Atrial distension, haemodilution, and acute control of renin release during water immersion in humans

• Published in: Acta physiologica Scandinavica Vol. 174; no. 2; pp. 91 - 99
• Main Authors: GABRIELSEN, A., PUMP, B., BIE, P., CHRISTENSEN, N. J., WARBERG, J., NORSK, P.
• Format: Journal Article
• Language: English
• Published: Oxford UK Blackwell Science Ltd 01.02.2002; Blackwell Science
• Subjects: Adult; Angiotensin II - blood; arginine vasopressin; Atrial Function; baroreceptors; Biological and medical sciences; Blood Pressure - physiology; Blood Proteins - analysis; cardiac output; Fundamental and applied biological sciences. Psychology; General aspects; Heart Rate - physiology; Hemodilution; Humans; Immersion - physiopathology; Male; Norepinephrine - blood; Osmotic Pressure; Plasma Volume - physiology; Pressoreceptors - physiology; Renin - blood; sympathetic nervous activity; Sympathetic Nervous System - physiology; Sympathetic Nervous System - physiopathology; Vertebrates: cardiovascular system; Heart; Water; Human; Enzyme; Electrical activity; Electrophysiology; Stimulation; Immersion; Sympathetic nervous system; Tank; Blood flow; Peptidases; Renin angiotensin system; Renin; Blood volume; Autonomic nervous system; Hydrolases; Hemodilution; Aspartic endopeptidases; Hemodynamics; Circulatory system; Baroreceptor; Exocrine secretion
• ISSN: 0001-6772; 1365-201X
• DOI: 10.1046/j.1365-201X.2002.00932.x

We tested the hypothesis that atrial distension (stimulation of cardiopulmonary baroreceptors) is not the single pivotal stimulus for the acute suppression of renin release during water immersion in humans and that immersion‐induced haemodilution constitutes an important additional stimulus. In nine healthy male subjects, identical increases in atrial distension were induced by two immersion procedures (of 30 min each); one without (WI) and one with attenuation (WI + cuff) of the concomitant haemodilution (estimated from changes in plasma protein concentration) by inflating thigh cuffs during immersion. During WI, central venous pressure (CVP) and left atrial diameter (LAD) increased (P < 0.05) by 5.5 ± 0.4 mmHg and 4.6 ± 0.5 mm, respectively, and plasma protein concentration and plasma renin activity (PRA) progressively decreased (P < 0.05) by 4.8 ± 0.5 g L–1 and 1.6 ± 0.2 ng mL–1 h–1 (to 49 ± 4% of baseline values), respectively. The WI + cuff caused similar atrial distension as WI (CVP and LAD increased by 6.9 ± 0.5 mmHg and 5.5 ± 0.5 mm, respectively), attenuated haemodilution (plasma protein concentration decreased by 1.9 ± 0.4 g L–1, P < 0.05 vs. WI), and markedly inhibited suppression of PRA, which decreased by 0.4 ± 0.1 ng mL−1 h−1 (to 87 ± 4% of baseline values, P < 0.05 vs. WI). Differences in renin release could not be accounted for by differences in mean arterial pressure. In conclusion, baroreceptor stimulation induced by atrial distension is not the single pivotal stimulus for the acute suppression of renin release in response to intravascular volume expansion by water immersion in humans. Haemodilution constitutes a significant and conceivably the principal stimulus for the acute immersion‐induced suppression of renin‐angiotensin system activity.