The effect of source of dietary carboyhydrate upon the concentration and distribution of phospholipids in the fractions of human blood was studied. Three healthy women received diets which contained 16% of the calories as protein, 40% as fat, and 44% as carbohydrate. During the four dietary periods of six days each, 80% of the carbohydrate was supplied alternately by sucrose (Sugar Diet) or by polysaccharides from natural sources (Complex Diet). Blood samples were drawn before breakfast on the final day of each dietary period. The total lipid, lipid phosphorus, and distribution of phospholipids were determined in erythrocytes, leukocytes, platelets, and plasma. Clotting time of the platelet-rich plasma of the subjects was determined. In periods of this length, no consistent changes in the blood lipids could be detected. The Sugar Diet appeared to increase the proportion of phosphatidyl choline and decrease the proportion of sphingomyelin slightly in the plasma and platelets. The phosphatidyl choline fraction of the leukocyte phospholipids decreased slightly after the Sugar Diet. No relationship was observed between in vitro coagulation time and the distribution of phospholipids in the blood fractions. One subject did demonstrate a marked increase in coagulation time after the diet containing complex carbohydrate. / Graduation date: 1969

Diets containing cyclopropenoid fatty acids (CPFA) were fed to rainbow trout. At a level of 223 ppm (from Sterculia foetida oil), these CPFA in six weeks reduced weight gain by as much as 50 percent over the control fish on the same diet without CPFA. Compounds containing the intact cyclopropene ring were recovered from the tissue lipids of the trout at approximately two-thirds of the level fed. These acids seemed to concentrate in the egg lipids of the adult female fish. At 223 and 2233 ppm (from S. foetida oil) and 50 ppm (from food grade cottonseed flour) the CPFA were demonstrated to alter lipid metabolism. In general, the CPFA fed fish had higher stearic and palmitic acid levels and lower oleic and palmitoleic acid levels in their tissue lipids than did the controls. On diets containing corn oil or corn oil plus salmon oil, fish fed CPFA tended to deposit more long chain unsaturated fatty acids than did their controls. When provided with tristearin as the sole dietary lipid, the CPFA fed fish reduced the level of unsaturation of their tissue lipids. / Graduation date: 1967

The reactions of aldehydes with proteins are of nutritional and physiological significance. The nutritive value of food materials can be impaired by a reaction necessitating additional dietary protein, and enzymes have been shown in vitro to be inhibited by reactions with aldehydes. Aldehydes present may arise from the autoxidation of lipid materials. A diversity of carbonyl products can occur. Several autoxidizing food lipid systems have been analyzed by other investigators, and the carbonyls present isolated and identified. In most cases the short chain aldehydes predominated. Reactions between aldehydes and proteins have been studied mainly with formaldehyde. Reactions between the aldehyde and many protein functional groups have been suggested including amino, amide, guanidyl, sulfhydryl and imidazole. The amino groups of the protein have received the most attention. The reactions proposed have included: a. methylolamine formation followed by condensation forming a cross link, or b. Schiff's base formation. The reactions have been found to be pH specific with the pH of maximum reaction depending upon the particular protein used. Possible reactions of dialdehydes with proteins have been little explored. Of interest are the possible reactions of malonaldehyde, one of the dialdehydes occurring in autoxidizing lipid systems. Herein, the action of malonaldehyde has been compared to that of formaldehyde, considered a reactive aldehyde, and to propionaldehyde, its monoaldehyde counterpart. The enzyme lipase was used as both the protein and the system of analysis for following the course of the reaction. Lipase activity was determined by potentiometrically titrating the fatty acids liberated from an olive oil emulsion. The commiercial bovine pancreatic lipase preparation used was found to have an activity optimum near pH 9.0. The relationship of the amount of enzyme present to the amount of fatty acids liberated was determined and found to be linear. Maximum stability of the control enzyme appeared between pH 6.0 and 6.5, while maximum lability in the presence of MA-Na (the sodium salt of the enolic form of malonaldehyde) was also near pH 6.0. Formaldehyde and propionaldehyde, however, both exhibited a non-pH-specific inhibition of lipase. Of the three aldehydes reacted with lipase at pH 6.0 and analyzed at pH 9.0, MA-Na was the most inhibitory. The reaction appeared to be two stage, the first being rapid and a function of the MA-Na concentration. The second stage was slower, and the rate was related linearly to the MA-Na concentration. Methanol-free formaldehyde did not inhibit lipase as effectively as MA-Na. Low concentrations (0.01 M) of formaldehyde had no apparent effect on the enzyme while concentrations above 0.05 M produced only slight changes in the degree of inhibition. Propionaldehyde showed only slight inhibition of lipase activity. Its reaction was two stage, with the second stage paralleling the inhibition seen in the control due to factors other than the aldehyde present. Reactions such as these, especially for the more reactive aldehydes such as malonaldehyde, may occur in vitro and in vivo with other proteins and could be of important nutritional or physiological significance. / Graduation date: 1964

