1. Military recruits frequently succumb to exertional heat stroke during intensive training. Since widespread endothelial injury is often associated with exertional heat stroke, the relationship between changes in three circulating endothelial cell markers (angiotensin-converting enzyme, von Willebrand factor antigen and thrombomodulin) and exertional heat stroke was studied.
2. Twelve recruits who had succumbed to exertional heat stroke during basic physical training (5000 m running) were included in the study. Another 10 age-matched healthy subjects who had gone through the same physical training regimen were selected as controls.
3. Blood was withdrawn on admission and on discharge for analyses of angiotensin-converting enzyme, von Willebrand factor antigen and thrombomodulin. Other physiological parameters and biochemical analyses reflecting renal and liver functions were also recorded.
4. Our results indicated that these subjects with exertional heat stroke exhibited impaired liver function as revealed by the significant elevation of both serum glutamic oxaloacetic transaminase (P < 0.05) and serum glutamic pyruvic transaminase (P < 0.05) as compared with normal healthy control subjects. Unfortunately, these values remained mostly somewhat elevated on discharge, although serum glutamic oxaloacetic transaminase was reduced dramatically. Indices of kidney functions, including creatinine clearance and uric acid and phosphorus secretion, were not significantly different from those observed in healthy controls.
5. Circulating angiotensin-converting enzyme activities in exertional heat stroke patients on admission were significantly lower than in normal subjects (10.68 ± 2.15 versus 21.21 ± 3.18 nmol hippuric acid min−1ml−1, P<0.05). In contrast, von Willebrand factor antigen, thrombomodulin and plasma renin activity were significantly elevated compared with corresponding values in healthy subjects (P < 0.001, 0.05 and 0.01 respectively). The values of these endothelial markers returned to normal on discharge.
6. These data suggest that the decrease in angiotensin-converting enzyme and increase in von Willebrand factor antigen and thrombomodulin associated with exertional heat stroke may reflect endothelial injuries. Since endothelial injuries may trigger haemostatic failure and/or disseminated intravascular coagulation, the monitoring of these values might be useful for the evaluation of endothelial status in patients suffering from exertional heat stroke.