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Biomedical subjects

R L Kinlough-Rathbone

Publications and source records attributed to R L Kinlough-Rathbone.

At least 109 records · Page 6Linked to original sources
PubMed1983

ADP-induced changes in [32P]phosphate labeling of phosphatidylinositol-4,5-bisphosphate in washed rabbit platelets made refractory by prior ADP stimulation.

Changes in 32P labeling of phosphatidylinositol-4,5-bisphosphate (PIP2) were examined during ADP-induced aggregation of washed rabbit platelets prelabeled with [32P]phosphate. ADP caused a significant decrease in the amount and 32P labeling of PIP2 at 10 and 60 sec. The decrease in labeling persisted at 2.5 min when the platelets were still aggregated, but disappeared by 10 min. Platelets refractory to ADP showed no further significant change in 32P in PIP2 when exposed to ADP; a decrease in PIP2 labeling could be induced, however, after platelets had recovered their disc shape and sensitivity to ADP. These data indicate that PIP2 may play a role in the response of platelets to ADP.

Adenosine Diphosphate↗
PubMed1983

Aspirin in the treatment of cardiovascular disease: a review.

Large-scale clinical trials of the use of aspirin in post-myocardial infarction patients were based on the assumption that inhibition of platelet activity would reduce thromboembolism associated with atherosclerosis, and that thromboembolism is a major cause of the clinical complications of atherosclerosis. However, spasm and occlusive thrombi may also contribute to this picture, and thus thromboembolism is probably only one of the mechanisms that cause the clinical complications. Aspirin inhibits thrombosis only if thromboxane A2 formation by platelets plays a major part in the growth of thrombi; aspirin has little effect on thrombosis when thrombin generation and fibrin formation are dominant factors. Nevertheless, analysis of the combined data from the six clinical trials indicates a highly significant (21 percent) reduction in reinfarction rate and a 16 percent reduction in cardiovascular mortality rate in patients treated with aspirin. Aspirin may be most useful in treating an as-yet-unidentified subgroup of patients.

Aspirin↗
PubMed1983

Reversal of shortened platelet survival in rats by the antifibrinolytic agent, epsilon aminocaproic acid.

Platelet survival in rabbits and rats is shortened by placing indwelling catheters in the aorta; this shortening appears to be at least partly related to the extent of vessel wall injury and platelet interaction with the repeatedly damaged wall. Treatment of rabbit platelets with plasmin and other proteolytic enzymes in vitro shortens their survival when they are returned to the circulation. Because platelets may be exposed to plasmin and other proteolytic enzymes in rabbits and rats with indwelling aortic catheters, we examined the effect of epsilon-aminocaproic acid (EACA) on platelet survival in rats. At a dose of 1 g/kg every 4 h, EACA significantly reduced whole blood fibrinolytic activity and prolonged the shortened platelet survival in rats with indwelling aortic catheters. Mean platelet survival for untreated rats with indwelling aortic catheters was 38.6 +/- 1.9 h, and for rats treated with EACA, 53.8 +/- 3.8 h. Scanning electron microscopy showed that the injured vessel wall of these animals was mainly covered with platelets and fibrin, whereas in control animals that did not receive EACA, the injured surface was mainly covered with platelets and little fibrin was observed. Thus shortened platelet survival during continuous vessel wall injury may result from the local generation of plasmin or the release of proteolytic enzymes at sites where platelets (and possibly leukocytes) interact with the vessel wall.

Aminocaproates↗
PubMed1983

Effect of aspirin and sodium salicylate on thrombosis, fibrinolysis, prothrombin time, and platelet survival In rabbits with indwelling aortic catheters.

We have studied the effect of different doses of aspirin on platelet function, PGI2 formation, platelet survival, thrombosis, fibrinolysis, and prothrombin time in rabbits with indwelling aortic catheters. The thrombi formed around indwelling aortic catheters were found to have a large fibrin component, and their formation was inhibited by heparin administration. Thus, in these experiments we examined the effect of aspirin (a weak inhibitor of thrombin-mediated platelet aggregation) under conditions in which thrombin was a major factor in the initiation and growth of the thrombi. Only very high doses of aspirin tended to inhibit thrombus formation over the 5-day period of observation, and a statistically significant inhibition of thrombus formation was produced by equivalent concentrations of sodium salicylate. The failure of high doses of aspirin to achieve a significant inhibition of thrombosis under the conditions of these experiments (whereas an equivalent dose of sodium salicylate was inhibitory) could be due to aspirin inhibition of PGI2 formation. Shortened platelet survival was not affected by aspirin treatment or the dose sodium salicylate that inhibited thrombus formation. The tendency to inhibit thrombus formation appeared to be unrelated to an effect on platelets but was associated with prolongation of the one-stage prothrombin time and increased whole blood fibrinolytic activity; doses of aspirin that inhibited platelet aggregation in response to sodium arachidonate or collagen, and PGI2 formation by the vessel wall, did not have a significant effect on the amount of thrombus present at 5 days. However, the high doses of aspirin that inhibited PGI2 formation were associated with a tendency to increased thrombus formation during the first 3 hr after insertion of the catheter. The results of these experiments show that when thrombin is an important factor in the formation of thrombi, aspirin is a weak inhibitor of thrombosis unless doses are used that provide sufficient salicylate to interfere with blood coagulation and promote whole blood fibrinolytic activity. These results also show that thrombus formation can be inhibited without an apparent change in platelet survival.

