose uptake by either insulin or prior exercise. The data indicate that insulin increases prostaglandin synthesis by perfused rat muscle, and that prior exercise blocks this effect. They suggest that under the conditions studied prostaglandins do not mediate the effects of insulin or prior exercise on glucose uptake.

Aminoisobutyric Acids↗
PubMed1986

Incorporation and redistribution of arachidonic acid in diacyl and ether phospholipids of bovine aortic endothelial cells.

The present experiments characterized the incorporation and redistribution of arachidonic acid in diacyl and ether phospholipids of bovine aortic endothelial cells. Confluent cultures were either continuously labeled or pulse labeled with [14C]arachidonic acid. Major lipid classes and ether-linked subclasses of phosphatidyl-ethanolamine (PE) and phosphatidylcholine (PC) were separated by high-performance liquid chromatography and thin-layer chromatography. During continuous labeling, total incorporation of arachidonic acid reached a peak at 8 h and was essentially constant up to 24 h. After 8 h, net label in total PC declined, whereas that in total PE continued to rise. In pulse labeling experiments radioactivity in diacyl PC continuously declined with concomitant increases in both diacyl- and alkenylacyl PE. The data demonstrate that transfer of arachidonic acid from diacyl PC to both diacyl- and alkenylacyl PE occurs in endothelial cells. In contrast to previous observations in platelets, transfer of arachidonic acid to alkenylacyl PE did not require agonist stimulation. This pathway may contribute to the enrichment of endothelial cell PE with arachidonic acid with the potential for subsequent metabolism to prostacyclin.

Acylation↗
PubMed1986

Solubilization and properties of Ca2+-dependent human platelet phospholipase A2.

Using a sonicated dispersion of radiolabeled 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine as substrate, we found that phospholipase A2 activity of human platelets was enhanced 2.4-fold by albumin (1 mg/ml). The enzyme was recovered predominantly in the cytosolic fraction of platelets with less than a third of its activity being associated with the membrane fraction. In the presence of 24 mM n-octyl-beta-D-glucopyranoside (octylglucoside) phospholipase A2 was effectively (more than 90%) extracted from platelet lysates without solubilization of platelet membranes. Ion exchange chromatography of the soluble enzyme yielded a phospholipase A2 of unchanged total activity and great stability. This phospholipase A2 was active only in the presence of divalent cations (Ca2+ greater than Sr2+ greater than Mg2+ = 0), required albumin for optimal activity and exhibited exclusive positional specificity for the acyl ester bond at the 2-position of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine. Indomethacin (500 microM), mepacrine (500 microM) and N-ethylmaleimide (4 mM) inhibited the phospholipase A2 by 69, 62 and 19%, respectively. The results are discussed in the light of previous findings on human platelet phospholipase A2.

Albumins↗
PubMed1986

Effect of streptozotocin-induced diabetes on prostaglandin production by rat cerebral microvessels.

Diabetes has been shown to result in reduced prostacyclin synthesis by macrovascular tissue in rats and humans. Other studies have shown that plasma levels of 6-keto-prostaglandin-F1 alpha (6-keto-PGF1 alpha) and synthesis of 6-keto-PGF1 alpha by isolated glomeruli are either unchanged or increased in diabetes. Thus, microvascular tissue may respond differently to diabetes than macrovascular tissue. Accordingly, we have studied the effects of streptozotocin-induced diabetes mellitus on prostaglandin synthesis by rat cerebral microvessel (RCMV). Prostaglandin synthesis from both endogenous and exogenous arachidonic acid was determined. The yield of RCMV from diabetic and control animals was similar. Under basal conditions and following stimulation of prostaglandin synthesis by melittin (5 micrograms/ml), RCMV production of prostacyclin (measured as immunoreactive 6-keto-PGF1 alpha) was greater than production of PGE2. Both 6-keto-PGF1 alpha and PGE2 production under basal and stimulated conditions were found to be similar for control and diabetic RCMV. The RCMV converted exogenous [3H]arachidonic acid predominately to PGD2 and to a lesser extent to 6-keto-PGF1 alpha. No significant differences in the conversion of exogenous [3H]arachidonic acid to PGD2 and 6-keto-PGF1 alpha was observed between control and diabetic RCMV. This study suggests that the effect of streptozotocin-induced diabetes mellitus on prostaglandin formation by microvascular endothelium is different from its effect on macrovascular tissue.

