No abstract

1. Several studies suggest an association between venous thromboembolism and the use of antipsychotic drugs, especially clozapine, but the biological mechanisms are unknown. It has been suggested that antipsychotic drugs enhance aggregation of platelets and thereby increase the risk of venous thrombosis. The purpose of the present study was to examine the effects of clozapine and its main metabolite, N-desmethyl clozapine, as well as olanzapine, risperidone and haloperidol, on platelet adhesion and aggregation and on plasma coagulation in vitro. 2. Blood was collected from healthy subjects free of medication. Platelet adhesion to different protein surfaces and aggregation were measured in microplates. The coagulation methods of activated partial thromboplastin time (APTT) and prothrombin time were performed in platelet-poor plasma. 3. Clozapine was the only compound that increased platelet adhesion and aggregation and shortened APTT. The effect appeared at therapeutic concentrations and was significant but weak. 4. This weak effect of clozapine on haemostasis may explain, in part, the association of this compound and venous thromboembolism.

Patients with IBD in remission have higher basal platelet surface P-selectin expression. An exaggerated platelet activity with increased expression of platelet P-selectin and release of inflammatory mediators such as RANTES, which is chemotactic and induce chemokine production, could have a reinforcing and aggravating influence on the inflammatory response and increase the susceptibility to IBD. In addition IL-8 has a down-regulating effect on platelet surface P-selectin expression and 5ASA medication seems to lower plasma RANTES. If 5ASA is responsible for lowering the concentration of RANTES this could be one of the beneficial outcomes of 5ASA medication.

Measurement and monitoring of magnesium (Mg) are important to prevent the development of serious and potentially fatal complications in critically ill patients. Although ion-selective electrodes are available and earlier reports suggest that free ionized magnesium (iMg2+) is the most useful test to estimate Mg status, most clinical laboratories still only measure total Mg. To compare the relationship among iMg2+, total Mg, and albumin in serum, samples were collected from 48 consecutive patients admitted to an intensive care unit or a primary health center. The mean serum level of iMg2+ in 44 patients was 0.53 mmol/L, the total Mg was 0.96 mmol/L, and the albumin was 34.93 g/L. The correlation between iMg2+ and total Mg in serum was r=0.585; the correlation between iMg2+ and albumin in serum was r=378; and the correlation between total Mg and albumin in serum was r=0.340. The mean percent iMg2+ in relation to total Mg in serum was calculated to be 55% in the patient samples. The important level of biologically active iMg2+ was not reflected upon analysis of total Mg in 25% of consecutive patients. This report shows that the correlation of iMg2+ and total Mg is weak, not only in critically ill patients but also in patients in whom Mg status is inquired as a whole.

It has been suggested that the accumulation of platelets at sites of vascular damage and inflammation regulates the function of leukocytes. In this study, we investigated the effects of platelets on the transmigration of neutrophil granulocytes through microporous membranes. We demonstrate that platelets markedly enhance both the random and the chemotactic migration of neutrophils. Stimulatory effects were acquired by adding paraformaldehyde-fixed platelets or the supernatants of platelets; however, the effects were lower or significantly higher, respectively, compared with viable platelets. The increased neutrophil migration was associated with an amplified polymerization of actin filaments and expression of CD11b/CD18. Previous investigations indicate that the initial adhesion between platelets and neutrophils is mediated by P-selectin exposed on the surface of platelets. In this study, the following observations suggest a role for P-selectin in the platelet-induced enhancement of neutrophil motility: (i) platelet supernatants contained substantial amounts of P-selectin, (ii) filtration of platelet supernatants markedly reduced the content of P-selectin and simultaneously decreased the potentiating effects on neutrophil motility, (iii) inhibition of P-selectin-mediated cell cell adhesion with sialyl Lewis X or by incubation in calcium-free medium reduced the enhancing effects of platelets on neutrophil responses, and (iv) purified and recombinant P-selectin mimicked the effects of platelets on neutrophil locomotion. In conclusion, we propose that platelets through P-selectin promote accumulation and emigration of neutrophils during inflammatory and thrombotic processes.