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Biomedical subjects

A C Tsai

Publications and source records attributed to A C Tsai.

17 recordsLinked to original sources
PubMed1992

Dietary beta-carotene reduces serum lipid concentrations in spontaneously hypertensive rats fed a vitamin A-fortified and cholesterol-enriched diet.

The effects of dietary beta-carotene on serum lipid concentrations were examined in spontaneously hypertensive (SH) rats. Groups of SH rats were fed a semipurified, vitamin A-fortified and cholesterol-enriched diet supplemented with 0, 125, 250 or 500 mg beta-carotene/kg diet for a period of 44 d. beta-Carotene supplementation resulted in significant dose-related decreases in serum total, LDL and HDL cholesterol concentrations and serum total, VLDL and LDL triacylglycerol concentrations. The ratio of HDL cholesterol to total cholesterol was unchanged or slightly increased by dietary beta-carotene. The study suggests that dietary beta-carotene has antihyperlipidemic effects in SH rats. The effects in humans and the mechanism of the effects remain to be investigated.

Animals↗
PubMed1979

Contribution of growth, fatness, and activity to weight disturbance after septohypothalamic cuts in adult hamsters.

The mechanism responsible for weight stability in adult hamsters was investigated by (a) transecting the dorsoventrally oriented nerve pathways between the septal area and hypothalamus (SH cuts) and (b) partitioning the observed increases in the rate of weight gain into three contributory components: changes in somatic growth, in body fatness, and in energy expended as voluntary activity on horizontal disks. Between 60% and 70% of the weight increase after SH cuts was due to acquisition of lean body mass, and 30%-40% of weight increase consisted of excess body fat. After SH cuts, serum growth hormone and insulin concentrations were increased on Day 14, food intake was increased between Day 2 and Day 42, skeletal lengths were greater on Day 77, and voluntary activity levels were 84% lower on Days 10-45, relative to control hamsters. It is concluded that dorsoventrally oriented nerve pathways in the septal area are involved in the control of growth, maintenance of body fat reserves, and voluntary activity and that they contribute to the maintenance of stable body weight in adult hamsters.

Adipose Tissue↗
PubMed1978

Effect of pectin, gum arabic and agar on cholesterol absorption, synthesis, and turnover in rats.

A series of five experiments was conducted to determine the effect of pectin, gum arabic and agar (5%) on cholesterol absorption, biosynthesis and turnover in rats. In the study of cholesterol absorption, a tracer dose of labeled cholesterol was included in the last meal. The rats were killed 12 hours later. The proportion of the labeled cholesterol recovered in the whole body was used as an estimation of the efficiency of absorption of dietary cholesterol. Cholesterol biosynthesis was estimated by determining the activity of labeled digitonin-precipitable sterols biosynthesized from labeled glucose which was included in a test meal. In turnover studies, rats were injected intravenously with labeled cholesterol using serum as a vehicle, and the activity of labeled cholesterol in tissues was determined after various time intervals. All three complex carbohydrates decreased cholesterol absorption and pectin had the greatest effect. Pectin and gum arabic increased cholesterol biosynthesis in rats fed a cholesterol-containing diet, but had no effect in a cholesterol-free diet. Pectin slightly increased the turnover of cholesterol, but gum arabic and agar had no effect. This work supports the hypothesis that pectin lowers cholesterol levels by interfering with cholesterol absorption and by increasing cholesterol turnover. The study also suggests that complex carbohydrates differ in their effects on cholesterol metabolism. The reason for these differences remains to be determined.

Absorption↗
PubMed1977

Effect of cholesterol feeding on tissue lipid perioxidation, glutathione peroxidase activity and liver microsomal functions in rats and guinea pigs.

