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.

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.

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.

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.

Feeding Australian Acacia gums and gum arabic leads to non-starch polysaccharide accumulation in the cecum of rats.

Exudative gums from two Australian Acacia species (A. pycnantha and A. baileyana) and gum arabic (from A. senegal) were fed to rats at graded levels (0, 20, 40, 80 g/kg), replacing cellulose in purified diets containing cholesterol plus cholic acid. Compared with consumption of the control diet containing cellulose only, consumption of the gums had no significant effects on concentrations of plasma or liver cholesterol. Plasma triacylglycerol concentrations were higher in rats fed gum arabic, whereas liver triacylglycerols were lower in rats fed the gums. The gums did not affect the total pool of volatile fatty acids in the ceca, as compared with results in controls, but did promote the relative contribution of propionate at the expense of acetate. In rats fed the diet containing cellulose (80 g/kg) the proportions of cecal acetate:propionate:butyrate were 76:15:9, whereas in the rats fed A. pycnantha gum, gum arabic and A. baileyana gum (80 g/kg) the ratios were 42:54: 4, 35:46:19 and 43:53:4, respectively. The low apparent fermentability of the gums was confirmed by the accumulation of non-starch polysaccharides in cecal digesta. In rats fed 80 g/kg A. pycnantha gum, 3.44 g of soluble non-starch polysaccharides was measured in the ceca, which was 58% of the dry weight of the cecal contents. We conclude that the biological activities of the Australian Acacia gums were similar to those of gum arabic and that these gums may have potential value as human food ingredients.

Effects of haematocrit value and glucagon on the metabolism of perfused rat liver.

Liver from adult male rats were perfused in situ for 30 min with either undiluted, defibrinated rat blood (haematocrit value 38%) or the same blood diluted with buffer to give a haematocrit of 20%. Perfusion with diluted blood lowered the PO2 of the effluent perfusate but this was insufficient to prevent the fall in O2 consumption due to the reduction in haematocrit. Glucagon (5 X 10(-9) M) increased hepatic O2 consumption with whole blood but not with diluted blood. perfusate K+ was increased by perfusion with diluted blood and glucagon. Bile flow was depressed and biliary K+ increased by glucagon but only in experiments with whole blood. Perfusate glucose was raised by lowering of hepatic O2 consumption but the hormonal stimulation of glucose output was the same at both haematocrits. Net ketogenesis was increased with perfusion with diluted blood and by glucagon. In the absence of glucagon there was a net secretion of triacylglycerols which was depressed by lowering of the haematocrit. Glucagon inhibited triacylglycerol secretion and the effect was greater with whole blood so that there was net uptake. While effects of glucagon were obtained during perfusion at a lower haematocrit, it would appear that whole blood was the medium that allowed their fullest expression.

Effects of food restriction and starvation-refeeding on volatile fatty acid concentrations in the rat.

Adult male rats were fed either ad libitum or at levels of 19 or 15 g of nonpurified diet per rat daily or subjected to 48 h of starvation followed by 24 h of refeeding. Concentrations of total and individual volatile fatty acids (VFA) in cecal contents were higher in rats fed ad libitum than in those restricted to 19 or 15 g/d. Only butyrate concentration was lower in rats given 15 g/d than in those given 19 g/d. In starved animals all cecal VFA declined within 24 h of food removal, but the greatest change was in butyrate, which fell to less than 12% of the initial value. Acetate and propionate fell further after 48 h, but their concentrations were restored to control values within 24 h of refeeding while butyrate remained depressed by 50%. Cecal pH was closely related to total VFA concentration, although the highest degree of correlation was with butyrate. Hepatic portal venous plasma VFA concentrations generally reflected those in cecal digesta except that the proportion of butyrate was relatively lower in this blood vessel than in cecal contents. Under all conditions acetate was the only VFA found in arterial plasma and in the fully fed state was lower than in hepatic portal venous plasma. Food restriction and starvation did not alter arterial concentrations, indicating abolition of net uptake. We conclude that all VFA are affected by availability of fermentable material to the large bowel microflora but that the disproportionate changes in butyrate may reflect preferential use of this acid by cells of the large bowel wall.

Effects of flow rate and insulin on triacylglycerol secretion by perfused rat liver.

