Evaluation of methods for the extraction of nitrite and nitrate in biological fluids employing high-performance anion-exchange liquid chromatography for their determination

Measurements of nitrite (NO(2)(-)) and nitrate (NO(3)(-)) in biological fluids are proposed as indices of cellular nitric oxide (NO) production. Determination of NO(2)(-) and NO(3)(-) in standard solutions is not difficult, however, determinations which reflect accurately cellular NO synthesis represent a considerable analytical challenge. Problems are often encountered arising from background NO(2)(-)/NO(3)(-) contamination in experimental solutions and laboratory hardware, and with methods for sample extraction. We investigated potential procedures for the extraction and determination of NO(2)(-) and NO(3)(-) in biological samples. Consequently, a protocol was devised which yielded acceptable results regarding extraction efficiency, assay reproducibility, sample throughput and contaminant minimisation. It entailed rigorous washing of all equipment with water of low NO(2)(-) and NO(3)(-) content, sample deproteinisation by centrifugal ultrafiltration through a 3K filter and analysis by high-performance anion-exchange liquid chromatography with UV detection. Retention times for NO(2)(-) and NO(3)(-) in standards and plasma were 4.4 and 5.6 min, respectively. Assay linearity for standards ranged between 31 nM and 1 mM. The limit of detection for NO(2)(-) and NO(3)(-) in standards was 3 pmol. Recoveries of NO(2)(-) and NO(3)(-) from spiked plasma (1-100 microM KNO(2)/KNO(3)) and from extracted standards (1-250 microM) were approximately 100%. Intra-assay and inter-assay RSDs for NO(2)(-) and NO(3)(-) in spiked and unspiked plasma were 10.6% or less. Assays on washed platelet supernatants demonstrated collagen-induced platelet generation of NO products and analysis of murine and rat cardiac perfusates was achieved. Our procedure may be suitable for routine determination of NO(2)(-) and NO(3)(-) in various biological fluids, e.g., plasma.

Platelet function in patients with hypercholesterolaemia

Platelets and plasma lipoproteins, particularly low density lipoprotein, have important roles in atherogenesis. Evidence from several sources suggests that important interactions occur between these individual components of the atherogeneic process. Here we review work from our own laboratory on platelet function in normal individuals and patients heterozygous for familial hypercholesterolaemia (FH). Data is presented on the role of platelet noradrenaline and also on altered cellular signalling in platelets from FH individuals who have plasma low density lipoprotein concentrations which are approximately double those seen in normal subjects.

Interaction between the effects of 5-hydroxytryptamine and adrenaline on the growth of platelet thrombi in the coronary artery of the anaesthetized dog

1. The interaction between adrenaline and 5-hydroxytryptamine (5-HT) has been quantitated on the rate of thrombus formation, in the stenosed coronary artery with damaged endothelium of the anaesthetized dog. 2. Changes in the plasma concentration of adrenaline were produced by varying the rate of an intravenous infusion of adrenaline and in the effects of 5-HT, by intravenous injections of the selective 5-HT2 receptor antagonist, ICI 170809. 3. Increases in the plasma concentration of adrenaline, which did not cause significant changes in blood pressure and heart rate, increased the rate of thrombus formation. 4. Antagonism of the 5-HT2 receptor by ICI 170809, in the absence of an infusion of adrenaline, abolished thrombus formation (mean ED50 0.41 microgram kg-1, i.v.). 5. The effects of adrenaline were non-competitively antagonized by ICI 170809; maximum effects were obtained in the dose-range 50-200 micrograms kg-1, i.v., when the mean dose-ratio increase in adrenaline required to restore equivalent rates of thrombus formation was 39 fold. 6. These results are consistent with a synergism between adrenaline and 5-HT and emphasize the importance of both on thrombus formation.

The influence of aspirin on plasma and platelet catecholamine levels, and platelet function in normal man

The aim of the study was to determine whether aspirin influences sympathoadrenal output in normal human subjects. Plasma and platelet adrenaline and noradrenaline levels were measured before and after chronic administration of oral aspirin (300 mg per day for 7 days). Catecholamine concentrations measured immediately following aspirin did not differ from control (pre-treatment) values. Platelet noradrenaline and plasma adrenaline levels were, however, significantly increased 2 weeks after cessation of treatment. Platelet TxB2 generation was significantly reduced following aspirin treatment indicating that platelet cyclooxygenase had been inhibited. Catecholamine concentrations did not correlate with TxB2 generation. In vitro platelet aggregation induced by ADP, adrenaline and collagen was reduced after aspirin providing additional confirmation of cyclooxygenase inhibition. However, the in vivo markers of platelet function, beta-TG and PF4 were unaffected. These data do not provide convincing evidence for an action of aspirin on sympathoadrenal outflow, either directly or via a prostaglandin (thromboxane) mediated effect, although this does not exclude a later, delayed effect. There was no evidence for interactions between thromboxane, catecholamine levels in plasma and platelets, and platelet function.

Platelet noradrenaline release in patients with familial hypercholesterolaemia

We have examined resting and thrombin (0.3 units ml-1) induced release of noradrenaline by washed platelets from 15 normal subjects and eight patients with heterozygous familial hypercholesterolaemia. Platelets from both normal and hypercholesterolaemic subjects showed irreversible aggregation with 0.3 units ml-1 thrombin. Extents of aggregation were 76.3% and 90.8% respectively, platelets from hypercholesterolaemic patients being significantly more sensitive (P less than 0.002). Under resting conditions platelet noradrenaline release was 136% greater (P less than 0.02) in hypercholesterolaemic patients than in normal subjects. Thrombin-stimulated release of noradrenaline was also higher (73%, P less than 0.05) in hypercholesterolaemics than in normals. The differences between resting and thrombin-stimulated release were greater for hypercholesterolaemic patients than normal subjects (P less than 0.05). Under resting conditions total platelet noradrenaline levels (sum of supernatant and platelet pellet concentrations) were similar in preparations from the two groups. However, following thrombin stimulation total noradrenaline concentrations were substantially greater (86%) in platelets from hypercholesterolaemics than normals (P less than 0.02). In hypercholesterolaemic patients thrombin stimulation was associated with an 101% increase (over resting levels) in total platelet noradrenaline (P less than 0.01), no increases being observed with normal subjects. We suggest that platelet membranes may be more permeable in patients with familial hypercholesterolaemia leading to increased non-specific release of catecholamines. Platelets from patients with familial hypercholesterolaemia may also be more responsive to stimulation with respect to catecholamine release. The results obtained on calculation of total platelet noradrenaline levels may indicate that abnormalities of platelet dense granules occur in familial hypercholesterolaemia. In this context the relative proportions of free and conjugated catecholamine may be of relevance.