Pyridine nucleotide synthesis by rat adipose tissue in vitro.

The synthesis of NAD and NADP by rat adipose tissue was measured in vitro. Nicotinamide-7-(14)C and NaH(2)(32)PO(4) were incorporated together into NAD with a (32)P/(14)C ratio of 1.82 and nicotinic-7-(14)C acid and NaH(2)(32)PO(4) with a ratio of 1.94. Nicotinic acid stimulated, by 90%, lipogenesis from glucose-U-(14)C by rat adipose tissue in vitro. Glucose plus insulin and refeeding for 48 hr after a 48 hr fast markedly increased the incorporation of nicotinic-7-(14)C into NAD in rat epididymal fat pads in vitro, but neither fructose, L-glutamine, nor insulin alone increased the synthesis of NAD in this tissue. Glucose-1-(14)C, ribose-1-(14)C, and to a greater extent glucose-6-(14)C are incorporated into the NAD of rat adipose tissue. Fasting followed by refeeding sharply increased the radioactivity of NAD-(14)C formed from glucose-1-(14)C and glucose-6-(14)C but not from ribose-1-(14)C. Increasing the ribose concentration from 2 mM to 10 mM increased its incorporation into adipose tissue NAD twofold. The nicotinic-7-(14)C acid incorporation into NAD increased over the 1st hr of incubation and remained constant for the next 3 hr. The concentration of NAD in the fat pads showed a similar response to the time of incubation. NADP concentrations increased over the entire 4 hr incubation period as did the incorporation of nicotinic-7-(14)C acid into NADP. The results of this study suggest that NAD is synthesized de novo by rat adipose tissue in vitro and that this synthesis is increased by factors which stimulate lipogenesis.