A trial of the effects of soya-bean flour and soya-bean saponins on plasma lipids, faecal bile acids and neutral sterols in hypercholesterolaemic men

1. The hypothesis that soya-bean saponins, by binding bile salts in the gastrointestinal lumen, are responsible for some of the plasma-cholesterol-lowering effect of soya-bean preparations, was tested. In a double-blind crossover study 50 g soya-bean flour/d, containing either 22 or 4 g saponins/kg (adjusted by ethanol extraction) was incorporated in biscuits as a substitute for biscuits or bread into the diet of ten outpatient hypercholesterolaemic men over two consecutive 4-week study periods. The diet was monitored to ensure constancy, saponin-rich foods excluded, faeces collected for bile acid and neutral sterol analysis, and blood taken for plasma lipoprotein lipid analysis. 2. Neither diet had any effect on cholesterol in any plasma lipoprotein fraction, on fasting plasma triglyceride, or on faecal bile acids and neutral sterols. 3. These results suggested that soya-bean saponins are not responsible for the hypocholesterolaemic effect of soya-bean products.

Impaired sensitivity to insulin of rat livers perfused with blood of diminished haematocrit

1. In livers from fed rats perfused with homologous whole blood of a haematocrit value of 37%, insulin decreased the perfusate concentrations of glucose and amino acids, production of ketone bodies (3-hydroxybutyrate + acetoacetate) and increased bile flow. 2. Perfusion with blood diluted with buffer to a haematocrit value of 17% decreased hepatic O2 consumption by 40-50%. Perfusate concentrations of glucose and lactate, the rate of ketogenesis and the ratios [lactate]/[pyruvate] and [3-hydroxybutyrate]/[acetoacetate] were all increased. 3. In livers perfused with blood of diminished haematocrit, effects of insulin on perfusate glucose an amino acids, ketogenesis and bile flow were abolished.

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.

Effects of fructose concentration on carbohydrate metabolism, heat production and substrate cycling in isolated rat hepatocytes

1. Hepatocytes from starved rats were incubated with 5mm-glucose, labelled uniformly with (14)C and specifically with (3)H at positions 1, 2, 3 or 6, and with fructose at concentrations of 2.5, 7.5 or 25mm. 2. In the absence of other substrates only 1% of the radioactivity initially present in [U-(14)C]glucose appeared in the metabolic products, CO(2), lactate, pyruvate, amino acids and glycogen. 3. Fructose at 2.5mm caused a 30% increase in the glucose concentration and a 4-fold increase in the apparent oxidation of [U-(14)C]-glucose. 4. The formation of (3)H(2)O from [1-(3)H]-, [2-(3)H]-, [3-(3)H]- or [6-(3)H]-glucose was 2.4, 4.3, 2.15 or 1.6% respectively in the control incubations and 4.1, 10.4, 7.7 or 5.1% with 2.5mm-fructose. 5. Fructose at 7.5 and 25mm decreased the (3)H(2)O yields to less than the control values, but had no apparent effect on the amount of [U-(14)C]glucose metabolized. 6. In the incubations with 5mm-glucose and 25mm-fructose there were significant decreases in heat production, O(2) consumption and in the ratio of O(2) uptake to heat output. 7. Fructose at 2.5mm caused a 64% increase in heat output, but only a 43% increase in O(2) uptake. 8. The radioisotopic and calorimetric data demonstrate that physiological concentrations of fructose greatly increase metabolism in hepatocytes from starved rats. These data also indicate increased cycling at glucose/glucose 6-phosphate and at fructose 6-phosphate/fructose 1,6-bisphosphate in the presence of 2.5mm-fructose, although the rates of cycling were actually decreased relative to the amount of glucose catabolized. 9. At concentrations of 2.5, 7.5 and 25mm, fructose depressed hepatocyte ATP concentrations by 20, 65 and 80% respectively. Although fructose at 7.5 and 25mm increased glucose and lactate release, O(2) consumption, production of heat and formation of(3)H(2)O from [1-(3)H]-, [2-(3)H]-, [3-(3)H]- or [6-(3)H]-glucose were lowered to values equal to, or less than, controls. These effects probably reflect a severe derangement of hepatic metabolism due to excess phosphorylation of fructose when present at high concentrations.

