Low LBNP tolerance in men is associated with attenuated activation of the renin-angiotensin system

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 279; no. 3; pp. 822 - R829
• Main Authors: Greenleaf, John E, Petersen, Trine Wellow, Gabrielsen, Anders, Pump, Bettina, Bie, Peter, Christensen, Niels Juel, Warberg, Jorgen, Videbaek, Regitze, Simonson, Shawn R, Norsk, Peter
• Format: Journal Article
• Language: English
• Published: Legacy CDMS 01.09.2000
• Subjects: Adaptation, Physiological - physiology; Adult; Aerospace Medicine; Blood Pressure - physiology; Central Venous Pressure; Epinephrine - blood; Humans; Hypotension - physiopathology; Lower Body Negative Pressure; Male; Norepinephrine - blood; Plasma Volume - physiology; Renin-Angiotensin System - physiology; Space life sciences; Vasopressins - physiology; Nasa Program Biomedical Research And Countermeasures; Nasa Discipline Regulatory Physiology; Nasa Center Arc; NASA Center ARC; NASA Program Biomedical Research and Countermeasures; NASA Discipline Regulatory Physiology
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.2000.279.3.r822

1  Danish Aerospace Medical Centre of Research and Clinic of Aviation Medicine, Rigshospitalet; DK-2200 Copenhagen; 2  Department of Physiology and Pharmacology, University of Southern Denmark, Odense, DK-5000 Odense; and 3  Department of Internal Medicine and Endocrinology, Herlev Hospital, DK-2730 Herlev, Denmark 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 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. hypotensive tolerance; vasopressin; central venous pressure; catecholamines