Effect of lactose content of nonfat milk diets on male rat serum lipids and lipoproteins

The lactose content of a semisynthetic diet containing 45% of calories as nonfat milk powder was modified by enzymatic hydrolysis with beta-galactosidase or bacterial fermentation with yogurt cultures. Three milk-based diets and a stock diet were fed for 28 days to male rats derived from the Sprague-Dawley strain. Energy consumption, growth rate, feed efficiency, liver weight, liver cholesterol and liver triglyceride concentrations were not significantly different between the four diets. At day 28 serum cholesterol and serum triglyceride concentrations were not different between the milk-based diets. No hypocholesterolemic effect of the milk-based diets was seen at any time compared to the stock diet. Two of four electrophoretic lipoprotein fractions varied with the lactose content of the milk-based diet. The faster alpha lipoprotein decreased while the slower alpha lipoprotein increased with decreasing content of dietary lactose. These data indicate that lactose differs from its constituent monosaccharides, galactose and glucose, in its effect on lipoprotein levels, even though total serum cholesterol and triglycerides do not differ.     

Effect of vasoactive intestinal polypeptide infused intrapancreatically on glucagon and insulin secretion

Synthetic vasoactive intestinal polypeptide (VIP) was infused at a dose of 50 ng/kg/min for 10 min into the cranial pancreaticoduodenal artery in anesthetized dogs. Both mean blood flow and plasma glucagon concentration in the cranial pancreaticoduodenal vein were significantly enhanced during the infusion, indicating a great augmentation in glucagon output. The pancreatic venous plasma concentration of insulin was not significantly raised, but its output increased during the infusion, again due to the increase in plasma flow. Plasma concentration of glucagon in the femoral artery was not significantly augmented, whereas that of insulin was enhanced during VIP infusion. Mean arterial plasma glucose levels rose gradually during the infusion. Intrapancreatic pretreatment with propranolol failed to exert any significant inhibiting effect upon the VIP-induced enhancement in plasma glucose, pancreatic venous blood flow, or bihormonal output. These results suggest that the vasoactive polypeptide of intestinal origin may regulate the function of the endocrine pancreas and that this effect may not be mediated mainly via the β-adrenergic receptor system.     

Effects of cigarette smoking and dietary lipids on rat lipoprotein metabolism

The effects of cigarette smoke inhalation on rat lipoprotein metabolism have been examined. Rats were subjected to cigarette smoke exposure over a 3-week period (two 1-h sessions/day) using a Bat-Mason inhalation machine. Rats exposed to cigarette smoke showed a decrease in total serum triglyceride and an increase in very low density lipoprotein cholesterol (VLDL-C). Administration of cigarette smoke to rats fed a saturated fat and cholesterol enriched diet also led to an increase in VLDL-C and a decrease in total serum triglycerides compared to controls. In addition, cigarette smoke exposure to animals fed the lipid enriched diet caused a decrease in high density lipoprotein cholesterol (HDL-C). Pair-feeding experiments indicated that the increase in VLDL-C and the decrease in HDL-C could not be solely attributed to the reduction in food intake and the small decrease in growth rate observed following cigarette smoke exposure. The changes observed in VLDL-C and HDL-C are at least qualitatively similar to the changes seen in human smokers compared to non-smokers.     

Lack of effect of purified cellulose and hemicellulose on the digestion and the intestinal absorption of dietary lipids in the rat

Fasted adult rats were intragastrically intubated an emulsified test meal containing both 14C-triolein and 3H-cholesterol, in the presence or absence of either purified hemicellulose (xylan) or cellulose (both 10% of meal solids). After a 1-hour digestion period, purified fibers did not significantly modify the rate of gastric emptying of lipids or the extent of triglyceride lipolysis in the stomach and the small intestine. The presence of cellulose or hemicellulose induced no change in the amounts of lipids and cholesterol found in the intestinal content, the mucosa, and the plasma, nor in the site of lipid mucosal uptake. As a whole, the present results show that cellulose or hemicellulose, which are the main fractions of dietary fiber in cereals, did not exert a determinant influence on the biochemical events involved in the digestion of dietary fats.     