Animals↗
PubMed1986

Effect of alternate-day regular and enteric-coated aspirin on platelet aggregation, bleeding time, and thromboxane A2 levels in bleeding-time blood.

The effectiveness of low-dose aspirin for primary prevention of cardiovascular mortality is being assessed among the nearly 22,000 United States physicians currently participating in the Physicians' Health Study. Because of occasional reports of gastric irritation among study participants, two enteric-coated aspirin preparations were tested as possible alternatives to regular compressed aspirin for platelet inhibition. Thirty-three volunteers were assigned randomly to one of four treatment groups: regular aspirin (325 mg), placebo, and two enteric-coated aspirin preparations (325 mg). Pills were administered every other day, duplicating the regimen used in the Physicians' Health Study. Bleeding times, platelet aggregation, and thromboxane A2 levels produced by aggregating platelets in vitro, as well as in collected bleeding-time blood, were determined. Measurements were taken before and after a single dose as well as after seven alternate-day doses. Regular and enteric-coated aspirin preparations were equally efficacious in prolonging the bleeding time, inhibiting platelet aggregation, and suppressing thromboxane A2 production. There was virtually complete suppression of thromboxane A2 production (over 99 percent), by platelets in vitro and in collected bleeding-time blood. The levels were still profoundly reduced (89 percent) 48 hours after the last dose. Enteric-coated aspirin may provide an alternative to regular aspirin in a low-dose regimen designed to inhibit platelet activity.

Adult↗
PubMed1986

The natural history of endothelial structure and function in arterialized vein grafts.

When the saphenous vein is used in the in situ position for arterial bypass surgery, it is associated with more optimal preservation of the endothelial lining and with improved graft patency compared with reversed vein grafts. However, it is not clear whether preservation of endothelial integrity persists after arterialization. The goal of this study was to establish whether preservation of the endothelium before arterialization is a critical factor in the development of late functional and morphologic abnormalities of autogenous vein grafts. Paired reversed and in situ vein grafts were created in 75 mongrel dogs. Veins to be used in the reversed position were excised and stored in either heparinized whole blood at 37 degrees C or saline solution at 4 degrees C. Veins were studied before and after arterialization. The veins were arterialized by anastomosis to the carotid artery and excised at intervals of 1 day to 12 weeks for studies of the luminal production of prostacyclin and thromboxane A2 in addition to luminal morphology. Before arterialization, normothermic whole blood preserved biochemical function of the endothelium significantly better than hypothermic saline solution, but not as well as the in situ vein procedure. Soon after arterialization, all three vein grafts showed significant functional and morphologic abnormalities consistent with injury of the vein graft. Morphologic healing of the endothelial monolayer progressed slowly back to normal; however, the biochemical capacity of the vein graft never matched that of the prearterialized vein, nor that of normal host arteries. Regardless of surgical technique, all vein grafts exhibited a period of abnormal structure and function, which exposed them to the risk of thrombogenesis. This period of potential leukocyte or platelet interaction with the vein wall could lead to release phenomena as well as proliferative changes in the vessel wall.

6-Ketoprostaglandin F1 alpha↗
PubMed1986

Beneficial effect of aspirin in maintaining the patency of small-caliber prosthetic grafts after thrombolysis with urokinase or tissue-type plasminogen activator.

Despite successful thrombolysis of occluded prosthetic grafts, rethrombosis remains a problem. We investigated the efficacy of aspirin in maintaining patency of polytetrafluoroethylene grafts (3 mm X 3.5 cm) in canine femoral arteries after thrombolytic therapy. After induction of thrombosis, either tissue-type plasminogen activator (t-PA) or urokinase (UK) was infused just proximal to the thrombus (4000 U/min) until complete thrombolysis was achieved. Five of the 10 UK-treated dogs and five of the 10 t-PA-treated dogs received aspirin immediately after recanalization, and aspirin was continued (325 mg/day) for 4 weeks or until occlusion occurred. A systemic aspirin effect was confirmed by marked depression of serum thromboxane B2 and absent platelet aggregation. Only two of the 10 grafts in the aspirin-free group remained patent for 4 weeks. The remaining eight grafts had all reoccluded by 2 weeks. None of the 10 grafts in the aspirin-treated group reoccluded during the 4 weeks. This significantly improved patency (p less than .001) in the aspirin-treated group was observed equally in grafts treated with t-PA or UK. Thus aspirin is a potent agent in preventing rethrombosis after thrombolytic recanalization of prosthetic grafts.

