ANGIOTENSIN-CONVERTING ENZYME-INHIBITION AND THE NOREPINEPHRINE SPILLOVER RESPONSE TO DYNAMIC EXERCISE

To determine whether prejunctional angiotensin II receptors facilitate norepinephrine (NE) release during exercise, normal volunteers exerci sed at similar to 25 or similar to 65% of maximal O-2 consumption (VO2 max) On two occasions. Steady-state NE kinetics were determined at res t and during exercise by using infusions of [H-3]NE. Arterial plasma N E and [H-3]NE were determined for calculation of NE spillover and clea rance. Before the second bout of exercise at similar to 25% of VO2max later that day, enalaprilat (n = 8) or nitroprusside (n = 5) sp as adm inistered intravenously to lower blood pressure to a comparable level and saline was infused as a time control (n = 4). Exercise at 25% of V O2max increased heart rate from 73 to 110 beats/min, plasma NE from 29 6 to 626 pg/ml, and NE spillover from 1.56 to 3.32 nmol . min(-1). m(- 2). The exercise effect was significant in each subgroup. At, rest and during exercise, the decrease in blood pressure and the increase in p lasma NE and NE spillover mere similar with enalaprilat and nitropruss ide. There was no drug effect in tile saline group. In a separate grou p (n = 7), exercise at similar to 65% of VO2max increased heart rate f rom 76 to 170 beats/min, plasma NE from 338 to 2,656 pg/ml, and NE spi llover from 1.87 to 11.65 nmol . min(-1). m(-2). In this group, 3 days of oral enalapril did not affect the NE spillover response to exercis e. Because the angiotensin-converting enzyme inhibitor did not attenua te the NE spillover response to exercise, we conclude that at the exer cise levels tested, prejunctional angiotensin II receptors do not appe ar to facilitate NE release.