Figure 226

Role of renal perfusion pressure in sodium (Na) retention. A, Results from studies in rats that had undergone myocardial infarction (MI) or placement of an arteriovenous fistula (AVF) [54]. Rats with small and large MIs were identified. Both small and large MIs induced significant Na retention when challenged with Na loads. Renal Na retention occurred in the setting of mild hypotension. AVF also induced significant Na retention, which was associated with a decrease in mean arterial pressure (MAP) [55,56]. Figure 2-3 has shown that Na excretion decreases greatly for each mm Hg decrease in MAP. B, Results of two groups of experiments performed by Levy and Allotey [57,58] in which experimental cirrhosis was induced in dogs by sporadic feeding with dimethylnitrosamine. Three cirrhotic stages were identified based on the pattern of Na retention. In the first, dietary Na intake was balanced by Na excretion. In the second, renal Na retention began, but still without evidence of ascites or edema. In the last, ascites were detected. Because Na was retained before the appearance of ascites, "primary" renal Na retention was inferred. An alternative interpretation of these data suggests that the modest decrease in MAP is responsible for Na retention in this model. Note that in both heart failure and cirrhosis, Na retention correlates with a decline in MAP.

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