Hypothermia in nature occurs in hibernating animals. It has applications in medicine in open heart surgery,organ and connective tissue preserving, altitude medicine and geriatrics. Despite the vastness of studies on hypothermia many of its biologic and physiologic effects including endocrine system alterations are still poorly recognized. In this study the effect of hypothermia on renin- angiotensin-aldosterone axis was explored.

          Ten male wistar albino rats (mean age 5 months) were anesthetized by intraperitoneal injection of chloralhydrat (0.5 m1/100gr body weight). Then animals were placed in hypothermia apparatus . Their body temperature were reduced to 25⁰ C. AngiotensinI(ANGI) and aldosterone (ALD) levels of serum were measured by radioimmunoassay before and after hypothermia
   induction and once every 24 hours for three days. Plasma renin activity (PRA) was also measured by using the standard formula of angiotensin determinates at two temperatures of 4⁰C and 37⁰C .

          The results showed that PRA,ANGI and ALD increased significantly immedietly after hypothermia (p<0.03). Later changes were followed as  these factors decreased to basal level, except in the case of aldosterone which maintained its increased level significantly for 24 hours (p<0.05).

          It seems that moderate hypothermia have stimulatory effect on PRA,ANGI and ALD that results of this study confirm it.