Low LBNP tolerance in men is associated with attenuated activation of the renin-angiotensin system.
Plasma vasoactive hormone concentrations [epinephrine (p(Epi)), norepinephrine (p(NE)), ANG II (p(ANG II)), vasopressin (p(VP)), endothelin-1 (p(ET-1))] and plasma renin activity (p(RA)) were measured periodically and compared during lower body negative pressure (LBNP) to test the hypothesis that responsiveness of the renin-angiotensin system, the latter being one of the most powerful vasoconstrictors in the body, is of major importance for LBNP tolerance. Healthy men on a controlled diet (2,822 cal/day, 2 mmol. kg(-1). day(-1) Na(+)) were exposed to 30 min of LBNP from -15 to -50 mmHg. LBNP was uneventful for seven men [25 +/- 2 yr, high-tolerance (HiTol) group], but eight men (26 +/- 3 yr) reached presyncope after 11 +/- 1 min [P < 0.001, low-tolerance (LoTol) group]. Mean arterial pressure (MAP) did not change measurably, but central venous pressure and left atrial diameter decreased similarly in both groups (5-6 mmHg, by approximately 30%, P < 0.05). Control (0 mmHg LBNP) hormone concentrations were similar between groups, however, p(RA) differed between them (LoTol 0.6 +/- 0.1, HiTol 1.2 +/- 0.1 ng ANG I. ml(-1). h(-1), P < 0.05). LBNP increased (P < 0. 05) p(RA) and p(ANG II), respectively, more in the HiTol group (9.9 +/- 2.2 ng ANG I. ml(-1). h(-1) and 58 +/- 12 pg/ml) than in LoTol subjects (4.3 +/- 0.9 ng ANG I. ml(-1). h(-1) and 28 +/- 6 pg/ml). In contrast, the increase in p(VP) was higher (P < 0.05) in the LoTol than in the HiTol group. The increases (P < 0.05) for p(NE) were nonsignificant between groups, and p(ET-1) remained unchanged. Thus there may be a causal relationship between attenuated activation of p(RA) and p(ANG II) and presyncope, with p(VP) being a possible cofactor. Measurement of resting p(RA) may be of predictive value for those with lower hypotensive tolerance.
Greenleaf
J E
JE
Danish Aerospace Medical Centre of Research and Clinic of Aviation Medicine, Rigshospitalet; DK-2200 Copenhagen, Denmark. jgreenleaf@mail.arc.nasa.gov
Petersen
T W
TW
Gabrielsen
A
A
Pump
B
B
Bie
P
P
Christensen
N J
NJ
Warberg
J
J
Videbaek
R
R
Simonson
S R
SR
Norsk
P
P
D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002496:Central Venous Pressure; D004837:Epinephrine / Q000097:blood; D006801:Humans; D007022:Hypotension / Q000503:physiopathology*; D008150:Lower Body Negative Pressure; D008297:Male; D009638:Norepinephrine / Q000097:blood; D010953:Plasma Volume / Q000502:physiology; D012084:Renin-Angiotensin System / Q000502:physiology*; D014667:Vasopressins / Q000502:physiology
D014667:Vasopressins; D009638:Norepinephrine; D004837:Epinephrine