Animals↗
PubMed1986

Low-dose enteric-coated aspirin: a practical approach to continuous-release low-dose aspirin and presystemic acetylation of human platelet cyclooxygenase.

Using a granular enteric-coated aspirin (ECA) preparation, we achieved continuous release of low-dose aspirin and associated inhibition of platelet reactivity. The lowest once-daily dose that produced greater than 90% inhibition of serum thromboxane (TX) A2 after 7 days was 80 mg. The time course of inhibition after the first dose indicated a gradual release of aspirin over a period of 8 hours. We subsequently fractionated this 80 mg dose into three times daily doses of 27 mg that were administered to nine healthy men for 7 days. This regimen resulted in 96% inhibition of serum TXA2 generation (P less than 0.001), inhibition of in vitro platelet aggregation (P less than 0.05), prolongation of the bleeding time by 75% (P less than 0.01), and a threefold increase in inhibition of platelet aggregation by prostacyclin (P less than 0.01) compared with pre-ECA values. In contrast to our previous study using daily 80 mg doses of ECA, after the 27 mg three times daily regimen we found a significant increase in circulating platelet cyclooxygenase activity 24 hours after the final dose (P less than 0.05). This immediate recovery indicates active megakaryocyte cyclooxygenase and suggests that acetylation of platelet cyclooxygenase was restricted to the presystemic circulation. We conclude that long-term dosing with 27 mg ECA three times daily results in profound inhibition of platelet TXA2 production, and diminished in vitro and in vivo platelet reactivity. This regimen provides a practical approach to achieving continuous release of low-dose aspirin and possible presystemic acetylation of platelet cyclooxygenase.

Acetylation↗
PubMed1985

Cumulative antiplatelet effect of low-dose enteric coated aspirin.

Enteric coated aspirin (ECA) at doses of 325-1300 mg is an effective alternative to regular aspirin for inhibition of platelet activity while avoiding gastric irritation. The objectives of this study were to determine: (1) the lowest chronic dose of ECA providing effective inhibition of platelet activities, (2) the time course of the inhibition, and (3) the reappearance of platelet cyclo-oxygenase activity. Seven subjects were studied before and after seven daily doses of 40-325 mg ECA. Serum thromboxane (TX) B2 levels indicated that the lowest dose of ECA resulting in greater than 90% inhibition of platelet cyclo-oxygenase was 80 mg/d. Platelet aggregation and ATP release in response to collagen (1 microgram/ml) and arachidonic acid (1 mM) were abolished and bleeding times were prolonged from 6.1 +/- 1.5 min to 9.7 +/- 2.8 min (mean +/- SD, P less than 0.01). Examination of platelet cyclo-oxygenase activity on a daily basis revealed that 24 h after the first 80 mg dose serum TXB2 had decreased by approximately 60% and was suppressed by more than 90% after four doses. Recovery of platelet cyclo-oxygenase activity after a single 80 mg dose of ECA was delayed for 48-72 h indicating that aspirin reached the systemic circulation. We conclude that chronic inhibition of platelet activity may be achieved in a cumulative manner with 80 mg ECA/d.

Adenosine Triphosphate↗
PubMed1985

Abnormal factor VIII coagulant antigen in patients with renal dysfunction and in those with disseminated intravascular coagulation.

Factor VIII antigen (VIII:CAg) exhibits molecular weight heterogeneity in normal plasma. We have compared the relative quantities of VIII:CAg forms present in normal individuals (n = 22) with VIII:CAg forms in renal dysfunction patients (n = 19) and in patients with disseminated intravascular coagulation (DIC; n = 7). In normal plasma, the predominant VIII: CAg form, detectable by sodium dodecyl sulfate polyacrylamide gel electrophoresis, was of molecular weight 2.4 X 10(5), with minor forms ranging from 8 X 10(4) to 2.6 X 10(5) D. A high proportion of VIII:CAg in renal dysfunction patients, in contrast, was of 1 X 10(5) mol wt. The patients' high 1 X 10(5) mol wt VIII: CAg level correlated with increased concentrations of serum creatinine, F1+2 (a polypeptide released upon prothrombin activation), and with von Willebrand factor. Despite the high proportion of the 1 X 10(5) mol wt VIII:CAg form, which suggests VIII:CAg proteolysis, the ratio of Factor VIII coagulant activity to total VIII:CAg concentration was normal in renal dysfunction patients. These results could be simulated in vitro by thrombin treatment of normal plasma, which yielded similar VIII:CAg gel patterns and Factor VIII coagulant activity to antigen ratios. DIC patients with high F1+2 levels but no evidence of renal dysfunction had an VIII:CAg gel pattern distinct from renal dysfunction patients. DIC patients had elevated concentrations of both the 1 X 10(5) and 8 X 10(4) mol wt VIII:CAg forms. We conclude that an increase in a particular VIII:CAg form correlates with the severity of renal dysfunction. The antigen abnormality may be the result of VIII:CAg proteolysis by a thrombinlike enzyme and/or prolonged retention of proteolyzed VIII:CAg fragments.

