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Metabolism of [¹⁴C]- and [³²P]Pyridoxal 5'-Phosphate and [³H]Pyridoxal Administered Intravenously to Pigs and Goats^1,2,

Biochemistry Department, Fort Wayne State Developmental Center, Fort Wayne, IN 46835 ^* Department of Mathematical Sciences, Indiana University-Purdue University, Fort Wayne, IN 46805

To gain more information about the kinetics of vitamin B-6 metabolism in vivo, the metabolism of tracer was examined after the simultaneous intravenous administration of [³²P] and [¹⁴C]pyridoxal phosphate and [³H]pyridoxal in two 93-kg pigs and two 60-kg goats. In the pigs, [¹⁴C] removal was monophasic with T of 16 and 18 min and clearance of 165 and 248 mL/min. In the goats, [¹⁴C] removal was biphasic with T of 49 and 114 min for 0–30 min and 209 and 227 min for 0.5–6 h (clearance 20 and 17 mL/min). Uptake of pyridoxal phosphate by liver and resecretion into the plasma were too small to cause a detectable decrease in the [³²P]:[¹⁴C] ratio. Pyridoxal removal from plasma was similar in both species, with a half-life of 12 min from 0–30 min and 50 min for 0.5–3 h. Clearance of [³H]pyridoxal in the four animals ranged from 412 to 2258 mL/min. Little [¹⁴C] entered the erythrocytes. The [³H] entered readily but was converted to pyridoxal phosphate faster in the pigs than in the goats. [¹⁴C] and [³H] were excreted as pyridoxic acid at the same rate. However, during the 54 h after injection the goats excreted 60% of the [³H] and [¹⁴C] doses in the urine compared with 30% in the pigs. About 5–10% of the [¹⁴C] and [³H] doses were recovered in goat milk over 54 h. Pyridoxal kinase activity was higher in lactating mammary tissue than in liver, kidney or muscle of goats.

KEY WORDS: • vitamin B-6 • plasma clearance • pigs • goats

¹ Supported in part by grant no. 85-CRCR-1-1554 and 88-372000-3666 from the U.S. Department of Agriculture Competitive Grant Program.

² Presented in part at the Annual Meeting of the Federation of American Societies for Experimental Biology, 1989, New Orleans, LA [Coburn, S. P., Mahuren, J. D., Kennedy, M. S., Schaltenbrand, W. E. & Townsend, D. W. (1989) Metabolism of intravenous [¹⁴C][³²P]pyridoxal-5'-phosphate and [³H]pyridoxal in swine and goats. FASEB J. 3: A668].

Manuscript received 8 March 1991. Revision accepted 29 July 1991.