INTRACEREBROVENTRICULAR LOSARTAN INHIBITS POSTPRANDIAL DRINKING IN SHEEP

We investigated the contribution of brain angiotensinergic mechanisms to postprandial drinking in sheep. Sheep in fluid balance were given 0 .8 kg chaff for 30 min, and water intake was measured for the next hou r. Intracerebroventricular infusion of the AT(1) type angiotensin II ( ANG II) receptor blocker losartan (1 mg/h) reduced postprandial drinki ng by similar to 70% (n = 7, P < 0.01) but did not affect food intake. The same losartan dose given intravenously had little or no effect on prandial drinking. Feeding increased Na+ concentrations in plasma and cerebrospinal fluid (CSF; n = 5, P < 0.05). Intracerebroventricular l osartan (1 mg/h) inhibited the drinking responses to intracarotid infu sion of ANG II (0.8 pg/min for 30 min, n = 4, P < 0.01) and to intrace rebroventricular infusion of 0.5 M NaCl (1 ml/h for 1 h, n = 5, P < 0. 05) but had no effect on drinking responses to intravenous infusion of 4 M NaCl (1.3 ml/min for 30 min). These findings indicate that a brai n ANG II-dependent mechanism is involved in postprandial drinking in s heep. They suggest also that the mechanism by which increasing CSF Na causes thirst involves brain ANG II and is different from the mechani sm subserving the drinking response to changes in blood Na+.