Effects of dietary cholesterol and phytosterol overload on Wistar rat plasma lipids

To study the effects of dietary phytosterols on plasma cholesterol, Wistar rats were fed diets containing a cholesterol overload (24 mg/day), to which phytosterols were added or not (24 or 96 mg/day). The cholesterol overload led to a marked increase in cholesterol, mainly linked to very-low-density and low-density lipoproteins. Phytosterols reduced those effects, the highest dose being most efficient. No undesirable effect was observed either on body or on liver weights. This shows that low doses of phytosterols are sufficient to significantly decrease a plasma cholesterol enhancement induced by a dietary cholesterol overload.     

Effects of lymph stasis on healing of rat intestinal anastomosis

The effects of lymphatic drainage on ileal anastomotic healing using interrupted polyglycolic acid sutures were studied in rats after division and obstruction of celiac-mesenteric lymphatics, and the data compared with sham-operated controls. In 4 of 20 rats with lymph stasis, but not sham-controls, anastomotic leakage was associated with generalized peritonitis and death. Histologic examination of the anastomotic site at 7 and 14 days revealed prolonged exudation with acute inflammatory reaction and less prominent granuloma formation where lymphatics were interrupted. Whereas foreign body giant cell reaction predominated at 14 days with lymph stasis, histiocytic and fibroblastic proliferation dominated in sham-controls. The data suggest that an intact lymphatic system favors optimal intestinal healing and repair.     

Effect of dietary lipids on paraoxonase-1 activity and gene expression

AimsAim of the paper was to summarize the literature about the effect of dietary lipids on activity of paraoxonase-1 (PON1), a multifunctional enzyme associated with high density lipoprotein (HDL). PON1 exerts a protective effect against oxidative damage of cells and lipoproteins and modulates the susceptibility of HDL and LDL to atherogenic modifications such as homocysteinylation.Data synthesisThe present review shows evidence that the amount and the composition of dietary lipids are key factors in the modulation of PON1. The effect of dietary lipids is also modulated by PON1 polymorphisms. The molecular mechanisms involved include an effect on PON1 hepatic synthesis or secretion and/or modification of PON1 interactions with HDL. Changes of PON1 activity could also be related to dietary intake of oxidized lipids that behave as PON1 inhibitors.ConclusionDietary fatty acids by the modulation of PON1 gene expression and activity could constitute an useful approach for the prevention of human diseases associated with oxidative damage.     

Effect of dietary calcium or phosphorus restriction and 1,25-dihydroxyvitamin D administration on rat intestinal 24-hydroxylase.

1,25-Dihydroxyvitamin D-24-hydroxylase (24-hydroxylase) modulates the biological effects of 1,25-dihydroxyvitamin D [1,25-(OH)2D] in tissues. The presence of 24-hydroxylase in intestinal mucosa and the mass of the intestine suggest that the intestine is a major site of catabolism of 1,25-(OH)2D. How intestinal levels of 24-hydroxylase are regulated under various dietary conditions, such as calcium (Ca) or phosphorus (P) restriction, is poorly understood. In a series of trials on weanling and mature rats, the effects of dietary Ca or P restriction were compared with the effects of exogenous 1,25-(OH)2D3 administration on intestinal 24-hydroxylase activity. Exogenous administration of 1,25-(OH)2D3, by single bolus injection or constant infusion, increased intestinal 24-hydroxylase activity significantly. Dietary Ca and P restriction both resulted in increased plasma 1,25-(OH)2D3 concentrations several-fold above control rat values (P less than 0.001) and to levels higher than those achieved by constant infusion of 1.3 ng 1,25-(OH)2D3/h. Dietary Ca restriction increased intestinal 24-hydroxylase 6- to 20-fold above that of rats fed a Ca-replete diet (P less than 0.001). Dietary P restriction had no significant effect on intestinal 24-hydroxylase activity. These data suggest that dietary Ca restriction results in increased plasma levels of 1,25-(OH)2D3, which, in turn, leads to up-regulation of intestinal 24-hydroxylase. Conversely, dietary P restriction prevents 1,25-(OH)2D3-mediated up-regulation of 24-hydroxylase.     