Acute effects of ethanol on the perfused rat liver. Studies on lipid and carbohydrate metabolism, substrate cycling and perfusate amino acids

1. Livers from fed rats were perfused in situ with whole rat blood containing glucose labelled uniformly with (14)C and specifically with (3)H at positions 2, 3 or 6. 2. When ethanol was infused at a concentration of 24mumol/ml of blood the rate of utilization was 2.8mumol/min per g of liver. 3. Ethanol infusion raised perfusate glucose concentrations and caused a 2.5-fold increase in hepatic glucose output. 4. Final blood lactate concentrations were decreased in ethanol-infused livers, but the mean uptake of lactate from erythrocyte glycolysis was unaffected. 5. Production of ketone bodies (3-hydroxybutyrate+3-oxobutyrate) and the ratio [3-hydroxybutyrate]/[3-oxobutyrate] were raised by ethanol. 6. Formation of (3)H(2)O from specifically (3)H-labelled glucoses increased in the order [6-(3)H]<[3-(3)H]<[2-(3)H]. Production of (3)H(2)O from [2-(3)H]glucose was significantly greater than that from [3-(3)H]glucose in both control and ethanol-infused livers. Ethanol significantly decreased (3)H(2)O formation from all [(3)H]glucoses. 7. Liver glycogen content was unaffected by ethanol infusion. 8. Production of very-low-density lipoprotein triacylglycerols was inhibited by ethanol and there was a small increase in liver triacylglycerols. Very-low-density-lipoprotein secretion was negatively correlated with the ratio [3-hydroxybutyrate]/[3-oxobutyrate]. Perfusate fatty acid concentrations and molar composition were unaffected by perfusion with ethanol. 9. Ethanol decreased the incorporation of [U-(14)C]glucose into fatty acids and cholesterol. 10. The concentration of total plasma amino acids was unchanged by ethanol, but the concentrations of alanine and glycine were decreased and ([glutamate]+[glutamine]) was raised. 11. It is proposed that the observed effects of ethanol on carbohydrate metabolism are due to an increased conversion of lactate into glucose, possibly by inhibition of pyruvate dehydrogenase. The increase in gluconeogenesis is accompanied by diminished substrate cycling at glucose-glucose 6-phosphate and at fructose 6-phosphate-fructose 1,6-bisphosphate.

Effects of saponins on bile acids and plasma lipids in the rat

1. The effects of feeding isolated saponins on plasma lipid concentrations and on concentrations of biliary and faecal bile acids and neutral sterols were studied in the rat. 2. The animals were given one of four diets, i.e. a standard low-cholesterol synthetic diet, the diet + 10 g saponins/kg, the diet + 10 g cholesterol/kg, the diet + 10 g cholesterol + 10 g saponins/kg. 3. Saponins partially reversed the hypercholesterolaemia caused by the high-cholesterol diet and increased both the rate of bile acid secretion and the faecal excretion of bile acids and neutral sterols. The proportionate contribution of the primary bile acids (particularly chenodeoxycholic) to faecal excretion was also increased by saponins. 4. The results are discussed in relation to the hypothesis that saponins act by inducing the adsorption of bile acids by dietary fibre.

Acute effects of nicotine on plasma free fatty acid concentrations and on the response to cold stress, in lean and obese (genotype ob/ob) mice

Lean and genetically obese (ob/ob) male and female mice were given nicotine by subcutaneous injection. Nicotine treatment was found to raise plasma free fatty acids by similar amounts in both lean and obese mice. In lean mice, nicotine caused depression of rectal temperature at ambient temperatures 22-25 degrees C and partially prevented the hypothermia in these mice when exposed to cold (o-3 degrees C). In obese mice, nicotine treatment did not alter either rectal temperature at 22-25 degrees C or the severe hypothermia on cold exposure. It is proposed that the effect of nicotine on free fatty acids is due to release of adrenal catecholamines and that this mechanism operates in both lean and obese animals. It is also proposed that, in obese mice under normal circumstances, there is a defect in the central nervous control of this adrenergic mechanism which may contribute to the observed fall in body temperature at low ambient temperatures.

