Studies on protein turnover in laying hens 産卵鶏の蛋白質代謝回転に関する研究

博士論文

In the present study, whole body and individual tissues protein turnover were measured in vivo in laying hens. The first experiment described in Chapter 1 dealt with the establishment of the method for measuring whole body protein turnover rates by a primed-continuous intravenous infusion of [15^N]methionine, the plasma enrichment of which was determined with a selected-ion monitoring GCMS. Changes in the time course of isotopic aboundance of free [15^N]methionine in plasma showed that an isotopic equilibrium was attained at about 3 hours after the commencement of the infusion. In Chapter 2 individual tissue protein synthesis was measured by a primed-continuous intravenous infusion of [15^N]methionine. Fractional rates of protein synthesis in the liver and oviduct were 95 and 85%/day, respectively and these values were considerably higher than those found in any other tissues. In contrast. breast and leg muscle showed lowest values. Changes in fractional rates of protein synthesis were highly correlated with those in RNA:protein ratio･ The experiment in Chapter 3 was conducted to investigate whether or not the estimate of protein synthesis in tissues and in the whole body of laying hens in vivo differs by using the L- and DL-forms of [15^N]metbionine as a tracer. It was found that the values for protein synthesis in tissues and in the whole body obtained with the DL-[15^N] methionine were underestimated by 4 to 36% depending upon the sites examined, and the adequate correction should be made accordingly. Effect of protein depletion and repletion on whole body protein turnover rates was investigated in White Leghorn laying hens maintained on a commercial layer diet in Chapter 4. The calculated whole body protein synthesis in the control period was 29 g/kg^0.75 per day, indicating a higher rate than tbose reported in adult mammals. Protein synthesis and degradation rates in the whole body of laying hens were reduced by feeding a protein-free diet for 7 days, and were completely restored and even exceeded the initial control values by refeeding the commercial diet for 7 days. In Chapter 5, transitional changes in whole body, liver and oviduct protein turnover were studied by protein starvation and refeeding in White Leghorn laying hens. Whole body protein turnover rates were reduced by protein starvation for 7 days, followed by complete restoration by protein repletion for 7 days. Protein starvation considerably reduced fractional and absolute rates of protein synthesis both in the liver and, to a greater extent, in the oviduct. It was suggested that a considerable portion of the reduced whole body protein synthesis could be accounted for by the reduced protein synthesis in these organs when laying hens were subjected to protein starvation. In Chapter 6, the effect of dietary deficiency of methionine or lysine on protein synthesis was investigated in the liver, oviduct which was subdivided into the magnum and remainder segment, and in the whole body in laying hens. Whole body protein synthesis of laying hens fed amino acid deficient diets was significantly lower than that of control hens. Protein synthesis in the liver', magnum and remainder oviduct was remarkably decreased by dietary deficiency of these amino acids with larger rates of decrease than those in the whole body. The proportions accounted for by the sum of reduction in protein synthesis of these tissues to that of whole body were 36 and 50% for methionine and lysine deficiency, respectively. The experiment in Chapter 7 was conducted to investigate whether or not protein synthesis in tissues and in the whole body of laying hens is affected by the position of an ovum passing along the oviduct during egg formation. Whole body protein synthesis was not significantly affected by the position of an ovum. When an ovum was at the magnum portion, protein synthesis in the entire oviduct showed highest values, whereas lowest ones were found in other tissues except for the liver. Liver protein synthesis was relatively constant, and was not significantly affected by the position of the ovum passing along the oviduct.

名古屋大学博士学位論文 学位の種類 : 農学博士(課程) 学位授与年月日 : 平成1年3月25日