The effect of cholesterol feeding on liver and aortic nonenzymatic lipid peroxidation and glutathione peroxidase activities, and on liver microsomal NADPH-dependent lipid peroxidation, codeine hydroxylation and cytochrome P-450 levels was examined in rats and guinea pigs. One percent cholesterol was added to a casein-sucrose-soybean oil basal diet for rats or a stock diet with 2% soybean oil for guinea pigs. The effect of vitamin E and cholestyramine was also examined in some experiments. Cholesterol feeding increased the rate of lipid peroxidation in liver and aortic homogenate both in rats and guinea pigs when fed non-vitamin E supplemented basal diets. Vitamin E supplementation prevented the increase in the aorta, but not as completely in the liver in rats, while the reverse was true in guinea pigs. The effect of cholestyramine was dependent on the level of vitamin E in the diet. Cholesterol feeding decreased glutathione peroxidase activities in rats and guinea pigs. In guinea pigs, cholesterol feeding also markedly decreased liver microsomal NADPH-dependent lipid peroxidation, codein hydroxylation and cytochrome P-450 levels especially when fed non-vitamin E supplemented basal diets. In rats, cholesterol feeding reduced liver microsomal NADPH-dependent lipid peroxidation and in some cases, increased microsomal codeine hydroxylation activities, but had no effect on microsomal cytochrome P-450 levels. Vitamin E supplementation increased liver and serum cholesterol levels in guinea pigs, but had no such effect in rats. Results of this study indicate that cholesterol feeding can result in various metabolic alterations in rats and guinea pigs. The implication of these alterations in atherogenesis requires further investigations.

Animals↗
PubMed1977

Serum insulin concentration, insulin release and degradation, glucose tolerance and in vivo insulin sensitivity in cholesterol-fed rats.

A series of experiments was conducted to elucidate the mechanism by which cholesterol feeding decreases serum insulin levels in rats and to determine the effect of this reduced insulin level on glucose metabolism. Rats were fed a casein-sucrose-soybean oil basal diet or this basal diet supplemented with 1% cholesterol (dissolved in hot oil) for periods longer than 30 days. Cholesterol feeding resulted in a decrease in serum insulin concentrations, although the decrease was not always significant. Cholesterol feeding did not affect fasting blood glucose levels, glucose tolerance, glucose-induced insulin release, pancreatic insulin content, in vivo insulin sensitivity, or in vitro glucose utilization in diaphragm and adipose tissue, but it significantly elevated the activity of liver glutathione-insulin transhydrogenase. On a per liver basis, the activity of this enzyme was approximately doubled. Results of this study suggest that cholesterol feeding has no significant effect on glucose utilization, but it can lead to a decrease in serum insulin concentration, probably by increasing the rate of insulin degradation in the liver.

Adipose Tissue↗
PubMed1976

Influence of certain dietary fibers on serum and tissue cholesterol levels in rats.

Pectin, carragheenan, agar gum arabic, cellulose and wheat bran were each fed to rats at a level of 5 to 7% to examine their effect on serum, liver and tissue cholesterol levels. Diets (casein-sucrose diet containing 10-15% soybean oil, or skim milk-wheat flour diet containing 10-15% soybean oil) supplemented with either 0, 0.2, or 0.5% cholesterol were used to test the possibly dietary interactions. Among the fibers tested, pectin displayed the most hypocholesterolemic effect. In some experiments, pectin lowered the level of cholesterol in the serum, liver, and aorta, but it elevated body cholesterol levels. Carragheenan was inconsistent in lowering serum cholesterol levels and tended to increase liver and carcass cholesterol levels. These results probably suggest that pectin and carragheenan can affect the distribution of cholesterol within the body. Gum arabic and agar did not lower serum cholesterol levels and in one case gum arabic elevated them. Furthermore, in some experiments they elevated liver body cholesterol levels. It appears that feeding of gum arabic and agar probably resulted in an expansion of the whole body cholesterol pool. Feeding of wheat bran or cellulose had no significant effect on either serum or liver cholesterol levels. The study indicates that the effect of dietary fiber is dependent on the composition of the diet. Furthermore, while some fibers such as pectin may exhibit a hypocholesterolemic effect in rats, other fibers such as gum arabic and agar may actually elevate serum or tissue cholesterol levels.

Acacia↗
PubMed1976

Studies of the effect of dietary cholesterol on hepatic protein synthesis, reduced glutathione levels and serine dehydratase activity in the rat.

