title: Determinants of the natriuresis after acute, slow sodium loading in conscious dogs.
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.
authors.affiliation: Department of Physiology and Pharmacology, University of Southern Denmark, Odense, DK-5000 Odense, Denmark. bie@imbmed.sdu.dk
authors.forename: P
authors.initials: P
authors.lastname: Bie
authors.forename: N C
authors.initials: NC
authors.lastname: Sandgaard
mesh_terms: D000804:Angiotensin II / Q000097:blood; D000818:Animals; D001127:Arginine Vasopressin / Q000097:blood / Q000652:urine; D009320:Atrial Natriuretic Factor / Q000097:blood; D001798:Blood Proteins / Q000032:analysis; D004231:Diuresis / Q000187:drug effects; D004285:Dogs; D005260:Female; D005919:Glomerular Filtration Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects; D007275:Injections, Intravenous; D007552:Isotonic Solutions / Q000008:administration & dosage / Q000494:pharmacology; D009318:Natriuresis / Q000187:drug effects*; D012462:Saline Solution, Hypertonic / Q000008:administration & dosage / Q000494:pharmacology; D012964:Sodium / Q000008:administration & dosage* / Q000494:pharmacology; D013997:Time Factors
chemical_list: D001798:Blood Proteins; D007552:Isotonic Solutions; D012462:Saline Solution, Hypertonic; D000804:Angiotensin II; D001127:Arginine Vasopressin; D009320:Atrial Natriuretic Factor; D012964:Sodium