Age related changes in the antilipolytic effects of nicotinic acid in rat adipose tissue.
The effect of nicotinic acid on lipolysis was tested in vitro in adipose tissue from three groups of rats, selected according to age: 6-7 weeks, 10-12 weeks and 16-20 weeks old. Although the changes were not statistically significant, the basal release of free fatty acid (FFA) was increased and glycerol was decreased by nicotinic acid (0.01-1 mM); the drug caused a statistically significant increase in basal FFA: glycerol ratio in a concentration-dependent manner. This ratio also increased with age in the absence of drug. (-)-Noradrenaline (10 microM) and theophylline (3 mM) each stimulated lipolysis. When glycerol release was calculated as a percentage increase, the effects of these drugs became more marked with age. By contrast, the highest absolute rate of induced release occurred in adipose tissue from the youngest rats. The lipolytic effect of 10 microM (-)-noradrenaline was generally unaffected by nicotinic acid except in adipose tissue from the oldest rats when the glycerol release was reduced by 1 mM nicotinic acid, although it did not alter FFA:glycerol ratio. The stimulation of glycerol release induced by 3 mM theophylline was not affected by the presence of nicotinic acid in the youngest rats, but the drug elicited a concentration-dependent antilipolytic effect in adipose tissue from 10-12 weeks old rats, which was even more pronounced in the oldest animals. Lower theophylline concentrations (0.6-1 mM) were also sensitive to nicotinic acid inhibition in the 6-7 weeks old rats. In the presence of theophylline, nicotinic acid had no effect on FFA:glycerol ratio. These data show a direct influence of age on the antilipolytic action of nicotinic acid.