Effects of insulin on the metabolism of the isolated working rat heart perfused with undiluted rat blood.

Working rat hearts were perfused with either buffer or with defibrinated, undiluted rat blood dialyzed to remove vasoconstrictor factors. With precautions taken for sterility in the preparation of the perfusate and the apparatus, hearts were obtained which were stable as judged by stroke rate and cardiac output. In these hearts, cardiac output and coronary flow averaged 46.0 and 1.7 ml/g heart per min, respectively. Perfusion with erythrocyte-free buffer depressed cardiac output by 30%, while coronary flow averaged 8.8 ml/g of heart per min. The mean stroke rate of blood-perfused hearts was 300 beats/min but only 240 beats/min during buffer perfusion. In blood-perfused hearts, insulin did not alter stroke rate but significantly lowered coronary flow. The hormone caused a transient increase in cardiac output in hearts perfused with buffer. Insulin did not alter glucose uptake in buffer-perfused hearts but increased lactate release in perfusions with blood. Both serum fatty acids and triacylglycerol fatty acids were significant metabolic fuels in hearts perfused with undiluted blood. The preparation described would appear to be potentially useful for the study of myocardial metabolism in vitro.

Plasma triacylglycerol secretion in sheep. Paradoxical effects of fasting and alloxan diabetes.

Plasma triacylglycerol and phospholipid concentrations were increased in fasting and diabetic sheep compared with fed animals. Secretion was measured in these animals using Triton WR1339 to block lipoprotein lipase. Triacylglycerol secretion was lowest in fed animals and, unlike non-ruminant species, increased by fasting and diabetes. These changes were in proportion to plasma free fatty acid concentration. However, no effect of Triton was found on plasma phospholipids under any of the conditions studied. It is suggested that the low rate of triacylglycerol secretion in normal animals is due to the limiting membrane found in the liver sinusoid of the sheep and that the greater rate in fasting and diabetes reflects the increased mass of intrahepatic triacylglycerol.

Failure of insulin to stimulate lipogenesis and triacylglycerol secretion in perfused livers from rats adapted to dietary fish oil.

Livers from male rats fed a standard commercial diet supplemented with 8% (w/w) marine fish or safflower oils were perfused for 70 min with undiluted blood in the presence and absence of insulin. Lipogenesis, as measured by the incorporation of 3H2O into liver and perfusate fatty acids, was inhibited by the feeding of fish oil. Net triacylglycerol secretion was also depressed by this dietary treatment. Infusion of insulin stimulated triacylglycerol secretion and the incorporation of newly synthesised fatty acids into liver and perfusate lipids with dietary safflower oil but not with fish oil. Hepatic cholesterol synthesis was also depressed by feeding fish oil. Net ketogenesis was raised by feeding fish oil and was depressed by insulin with both safflower and fish oil. Blood glucose was raised in the fish oil group but with both dietary oils the hormone exerted a significant hypoglycaemic effect. The data are discussed with respect to the observations that in vivo dietary fish oil (but not safflower oil) opposes the hypertriglyceridaemia arising from the hepatic overproduction of very-low-density lipoproteins.

Comparative effects of dietary fish oil and carbohydrate on plasma lipids and hepatic activities of phosphatidate phosphohydrolase, diacylglycerol acyltransferase and neutral lipase activities in the rat.

In rats fed a fish oil-enriched diet, plasma triacylglycerols were lowered 51%. At the same time there was a mean 45% reduction in Mg2+-dependent phosphatidate phosphohydrolase activity in liver microsomes and a mean 20% decrease in microsomal triacylglycerol (neutral) and diacylglycerol hydrolase activities, but not of diacylglycerol acyltransferase. These observations support the hypothesis that decreases in the activities of phosphatidate phosphohydrolase and of both lipases are involved in the expression of the inhibitory effects of fish oil feeding on hepatic lipoprotein triacylglycerol secretion. Conversely, the feeding of a sucrose-enriched diet resulted in a mean 39% rise in plasma triacylglycerols, a 19% increase in triacylglycerol hydrolase and a mean 45% increase in Mg2+-dependent microsomal phosphohydrolase activity. The effects of the two nutritional interventions on phosphatidate phosphohydrolase activity confirm a key function for this enzyme in triacylglycerol formation.

Dependence on blood acetate concentration of the metabolic effects of ethanol in perfused rat liver.

