ON the serotonin liberation from rat platelets due to betaadrenoceptor blocking drugs

Determination of the cell lytic properties of amphiphilic inhibitors of the cytosolic phospholipase A2 against human platelets by measuring the liberation of serotonin with high-performance liquid chromatography and fluorescence detection

A procedure for the determination of the influence of detergents on the cell integrity of human platelets by measuring the release of serotonin with high-performance liquid chromatography and fluorescence detection is presented. After exposure of the platelets to the test compounds the cells and cell fragments, respectively, are centrifuged off. In the supernatants the liberated serotonin is determined directly without a further sample clean up. The amphiphilic inhibitors of cytosolic phospholipase A2 (cPLA2), arachidonyltrifluoromethyl ketone (AACOCF3), palmityltrifluoromethyl ketone (PACOCF3) and methyl arachidonylfluorophosphonate (MAFP), and the polyoxyethylene detergent Brij 58 were investigated for their cell lytic properties with this method. All compounds lysed the platelets liberating serotonin at a concentration of 33 microM. AACOCF, and Brij 58 even caused cell lysis at lower concentrations.

Influence of propranolol, pindolol, practolol and talinolol on arachidonic acid (AA)- and U-46619-induced aggregation and on AA-induced thromboxane A2 formation in platelets

The effects of four beta-adrenoceptor blocking agents on arachidonic acid (AA)-induced platelet aggregation and thromboxane (TX) formation in human and rabbit platelet-rich plasma (PRP) as well as their influence on prostaglandin endoperoxide analogue (U-46619)-induced aggregation in human PRP were studied. The potency against AA-induced aggregation decreased in the following sequence: pindolol greater than propranolol greater than talinolol greater than practolol (without effect). Pindolol (0.1-1.0 mmol/l) inhibited both AA-induced aggregation and TX formation. The cyclooxygenase activity in ram seminal vesicle microsomes was suppressed by both pindolol isomers. Propranolol was without effect on the cyclooxygenase. This supports the assumption that the inhibitory activity of pindolol on AA-induced platelet aggregation is mediated by its inhibiting effect on platelet cyclooxygenase as the first step of the TX formation. Propranolol (IC50:0.2 mmol/l), talinolol (IC50:0.7 mmol/l) and pindolol (IC50:1.3 mmol/l) inhibited the U-46619-induced aggregation, whereas practolol remained without effect. The spectrum of the reported data with propranolol, talinolol and practolol may be assumed to allow the correlation of the results to both the membrane stabilizing effects and to lipophilicity of the drugs.