Effects of acute hypoxia on renal and endocrine function at rest and during graded exercise in hydrated subjects

Abstract

Renal effects of altitude hypoxia are unclear. Renal and hormonal function was investigated in eight males at rest and during graded exercise at sea level (SL) and 48 h after rapid ascent to 4,350 m (HA). HA did not change resting values of effective renal plasma flow (ERPF), glomerular filtration rate (GFR), sodium clearance (CNa), urine flow, or lithium clearance (CLi), which was used as an index of proximal tubular outflow. At rest, HA increased plasma norepinephrine concentration and decreased plasma concentrations of renin and aldosterone. Exercise decreased ERPF similarly in both environments. Normoxic exercise progressively reduced GFR, but at HA GFR only decreased during heavy exercise. This resulted in a higher filtration fraction during light and moderate hypoxic exercise. However, calculated absolute proximal reabsorption rate (GFR-CLi) at HA was higher during low-intensity exercise, and there were no significant differences between exercise-induced decreases in CLi, CNa, and urine flow at HA compared with SL. Exercise gradually increased plasma norepinephrine, but values were higher at HA during light and moderate exercise. The small changes in the renal response to low-intensity hypoxic exercise may be secondary to increased adrenosympathetic activity. However, antidiuretic and antinatriuretic effects of exercise were maintained in hypoxia and in both environments seemed to be the consequence of decreased proximal tubular outflow. The results demonstrate that renal glomerular and tubular function is well preserved in acute hypoxia despite marked hormonal changes.

Chronic Kidney Disease at High Altitude

“…8 Renal blood flow (RBF) increases 8 to 20% during acute hypoxia, 9 -11 then returns to baseline after several days. 11,12 The effect on GFR is similar. 12,13 In highaltitude residents, RBF is decreased 12% and renal plasma flow by 30 to 40% largely as a result of secondary polycythemia.…”

Impairment of renal function during moderate physical exercise in cirrhotic patients with ascites: Relationship with the activity of neurohormonal systems

“…The activity of the renin-aldosthetic nervous systems. [5][6][7][8][9][10] The mechanism of this, however, terone and sympathetic nervous systems and the plasma is different from that occurring during postural changes. levels of antidiuretic hormone (ADH) and atrial natriWhereas postural changes affect neurohormonal vasoactive uretic peptide (ANP) were determined at the end of each systems through a baroreceptor-mediated mechanism, the period.…”

“…[5][6][7][8]11,12,[22][23][24][25][26] A close relationship exists between the intensity of exercise ferences were only observed in baseline PRA, NE, and pulse rate and post-exercise PRA and NE ( Figs. 1 and 2; Table 3).…”

“…8 When physical exercise is intense (ú7 METs) there is a decrease in GFR, free-water DISCUSSION clearance, urine volume, and sodium excretion. [5][6][7][8][13][14][15] Filtration fraction increases, 15 indicating that renal vasoconstricPhysical exercise in healthy subjects is associated with mation occurs predominantly in the efferent arterioles. The jor changes in endogenous vasoactive systems, systemic and mechanisms leading to the reduction in renal perfusion and regional hemodynamics, and respiratory function.…”

“…42 Because NO is also a potent vasodilator of the there is no decrease in GFR and renal excretory function. [5][6][7][8][13][14][15] In fact, a modest but significant increase in GFR, renal circulation, 43 it may be speculated that an impaired synthesis of NO may also contribute to exercise-induced renal urine volume, and sodium excretion has been reported by some investigators. 8,13,27 impairment in patients with cirrhosis and ascites.…”