In:
American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 279, No. 3 ( 2000-09-01), p. R822-R829
Abstract:
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.
Type of Medium:
Online Resource
ISSN:
0363-6119
,
1522-1490
DOI:
10.1152/ajpregu.2000.279.3.R822
Language:
English
Publisher:
American Physiological Society
Publication Date:
2000
detail.hit.zdb_id:
603839-6
detail.hit.zdb_id:
1477297-8
SSG:
12
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