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Dietary Protein Quality Alters Ornithine Decarboxylase Activity but Not Vitamin B-6 Nutritional Status in Rats^1,2,3,

Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, CO 80523

Weanling male rats were fed diets that varied in protein quality (casein or wheat gluten) and vitamin B-6 (0.0, 0.5, 1.0 and 1.5 mg pyridoxine HCl/kg diet) to test the hypotheses that low protein quality would depress vitamin B-6 nutritional status and that activity of ornithine decarboxylase (ODC) would be a sensitive functional indicator of vitamin B-6 nutritional status. The wheat gluten diet depressed body weight gain -17% at higher vitamin B-6 levels, as expected. However, vitamin B-6 nutritional status was not worse in gluten-fed compared with casein-fed groups, as evidenced by static measures (B-6 vitamer concentrations in plasma and tissues) and a functional indicator (tryptophan load test). The activity of ODC (holo- and total) in liver, kidney and small intestine did not vary significantly at the three higher levels of vitamin B-6 intake. In groups fed casein, total ODC activity in these tissues was two- to fivefold higher in rats fed diets containing 0.0 mg vitamin B-6/kg compared with higher B-6 levels, without corresponding differences in ODC mRNA abundance in liver and kidney. Concentrations of B-6 vitamers (except pyridoxal phosphate in plasma) increased linearly with dietary vitamin B-6 in plasma, liver, kidney and intestine. These data suggest that low quality protein fed as wheat gluten suppresses growth but not vitamin B-6 nutritional status, and that ODC activity is not a sensitive functional indicator of marginal vitamin B-6 status.

KEY WORDS: • vitamin B-6 • ornithine decarboxylase • nutritional status • protein quality • rats

¹ Funded by the Colorado State University Experiment Station (Project W-143, Nutrient Bioavailability).

² Presented in part at Experimental Biology 94, April 24–28, 1994, Anaheim, CA [Sampson, D. A., Yan, X. L., Clarke, S. D. & Harrison, S. C. (1994) Vitamin B6 deficiency elevates ornithine decarboxylase activity but not mRNA abundance. FASEB J. 7: A919 (abs. 5327)].

³ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁴ To whom correspondence should be addressed.

Manuscript received 12 September 1994. Revision accepted 16 December 1994.