Animals↗
PubMed1983

Changes in the properties of platelets from rats with experimentally induced shortened platelet survival.

Platelet survival is shortened in experimental animals in which indwelling aortic catheters have been placed. We have examined the properties of platelets harvested from rats on day 1 or day 6 after insertion of indwelling aortic catheters. Platelets taken from these animals at 6 days (but not at 1 day) survived in normal rats or in rats with indwelling catheters for a significantly longer time than platelets from sham-operated rats. The catheters caused a persistent fall in the platelet count, an increase in the proportion of platelets in the most dense fraction after separation on discontinuous Stractan density gradients, and a decrease in mean sialic acid and protein per 10(9) platelets, but not change in modal size as determined with a Coulter Counter Channelyzer. No significant differences in the sensitivity to aggregating and release-inducing agents (ADP, thrombin, or collagen) were observed. It seems likely that chronic damage of the vessel wall shortened platelet survival and increased platelet turnover, although the increase in platelet production was not sufficient to maintain the platelet counts at the same values as in the sham-operated animals. The prolonged survival times in recipient rats of platelets from rats with indwelling aortic catheters indicate that a population of predominantly young platelets exists in these animals. Their increased density supports this conclusion.

Animals↗
PubMed1982

The inhibitory effects of exogenous arachidonic acid on rabbit platelet aggregation and the release reaction.

Although arachidonic acid causes rabbit platelet aggregation and the release of granule contents in suspensions of washed platelets when used in concentrations of approximately 50-300 microM, higher concentrations (500 microM) cause neither aggregation nor release. Suspensions of platelets from rabbits wee exposed to arachidonic acid (250 microM) for 15 min, allowed to recover in the presence of PGE1 for 30 min, washed, and resuspended; in some experiments, the platelets were treated with aspirin before being exposed to arachidonic acid. Aggregation of platelets pretreated with arachidonic acid was inhibited in response to ADP; this effect was greater with the non-aspirin-treated platelets and persisted for at least 4 hr after resuspension. The association of 125I-fibrinogen with the platelets as a result of ADP stimulation was also inhibited. Aggregation and release of granule contents in response to collagen and low concentrations of thrombin was inhibited, but the inhibition could be overcome by higher concentrations. Thrombin induced further release of granule contents from platelets exposed to arachidonic acid without pretreatment with aspirin. Platelets that had been exposed to arachidonic acid, either with or without pretreatment with aspirin, did not aggregate or undergo further release upon stimulation with arachidonic acid after they were washed and resuspended. Inhibition of the lipoxygenase pathway with eicosatetraynoic acid (ETYA) or nordihydroguaiaretic acid (NDGA) did not affect the inhibition caused by arachidonic acid, so it is unlikely that a product of this pathway is responsible for the inhibition. Mixing experiments indicated that the pretreated platelets did not form a thromboxane-A2-like activity, and that they were unresponsive to aggregation and release induced by products formed from arachidonic acid. Experiments with 3H-arachidonic acid showed that after 45 min of incubation with platelets, only 1.1% of the 3H-arachidonic acid remained as free arachidonic acid in the platelets. Although cyclic-AMP was slightly increased 1 min after the addition of arachidonic acid, the cyclic-AMP concentration was the same as that of control platelets after the platelets were washed and resuspended, indicating that increased cyclic-AMP is not likely to be responsible for the persistent inhibitory effect. Thus, the inhibitory effect of pretreatment with arachidonic acid is a general effect on responses to a variety of aggregating agents that act through different mechanisms, and the inhibition is not related to thromboxane-A2 formation. The possibility of membrane perturbation resulting in the unavailability of receptors may explain the persistent inhibitory effect, but the responsible reactions have not been identified.

Adenosine Diphosphate↗
PubMed1982

Effect of dipyridamole and prostacyclin on rabbit platelet adherence in vitro and in vivo.

The adherence of 51Cr-labeled platelets to the subendothelium of rabbit aortas was inhibited in vitro and in vivo by high concentrations of dipyridamole (100 microM in vitro, 2.5 or 12.5 mg/kg in vivo). Dipyridamole (100 microM) inhibited release of 14C-serotonin from platelets that adhered to the subendothelium or to a collagen-coated glass surface; lower concentrations of dipyridamole had only a slight inhibitory effect. Scanning electron microscopy showed that many of the platelets that adhered to the subendothelium were rounded, with few pseudopodia. The combination of dipyridamole with PGI2 was no more inhibitory of platelet adherence than either agent alone; however, this combination of inhibitors exerted synergistic inhibitory effects on aggregation and release of 14C-serotonin from platelets aggregated by collagen. The effects of dipyridamole on platelet adherence are a consequence of the action of dipyridamole alone and do not appear to result from its interaction with PGI2 formed by injured vessels in vivo, since the inhibitory effect is not influenced by aspirin inhibition of PGI2 formation, either at the shear rates in the in vitro studies or under the shear conditions found in rabbit aortas in vivo.