The suckling rat obtains about 70% of its energy from the catabolism of lipid, compared to only about 25% in the adult rat. In addition, lipids are in great demand for membrane synthesis in the rapidly growing tissues. Thus the suckling rat represents an important system in which to study lipid metabolism. In this dissertation research the following experiments were performed on rats during the suckling period: (1) Determination of the concentration and fatty acid composition of triacylglycerols, cholesteryl esters, phospholipids, and free fatty acids in dam's milk, and in suckling rat lymph, portal plasma, vena cava plasma and liver; (2) Determination of positional distribution of fatty acids among the three different positions in triacylglycerols of milk, lymph, plasma and liver; (3) Isolation of plasma and mesenteric lymph lipoproteins by density gradient centrifugation, and identification of the individual classes of lipoproteins by measurement of their density and by polyacrylamide gel electrophoresis; (4) Determination of the concentration of each lipoprotein by refractometry and determination of the concentration and fatty acid composition of different lipid components in each lipoprotein fraction; (5) Studies of physical properties of the lipoproteins using analytical ultracentrifugation; (6) Determination of apoprotein composition and concentration in each lipoprotein fraction. The results show that the suckling rat consumes a diet which is rich in medium chain fatty acids (35% of total milk fatty acids). Mesenteric lymph triacylglycerols carry a significant amount of these medium chain fatty acids, unlike the adult in which they would be transported as free fatty acids, unlike the adult in which they would be transported as free fatty acids via the portal vein. Medium chain fatty acids are enriched at the sn-3 position in all triacylglycerols. Lymph contains chylomicrons, very low density lipoproteins, and high density lipoproteins, but no low density lipoproteins. Plasma contains all classes of lipoproteins but at concentrations higher than found in the adult, especially low density lipoproteins which are present at levels six times that found in the adult. The plasma very low density lipoproteins have a lipid composition which resembles that of chylomicron remnants. Apoprotein, lipid composition, and electrophoresis patterns show that the plasma lipoproteins in the suckling rat are heterogeneous.

Thesis (M.Sc.(Med.)--University of the Witwatersrand, Faculty of Health Sciences, 2000.

No description available.

Secretin, the first hormone commencing the field of endocrinology, has been studied for its pleiotropic role in the body inclusive of its neuroactive and body water homeostatic and gastrointestinal functions. Yet, the metabolic effect of secretin remains elusive and is being proposed recently for a revisit. Recent discovery from our lab showed an anorectic response for secretin, while its role in lipid homeostasis remains largely unexplored. Exerting functions such as exocrine pancreatic secretion and gastric motility inhibition, intestinal fatty acid induced release of secretin was recently shown to be mediated by CD36. Fasting related increase in plasma secretin concentration has been proposed to be involved in lipolysis but evidences regarding lipolytic actions of secretin remain contradictory. Recent report has suggested that secretin stimulates both lipolysis and lipogenesis in adipose cells. Thus, we hypothesize that secretin modulates lipid homeostasis, which was examined under two opposite, energy deficient and energy excess, conditions. Under energy deficient/starved state, secretin level in circulation and secretin receptor level in epididymal adipose tissue were found to be upregulated. Using secretin receptor knockout (SCTR-/-) and secretin knockout (SCT-/-) mice as controls, it was found that secretin stimulated a dose- and time-dependent lipolysis in vitro and acute lipolysis in vivo. H-89, a protein kinase A (PKA) inhibitor, attenuated the lipolytic effects of secretin in vitro, while secretin induced an increase in cAMP dependent PKA activity in vivo. Using western blot analysis, secretin was found to phosphorylate hormone sensitive lipase (HSL) at serine residue 660. Additionally, immunofluorescent studies revealed that secretin stimulated translocation of HSL from cytosol to surface of lipid droplet subsequently leading to lipolysis. Under excess energy condition, when SCTR-/- mice and its littermates SCTR+/+ mice were subjected to high fat diet (HFD) feeding for 3 months, it was found that SCTR-/- mice gained lesser weight. Nuclear magnetic resonance imaging revealed that SCTR-/- mice exhibited lower body fat content. Additionally, HFD-associated hyperleptinaemia was alleviated in SCTR-/- mice along with metabolic syndrome as they performed better in insulin and glucose tolerance tests. Continuous monitoring by indirect calorimetry revealed similar food intake, energy expenditure and locomotor activity between SCTR-/- and SCTR+/+ mice. Interestingly, intestinal fatty acid absorption, measured by a noninvasive method, was impaired in HFD-fed SCTR-/- mice. While postprandial triglyceride release was reduced in SCTR-/- mice, it also had a significant reduction in transcript and protein levels of CD36 and its downstream mediator MTTP. Secretin, when incubated with isolated enterocytes, upregulated the expression of CD36. In summary, during starvation, secretin stimulates lipolysis through a HSL and PKA mediated pathway. When fed a HFD, SCTR-/- mice is resistant to diet induced obesity due to impaired intestinal lipid absorption. A novel short positive feedback pathway between CD36 and secretin, functioning to maximize lipid absorption, is also being proposed. Thus for the first time, two independent role of secretin in lipolysis and in intestinal lipid absorption were discovered along with their mechanistic insights. This study paves way for developing new therapeutic strategies against metabolic disorders associated with lipid metabolism. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

published_or_final_version / Medicine / Master / Doctor of Medicine

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No description available.