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The influence of nicotinic acid on Iipolysis stimulated by glucagon, epinephrine and DBAMP has been examined in vitro in isolated fat cells of rats. The Iipolytie effeet of glucagon was inhibited at all COIlcentrations by nieotinie acid (1 pgJ m1). This inhibiting effect could also be observed at high glucagon eoncentrations (1 JJg/rnl) and at maximallipolysis, so that a competitive antagonism between glucagon and nieotinic acid does not seem to exist. Against that the Iipolytie effect of epinephrine was inhibited by nicotinie acid (1 JJg/ml) only at low hormone concentrations (0.05 pgJmI), the effeet of higher epinephrine concentrations (up to 11l8lml) was not influenced even by high concentrations of nicotinie acid (up to 100 pg/m1). Similar to the results found with epinephrine, lipolysis stimulated by DBAMP was found to be inhibited by nicotinie acid (1 pg/ml) only at low concentrations (400 pg/rnl); at higher concentrations of DBAMP such an effeet eould no longer be signifieantly ascertained. The different behavior of nicotinie acid towards epinepluine on one hand and glucagon on the other, especially at medium concentrations and submaximallipolysis, suggests an interference with the a~ tivation process of adenylcyclase at the enzyme level and stronger inhibition of the glucagon effect. Because of the inhibiting effect towards low coneentrations of DBAMP an additional direct effeet of nicotinie acid on the activation process of triglyceride lipase by eyelie 3', 5'-AMP or DBAMP must be assumed.

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