Search PubMed⌕ Search

Biomedical subjects

H Holmsen

Publications and source records attributed to H Holmsen.

At least 181 records · Page 10Linked to original sources
PubMed1975

The role of thrombin in ADP-induced platelet aggregation and release: a critical evaluation.

The role of thrombin in ADP-induced aggregation and release in vitro was critically examined. The addition of heparin or hirudin to citrated platelet rich plasma did not prevent aggregation or release. The addition of citrate to heparinized plasma restored secondary aggregation and release. Hirudin did not prevent irreversible aggregation. These results are incompatible with the hypothesis that thrombin is a primary and necessary mediator of platelet aggregation (Ardlie & Han, 1974; Han & Ardlie, 1974a, b, c). This hypothesis is based in part on the assumption that EDTA enhances the elution of clotting factors from platelets; we found no enhanced elution of factors II, V, X, VIII, IX or XI when platelets were washed in EDTA.

Adenosine Diphosphate↗
PubMed1975

ADP-induced refractory state of platelets in vitro. I. Methodological studies on aggregation in platelet rich plasma.

ADP-induced aggregation was determined at various times of incubation with ADP in unstirred human platelet rich plasma (PRP) to which adenosine deaminase was added. In the early stages of incubation the shape change response was absent, the aggregation response was poor, and not reversible. These three parameters returned slowly towards normal as the incubation proceeded. Pronounced impairment of the aggregation response was present after all added ADP had been degraded in plasma. Log dose-response (rate of aggregation) curves for the platelets incubated with ADP had shifted to higher ADP concentrations and had also a small decrease in maximal height and in the slope compared to those obtained with control platelets. However, the shift in log dose response to higher ADP concentrations was far more striking, so the increase in log dose (R) necessary to obtain the same rate of aggregation as with control PRP was taken as a measure of refractoriness of aggregation towards ADP. R increased with the time of incubation to an optimal value and then decreased. The magnitude of the optimal value and the time at which optimum was reached increased with the concentration of the ADP incubated with the platelets. The variations in R during incubation did not correlate with the breakdown of added ADP. The platelets began to recover their ability to aggregate with ADP while there was still ADP in the system.

Adenosine Deaminase↗
PubMed1975

Adenine nucleotide metabolism during the aggregation of human platelets by bovine factor VIII.

Human platelets, prelabelled with [3H]-adenine in vitro, were aggregated biphasically by bovine fibrinogen/factor VIII, and the amounts and specific radioactivity of ADP and ATP as well as the radioactivity of ATP, ADP, AMP, IMP and hypoxanthine + inosine were determined intracellularly and extracellularly. During the second phase of aggregation, ATP and ADP were released (50% of total) with a specific radioactivity 15-20 times lower than that of the ATP and ADP retained in the cells. The specific radioactivity of the ATP and ADP in the cells increased during release. Radioactive ATP was converted to radioactive hypoxanthine during release. These findings correlated well with those obtained with collagen, and indicate that bovine factor VIII induces the platelet release reaction whereby the storage (non-metabolic) pool of ATP and ADP is released while the metabolic pool is retained.

Adenine Nucleotides↗
PubMed1975

Short communication: possible association of newly absorbed serotonin with nonmetabolic, granule-located adenine nucleotides in human blood platelets.

[3H]-adenine-labeled human platelets in plasma were incubated with or without nonradioactive serotonin. Release reaction was then induced by ADP, epinephrine, collagen, or thrombin. Platelets that had been incubated with serotonin released four times as much serotonin as platelets incubated without serotonin. The specific radioactivities of the ATP and ADP released to plasma during release reaction induced with all four inducers were the same in both systems. This shows that when serotonin is taken up by human platelets, it enters the compartment containing nonmetabolic, granula-stored ATP, and not the compartment with metabolic extragranular ATP. These results suggest that the mechanism of serotonin storage in human platelets is similar to that in other species investigated, i.e., rabbit, guinea pig, and pig.

Adenine↗
PubMed1975

Metal ion contents of gel-filtered platelets from patients with storage pool disease.

Platelets from nine patients with storage pool disease (SPD) and from ten control subjects were isolated by gel filtration into a suspension medium permitting the direct determination of platelet Mg-2+, Ca-2+, and K+ levels. The total intracellular levels of ATP and ADP, as well as the incorporation patterns of 14-C-adenine into the metabolic nucleotide pool, were also determined in these platelet suspensions. The gel-filtered platelets (GFP) from SPD patients exhibited slightly lowered levels of ATP and substantially reduced amounts of ADP, in agreement with previous studies using PRP suspensions. Diminished aggregation responses to ADP, epinephrine, and to collagen in particular, similar to those observed previously in PRP, were obtained in GFP from SPD patients. However, GFP from the patients exhibited more variable aggregation responses to addition of ADP and epinephrine than did GFP from the control subjects. Increases in the extent of radioactive hypoxanthine formation, observed previously in normal platelets as a result of isolation into the suspension medium used in these studies, were significantly reduced in the GFP from SPD patients. The levels of platelet Mg-2+ and K+ determined in GFP from the patients were not significantly different from the levels of these ions in GFP from control subjects. However, substantial reductions in platelet Ca-2+ were found in the SPD platelets. A strong correlation was obtained between this reduction in platelet Ca-2+ and the reduction in ADP in these platelets. No such correlation was apparent between the ATP and Ca-2+ deficiencies. These results suggest that a major portion of platelet Ca-2+ may be located in the dense granules and support previous hypotheses that granular ADP and/or Ca-2+ may play a role in the release reaction. The finding of normal levels of platelet Mg-2+ and K+ in SPD platelets, however, suggests that these latter ions are not located in the dense granules.