In livers from fed rats perfused with recirculating blood, infusion of ethanol produced an inhibition of ketogenesis followed by substantially increased production. Perfusate lactate concentrations fell markedly following the increase in ketone body formation. In these experiments perfusate acetate rose continuously, reaching a concentration of 10 mM at 70 min, while in a control liver concentrations remained very low. During non-recirculating perfusion with 3 mM acetate there was output of lactate, whereas at 10 mM acetate ketogenesis was greatly stimulated and there was net lactate uptake. These data support the concept that there is a concentration of acetate in the region of 5 mM, below which it competes with lactate for lipogenesis. Above this level acetate may penetrate the mitochondrion and stimulate ketogenesis and gluconeogenesis. Effects of ethanol in vitro may depend on the concentrations of acetate attained in the experimental system.

The adaptive effects of dietary fish and safflower oil on lipid and lipoprotein metabolism in perfused rat liver.

To elucidate the mechanisms underlying the plasma triacylglycerol-lowering effects of certain fish oils, livers from male rats fed either a standard commercial diet (controls) or diets supplemented with 15% (w/w) fish or safflower oils were perfused with undiluted rat blood. Rates of hepatic lipogenesis, measured by the incorporation of 3H2O into fatty acids, followed the order: control greater than safflower oil greater than fish oil. Secretion of newly synthesized fatty acids in very-low-density lipoproteins was also inhibited by the feeding of both oil-supplemented diets with the greater suppression being seen in livers from animals fed fish oil. The hepatic release of very-low-density lipoprotein triacylglycerol mass was also significantly depressed in animals fed the fish oil-supplemented diet but not in those fed safflower oil. Ketogenesis did not differ between livers from rats fed the control and safflower oil diets but was significantly raised in the fish oil group. Increased ketogenesis with fish oil was paralleled by a decrease in the sensitivity of carnitine palmitoyl transferase of isolated mitochondria to inhibition by malonyl-CoA. The inhibitory effect of malonyl-CoA in the safflower oil group was intermediate between that in the fish oil and control groups. Activities of glycerophosphate acyltransferase with either palmitoyl-CoA or oleyl-CoA were increased by feeding oil-supplemented diets. Activity with palmitoyl-CoA that was suppressible by N-ethylmaleimide was also considerably diminished in both groups. The results indicate that the lowering of plasma triacylglycerols by fish oil reflects: (a) diminished lipogenesis; (b) increased fatty acid oxidation possibly in peroxisomes; and (c) diminished secretion of triacylglycerols by the liver.

The effects of dietary fish oil on hepatic high density and low density lipoprotein receptor activities in the rat.

Rats were fed either a standard ration diet or that diet supplemented with 8% by wt of a marine fish oil or safflower oil. After 10 days, plasma triacylglycerols, total cholesterol, high density lipoprotein (HDL) cholesterol, hepatic cholesterol and fatty acid synthesis and hepatic low density lipoprotein (LDL) receptor activity were significantly depressed while HDL receptor activity was significantly increased in rats fed fish oil. Fish oil-induced effects on cholesterol metabolism in the rat therefore include reciprocal changes in the activities of hepatic LDL and HDL receptors.

Adaptive effects of dietary ethanol in the pig: changes in plasma high-density lipoproteins and fecal steroid excretion and mutagenicity.

Six young mature male pigs were maintained on a high fat, low fiber "Western" type diet. Substitution of ethanol for sucrose raised plasma total cholesterol, an increase that was solely due to a rise in high-density lipoproteins. Plasma triacylglycerols and apo-B concentrations were unchanged and although apo-A1 rose with ethanol, this was not statistically significant. Ethanol did not alter total fecal steroids but both bile acids and the ratio of bile acids/neutral sterols were increased. In fecal extracts from these animals, mutagenic activity in the Ames bacterial test was also raised. The data are discussed in relation to the relationships between dietary ethanol and coronary heart disease and colorectal cancer.

Effects of dietary saponins on fecal bile acids and neutral sterols, plasma lipids and lipoprotein turnover in the pig.

Four young mature male pigs, 110 to 120 kg of body weight, were maintained on a low (0.01%) cholesterol diet. A double changeover design was used so that at any time two pigs received additionally 20 g/day of saponins as a 0.33% solution in drinking water. Saponins raised concentrations of fecal bile acids and neutral sterols and increased the contribution of primary acids to excretion. Neither the concentration of total plasma cholesterol nor low-density and high-density lipoprotein cholesterol were affected by saponins. There was also no change in either absolute or fractional catabolic rate of low-density or high-density lipiproteins. The data are discussed in relation to the effects of cholestyramine on plasma cholesterol and bile acid excretion in the pig and to the possible role of saponin-containing foods in the control of plasma cholesterol in man.