A basal diet or a basal diet plus 1% of cholesterol and 0.33% cholic acid was fed to rats for varying lengths of time and (1) the activities of liver phosphoenolpyruvate-carboxykinase (PEP-CK), tyrosine transaminase (TT), and serine dehydratase (SD); (2) the rate of total hepatic protein synthesis and (3) the concentration of hepatic reduced glutathione (GSH) were quantitated. The specific activity of PEP-CK was significantly depressed by cholesterol plus cholic acid feeding, while the specific activity of TT was unchanged. No significant effect of dietary cholesterol plus cholic acid was found on the total liver activities. In contrast, SD specific activity was increased 3-fold. The rate of (U-14C)-L-leucine incorporation into total TCA precipitable protein following ingestion of cholesterol plus acid was significantly reduced when the data were expressed as dpm (U-14C)-L-leucine/mg protein. After correcting this expression for specific radioactivity of the liver tissue free leucine pool, no significant effect of dietary cholesterol plus cholic acid on hepatic protein synthesis existed. In fact, the amount of 14C-leucine incorporated into protein on a total liver basis was 50% greater for the cholesterol group. On a per gram of liver basis, the concentration of GSH in the liver of rats fed a cholesterol plus cholic acid diet was significantly decreased. Considering the liver enlargement in rats fed cholesterol plus cholic acid, total organ GSH was found to be significantly greater than for rats fed a basal diet.

Animals↗
PubMed1975

Determination of carnitine turnover in choline-deficient and cold-exposed rats.

Two experimetns were conducted to study the body pool size and turnover rate of carnitine in rats. The turnover of carnitine was determined by injection of a tracer dose of L-[methyl-14C] carnitine. In experiment 1, carnitine body pool size and turnover in rats fed a choline-deficient basal diet were compared with values obtained from rats fed the basal diet supplemented with choline. These rats were maintained at 22degrees. In experiment 2, carnitine body pool size and turnover were determined in cold-exposed (2degrees) rats fed the choline-deficient basal diet. Carnitine body pool sizes of rats maintained 22degrees and fed the choline-deficient basal diet and the choline-supplemented diet were 35.6 and 41.8 mumoles/100 g body weight, respectively. Carnitine body pool size of rats maintained at 2degrees and fed a choline-deficient basal diet were 6.6 and 56.1 days, for rats fed a choline-supplemented diet, 6.7 and 40.2 days, and for rats maintained at 2degrees and fed a choline-deficient diet, 2.9 and 36.4 days, respectively. Carnitine turnover times obtained with DL-[14C]carnitine in our previous study longer than turnover times obtained with DL-[14C]carnitine in our previous study (j. nutr. 104, 782-792). These observations suggest that D-carnitine is not metabolized the same way as L-carnitine, and that D-carnitine is not cleared from the body within 2 days after injection. The results also suggest that carnitine metabolism can be influenced by the amount of choline in the diet and by cold exposure.

Animal Nutritional Physiological Phenomena↗
PubMed1975

Effect of dietary cholesterol on hepatic lipogenesis and plasma insulin and free fatty acid levels in rats.

In order to further investigate the metabolic alterations in the liver of cholesterol-fed rats, the following parameters were determined: (a) the activities of hepatic glucose-6-phosphate dehydrogenase, NADP-malate dehydrogenase, citrate cleavage enzyme, acetyl CoC carboxylase, and fatty acid synthetase; (b) the rate of hepatic fatty acids synthesis in vivo or in vitro; and (c) the concentration of immunoreactive insulin, free fatty acids, and glucose in the plasma. The experimental diets usually contained 1.5% cholesterol and 0.5% cholic acid. Cholesterol feeding resulted in a three- to fourfold decrease in the activities of hepatic glucose-6-phosphate dehydrogenase, NADP-malate dehydrogenase, and citrate cleavage enzyme and up to a two-fold decrease in the activities of acetyl CoA carboxylase and fatty acid synthetase. The rate of fatty acid synthesis was not sifnigicantly decreased when rats were fed the cholesterol-supplemented diets for only 2 to 4 weeks, despite marked decreases in the activities of the lipogenic enzymes. But when cholesterol feeding was continued for periods longer than 5 weeks, there was a significant decrease in the rate of fatty acid synthesis in the liver. Cholesterol feeding decreased the levels of circulating insulin and elevated plasma free fatty acid levels. Plasma glucose levels were not significantly changed. Cholesterol feeding can result in a wide range of metabolic alterations. These metabolic alterations may have some impact on the development of hypercholesterolemic-related metabolic disorders.

