Sympathetic-adrenal medullary and cardiovascular responses to acute cold stress in adult and aged rats.

In this study, adult (5 months) and aged (22 months) Fischer 344 (F-344) male rats were surgically prepared with chronic tail artery cannulae. Two days after surgery, rats were stressed by immersion in 12 degrees C water for 10 min. Blood samples (0.5 ml) were collected before and at timed intervals after cold immersion (0, 15 and 60 min) and were later assayed for content of norepinephrine and epinephrine. Consistent with earlier studies from this laboratory, there were no differences between ages in basal plasma levels of either catecholamine or in mean arterial pressure or core temperature. However, basal heart rates of aged rats were approximately 10% greater than values for adult rats. During cold immersion, aged rats had greater decrements in heart rate compared to adults but there were no age-related differences in mean arterial pressure or core temperature. Immediately following cold immersion, increments above basal values for plasma norepinephrine and epinephrine (4.2-4.6 and 11.8-14.1-fold, respectively) were similar for 5- and 22-month-old rats. However, in aged rats plasma norepinephrine was greater at 60 min post-immersion and plasma epinephrine was greater at 15 and 60 min post-immersion compared to values for adults.(ABSTRACT TRUNCATED AT 250 WORDS)