Metabolic effects of carbon monoxide in relation to atherogenesis.

The acute and chronic effects of carbon monoxide (CO) are reviewed. Direct effects of CO-induced hypoxia on arterial metabolism may facilitate deposition of cholesterol in the intimal surface and exacerbate existing atherosclerosis. Other studies indicate that CO may alter hepatic metabolism so as to inhibit both the secretion of very low density lipoproteins and the clearance of chylomicron remnants. The former change would diminish and the latter enhance atherogenesis. These findings are considered and avenues of future investigation suggested.

The effect of intermittent carbon monoxide exposure on experimental atherosclerosis in the rabbit.

(1) Twenty-four female New Zealand White rabbits were fed commercial diet plus 2% cholesterol. Twelve of these animals were exposed to carbon monoxide for 4 hours per day, seven days per week for 10 weeks. The carbon monoxide exposure was such that the mean blood carboxy-haemoglobin was raised to approximately 20% during each exposure period. Twelve control animals breathed atmospheric air under the same conditions of confinement as the carbon monoxide-exposed group. (2) No significant differences in the plasma levels of cholesterol, triglycerides or glutamate oxalacetate transaminase were observed between the two groups during the experiment. (3) When the animals were sacrificed at the end of the experiment no significant differences were observed between the two groups in the aortic content of triglycerides, cholesterol or phospholipids. (4) The extent of coronary artery atherosclerosis was statistically significantly higher in the carbon monoxide group than in the control group. (5) Ultracentrifugal analysis of plasma lipoproteins revealed that there was significantly more cholesterol in the d less than l.006 fraction from the CO-exposed rabbits. (6) These findings, are discussed with particular reference to the claim that the causal agent in tobacco smoke associated arterial disease is carbon monoxide.

Time-course of changes in plasma lipids in diabetic rats fed diets high in fish or safflower oils.

Adult male rats were maintained for 10 days on a standard chow diet or that diet supplemented with either safflower or marine fish oils, and then rendered diabetic with streptozotocin (40 mg/kg of body weight) and circulating metabolites determined over the next 3 days. Pre-diabetic concentrations of glucose and insulin did not differ between groups, and the severity of hyperglycaemia and lowering of insulin in streptozotocin-treated animals were also similar. Pre-diabetic concentrations of plasma free fatty acids and triacylglycerols were lower, and blood ketone bodies were higher in non-diabetic rats fed fish oil than in both other groups. However, following streptozotocin treatment, plasma free fatty acids rose significantly more in both groups of oil-fed animals than in chow-fed ones. Plasma triacylglycerols were unaltered from pre-treatment levels in rats fed chow, but rose considerably in both groups fed oil-supplemented diets. In a subsequent experiment it was shown that the increase in triacylglycerols persisted for up to 11 days after streptozotocin and the hypertriglyceridaemia was greatest in the fish oil group. The rise would seem to result from defective clearance of lipoproteins of dietary origin. It appears that fish oil-supplemented diets should be avoided in diabetics until the possibility of increased hypertriglyceridaemia has been excluded by controlled studies.

Blood carbonmonoxyhaemoglobin levels are chronically elevated in alcoholics treated for detoxification.

Self-reported daily consumption of cigarettes and ethanol was recorded from a group of 59 ethanol-dependent persons admitted to a detoxification clinic at 2000-2400 h and averaged 40 cigarettes per day and 320 g ethanol per day, respectively. In consequence, concentrations of blood COHb and ethanol were high. Mean values for COHb were 8.5 and 9.9% in men and women, respectively, while the corresponding levels for ethanol were 220 and 280 mg/100 ml. Blood acetate concentrations were also elevated and correlated negatively with mixed venous oxygenhaemoglobin concentrations. The mean carbonmonoxyhaemoglobin concentration at 0700 h was found to be approximately 65% of that on admission. Biochemical and haematological analysis, past medical history and current physical examination revealed a high degree of ethanol and/or cigarette-related pathology. Studies on lipid and lipoprotein metabolism in ethanol-dependent persons should take into account their simultaneous high cigarette abuse.

Fish oil and oat bran in combination effectively lower plasma cholesterol in the rat.

