TY - JOUR

T1 - Renal and sympathoadrenal responses in space

AU - Christensen, N J

AU - Drummer, C

AU - Norsk, P

PY - 2001/9/1

Y1 - 2001/9/1

N2 - According to a classic hypothesis, weightlessness should promote the renal excretion rate of sodium and water and lead to a fluid- and electrolyte-depleted state. This hypothesis is based on experiments in which weightlessness has been simulated in humans by head-down bed rest and water immersion. However, after 5 to 6 days of space mission, the diuretic and natriuretic responses to an intravenous isotonic saline load were attenuated and plasma norepinephrine and renin concentrations increased compared with those of the acute supine position before flight. Renal fluid excretion after an oral water load was also attenuated in space. Similar decreases were not observed during head-down bed rest. Sympathetic activity is of major importance in regulating blood volume and renal function. Studies in space have indicated that, compared with that while in a supine position on Earth, sympathoadrenal activity is increased during space flights as measured using plasma concentration and urinary excretion of norepinephrine and epinephrine. The space-induced activation of antinatriuretic mechanisms and sympathoadrenal activity could have been caused by early in-flight reduction in total and central blood volume. The decreased plasma volume may be explained by such factors as redistribution of plasma from the lower to the upper body (thin legs and puffy face), reduced food intake, and decreased muscle activity. The decrease in plasma volume and the subsequent increase in sympathetic activity is due, at least in part, to the abrupt cessation of activity in large muscle groups during microgravity, which normally counteracts the effects of gravity in the upright posture. This would lead to accumulation of albumin and fluid in the interstitial space.

AB - According to a classic hypothesis, weightlessness should promote the renal excretion rate of sodium and water and lead to a fluid- and electrolyte-depleted state. This hypothesis is based on experiments in which weightlessness has been simulated in humans by head-down bed rest and water immersion. However, after 5 to 6 days of space mission, the diuretic and natriuretic responses to an intravenous isotonic saline load were attenuated and plasma norepinephrine and renin concentrations increased compared with those of the acute supine position before flight. Renal fluid excretion after an oral water load was also attenuated in space. Similar decreases were not observed during head-down bed rest. Sympathetic activity is of major importance in regulating blood volume and renal function. Studies in space have indicated that, compared with that while in a supine position on Earth, sympathoadrenal activity is increased during space flights as measured using plasma concentration and urinary excretion of norepinephrine and epinephrine. The space-induced activation of antinatriuretic mechanisms and sympathoadrenal activity could have been caused by early in-flight reduction in total and central blood volume. The decreased plasma volume may be explained by such factors as redistribution of plasma from the lower to the upper body (thin legs and puffy face), reduced food intake, and decreased muscle activity. The decrease in plasma volume and the subsequent increase in sympathetic activity is due, at least in part, to the abrupt cessation of activity in large muscle groups during microgravity, which normally counteracts the effects of gravity in the upright posture. This would lead to accumulation of albumin and fluid in the interstitial space.

KW - Adrenal Glands

KW - Arginine Vasopressin

KW - Blood Volume

KW - Diuresis

KW - Epinephrine

KW - Head-Down Tilt

KW - Humans

KW - Immersion

KW - Kidney

KW - Muscle, Skeletal

KW - Natriuresis

KW - Norepinephrine

KW - Sodium Chloride

KW - Space Flight

KW - Sympathetic Nervous System

KW - Weightlessness

U2 - 10.1053/ajkd.2001.27758

DO - 10.1053/ajkd.2001.27758

M3 - Journal article

C2 - 11532706

VL - 38

SP - 679

EP - 683

JO - American Journal of Kidney Diseases

JF - American Journal of Kidney Diseases

SN - 0272-6386

IS - 3

ER -