Sustained suppression of voluntary sodium intake of spontaneously hypertensive rats (SHR) in hypobaric hypoxia.

Spontaneously hypertensive rats (SHR) of the Okamoto-Aoki-strain (n = 20) and normotensive rats (NCR) of a random-bred Wistar strain (n = 20) were kept in low-pressure chambers for 13 days at sea-level atmospheric pressure, then for 20 days at a simulated altitude of 4000 m, and subsequently again for 10 days at sea-level. The unrestrained animals were placed singly in metabolic cages and had free access to food, water, and a 2.5% NaC1-solution. Exposure to hypobaric hypoxia led to a transient decrease of daily food and water intake in both strains of animals and a slight reduction of saline consumption in the NCR. In contrast, the SHR showed a massive and sustained suppression of their voluntary intake of hypertonic saline throughout high-altitude exposure. Renal electrolyte and water excretion followed the reactions of salt and water intake. - In an additional series of experiments it was found that SH-rats react with a decrease of their systemic arterial blood pressures in hypobaric hypoxia only on condition that food and water but no additional salt is available to the animals. The data suggest that the antihypertensive effects of chronic high-altitude hypoxia depend both on the availability of salt and a reduction of salt appetite.