Male rats were fed a semi-purified diet containing oat bran or wheat bran with or without a marine fish oil to investigate the effects of such combinations on lipid metabolism. Oat bran alone and wheat bran plus fish oil gave lower plasma cholesterol concentrations than wheat bran alone while oat bran plus fish oil gave the lowest. Oat bran increased plasma triacylglycerols compared with wheat bran but oat bran plus fish oil gave concentrations similar to those seen with wheat bran plus fish oil. Oat bran gave higher hepatic cholesterol synthesis rates and a higher activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase compared to wheat bran. The addition of fish oil to either bran diet decreased cholesterol synthesis but HMG CoA reductase activity was not reduced. Oat bran increased hepatic acyl coenzyme A:cholesterol acyl transferase (ACAT) activity and increased the ratio of esterified to unesterified cholesterol in hepatic microsomal membranes compared with wheat bran. Fish oil decreased hepatic LDL receptor activity and increased HDL binding activity when added to the wheat bran diet but these effects were not seen with oat bran. Oat bran also had no effect on hepatic lipoprotein receptor activity compared with wheat bran. These results show that fish oil and oat bran have complementary cholesterol lowering effects in the rat.

Soluble fiber polysaccharides: effects on plasma cholesterol and colonic fermentation.

Many soluble-fiber polysaccharides, used as stabilizers and thickeners by the food industry, lower plasma cholesterol and slow small intestinal transit and nutrient absorption. Although nondigestible by human enzymes, these polysaccharides are fermented by the large-bowel microflora, yielding short-chain fatty acids that are absorbed and contribute to energy. The caloric yield from fiber polysaccharides needs to be quantified. Short-chain fatty acid production from soluble fibers is modified by the presence of insoluble fibers but, in total, is probably less than from other carbohydrates, e.g., resistant starch. Short-chain fatty acids do not seem to mediate effects of fiber on plasma cholesterol, but in the large bowel they exert the trophic and antineoplastic effects of dietary fiber. The mechanism for cholesterol reduction by soluble fibers relates to enhanced steroid excretion and altered fat absorption and may be a function of the viscosity of these fibers in solution. The relationships between the chemical structure of soluble polysaccharides and their documented physiologic effects are not yet clear. By using polysaccharides of defined structure and properties, it should be possible to identify those characteristics that predict physiologic actions.

Plasma triglyceride secretion in squirrel monkeys: effects of nicotine.

The acute effects of intravenous nicotine on the appearance of plasma triglycerides have been studied in anaesthetised squirrel monkeys given Triton-WR 1339. At both dose levels studied, 4 and 10 mug/kg/30 sec, nicotine caused a stimulation in the rate of accumulation of plasma glycerides, the larger dose producing the greater effect. Nicotine caused a transient elevation in plasma free fatty acids (FFA), also in proportion to the dose given. It is suggested the changes in plasma glycerides are due to enhanced hepatic secretion secondary to increased plasma FFA. The administration of Triton-WR 1339 caused a rapid and sustained fall in plasma cholesterol concentrations. This fall was similar to that observed in plasma Triton and evidence is presented to suggest that Triton and cholesterol are removed from the circulation by a similar mechanism. There was no effect of nicotine on plasma cholesterol. The implications of the effects of nicotine of plasma triglycerides in relation to coronary heart disease are discussed briefly.

Resistant starch, large bowel fermentation and a broader perspective of prebiotics and probiotics.

The metabolic end products of the large bowel microbiota contribute significantly to human health. After weaning to solid foods, some of the most important of these are the short chain fatty acids (SCFA) produced by the fermentation of undigested dietary components and endogenous secretions. The main SCFA are acetate, propionate and butyrate which have numerous documented effects promoting large bowel function. Of the major acids, butyrate seems especially important. It is a major metabolic fuel for colonocytes and promotes a normal phenotype in these cells, potentially lowering the risk of diseases such as colo-rectal cancer. Imbalances in the microbiota are thought to predispose to large bowel dysfunction and probiotics are being developed to correct this. However, most commercial products contain bacteria (lactobacilli and bifidobacteria) which are dominant species in milk-fed infants but have limited roles in adults. Prebiosis is defined usually by the specific stimulation of these bacteria. However, the end products of most probiotics do not include butyrate or propionate which raises questions about their effectiveness in promoting bowel health in adults. Resistant starch (RS) is a dietary fibre component and its fermentation generally favours butyrate production. Dietary RS intakes and faecal butyrate levels are high in populations at low risk of diet-related large bowel diseases. Conversely, RS intakes and faecal butyrate levels are very low in high risk groups. This raises the possibility that greater RS consumption could be of health benefit. RS is not regarded widely as a prebiotic but (according to the accepted definition) most forms show the requisite features in stimulating specific bacteria, giving raised total SCFA and butyrate levels and a consequent benefit to the host. Current efforts to improve public health through increasing RS consumption could be facilitated by greater recognition of its prebiotic role.