A comparison of head‐down tilt with low‐dose infusion of atrial natriuretic peptide in man.

Abstract

SUMMARY1. Procedures that increase atrial pressure, such as head-down tilt, result in an increase in plasma atrial natriuretic peptide (ANP) and a natriuresis, but a direct cause-and-effect relationship between these two responses has not been established. This study was undertaken to compare the effects of head-down tilt with exogenous ANP on renal function.2. Eight normal sodium-replete volunteers underwent a 3 h placebo infusion, a 3 h ANP infusion at 1-2 pmol kg-' min-' and a 3 h period of head-down tilt. Each procedure was performed on a separate day, in random order.3. ANP and head-down tilt produced similar increases in sodium excretion (65 + 24 and 68 + 16 %, respectively). ANP did not increase urine flow significantly more than placebo. Head-down tilt increased urine flow significantly more than placebo and ANP.4. Plasma ANP rose from 8-1 +1P0 to 11-4 + 2-5 pg ml-' during head-down tilt and from 6-5 + 1-4 to 32-3 + 107 pg ml-' with ANP infusion.5. ANP infusion had no significant effects on systemic haemodynamics whilst head-down tilt increased cardiac output and reduced heart rate and an index of systemic vascular resistance.6. ANP infusion, whilst achieving a natriuretic response similar to that of tilt, was associated with a 3-fold higher mean plasma ANP level. Although plasma ANP rose during both ANP infusion and tilt, there was a lack of correlation between natriuretic response and plasma ANP.7. The results are not compatible with a direct cause-and-effect relationship between plasma ANP and sodium excretion during head-down tilt.

Acute Effects of Head‐Down Tilt and Hypoxia on Modulators of Fluid Homeostasis

“…There was no significant difference between overall mean values when comparing the hypoxic and normoxic runs. However, HD stimulated a significant (P < .001) release of ANP in both hypoxic and normoxic conditions, but at 15 and 55 minutes during HD the increase in ANP was 35% less with hypoxia (P < .10).…”

Atrial plasma ANP and NH2‐terminal proANP during right atrial pressure increase in humans

“…Atrial natriuretic peptide (ANP) is a hormone stored in atrial myocytes and released into blood circulation in response to various stimuli the most important being right atrial pressure or stretch, for review, see Ruskoaho (1992). In man, head-out immersion (Ogihara et al 1986, Epstein et al 1987, Leung et al 1987, Warner et al 1991, Nakamitsu et al 1994, or headdown tilt (Allen et al 1989, Arjamaa et al 1992 are among the factors that elevate plasma ANP. Nose et al (1994), measuring the right atrial pressure with an intraluminal catheter, showed a correlation between plasma ANP and right atrial pressure during prolonged exercise in man.…”

Circadian rhythm and postural change in natriuresis in non-dipper type of essential hypertension

“…In addition, when posture is changed from standing to supine, plasma renin activity and plasma concentrations of aldosterone have been reported to decrease 16 and plasma arterial natriuretic peptide to increase. 25 In this study, however, we did not measure these parameters. Further studies are required to clarify the mechanisms of the disturbed natriuresis in non-dippers.…”