CHANGES IN PLATELET HALF-LIFE, SENSITIVITY TO PROSTANOIDS AND AGGREGATION INDUCED IN THE DOG BY BODY HYPOTHERMIA

During body cooling, there is a progressive thrombocytopenia, which is reversible after rewarming and is not prevented by previous treatement with aspirin, ticlopidine or prostacyclin.In this work, in order to evaluate if hypothermia induces alterations of platelet function we studied, in the dog, the platelet aggregation (PA) and the inhibitory action of PGE1 and of a stable prostacyclin analog, l loprost, before hypothermia(37°C.) and after rewarming(37°C.).Platelet half-life was also studied in another group of dogs before induction of hypothermia and after rewarming and recuperation of the animals. PA has been evaluated by platelet counting in whole blood.P1atelet half-life was estimated by serial determinations of MDA following administration of aspirin.PA induced by ADP (30μM) decreased 40% after rewarming(n=8). Platelet sensitivity to PGE1 (35 nM -1.4 μM f.c.) and Iloprost (7nM-172nM f.c.) was also decreased after rewarming: inhibition index 2.08±1.082 versus 1.19±0.362 (n=8; p<0.01) and 2.48<1.250 versus 1.10±0.227 (n=8; p<0.005) respectively.Platelet half-life increased after hypothermia from 3.99±0.730 days to 4.48±0.846 days(n=8 p<0.05).In the control group(n=6) platelet half-life determined twice with one week interval, did not change significantly.

We conclude that body hypothermia decreases platelet reactivity to ADP; renders platelets less sensitive to the inibitory effect of prostanoids and increases platelet half-1 ife.These results are probably due to alterations in platelet membrane induced by cooling and rewarming the animals.