Fluid intake, distribution, and excretion during lateral ventricular infusions of carbachol in rats.

Infusion of carbachol into the lateral ventricles of rats at rates of 400 or 2000 ng/h for 6 h produced dose-related natriuresis, kaliuresis, and water drinking but no consumption of hypertonic NaCl solution. Electrolyte excretion and water intake were maximal during the first 2 h, and no further increases occurred after 4 h. Sodium losses were estimated as 15-30% of total extracellular sodium. Continuous infusion of 2000 ng/h carbachol for 6 days produced a chronic increase of water intake but no increased consumption of saline. Sodium balances were negative during the first day of infusion, but gradually returned to normal over 6 days. Plasma volume, hematocrit, and plasma sodium and potassium concentrations were normal in carbachol-infused animals on the 6th day. Cholinergic stimulation of the brain thus appeared to interfere with the usual salt appetite following sodium loss.