Altered vitamin B6 homeostasis during aminophylline infusion in the beagle dog

The effect of intravenous infusion of aminophylline, a strong inhibitor of pyridoxal kinase, on intra- and extracellular vitamin B6 homeostasis was investigated in four beagle dogs. Plasma and erythrocyte pyridoxal levels increased by 118% and 117% respectively after 3 hours of aminophylline infusion, (4 mg/kg body weight/hour), however, infusion of beta-hydroxyethyltheophylline, which does not inhibit pyridoxal kinase, had no effect on either intra- or extracellular vitamin B6 aldehyde derivative levels. It is suggested that theophylline induced pyridoxal kinase inhibition resulted in a disturbed equilibrium between pyridoxal and pyridoxal 5'-phosphate.