[Lack of interference by carbamylcholine on the renin-angiotensin system thirst mechanism]

The thirst mechanism by carbamylcholine and the possible interactions with the renin-angiotensin system have been investigated. Rats placed in metabolic cages in order to measure the drunk water and the emitted urine were used. Carbamylcholine has been injected together with captopril, an inhibitor of the enzyme converting angiotensin I into angiotensin II, and with propranolol, which blocks the renin beta-receptors respectively. When given in combination with these substances, the thirst by carbamylcholine was not reduced; this result does not favour the hypothesis of a role of the renin-angiotensin system. On the contrary, the thirst by carbamylcholine seems to be due to a vasomotor action. These results confirm the hypothesis that an unbalance between the blood circulating mass and the venous vessels underlies the regulation of the thirst.