Age-related changes in haemostatic responses to localized cold-induced stress in rats

ABSTRACT

In the present work, age-related changes in haemostatic responses to localized cold stress in rats were investigated. The role of vitamin E supplementation, on the haemostatic responses of those stressed rats, was also studied. Three different age groups were studied; young mature rats [4 months], middle-age rats [14 months] and old-age rats [24 months]. The animals were subjected either to acute localized cold stress [1 hour] or to chronic localized cold stress [3 hours daily, for 15 days]. Age-matched control rats were maintained under standard conditions of boarding. A group of old rats was injected intramuscularly by vitamin E in a dose of 150 mg/kg-body weight/day, prior to the stress induction [daily, for 15 days]. Exposure to acute localized cold stress produced a significant elevation in the mean arterial blood pressure in the three different age groups of rats, compared to their age matched controls. On the other hand, chronic exposure to localized cold stress resulted in significant elevation in the mean arterial blood pressure [MAP] and plasma malondialdehyde [MDA] level, with an increase in platelet aggregation, and a decrease in platelet count. In addition, there were shortening in prothrombin and partial thromboplastin times, as well as a reduction in antithrombin III activity and an increase in the levels of plasma fibrinogen and fibrin degradation products in all stressed rat groups, compared to their age matched unstressed controls. These platelet hyperaggregability and blood hypercoagulability states observed in stressed rats raise the risk of thrombo-embolic manifestations. Vitamin E supplementation in old rats subjected to chronic localized cold stress produced a significant decrease in MAP and plasma MDA level, as well as inhibited the activated coagulation system induced by cold exposure in old age, evidenced by decreased platelet aggregation in response to ADP and plasma fibrinogen level, in concurrence with prolonged PTT and stimulated AT-III activity compared to stressed old rats. Further, the value of all these parameters were corrected to near normal levels, being non significantly different from the corresponding values in the normal old rats. Therefore, the therapeutic intervention with vitamin E might improve the stress- induced derangement in the haemostatic profile