Saline-induced natriuresis and renal blood flow in conscious dogs: effects of sodium infusion rate and concentration.
OBJECTIVE
This study focused on static and dynamic changes in total renal blood flow (RBF) during volume expansion and tested whether a change in RBF characteristics is a necessary effector mechanism in saline-induced natriuresis.


METHODS
The aortic flow subtraction technique was used to measure RBF continuously. Identical amounts of NaCl (2.4 mmol kg(-1)) were given as slow isotonic (Iso, 120 min), slow hypertonic (Hyper, 120 min), and rapid isotonic loads (IsoRapid, 30 min).


RESULTS
During Iso and IsoRapid, arterial blood pressure increased slightly (6-7 mmHg), and during Hyper it remained unchanged. Iso and Hyper increased sodium excretion (4 +/- 1 to 57 +/- 27 and 10 +/- 4 to 79 +/- 28 micromol min(-1), respectively) and decreased plasma renin activity (by 38% and 29%), angiotensin II (by 56% and 58%) and aldosterone (by 47% and 65%), while RBF remained unchanged. IsoRapid caused a similar increase in sodium excretion (to 72 +/- 19 micromol min(-1)), a similar decrease in renin system activity, but a 15% elevation of RBF (282 +/- 22 to 324 +/- 35 mL min(-1)). Selected frequency domain parameters of RBF autoregulation did not change in response to any load.


CONCLUSIONS
In response to slow saline loading simulating daily sodium intake, the rate of sodium excretion may increase 10-20-fold without any change in mean arterial blood pressure or in RBF. Regulatory responses to changes in total body NaCl levels appears, therefore, to be mediated primarily by neurohumoral mechanisms and may occur independent of changes in arterial pressure or RBF.
Sandgaard
N C F
NC
Department of Physiology and Pharmacology, University of Southern Denmark, Odense, Denmark. ncfsand@dadlnet.dk
Andersen
J L
JL
Holstein-Rathlou
N-H
NH
Bie
P
P
D000450:Aldosterone / Q000097:blood; D000818:Animals; D001127:Arginine Vasopressin / Q000097:blood; D009320:Atrial Natriuretic Factor / Q000097:blood; D001794:Blood Pressure / Q000187:drug effects; D001810:Blood Volume; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005260:Female; D006400:Hematocrit; D006706:Homeostasis; D007668:Kidney / Q000098:blood supply* / Q000378:metabolism*; D023421:Models, Animal; D009318:Natriuresis / Q000187:drug effects*; D009997:Osmotic Pressure; D010052:Ovariectomy; D012039:Regional Blood Flow / Q000187:drug effects; D012462:Saline Solution, Hypertonic / Q000378:metabolism / Q000494:pharmacology*; D014655:Vascular Resistance
D012462:Saline Solution, Hypertonic; D001127:Arginine Vasopressin; D000450:Aldosterone; D009320:Atrial Natriuretic Factor