Aged↗
PubMed1985

Influence of platelet volume on the ability of prostacyclin to inhibit platelet aggregation and the release reaction.

The influence of mean platelet volume (MPV) and platelet count on in vitro platelet sensitivity to prostacyclin (PGI2) was studied with human size-dependent platelet subpopulations prepared by counterflow centrifugation. The original unfractionated platelet suspension and each of five size-dependent platelet fractions were suspended in buffer at a platelet count of 2 X 10(8)/ml. The percent decrease in the extent of platelet aggregation and adenosine triphosphate (ATP) release in response to 10 micrograms/ml collagen was determined over a range of PGI2 concentrations in a Lumi-Aggregometer. A significant positive correlation between MPV and the concentration required to give 50% inhibition for both platelet aggregation and ATP release (r = 0.99, p less than 0.001 and r = 0.99, p less than 0.001, respectively) was observed. In separate experiments, the effect of platelet count on the ability of a given dose of PGI2 to inhibit platelet aggregation and ATP release was determined, and a significant inverse correlation was noted (r = 0.99, p less than 0.01 and r = 0.98, p less than 0.01, respectively). Our data indicate that the sensitivity of human platelets to the inhibitory effects of PGI2 is dependent on both the platelet volume and the platelet count. Thus, the presence of a greater platelet mass, resulting from either an increased MPV or an increased platelet count, decreases the inhibitory effectiveness of PGI2 on both platelet aggregation and the release reaction.

Adenosine Triphosphate↗
PubMed1984

Metabolism of platelet-activating factor in human platelets. Transacylase-mediated synthesis of 1-O-alkyl-2-arachidonoyl-sn-glycero-3-phosphocholine.

The present study demonstrates that inactivation of exogenous 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (alkylacetyl-GPC; platelet-activating factor) by human platelets is mediated by the sequential action of two enzymes, 1) a Ca2+-independent acetylhydrolase recovered in the cytosolic fraction of platelets that deacylates alkylacetyl-GPC forming alkyllyso-GPC and 2) a CoA-independent, N-ethylmaleimide-sensitive transacylase associated with platelet membranes that incorporates a long-chain fatty acid into alkyllyso-GPC to produce alkylacyl-GPC. Separation of platelet phospholipids and subsequent resolution into individual molecular species by high-performance liquid chromatography revealed that the newly formed alkylacyl-GPC was exclusively alkylarachidonoyl-GPC and that the arachidonoyl group for acylation of alkyllyso-GPC was provided by phosphatidylcholine. We conclude that the previously described platelet arachidonoyl transacylase (Kramer, R.M., and Deykin, D. (1983) J. Biol. Chem. 258, 13806-13811) may play an important role in the metabolism of platelet-activating factor.

Acyltransferases↗
PubMed1984

Coenzyme A-mediated arachidonic acid transacylation in human platelets.

Platelet membranes contain two distinct transacylase activities catalyzing the synthesis of arachidonoyl phosphatides by acylation of added lysophosphatides with endogenous esterified arachidonate. In the absence of CoA, arachidonate is incorporated only into ethanolamine lysophosphatides with a high preference for the plasmalogen form (Kramer, R. M., and Deykin, D. (1983) J. Biol. Chem. 258, 13806-13811). In the presence of CoA, however, lysophospholipids are acylated in the order 1-acyl-lysophosphatidylserine greater than 1-acyl-lysophosphatidylethanolamine greater than 1-acyl-lysophosphatidylinositol. The CoA-mediated transacylation reaction was characterized with 1-acyl-lysophosphatidylserine as acyl acceptor. It was highly specific for arachidonate and preferentially used phosphatidylcholine as the arachidonoyl donor. This enzymatic pathway may be part of a deacylation-transacylation cycle for remodeling of phospholipids synthesized de novo (according to the Lands pathway) representing a mechanism for enrichment of phospholipids with arachidonic acid.

