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published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

No description available.

Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Nutrition and Food Science. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 69-78. / M.S.

published_or_final_version / abstract / toc / Physiology / Master / Master of Philosophy

published_or_final_version / Physiology / Master / Master of Philosophy

We developed a methodology to measure plasma hepatic glutathione (GSH) turnover and we tested it in rats treated with an inhibitor of GSH synthesis. Our goal was to determine whether protein intakes above NRC recommendations maximize hepatic GSH stores and turnover in vivo. We also wished to learn if plasma GSH, cysteine, or methionine concentrations or plasma GSH turnover could be used as noninvasive predictors of liver GSH status. Rats were fed purified diets containing 0, 5, 10, 20 or 40% casein for one week. The 0 and 5% casein diets were considered inadequate in protein, 10% marginal, 20% adequate and 40% excessive. Liver GSH content (mmol/liver) of rats fed 0 and 5% casein diets was 12.29 $ pm$ 1.11 and 16.43 $ pm$ 0.95, respectively, and increased to 23.62 $ pm$ 1.82 in the 10% group. Liver GSH content did not differ between the 20 and 40% groups. As dietary casein increased from 0-20%, free plasma GSH and cysteine concentrations and plasma GSH turnover increased, but did not increase further with the 40% diet. A sigmoidal relationship between plasma GSH turnover and hepatic GSH content was demonstrated. The best predictor of liver GSH content was not free plasma GSH concentration nor plasma GSH turnover, but the free plasma cysteine concentration.

Hydrostatic pressure has been demonstrated to induce major changes in secondary structure of whey proteins resulting in an increased digestibility in vitro, and possibly an improvement of the glutathione (GSH) inducing effect of whey proteins in vivo. Micro filtration and ion-exchange, two commonly used processing techniques in whey protein manufacture, generate whey proteins with different compositions. Two animal studies were designed to compare the digestibility and GSH inducing effects of whey protein isolates (WPIs) treated with three repeated pulse cycling of pressure (3-cycle) or single pulse of high pressure (1-cycle) and pressurized microfiltrated and ion-exchange WPIs. The results indicate that special hydrostatic pressure treatment on the proteins improves its growth stimulating effect, but does not enhance the GSH-inducing effect of WPI in the healthy growing rats. Difference among commercial whey protein products is also an important factor that affects the biological properties of the pressurized whey proteins. In conclusion, both proper pressure treatment and product composition should be considered in order to find the most bio-effective whey protein preparation.

Glucose is a principle precursor for milk lactose and de novo synthesis of milk fat; therefore exercising during lactation could create competition for glucose between exercising muscle and lactating mammary gland. This study investigated the combined effects of maternal dietary glucose (20%, 40%, 60%), exercise (chronically exercised, sedentary) and litter size (8, 12 pups) on rat mammary gland composition, milk composition, milk yield and pup growth. Chronic exercise increased milk fat concentrations and an interaction between chronic exercise and 20% dietary glucose decreased milk lactose concentrations compared to 40% or 60% glucose diets. Restricting maternal dietary glucose also decreased milk fat concentrations and exercise decreased mammary fat. In addition, pups of dams fed the 40% glucose diet were heavier on lactation day 15 than pups of dams fed the 60% diet. These results suggest that competition for glucose occurs and that a 40% glucose maternal diet may be more appropriate for pup growth.

Thesis: M.S., Massachusetts Institute of Technology, Department of Nutrition and Food Science, 1977 / Vita. / Bibliography : leaves 64-67. / M.S. / M.S. Massachusetts Institute of Technology, Department of Nutrition and Food Science