Lumeng L, Schenker S, Li T K, Brashear R E, Compton M C
J Lab Clin Med. 1984 Jan;103(1):59-69.
This study was undertaken to characterize the metabolic fate of plasma pyridoxal 5'-phosphate (pyridoxal-P), the role of various organs in mediating its degradation, and the contribution of urinary excretion. Anesthetized dogs underwent sham operation, hepatectomy, nephrectomy, or combined surgical removal of the stomach, small intestine, and the spleen; however, the kinetics of plasma pyridoxal-P clearance after the intravenous administration of 2.5 mg of this B6 vitamin were not altered. In anesthetized sham-operated dogs and in unanesthetized dogs, pyridoxal (product of pyridoxal-P hydrolysis) but not 4-pyridoxic acid (oxidation product of pyridoxal) accumulated in plasma and urine after pyridoxal-P administration. Urinary excretion of pyridoxal-P was negligible and it could not account for the rapid clearance of pyridoxal-P from the plasma. The rate of pyridoxal-P hydrolysis mediated by plasma alkaline phosphatase and the cellular elements in whole blood in vitro was also too slow to account for the rapid disappearance of plasma pyridoxal-P in vivo. These results indicate that (1) normally, the overall capacity of the body to hydrolyze circulating pyridoxal-P in plasma is so large that removal of the liver, kidneys, or the intestinal tract and spleen has little or no effect on the rate of plasma pyridoxal-P decay; and (2) plasma pyridoxal-P decay normally proceeds by way of hydrolysis to form pyridoxal. Because pyridoxal is not further oxidized by the liver and the amount of pyridoxal excreted in the urine accounts for less than 25% of the pyridoxal that can be derived from the injected pyridoxal-P load, the preponderant metabolic fate of plasma pyridoxal-P most likely involves its hydrolysis to pyridoxal and then the uptake of pyridoxal by extrahepatic tissues.
本研究旨在表征血浆中磷酸吡哆醛（pyridoxal-P）的代谢命运、各器官在介导其降解中的作用以及尿排泄的贡献。对麻醉的犬进行假手术、肝切除术、肾切除术或联合切除胃、小肠和脾脏；然而，静脉注射2.5mg这种维生素B6后，血浆中磷酸吡哆醛清除的动力学并未改变。在麻醉的假手术犬和未麻醉的犬中，注射磷酸吡哆醛后，血浆和尿液中积累的是吡哆醛（磷酸吡哆醛水解产物）而非4-吡哆酸（吡哆醛氧化产物）。磷酸吡哆醛的尿排泄量可忽略不计，且无法解释血浆中磷酸吡哆醛快速清除的现象。体外血浆碱性磷酸酶和全血细胞成分介导的磷酸吡哆醛水解速率也太慢，无法解释体内血浆中磷酸吡哆醛的快速消失。这些结果表明：（1）正常情况下，机体水解循环于血浆中的磷酸吡哆醛的总体能力非常大，以至于切除肝脏、肾脏或肠道及脾脏对血浆中磷酸吡哆醛的衰减速率几乎没有影响；（2）血浆中磷酸吡哆醛的衰减通常通过水解形成吡哆醛的方式进行。由于吡哆醛不会被肝脏进一步氧化，且尿中排泄的吡哆醛量占注射的磷酸吡哆醛负荷所产生的吡哆醛的比例不到25%，血浆中磷酸吡哆醛的主要代谢命运很可能是先水解为吡哆醛，然后被肝外组织摄取。