ATP Citrate (pro-S)-Lyase↗
PubMed1975

Lipid peroxidation and glutathione peroxidase activity in the liver of cholesterol-fed rats.

The effects of cholesterol feeding on lipid peroxidation and on glutathione peroxidase activity in the liver of rats were examined. Cholesterol (1 or 1.5%) was added to two basal diets containing either 10% soy oil (diet 1) or 15% soy oil plus 100 IU of alpha-tocopherol/kg of diet (diet 2). The rate of lipid peroxidation in the liver was determined in vitro by the thiobarbituric acid test and by conjugated diene measurement (234 nm). Cholesterol feeding elevated the rate of lipid peroxidation in the liver of rats fed diet 1 or 2. The rate of lipid peroxidation in rats fed diet 2 increased with duration of feeding suggesting an increased need for antioxidant as the levels of cholesterol or other lipids in the liver elevated. Cholesterol feeding also decreased the activity of liver glutathione peroxidase and pentose phosphate pathway dehydrogenases. Glutathione peroxidase activities increased with the duration of feeding in rats fed basal diet 2, but they remained unchanged in rats fed the same diet supplemented with cholesterol. The study suggests that cholesterol feeding in rats can increase the susceptibility of the tissue to lipid peroxidation and also can lead to a depression in the activity of glutathione peroxidase.

Animals↗
PubMed1975

Influence of alterations in meal frequency on lipogenesis and body fat content in the rat.

Rats were allowed to eat only 2 hr per day (meal-fed) or were fed ad libitum (nibbler) for 12 wk; another group of animals was meal-fed for 3 wk and then fed ad libitum (converted I) while the fourth group of rats (converted II) was meal-fed for 3 wk, allowed to nibble for the next 3 wk, meal-fed from the 6th to 9th wk and then returned to ad libitum feeding for the last 3 wk. Body fat gain and food efficiency was increased in converted I rats. The lipogenic capacity of adipose tissue from meal-fed rats was greater than observen meal-fed rats were reverted to ad libitum feeding whereas lipogenic activity increased rapidly when ad libitum fed rats were switched to meal-feeding.

Acetyl-CoA Carboxylase↗
PubMed1975

Effects of dietary carbohydrate source on growth, plasma metabolites and lipogenesis in rats, pigs, and chicks.

Rats, chicks, and pigs were fed diets containing fructose or glucose. Plasma triglyceride levels were elevated in rats but not in chicks or pigs fed diets containing fructose. The rate of fatty acid synthesis in rat liver but not in chick liver was elevated when fructose-containing diets were fed. Conversely, the rate of fatty acid synthesis in rat adipose tissue but not in pig adipose tissue tended to be depressed when fructose-containing diets were fed. These results indicate that there are species-specific as well as organ-specific metabolic responses to various dietary carbohydrates.

Adipose Tissue↗
PubMed1975

Influence of dietary safflower oil and tallow on growth, plasma lipids and lipogenesis in rats, pigs and chicks.

Rats, chicks and pigs were fed diets containing safflower oil or tallow. Plasma triglyceride levels were elevated when tallow, rather than safflower oil was added to the diet of rats, unchanged in chicks and lowered when tallow, rather than safflower oil was fed to pigs. The rate of fatty acid synthesis in rat and chick liver was higher, whereas the rate of lipogenesis in adipose tissue preparations from rats and pigs was lower when tallow, rather than safflower oil was fed. These results indicate that there are species-specific, as well as organ-specific, metabolic responses to various dietary fats.

Adipose Tissue↗