Hypothalamic regulation of spontaneous salt intake in the rat

Abstract

Adult male rats, maintained in metabolism cages, were epleted of Na [sodium] by hydrochlorothiazide administration and a salt-free synthetic diet that contained sufficient K [potassium] to balance urinary losses of the latter cation. Before and after the depletion period the rats were presented with a free choice of tap water, physiological saline, and a saline containing 20 g/1 NaCl [sodium chloride]. During administration of the diuretic only tap water was available. Normal rats reacted to the depletion by markedly increasing spontaneous salt intake and regaining salt balance with some overshooting, within 3 days. The same animals were then subjected to hypothalamic electrolytic lesions at various sites in the midhypothalamus, and the response to a new depletion period was again tested. With lesions in the region of the ventromedial nucleus of the hypothalamus the animals failed to increase salt intake after depletion[long dash]with other lesions, even in the close vicinity of the ventromedial nucleus, this effect was not observed.