Animals↗
PubMed1982

Thrombin generation and fibrin formation following injury to rabbit neointima. Studies of vessel wall reactivity and platelet survival.

Using platelets prelabeled with 51Cr, we have quantified the effect of injury to the neointima on platelet accumulation, thrombus formation at different times following injury, and the effect of injury to the neointima on platelet survival. Platelet accumulation on the neointima is largely determined by activation of coagulation and thrombus formation; this contrasts with platelet accumulation on the subendothelium where coagulation does not play a major role and where few thrombi form. Heparin treatment significantly inhibits platelet accumulation on the injured neointima but is without effect on platelet accumulation on the subendothelium. Like the subendothelium, the neointima rapidly becomes nonreactive to further platelet accumulation, and the platelets and platelet-fibrin thrombi are lost from the surface in the first few days after injury. Despite the formation of extensive platelet thrombi on the injured neointima, platelet survival is unaffected.

Animals↗
PubMed1982

Changes in phosphatidylinositol-4,5-bisphosphate 10 seconds after stimulation of washed rabbit platelets with ADP.

Adenosine diphosphate (ADP) induced aggregation of rabbit platelets, without the release reaction, causes a significant decrease (7%) in the amount of phosphatidylinositol-4,5-bisphosphate (PIP2) at 10 sec and at 60 sec (11%). In platelets prelabeled with 32P-phosphate, this decrease in PIP2 is associated with a decrease in PIP2 radioactivity, which is significant at 50 sec. The decrease in PIP2 is sufficient to mobilize about 0.18 nmole Ca2+/10(9) platelets. In view of the key role played by Ca2+ in ADP-induced platelet shape change and aggregation, this evidence is compatible with the hypothesis that changes in PIP2 can be a source of calcium for cellular responses to agonists.

Adenosine Diphosphate↗
PubMed1981

The effect of phospholipase inhibitor mepacrine on platelet aggregation, the platelet release reaction and fibrinogen binding to the platelet surface.

We have examined whether inhibition by mepacrine or freeing of arachidonic acid from platelet phospholipids inhibits platelet aggregation to collagen, thrombin or ADP, and the release reaction induced by thrombin or collagen. Loss of arachidonic acid was monitored by measuring the amount of 14C feed from platelets prelabelled with 14C-arachidonic acid. Mepacrine inhibited 14C loss by more than 80% but did not inhibit thrombin-induced platelet aggregation and had a small effect on release. ADP-induced platelet aggregation did not cause 14C loss. Mepacrine inhibited ADP-induced platelet aggregation by inhibiting the association of fibrinogen with platelets during aggregation. The effect of mepacrine on fibrinogen binding could be considerably decreased by washing the platelets but the inhibition of 14C loss persisted. Platelets pretreated with mepacrine and then washed show restoration of aggregation to collagen. Thus, mepacrine has two effects; 1. it inhibits phospholipases, 2. it inhibits fibrinogen binding. Freeing of arachidonic acid is not necessary for platelet aggregation or the release reaction.

Adenosine Diphosphate↗
PubMed1981

Inhibitors of ADP-induced platelet aggregation prevent fibrinogen binding to rabbit platelets and cause rapid deaggregation and dissociation of bound fibrinogen.

125I-fibrinogen binds to washed rabbit platelets when they ar stimulated wit ADP, and it has previously been observed that fibrinogen binding is prevented by several inhibitors of ADP-induced aggregation. We have now shown that other inhibitors of aggregation, the phosphodiesterase inhibitors caffeine and dipyridamole, and colchicine and cytochalasin B which affect the platelet cytoskeleton, also inhibit specific 125I-fibrinogen binding. A positive correlation was observed between ADP-induced aggregation and fibrinogen binding at limiting concentrations of these inhibitors. Colchicine and cytochalasin B appear to act independently, with no indication of synergism. When any of these inhibitors, as well as those previously tested (EDTA, EGTA, PGE1 and PGI2) was added to platelets that had already been stimulated with ADP and undergone considerable aggregation and fibrinogen binding, it caused rapid deaggregation of the platelets and dissociation of bound fibrinogen, although in some cases the inhibitory effects were not as pronounced as when the inhibitor was added before ADP stimulation. These observations reinforce the concept that fibrinogen plays an essential role in the formation of ADP-induced platelet aggregates.

Adenosine Diphosphate↗
PubMed1980

Prostaglandins and platelets.

Release of arachidonate from cell membrane phospholipids by activation of phospholipase A1 is a key step in the formation of prostaglandins and thromboxanes. In platelets PGH2 and TXA2 are formed from arachidonate and can cause aggregation and the release of granule contents; in vascular tissue, PGI2 is formed instead and, by increasing platelet cAMP, inhibits platelet reactions. There is considerable interest in inhibitors of the enzymes in these pathways as drugs to modify thrombus formation. Results of the clinical trials, however, indicate that drugs which inhibit cyclo-oxygenase may not have a major effect on the thromboembolic complications of arterial disease.

Arachidonic Acids↗