NATRIURESIS OF FASTING IN INTACT AND ADRENALECTOMIZED RATS

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Abstract
Experiments were carried out in an attempt to elucidate the mechanism of fasting-induced natriuresis in conscious rats. Female animals were given a low Na diet and saline in a fixed concentration for at least 3 days, and deprived of food thereafter. The Na balance significantly shifted to a negative one independently of the K supply in intact rats. Similar observations were made in the dexamethasone-replaced, adrenalectomized rats which were not affected by further administration of aldosterone. The diuretic effect of insulin in fasted intact rats was not evident in the fed diabetic rats in which diabetes had been induced by streptozotocin. Such findings suggested participation of factors other than insulin. The natriuresis of fasting in intact rats appears to involve 2 factors, 1 of which is independent of the Na intake level. Dependence on the Na intake level may be derived from alteration of the solute diuresis-like effect of drinking saline when animals are fasted. Neither aldosterone nor insulin is a major causal factor involved in fasting-induced natriuresis.