Intestinal hydrolysis of pyridoxal 5'-phosphate in vitro and in vivo in the rat: effect of ethanol.

The effect of ethanol on intestinal hydrolysis of pyridoxal 5'-phosphate (PLP), the first step in PLP absorption, was evaluated in the rat. Models included PLP decay during in vitro incubation and PLP luminal disappearance during in vivo perfusion of jejunal segments. Ethanol inhibited PLP in vitro decay (pH = 7.4 and 3.0) and in vivo disappearance (pH = 7.4) in a concentration-dependent manner (1-4% w/v). At pH = 7.4, 4% w/v ethanol inhibited in vitro PLP decay by 48% (p less than 0.001) and in vivo PLP disappearance by 55% (p less than 0.001). This inhibition was reproduced in vitro with other alcohols but not with osmotic controls, paralleled in vitro changes in phosphatase activity in the presence of ethanol, and was completely reversed in vivo after ethanol was removed from the perfusing solution. The inhibition of intestinal PLP hydrolysis may possibly be one of the mechanisms by which a high percentage of alcoholics become biochemically vitamin B6 deficient.