Investigations on the Influence of Nicotinic Acid on Lipolysis in Isolated Fat Cells of Rats

Abstract

The influence of nicotinic acid on lipolysis stimulated by glucagon, epinephrine and DBAMP has been examined in vitro in isolated fat cells of rats.

The lipolytic effect of glucagon was inhibited at all concentrations by nicotinic acid (1 µg/ml). This inhibiting effect could also be observed at high glucagon concentrations (1 µg/ml) and at maximal lipolysis, so that a competitive antagonism between glucagon and nicotinic acid does not seem to exist. Against that the lipolytic effect of epinephrine was inhibited by nicotinic acid (1 µg/ml) only at low hormone concentrations (0.05 µg/ml), the effect of higher epinephrine concentrations (up to 1 µg/ml) was not influenced even by high concentrations of nicotinic acid (up to 100µg/ml). Similar to the results found with epinephrine, lipolysis stimulated by DBAMP was found to be inhibited by nicotinic acid (1 µg/ml) only at low concentrations (400µg/ml); at higher concentrations of DBAMP such an effect could no longer be significantly ascertained. The different behavior of nicotinic acid towards epinephrine on one hand and glucagon on the other, especially at medium concentrations and submaximal lipolysis, suggests an interference with the activation process of adenylcyclase at the enzyme level and stronger inhibition of the glucagon effect. Because of the inhibiting effect towards low concentrations of DBAMP an additional direct effect of nicotinic acid on the activation process of triglyceride lipase by cyclic 3', 5'-AMP or DBAMP must be assumed.

Key words

Lipolysis - Isolated Fat Cells - Nicotinic Acid - Glucagon - Dibutyryl-3'-5'-AMP - Epinephrine

1 The investigations have been supported by the Deutsche Forschungsgemeinschaft. Parts of the results were reported in extracts at the 76^th Kongress der Dtsch. Ges. inn. Med., Wiesbaden, 1970