Determinants of the natriuresis after acute, slow sodium loading in conscious dogs

Am J Physiol Regul Integr Comp Physiol. 2000 Jan;278(1):R1-R10. doi: 10.1152/ajpregu.2000.278.1.R1.

Abstract

The relative importance of systemic volume, concentration, and pressure signals in sodium homeostasis was investigated by intravenous infusion of isotonic (IsoLoad) or hypertonic (HyperLoad) saline at a rate (1 micromol Na(+) x kg(-1) x s(-1)), similar to the rate of postprandial sodium absorption. IsoLoad decreased plasma vasopressin (-35%) and plasma ANG II (-77%) and increased renal sodium excretion (95-fold), arterial blood pressure (DeltaBP; +6 mmHg), and heart rate (HR; +36%). HyperLoad caused similar changes in plasma ANG II and sodium excretion, but augmented vasopressin (12-fold) and doubled DeltaBP (+12 mm Hg) without changing HR. IsoLoad during vasopressin clamping (constant vasopressin infusion) caused comparable natriuresis at augmented DeltaBP (+14 mm Hg), but constant HR. Thus vasopressin abolished the Bainbridge reflex. IsoLoad during normotensive angiotensin clamping (enalaprilate plus constant angiotensin infusion) caused marginal natriuresis (9% of unclamped response) despite augmented DeltaBP (+14 mm Hg). Cessation of angiotensin infusion during IsoLoad immediately decreased BP (-13 mm Hg) and increased glomerular filtration rate by 20% and sodium excretion by 45-fold. The results suggest that fading of ANG II is the cause of acute "volume-expansion" natriuresis, that physiological ANG II deviations override the effects of modest systemic blood pressure changes, and that endocrine rather than hemodynamic mechanisms are the pivot of normal sodium homeostasis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Angiotensin II / blood
  • Animals
  • Arginine Vasopressin / blood
  • Arginine Vasopressin / urine
  • Atrial Natriuretic Factor / blood
  • Blood Proteins / analysis
  • Diuresis / drug effects
  • Dogs
  • Female
  • Glomerular Filtration Rate / drug effects
  • Hemodynamics / drug effects
  • Injections, Intravenous
  • Isotonic Solutions / administration & dosage
  • Isotonic Solutions / pharmacology
  • Natriuresis / drug effects*
  • Saline Solution, Hypertonic / administration & dosage
  • Saline Solution, Hypertonic / pharmacology
  • Sodium / administration & dosage*
  • Sodium / pharmacology
  • Time Factors

Substances

  • Blood Proteins
  • Isotonic Solutions
  • Saline Solution, Hypertonic
  • Angiotensin II
  • Arginine Vasopressin
  • Atrial Natriuretic Factor
  • Sodium