1. Fatty acid synthesis, measured in the perfused liver of genetically obese (ob/ob) mice with 3H2O or [14C]actate, did not show the inhibition by [8-arginine]vasopressin (antidiuretic hormone) that is observed in livers from normal mice. 2. Hepatic glycogen breakdown in obese mice was stimuulated by vasopressin, but not as extensively as in lean mice. 3. If obese mice received a restricted amount of food, then fatty acid synthesis still did not respond to vasopressin, but glycogen breakdown was fully stimulated. 4. Cholesterol synthesis was not inhibited by vasopressin in livers from obese mice. 5. Vasopressin inhibited fatty acid synthesis in intact lean mice, but not in obese animals. 6. These results suggest that genetic obesity could be due to an inborn error within the mechanisms (other than adenylate cyclase) which mediate responses to extracellular effectors.
