THIRST INDUCED BY INCREASING BRAIN SODIUM CONCENTRATION IS MEDIATED BY BRAIN ANGIOTENSIN

Thirst, the longing or compelling desire to drink, arises physiologica lly by two main mechanisms-extracellular and cellular dehydration. The hormone angiotensin II has been implicated in the former but not in t he latter brain mechanism. To test this apparent difference, experimen ts in 5 mammalian species examined the effect of intracerebroventricul ar infusion of losartan, an angiotensin II type I receptor antagonist, on the thirst induced by intracerebroventricular infusion of an artif icial cerebrospinal fluid made hypertonic by the inclusion of 500 mM N aCl. The losartan infusion reduced the water intake due to increased b rain sodium concentration in all 5 species, cattle, sheep, rabbits, ra ts and mice. Thus, the thirst evoked by cellular dehydration, as well as the thirst evoked by extracellular dehydration, may be mediated by angiotensin II.