Hypothalamic lesions abolish cardiovascular responses to chronic saline ingestion

In rats made to drink isotonic saline solution instead of water for 5 wk, systolic pressure and heart rate, whether recorded indirectly from the tail or directly from femoral catheters, rose slightly. When the ventromedial hypothalamus was stimulated electrically, increases in arterial pressure and sympathetic neural firing were larger in saline-drinking than in water-drinking rats. By contrast, pressor responses to injections of norepinephrine or tyramine were unaltered. Following bilateral destruction of the ventromedial hypothalamus in other rats, none of the effects of chronic saline ingestion was elicited. Although neither the site nor the mechanism causing sympathetic overactivity has been determined, our results are in accord with the interpretation that salt loading elevates blood pressure, at least in part, by stimulating the ventromedial hypothalamus to increase sympathetic activity.