Effect of physiologic concentration of lactose on prevention of postweaning decline of intestinal lactase

Postweaning decline of intestinal lactase activity due to decreasing substrate concentration was investigated in this study, using litters of rats maintained on either a control (8% dextrose) or lactose-enriched diet (8% lactose). The 8% lactose was used because this supplies the same amount of calories as the lactose in the maternal milk of rats. The rats were sacrificed at 3, 4, 5, 8, 12 and 16 weeks, to establish a continuum of activity. Assay of lactase activity in mucosa from the jejunal and ileal segment in these rats failed to reveal any significant difference in either lactase, sucrase or maltase activity, regardless of whether the activities were expressed in terms of the whole intestine, per gram of intestine, or per 100 g of body weight. These results do not support the theory that postweaning decline of intestinal lactase reflects only a decreasing amount of substrate in the diet.     

The effect of dietary lipids on microsomal electron transport proteins in the rat

Feeding a fat-free diet for 3 weeks decreases the activity of ascorbate:ferricytochrome b5 oxidoreductase and increases NADH:monodehydroascorbate oxidoreductase in rat liver microsomes. Contrary to Vmax, the apparent Km for monodehydroascorbate of the first enzyme was not depressed. The activity of ascorbate:ferricytochrome b5 oxidoreductase is increased by incubation with microsomal lipid extract, thus showing that the loss of activity results from dietary-induced changes of microsomal fatty acid composition.     

Effect of dietary fat on the small intestinal mucosa.

The presence of food within the small intestinal lumen promotes mucosal cell proliferation. To define the trophic role of triglycerides, three groups of eight female Wistar rats were isocalorically fed for four weeks with either Vivonex, or Vivonex with 50% calorie substitution with an essential fatty acid mixture, or Vivonex with 50% calorie substitution with a saturated fatty acid mixture. Although Vivonex caused greater body weight gain, both essential fatty acids and saturated fatty acids increased small intestinal weight, mucosal weight, protein and DNA overall, and in each of three intestinal segments (proximal, middle and distal), compared with Vivonex. Mucosal indices were similar for essential fatty acids and saturated fatty acids. These results show that triglycerides, regardless of essential fatty acid content, are trophic to the rat small intestinal mucosa.     

Effect of oxytetracycline on bacterial intestinal metabolism of neutral sterols and on serum lipids

The effect of oral oxytetracycline administration to five healthy male volunteers on intestinal bacterial metabolism of faecal neutral sterols was studied. A reduction in bacterial transformation of cholesterol to coprostanol and coprostanone was observed which lasted 1-2 weeks after 5 days' intake of oxytetracycline (1000 mg/day). In addition, a reduction in the amount of esterified neutral sterols in faeces was observed. The significant changes in the intestinal metabolism of cholesterol had no effect on the levels of serum cholesterol, HDL-cholesterol, LDL-cholesterol, or triglycerides.     

Influence of dietary fiber on insulin receptors in rat intestinal mucosa.

This study was designed to determine the effect of dietary carbohydrate and fiber on mucosal insulin receptors, in order to correlate changes in cellular proliferation with hormonal responsiveness. In two protocols insulin binding was significantly affected by the consumption of dietary fiber. Compared to fiber-free, feeding corn bran increased binding in the duodenum 30% and ileum 50% but decreased binding in the jejunum 44%, and feeding guar gum increased binding in the colon 73% but decreased binding in the jejunum 40%. Feeding wheat bran or oat bran increased binding 50% in the small intestine compared to cellulose or fiber-free. Receptor autophosphorylation was 30% higher with fiber-free or wheat bran feeding than cellulose or oat bran. These changes in receptor binding and activity may correlate with altered rates of cell proliferation induced by dietary fiber.     

Differential effects of dietary fibers on rat intestinal circular muscle cell size

The relationship between dietary fiber and intestinal circular muscle cell size was investigated in rats by feeding defined diets supplemented with four different sources of fiber. In the first study, a 20% wheat bran supplement was fed to 10 rats for nine weeks. This resulted in larger muscle cell size, with a 22.5% increase in the proximal (P<0.02) and 77.9% increase in the distal colon (P<0.001) when compared with a control group of 10 rats fed a fiber-free diet. In the second study, which lasted four weeks, a control group of 10 rats was fed a fiber-free diet, while similar sized experimental groups were fed the same basal diet plus either 20% oat bran, 10% pectin, or 10% guar. Muscle cell size was decreased by 20.6% in the proximal jejunum of the oat bran-and pectin-fed groups (P<0.05) and by 43% in the proximal colon of the oat bran-fed group, when compared with the controls (P<0.05). These results show that the effects of high fiber diets on intestinal muscle cell size depend on the type of fiber consumed.     

