Dose-Response Relation of CSF Sodium and Renal Sodium Excretion, and Its Absence in Homozygous Brattleboro Rats

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Abstract
Constant intraventricular infusion (3.3-6.6 .mu.l/min) of artificial CSF with Na concentrations of 100, 150, 200, 250, 300 and 350 mM produced a linear dose-related change in renal Na excretion in conscious, unrestrained Sprague-Dawley rats. The periventricular receptors stimulated were able to evoke substantial changes in body Na balance; the 350 mM Na CSF produced an estimated 14% deficit in the content of Na in the extracellular fluid over a 5 h infusion period. This is the 1st demonstration of such a dose-response relation over a wide range of CSF Na concentration (above and below normal) in conscious animals. Both the dose-response relation, and the magnitude of the effects, suggests an important physiologic role for this control mechanism. The natriuresis in response to 300 mM Na infusion was identical in Long-Evans Brattleboro rats heterozygous for diabetes inspidus (DI), and in Sprague-Dawley rats, but was completely absent in homozygous animals. Although the experimental methods (conscious unrestrained rats) precluded simultaneous evaluation of efferent pathways other than antidiuretic hormone (ADH), the evidence from the DI rats suggests that ADH may be the efferent pathway for the response.

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