Vitamin C synthesis in animals proceeds from glucuronate, which is first reduced to L-gulonate. After lactonization, the latter is oxidized by L-gulonolactone oxidase, an enzyme that is deficient in man.  Vitamin C formation in animals (and, in man, the formation of the pentose L-xylulose, also derived from glucuronate) is known to be enhanced by a series of xenobiotics, including aminopyrine and chloretone. We have recently investigated the mechanism of this effect in isolated hepatocytes and showed that it is due to a rapid stimulation of the conversion of UDP-glucuronate to glucuronate. 

Formation of L-ascorbate and L-xylulose from UDP-glucuronate in liver. The formation of glucuronate from UDP-glucuronate is stimulated by aminopyrine and other agents. The precise mechanism of this formation is still unknown.