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Efficacy of the Rat Bioassay for the Determination of Biologically Available Vitamin B-6^1,2,

Food Science and Human Nutrition Department, University of Florida, Gainesville, FL 32611

Research was conducted to evaluate the merits of rat bioassays in studies concerning the bioavailability of vitamin B-6. A protocol was devised, which included pair-feeding and prevention of coprophagy. Plasma pyridoxal 5'-phosphate (PLP) was measured by a rapid chromatographic method as an indicator of vitamin B-6 status. Pyridoxamine and pyridoxal exhibited 70% molar activity relative to pyridoxine at suboptimal dietary levels. Selected foods (spinach, cornmeal and potato) were evaluated at three dietary levels with this protocol. Analysis of dose-response curves (dietary vitamin B-6 vs. plasma PLP) by slope-ratio methods yielded imprecise estimates of the relative vitamin B-6 bioavailability. This low precision, in addition to the potential for interference by direct absorption of B-6 vitamers synthesized by intestinal microflora, indicates the need for improved methods for measurement of biologically available vitamin B-6. It was concluded that rat bioassay methods, even as modified here, may be frequently unsuitable for use in studies of vitamin B-6 bioavailability. Results presented provide further support for the use of plasma PLP as an indicator of vitamin B-6 nutriture.

KEY WORDS: • vitamin B-6 • bioavailability • rat bioassay • pyridoxal 5'-phosphate (plasma) • HPLC

¹ Florida Agricultural Experiment Stations Journal Series No. 6190.

² This research was supported in part by Grant No. 5901-0410-9-0305-0 from the Competitive Research Grants Office, U.S. Department of Agriculture, and Grant No. 564 from the Nutrition Foundation, Inc.

Manuscript received 30 July 1985. Revision accepted 5 September 1985.