Effects of Interrupting Intravenous Saline Infusion on Sodium Excretion in the Dog

Abstract

Systemic and renal hemodynamics, and plasma antinatriferic activity (AA) were measured before, during 2 h of saline loading, and for 1 h immediately after stopping saline infusion in dogs. During loading, mean arterial pressure (MAP), central venous pressure (CVP), renal blood flow (RBF), glomerular filtration rate (GFR), and AA increased as sodium excretion as (U_NaV) rose progressively. During the post-loading period, MAP, CVP, and AA returned to baseline, RBF and GFR remained elevated, while U_NaV fell. Only 52 ± 3% of the total sodium load was excreted during the study. These data show that AA is not regulated by the absolute volume of extracellular fluid. The correlation of AA with changes in systemic hemodynamics suggests ‘volume receptors’ in the resistance and/or capacitance circulation. The data suggest that the post-loading fall in U_NaV i_s due at least in part to decreased levels of a humoral natriuretic factor.

Enhanced increase of plasma sodium pump inhibitory activity to saline expansion in vagosympathectomized and anaesthetized dogs

“…This observation suggests that the activation of cardiopulmonary and/or aortic baroreceptors in intact animals exerts inhibitory control on the synthesis and/or release of PAA. However, PAA also increased in the CTR group at the end of saline expansion, con®rming the ®ndings of several investigators (Buckalew & Adkins 1978, Bealer et al 1983, Kramer et al 1974, and suggesting that, in addition to the above inhibitory mechanism, some other excitatory mechanism linked to intravascular and/or extravascular components of Na and H 2 O balance is operating in the intact animal.…”

“…To learn more about this, the post-expansion phase was manipulated. Because Buckalew & Adkins (1978) had shown, in intact dogs, that during this phase ex- tracellular¯uid volume contracts and MAP and RAP return to baseline levels and PAA decreases, we tried to dissect the effects of a drop in water and sodium balance from those of a drop in haemodynamic variables (MAP and RAP) on PAA. With this aim, saline boluses were manually administrated (i.v.)…”

Natriuretic Hormones, Endogenous Ouabain, and Related Sodium Transport Inhibitors

“…The atrial distention arising from balloon inflation requires intact cardiac but not renal nerves, the stretch can be reversed in seconds, and the evoked natriuresis declines rapidly ( 21 ). Critically, the kinetics of the decline in natriuresis are uncontaminated by residual volume that typically would remain following a saline load ( 78 ). The second experimental paradigm is the natriuresis evoked by infusion of hypertonic saline into the brain.…”