Effect of dietary vitamin E on plasma lipids and atherogenesis in restricted ovulator chickens

Restricted ovulator hens, which develop hyperlipidemia, were fed 1000 IU vitamin E per k of diet. These hens maintained their hyperlipidemia but plasma peroxide levels were reduced to those of laying hens. The intimal thickness of the aorta was measured by light microscopy. Hyperlipidemic hens which had high plasma peroxide levels had an increased intimal thickness as compared to laying hens. Hyperlipidemic hens which had their plasma peroxide levels reduced by dietary vitamin E had intimal thicknesses the same as laying hens. It is suggested that hyperlipidemia without lipid peroxidation either does not promote atherogenesis or does so at a reduced rate.     

Effects of exercise, dietary cholesterol, and dietary fat on blood lipids

Exercise, a low fat diet, or a diet low in saturated fat content can each lower plasma total cholesterol and low-density lipoprotein (LDL) cholesterol. We investigated whether these factors together could prevent the lipid-raising effects of dietary cholesterol. Ten healthy, athletic, normolipidemic male volunteers were studied. Two diets of 4 weeks duration each were compared in a randomized, blind crossover design. Diets were identical except for cholesterol content: one contained 600 mg/d; the other 200 mg/d. Both diets contained 15% of calories as protein, 55% as carbohydrate, 30% as fat, and the polyunsaturated fat to saturated fat ratio was 1.5. Exercise level and body weight were kept constant in each subject. As compared with plasma values obtained following the 200-mg/d cholesterol diet, mean values following the 600-mg/d cholesterol diet significantly increased for LDL cholesterol and apolipoprotein B by 10% and 13%, respectively. Mean plasma triglycerides, high-density lipoprotein 2 and 3, and apolipoprotein A-1 levels did not change significantly. Individual responses, however, were highly variable. Three subjects increased LDL cholesterol by more than 25%; 2 subjects increased LDL cholesterol by 10% to 25%; and 5 subjects had 5% or less change in LDL cholesterol. A dietary cholesterol increase can significantly elevate plasma LDL cholesterol and apolipoprotein B in certain normolipidemic, healthy men even when they are exercising regularly and consuming a moderately fat restricted, low saturated fat diet. Dietary cholesterol restriction may therefore be justifiable even when other life-style and dietary measures to minimize blood cholesterol are undertaken.     

Effect of intestinal ischemia on diamine oxidase activity in rat intestinal tissue and blood

This study examines the effect of increasing duration of intestinal ischemia on the mucosal integrity and the release of the enzyme diamine oxidase from the small intestine. Acute ischemia was produced by the occlusion of the superior mesenteric artery, and the subsequent changes in DNA and 125I-albumin content in the lumen were taken as indices of intestinal lesions. Diamine oxidase activity was measured in the intestinal lumen, mucosa, lymph, and serum. Occlusions of the superior mesenteric artery for periods of more than 60 min resulted in significant leakage of 125I-albumin (i.v.) into the lumen. In contrast, luminal DNA content rose significantly after 15 min of ischemia and continued to increase proportionally with the increased duration of the occlusion up to 120 min. Similarly, diamine oxidase activity was augmented in the lumen after 15 min of occlusion and rose sharply as the ischemic period was lengthened up to 60 min, leveling off thereafter. Increases in the diamine oxidase activity were also observed in the intestinal lymph and serum, reaching levels that were 2.6 and 3.6 times that of the control respectively after 60 min of ischemia. These findings suggest that intestinal ischemia reduces the diamine oxidase content in the intestinal mucosa by desquamation of the surface epithelial cells and by releasing the enzyme into the intestinal interstitial fluid, from which at least a portion is transported to the blood via the lymphatics. The early release of diamine oxidase seems to occur before the mucosal barrier is broken.