RENAL DENERVATION ALTERS CARDIOVASCULAR AND ENDOCRINE RESPONSES TO HEMORRHAGE IN CONSCIOUS NEWBORN LAMBS

To investigate the role of renal sympathetic nerves in modulating card iovascular and endocrine responses to hemorrhage early in life, we car ried out three experiments in conscious, chronically instrumented lamb s with intact renal nerves (intact; n = 8) and with bilateral renal de nervation (denervated; n = 5). Measurements were made 1 h before and 1 h after 0, 10, and 20% hemorrhage. Blood pressure decreased transient ly after 20% hemorrhage in intact lambs and returned to control levels . In denervated lambs, however, blood pressure remained decreased afte r 60 min. After 20% hemorrhage, heart rate increased from 170 +/- 16 t o 207 +/- 18 beats/min in intact lambs but not in denervated lambs, in which basal heart rates were already elevated to 202 +/- 21 beats/min . Despite an elevated plasma renin activity (PRA) measured in denervat ed (12.0 +/- 6.4 ng ANG I.ml(-1).h(-1)) compared with intact lambs (4. 0 +/- 1.1 ng ANG I.ml(-1).h(-1)), the increase in PRA in response to 2 0% hemorrhage was similar in both groups. Plasma levels of arginine va sopressin increased from 11 +/- 8 to 197 +/- 246 pg/ml after 20% hemor rhage in intact lambs but remained unaltered in denervated lambs from baseline levels of 15 +/- 10 pg/ml. These observations provide evidenc e that in the newborn, renal sympathetic nerves modulate cardiovascula r and endocrine responses to hemorrhage.