Potentiation of hyperphagia and relief of hypothermia in the genetically obese mouse (genotype, ob/ob) by alpha-methyl tyrosine

DL-alpha-methyl-p-tyrosine methyl ester hydrochloride affected the hyperphagia and hypothermia characteristic of the genetically obese mouse (genotype, ob/ob) throughout an experimental period of 5 days. Intraperitoneal injections of 100 mg/kg body weight, daily, resulted in a significant increase in the average daily food consumption by 60 per cent, already elevated 35 per cent above that of lean litter-mates. The drug, administered at the same dose, caused a similar percentage elevation of food intake in the lean litter-mates. Rectal temperatures of obese mice were raised significantly throughout the 5-day period by an average of 0.95 degrees C, following administration of the drug. There was a significant rise of 0.75 degrees C in the rectal temperature of lean mice on 2 of the 5 days in the period. Body weight remained unchanged. Further experiments are necessary to determine the site of action at which DL-alpha-methyl-p-tyrosine brings about these effects at this dose in lean and obese mice.

Peripheral vascular disease in cigarette smokers and impaired hepatic metabolism of lipoprotein remnants

The metabolism of very-low-density lipoproteins and chylomicrons includes the extrahepatic hydrolysis of their triglycerides by lipoprotein lipase. This results in cholesterol-rich "remnants" which are further metabolised by the liver. There is experimental evidence that in both patients with type-III hyperlipoproteinaemia and cigarette smokers hepatic-remnant metabolism may be depressed. In type-III hyperlipoproteinaemia the defect is inherited while in smokers it occurs in response to raised blood concentrations of carboxyhaemoglobin. The striking clinical similarity between type-III hyperlipoproteinaemic patients and smokers--namely, a high incidence of peripheral vascular disease--may be due to a common cause, the accumulation of cholesterol-rich remnants in the plasma.

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.

Comparative effects of fructose and glucose on the lipid and carbohydrate metabolism of perfused rat liver

1. Livers from rats fed on a standard diet were perfused with whole blood, and infused continuously with glucose and fructose at equimolar rates. 2. Infusion of fructose increased both the secretion of very-low-density-lipoprotein (VLDL)-triglycerides and the incorporation of free fatty acids (FFA) from the perfusate into VLDL-lipids, but neither of these two processes was affected by infusion of glucose. 3. Infusion of fructose decreased the oxidation and increased the esterification of FFA, but glucose infusion had no effect on these processes. When fructose and glucose were infused together was a further decrease in oxidation. 4. When fructose was infused alone or together with glucose, blood concentrations rapidly became stabilized at those found in the hepatic portal vein in vivo, with similar rates of hepatic uptake to those found in the intact animal. Infusion of glucose alone resulted in continuously increasing perfusate glucose concentrations, and rates of uptake which were only 20% of those for fructose. Blood glucose concentrations were reduced, and lactate concentrations were increased by fructose infusion, and when glucose and fructose were infused together there was a greatly increased rate of glucose uptake. 5. Liver glycogen was not affected by the infusion of fructose or glucose alone; however, their combined addition significantly increased its concentration. 6. Uptake of perfusate FFA was not affected by either fructose or glucose infusions. 7. The results are discussed in terms of the differences in nutrition and metabolism between glucose and fructose, with particular reference to the development of hypertriglyceridaemia.

Acute effects of carbon monoxide on the metabolism of perfused rat liver

1. Perfusion of livers with whole blood containing carboxyhaemoglobin decreased hepatic O(2) consumption and triglyceride secretion and raised free fatty acid oxidation. 2. Perfusion with [(14)C]carboxyhaemoglobin indicated that there was negligible hepatic uptake of (14)CO. 3. The observations appear to be due to a decrease in O(2) consumption rather than to specific effects of carboxyhaemoglobin.

The effect of tobacco smoke and some of its constitutents on triglyceride secretion in the squirrel monkey

The acute effects of tobacco smoke and some of its constituents on plasma free fatty acid levels and on triglyceride secretion were studied in anaesthetized squirrel monkeys given Triton WR-1339. All the treatments raised plasma free fatty acids in the order high tar smoke greater than medium tar vapour phase = air:CO greater than medium tar smoke. Plasma triglyceride secretion in animals inhaling high tar smoke did not differ from controls. There was a transient rise in triglyceride secretion in animals inhaling vapour phase but the largest increase (after a significant delay) was in monkeys breathing air:CO. Maximal concentrations of blood carboxyhaemoglobin did not differ between the experimental groups. It is suggested that, under these experimental conditions, there are present in the particulate phase of tobacco smoke factors which inhibit hepatic triglyceride secretion.