Adenine↗
PubMed1975

Content and thrombin-induced release of acid hydrolases in gel-filtered platelets from patients with storage pool disease.

The levels of four acid hydrolases, beta-N-acetyl glucosaminidase, beta-glucuronidase, beta-galactosidase, and acid phosphatase, and the extent of their release (release II) by thrombin was determined in platelets from nine normal subjects, nine patients with storage pool disease, and in normal platelets which had been exposed to aspirin. The levels of all four hydrolases were normal in patients with SPD. However, release of three of these hydrolases (acid phosphatase was an exception) by low concentrations of thrombin (0.015 and 0.04 U/ml) was decreased in the patients as a group, although considerable variation in the extent of release of each enzyme was noted. In contrast, aspirin failed to inhibit release II in normal platelets (except for a slight impairment in the release of beta-N-acetyl glucosaminidase), although release I (serotonin, ATP and ADP) was inhibited. All release defects could be overcome by using higher concentrations of thrombin (0.2 U/ml). The normal levels of acid hydrolases in the platelets of patients with SPD (who are deficient in the platelet dense granules) suggest that these enzymes are not normally stored in the dense granules, but rather in alpha-granules. The findings also support the conclusions of previous studies that the release reaction is impaired in SPD. This release defect appears to be different from that seen in normal platelets after exposure to aspirin.

Acetylglucosaminidase↗
PubMed1975

Studies on gel-filtered human platelets: isolation and characterization in a medium containing no added Ca2+, Mg2+, or K+.

We have adapted the gel filtration technique for separation of human platelets from the plasma constituents to permit use of an eluant containing no added Ca2+, Mg2+, and K+, and hence allow direct determination of the intracellular concentrations of these ions in the isolated platelets. The eluant employed is modified Ca2+-free Tyrode's buffer which contains Sr2+ (0.2 mM) as a substitute for Mg2+ and lacks added K+. The functional metabolic, and morphological properties of these isolated platelets have been determined ael-filtered platelets (GFP) to low concentrations of ADP and adrenaline was qualitatively similar to that of platelet-rich plasma (PRP). However, a slower response was observed for the GFP. This rate difference was partially or completely reversed by addition of apyrase to the medium. Analysis of the total adenine nucleotide content and the pattern of 14C incorporation into the metabolic adenine nucleotide pool indicated that isolation in this medium caused to significant change in the ATP and ADP contents or in the adenylate energy change in comparison with the PRP. However, a significant increase in the extent of hypoxanthine production from ATP was noted in GFP isolated in media lacking Mg2+. Inclusion of Mg2+ in the elution media prevented this increased hypoxanthine production. The intracellular concentrations of Ca2+, Mg2+, and K+ of the GFP as determined by atomic absorption analysis were in good agreement with the values obtained for platelets separated from plasma by high-speed centrifugation. Platelet Ca2+ and Mg2+ levels remained stable despite the lack of significant extracellular levels of these ions. However platelet K+ fell to about 30 per cent of its initial value after incubation of 90 minutes at 23 degrees C. and a coincident increase was observed in extracellular K+ concentration. This procedure for platelet isolation may be of particular value for studies on the role of Ca2+, Mg2+, and K+ in platelet physiology and metabolic processes.

Adenine↗
PubMed1974

Effects of antimycin and 2-deoxyglucose on adenine nucleotides in human platelets. Role of metabolic adenosine triphosphate in primary aggregation, secondary aggregation and shape change of platetets.

1. Human platelet-rich plasma prelabelled with [(3)H]adenine was incubated at 37 degrees C with antimycin A and 2-deoxy-d-glucose. Variations in the amounts of ATP, ADP and P(i), and in the radioactivity of ATP, ADP, AMP, IMP, hypoxanthine+inosine and adenine were determined during incubation. Adrenaline- and ADP-induced platelet aggregation and the ADP-induced shape change of the platelets were determined concurrently. 2. 2-Deoxyglucose caused conversion of [(3)H]ATP to [(3)H]hypoxanthine+inosine. The rate of this conversion increased with increasing 2-deoxyglucose concentration and was markedly stimulated by addition of antimycin, which had no effect alone. At maximal ATP-hypoxanthine conversion rates, the IMP radioactivity remained at values tenfold higher than control, whereas [(3)H]ADP and [(3)H]AMP radioactivity gave variations typical for product/substrates in consecutive reactions. The specific radioactivityof ethanol-soluble platelet ATP decreased during incubation to less than one-tenth of its original value. The amounts and radioactivity of ethanol-insoluble ADP did not vary during incubation with the metabolic inhibitors. 3. The rate of ADP- and adrenaline-induced primary aggregation decreased as the amount of radioactive ATP declined, and complete inhibition of aggregation was obtained at a certain ATP concentration (metabolic ATP threshold). This threshold decreased with increasing concentration of inducer ADP. 4. Secondary platelet aggregation (release reaction) had a metabolic ATP threshold markedly higher than that of primary aggregation. 5. Shape change was gradually inhibited as the ATP radioactivity decreased, and had a metabolic ATP threshold distinctly lower than that of primary aggregation, and which decreased with increasing concentration of ADP. 6. A small but distinct fraction of [(3)H]ATP disappeared rapidly during the combined shape change-aggregation process induced by ADP in platelets incubated with metabolic inhibitors, whereas no ATP disappearance occurred during aggregation in their absence.

Adenine↗