Effects of acute arterial bleeding on renal sympathetic nerve activity in young and old anesthetized rats

We compared the change in renal sympathetic nerve activity (RNA) during hemorrhage in young and old rats. Young (10 weeks) and old (80 weeks) male Wistar rats were anesthetized, and RNA together with arterial pressure (AP) and heart rate (HR) were measured under spontaneous respiration. Acute arterial bleeding, 1ml/100g body weight, was carried out to induce hypotension and hypovolemia. With bleeding, mean AP (MAP) decreased from 110 +/- 12 to 23 +/- 11mmHg (mean +/- SEM) and from 93 +/- 15 to 15 +/- 6mmHg in young and old rats, respectively. The difference in the change of MAP between the young and old rats was not significant. With bleeding, mean RNA increased by 46 +/- 21% and 20 +/- 16% in young and old rats, respectively. The increase in mean RNA of the old rats was significantly lower than that of the young rats. We estimated the gain of the baroceptor-renal sympathetic nervous system by using the formula delta RNA/RNA/delta MAP/MAP. The gain was 0.61 +/- 0.34 and 0.23 +/- 0.18 in young and old rats, respectively. The difference in the gain was statistically significant (p < 0.05). We concluded that the gain of baroceptor-sympathetic nerve system in acute arterial hemorrhage is attenuated with aging.