Time-course of changes in blood glucose and ketone bodies, plasma lipids and liver fatty acid composition in streptozotocin-diabetic male rats

Male rats were given streptozotocin (100 mg/kg) by intraperitoneal injection. Groups of control and streptozotocin-treated animals were sacrificed at daily intervals for 4 days after injection. Over this period, treated rats lost weight continuously while control animals progressively gained weight. Within 24 h of treatment blood glucose and plasma free fatty acids were raised to levels which were sustained for the remainder of the experiment. After 48 h blood ketone bodies, plasma cholesterol and triglycerides were maximally raised and liver glycogen and blood lactate similarly lowered. The percentage composition of major fatty acids in liver lipids was unchanged until 4 days after treatment when there were significant increases in the proportion of oleate and linoleate and reductions in stearate and arachidonate. The data confirm that streptozotocin induces a rapid and sustained diabetes. It is suggested that metabolic experiments, in streptozotocin-diabetic rats, may be performed 48 h after treatment.

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.

Regulation of hepatic lipogenesis by plasma free fatty acids: simultaneous studies on lipoprotein secretion, cholesterol synthesis, ketogenesis and gluconeogenesis

1. An inverse logarithmic relationship was found between lipogenesis and the concentration of serum free fatty acids perfusing the rat liver. 2. Increased concentrations of serum free fatty acids did not alter cholesterol synthesis, triglyceride secretion or increase gluconeogenesis. 3. No direct relationship was found between ketogenesis and either lipogenesis or gluconeogenesis.

The immediate effects of insulin and fructose on the metabolism of the perfused liver. Changes in lipoprotein secretion, fatty acid oxidation and esterification, lipogenesis and carbohydrate metabolism

1. When livers from fed rats were perfused with blood containing elevated concentrations of rat insulin or blood to which fructose was added, the oxidation of free fatty acids was depressed and their esterification was increased. 2. Raised concentrations of insulin or addition of fructose increased secretion of triglyceride in very-low-density lipoproteins, but only insulin caused more of the free fatty acids taken up by the liver to be incorporated into very-low-density lipoproteins. 3. When insulin and fructose were added together the combined effect on oxidation and esterification of free fatty acids and on secretion of very-low-density lipoproteins was equal to the sum of the effects of either alone. No statistically significant interaction between the effects of fructose and insulin was found for any of the parameters investigated. 4. Bovine insulin had similar effects, in most respects, to comparable studies with raised concentrations of rat insulin. 5. Lipogenesis was increased in the livers treated with fructose plus bovine insulin. 6. A significant proportion of the fatty acids in very-low-density lipoproteins were derived either from the liver triglyceride pool or from lipogenesis. This fraction was increased both by treatment with insulin or fructose, and was augmented further when both insulin and fructose were present together. 7. The uptake of fructose by the perfused liver was similar to that found in vivo. It was unaffected by the presence of insulin. 8. Addition of fructose to the perfused liver caused perfusate lactate concentrations to increase, as a result of diminished hepatic uptake of lactate. 9. The uptake of free fatty acids by the perfused liver was unaffected by the addition of either insulin or fructose. 10. The distribution among the various lipid classes in plasma lipoproteins of label arising from the hepatic uptake of [(14)C]oleate was unaltered by the addition of either fructose or insulin. 11. It is suggested that the effects described are due principally to control of the balance between esterification of fatty acids and lipolysis of the ensuing triglyceride, fructose enhancing esterification and insulin inhibiting lipolysis.

The concentration of fructose, glucose and lactate in the splanchnic blood vessels of rats absorbing fructose

The concentrations of fructose, glucose and lactate were measured in the hepatic portal vein, hepatic vein and systemic aorta of fed and fasting rats given a large meal of fructose by gastric intubation. The maximum concentration of fructose found in portal vein blood was within the range 20–40 mg/100 ml. The corresponding range in the systemic circulation was 2–6 mg/100 ml. A fractional hepatic fructose uptake of 54.9% and 71.5% was found in fed and fasting rats, respectively. Little fructose was removed by extrahepatic tissues. Fructose feeding lowered the concentration of glucose in the hepatic vein of fed animals but did not alter glucose concentrations in any other vessels sampled in fed or fasting rats. The absorption of fructose raised blood lactate concentrations in all vessels sampled of both fed and fasting animals. It is suggested that this effect is due to reduction in hepatic uptake of lactate. Fructose feeding did not increase lactate production by the intestine, neither was there any evidence of significant intestinal conversion of fructose to glucose.