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

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

Age-related changes in haemostatic responses to oxidative stress

Altered haemostatic mechanisms are known to occur in stressful situations, yet the pathophysiology of stress related dyshaemostasis is still poorly understood. In the present work, age-related changes in haemostatic responses to oxidative stress in rats with different ages were investigated. Also, the effects of vitamin E supplementation, prior to stress induction, on the haemostatic responses of those stressed rats were evaluated. Three different age groups were studied, young mature rats [4 months], middle age [14 months] and old rats [24 months]. The animals were subjected to oxidative stress by adding H[2]O[2] solution to their drinking water, in a final concentration of 3%, daily, for 21 days. The age-matched control rats drink normal tap water. A group of old rats was injected intramuscularly by vitamin E in a dose of 150 mg/kg body weight, prior to the stress induction, daily, for 21 days.Results obtained in this study demonstrated an elevation in mean arterial blood pressure, plasma malondialdehyde, and plasma fibrinogen concentrations, and fibrin degradation products, in addition to shortened prothrombin and partial thromboplastin times and inhibited antithrombin III activity, in the young and old rats subjected to H[2]O[2]-induced oxidative stress, being statistically significant compared to their age matched controls. Moreover, there were an increase in platelet aggregation and a decrease in platelet count in the stressed young and old groups, but they were statistically significant only in old rats, compared to their age matched controls. However, stressed middle-age rats showed non-significant changes in the studied parameters, except for the mean arterial blood pressure that was significantly elevated, compared to their age matched controls. From these results, it is clear that the changes in the haemostatic responses to stress were more manifest in the young and old rats, with more marked responses in the older ones. On the other hand, vitamin E supplementation in old rats, prior to the stress induction, produced a decrease in mean arterial blood pressure, platelet aggregation, plasma fibrinogen concentration and fibrin degradation products, as well as increase in platelet count and antithrombin III activity. All these changes were statistically significant compared to the vitamin E-unsupplemented stressed old rats, but they were non significantly changed from the normal controls. It is concluded that vitamin E injection, prior to stress induction, produces marvelous effects on the stress-induced derangement of the haemostatic system