Intracerebroventricular glycerol: a potent inhibitor of ADH-release and thirst

Infusions of isotonic or hypertonic (0.3 or 0.5 M) glycerol into the lateral cerebral ventricle (60 min, 0.02 ml/min) of non-hydrated goats invariably induced a conspicuous and sustained water diuresis. Corresponding infusions of 0.3 M glycerol/0.16 M NaCl were almost equally efficient in this respect. A more short-lasting and less pronounced water diuresis was obtained in response to equivalent infusions of pure d-glucose, and the response to 0.3 M glucose/0.16 M NaCl was variable. Intravenous injections of vasopressin blocked the glucose-induced diuresis, but only postponed the glycerol-induced diuresis. Intracerebroventricular (IVT) infusions of 0.5 M glycerol caused a sustained, complete inhibition of the urge to drink in the 48 h dehydrated goat, whereas IVT glucose only attenuated dehydrative drinking. Twenty min after the infusions of glycerol the CSF [Na+] in the lateral ventricle was about 15% below normal. About 10% reduction of CSF [Na+] was obtained 20 min after the IVT infusion of glycerol/NaCl. The corresponding infusion of pure d-glucose reduced the CSF [Na+] by less than 5%. The glycerol and glycerol/NaCl infusions caused a moderate reduction of renal Na+ + K+ excretion. The possibility is discussed that the observed effects of IVT glycerol is a manifestation of its efficiency to inhibit choroidal and/or juxtaventricular (Na+-K+)-ATPase activity.