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Glucose Kinetics in Vitamin A Deficient Chickens

Departments of Physiology and Biophysics, and Animals Sciences, Colorado State University, Fort Collins, Colorado 80523

In order to further elucidate changes in carbohydrate metabolism in marginally vitamin A deficient chickens, the following experiments were conducted. Single Comb White Leghorn chicks were randomly assigned to diets containing 300 or 6,000 IU of retinyl palmitate/kg feed representing 20% and 300% of requirement, respectively. The vitamin A deficient group had a significantly reduced rate of body weight gain. Although glycogen concentrations were similar between the two groups, both skeletal muscle and liver glycogen had a higher standardized specific activity in the deficient birds. At approximately 16 weeks of age, they were given a single intra-arterial injection of [U-¹⁴C]glucose. Serial blood samples were collected to determine glucokinetics. In addition, respired air was monitored for ¹⁴CO₂, and liver and muscle glycogen specific activity were determined at 3 hours. The mean plasma glucose concentration (P < 0.001), the glucose pool size (P < 0.02) and the glucose entry rate (P > 0.05) were greater in the deficient birds than in the controls. The glucose space and turnover time of the glucose pool were similar. Based on the appearance of ¹⁴CO₂ in the respired air, the control birds oxidized a greater proportion of the tracer glucose. We have concluded that marginally vitamin A deficient chickens can adequately utilize glucose for oxidation and conversion to glycogen, and that apparent alterations are primarily due to the increase in circulating glucose for which there was no obvious explanation.

KEY WORDS: • glycogen • turnover time • pool size • substrate level

Manuscript received 22 December 1975.