Acylation↗
PubMed1984

Favorable balance of prostacyclin and thromboxane A2 improves early patency of human in situ vein grafts.

Graft thrombosis soon after reconstruction remains a major obstacle to the use of reversed vein grafts in infrapopliteal reconstruction. Our clinical experience with in situ vein grafts corroborates Leather's results by demonstrating an overall graft patency of 95% below the knee at 1 year and 94% in the infrapopliteal group. It has been postulated that this improved early patency rate of in situ vein grafts is the result of more optimal preservation of the endothelium of the vein graft. To investigate this hypothesis, human saphenous veins were handled by an in situ and a reversed technique. The intact vein segments were then tested for luminal production of prostacyclin and thromboxane A2 and fixed for scanning electron microscopic analysis of the surface morphology. This study demonstrated that endothelial cell prostacyclin release is enhanced in human in situ vein segments but not in reversed vein segments. In addition, luminal production of thromboxane A2 is significantly greater in the reversed than in the in situ vein segments. These findings are associated with marked endothelial structural damage in the reversed veins and minimal endothelial disruption in the in situ veins. Therefore the ratio of the antiaggregatory vasodilator prostacyclin to the proaggregatory vasoconstrictor thromboxane A2 is significantly more favorable for the in situ vein segment than for the reversed vein segment. The observed excellent early patency of the in situ vein grafts in our poor-risk patient population may in part be the result of this favorable balance of prostacyclin and thromboxane A2 and the more optimally preserved endothelial morphology.

Aged↗
PubMed1984

Luminal release of prostacyclin and thromboxane A2 by arteries distal to small-caliber prosthetic grafts.

Myointimal hyperplasia distal to prosthetic grafts may be due to a local imbalance of prostacyclin and thromboxane A2 that exaggerates platelet adherence. This study evaluated prostacyclin and thromboxane A2 production by arteries distal to prosthetic grafts. In 12 dogs, control segments of both iliac arteries were excised and a 5 cm segment of polytetrafluoroethylene was grafted end to end. One iliac artery was circumferentially dissected from the distal anastomosis to the inguinal ligament. The contralateral artery was not dissected. Of the 24 grafts, 19 remained patent and the arteries distal to these grafts were studied. After excision, each artery was analyzed for its ability to produce prostacyclin and thromboxane A2. Our data indicate that the luminal surface of a normal artery spontaneously produces both prostacyclin and thromboxane A2 and that the arterial wall distal to a prosthetic graft produces increased levels of these arachidonic acid metabolites. However, only those arteries not surgically dissected maintain a normal balance of prostacyclin and thromboxane A2. The dissected artery may thus be more susceptible to platelet interaction and myointimal hyperplasia.

Animals↗
PubMed1984

Platelet size and age determine platelet function independently.

This study was undertaken to examine the interaction of platelet size and age in determining in vitro platelet function. Baboon megakaryocytes were labeled in vivo by the injection of 75Se-methionine. Blood was collected when the label was predominantly associated with younger platelets (day 2) and with older platelets (day 9). Size-dependent platelet subpopulations were prepared on both days by counterflow centrifugation. The reactivity of each platelet subpopulation was determined on both days by measuring thrombin-induced aggregation. Platelets were fixed after partial aggregation had occurred by the addition of EDTA/formalin. After removal of the aggregated platelets by differential centrifugation, the supernatant medium was assayed for remaining platelets and 75Se radioactivity. Comparing day 2 and day 9, no significant difference was seen in the rate of aggregation of a given subpopulation. However, aggregation was more rapid in the larger platelet fractions than in the smaller ones on both days. A greater percentage of the 75Se radioactivity appeared in the platelet aggregates on day 2 than on day 9. This effect was independent of platelet size, as it occurred to a similar extent in the unfractionated platelets and in each of the size-dependent platelet subpopulations. The data indicate that young platelets are more active than older platelets. This study demonstrates that size and age are both determinants of platelet function, but by independent mechanisms.

Animals↗