Studies of a Humoral Sodium Transport Inhibitory Activity in Normal Dogs and Dogs with Ligation of the Inferior Vena Cava

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Abstract
Plasma ultrafiltrates of dogs acutely expanded with saline inhibit toad bladder sodium transport. The present studies were performed to delineate further the chemical and physiological characteristics of this inhibitory activity. Column chromatography with Sephadex G-10 showed the activity to be present in the fraction ahead of the salt peak. Sodium balance studies in normal dogs were performed to determine the relationship between factor activity and the daily fluctuations of renal sodium excretion. A significant correlation was observed between the presence of humoral inhibitory activity and spontaneous antinatriuresis. In the absence of antinatriuresis, inhibitory activity was absent, regardless of the level of sodium intake. In normal dogs given saline loads acutely, inhibitory activity was present 60 and 120 minutes after the beginning of saline loading. In dogs with constriction of the inferior vena cava, no activity was observed during saline loading for up to 120 minutes. The data are compatible with the interpretation that the humoral sodium transport inhibitory activity is a natriuretic hormone released in response to expansion of the extracellular fluid volume.

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