In rat livers perfused with undiluted rat blood at perfusion rates of 6, 12, or 18 ml/min, hepatic O2 consumption rose with blood flow. Lipogenesis was unaffected by blood flow in control livers and was enhanced by insulin at 12 and 18 ml/min. Very-low-density lipoprotein triacylglycerol secretion also rose with increased flow and was stimulated by insulin at both 6 and 12 ml/min. When glucose was added to livers perfused at 12 or 18 ml/min, uptake was independent of perfusion rate and was slightly stimulated by insulin. Total lipogenesis and the secretion of newly synthesized fatty acids in very-low-density lipoprotein triacylglycerols were unaffected by insulin at either flow rate. The hormone stimulated triacylglycerol secretion at 18 ml/min but inhibited it at 12 ml/min. It seems that in perfused liver, effects of insulin on lipogenesis and very-low-density lipoprotein secretion may be modified not only by changes in O2 consumption (in this case through alterations in blood flow) but also by the choice of substrate.

Soluble wheat pentosans exhibit different anti-nutritive activities in intact and cecectomized broiler chickens.

The role of the ceca in the anti-nutritive effect of wheat pentosans was studied in intact and cectomized broiler chickens. Addition of wheat pentosans (equivalent to 30 g pure arabinoxylans/kg diet) depressed the digestibilities of starch, protein and fatty acids in both types of birds. Cecectomized birds were less efficient (P < 0.01) in dry matter and energy utilization, but starch digestion was not influenced by cecectomy. Inclusion of isolated wheat pentosans decreased the fecal protein digestibility by 18% in intact birds and by 7% in cecectomized chickens, with the bird type x pentosan interaction being significant (P < 0.05). The ileal pentosan digestibility was not affected either by addition of isolated pentosans or by cecectomy; however, the fecal pentosan digestibility was significantly (P < 0.001) influenced. Thus, in intact birds the fecal pentosan digestibility coefficient was 0.216 in birds fed the control diet and 0.646 in those fed the diet with wheat pentosans; in cecectomized chickens the corresponding values were 0.193 and 0.399, indicating a significant influence of the hindgut microflora on pentosan digestion. The ileal and fecal digestibilities of fatty acids were also determined. There was no interaction between bird type and pentosan addition in the ileal digestibilities of fatty acids. Depressions in the fecal digestibilities of fatty acids 14:0 and 18:0 were significantly (P < 0.05) greater in intact birds. Our results indicate that anti-nutritive effects of wheat pentosans in poultry are partially due to an increased activity of hindgut microflora.

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.

O2 dependence of insulin stimulation of glucose uptake by perfused rat liver: effects of carboxyhaemoglobin and haematocrit.

Livers from fed male rats were perfused in a non-recirculating system with undiluted rat blood containing 14 mM glucose. In these experiments there was a substantial uptake of glucose which was stimulated by insulin. Perfusion with blood containing carboxyhaemoglobin at a concentration of 40% of total haemoglobin lowered O2 consumption and abolished hepatic glucose uptake in control and insulin-infused livers, respectively. In experiments with rat erythrocytes resuspended in buffer to haematocrit values of 38 and 22%, O2 consumption and control and insulin-stimulated rates of glucose uptake were similar to corresponding perfusions with undiluted blood and blood containing carboxyhaemoglobin. It is concluded that serum factors are of relatively small importance and that hepatic glucose uptake is dictated by O2 supply.

Non-starch polysaccharide-degrading enzymes increase the performance of broiler chickens fed wheat of low apparent metabolizable energy.

The effect of a commercial glycanase product (Avizyme TX) on the performance of 4-wk-old broiler chickens fed wheats with low and normal apparent metabolizable energy values was studied. Controls were fed a corn-based diet. Supplementation with the enzyme product significantly (P < 0.01) increased the apparent metabolizable energy of the low metabolizable energy wheat from 12.02 to 14.94 MJ/kg dry matter. The apparent metabolizable energy value of the normal wheat was increased from 14.52 to 14.83 MJ/kg dry matter; this was, however, not significant. Birds fed the low metabolizable energy wheat diet had significantly (P < 0.01) higher digesta viscosity and lower small intestinal starch and protein digestibilities than birds fed the normal wheat diet. Chickens fed the low metabolizable energy wheat tended to grow less than those fed the normal wheat diet. When the low metabolizable energy wheat+enzyme diet was fed, digesta viscosity was significantly (P < 0.01) lower (20.28 vs. 10.36 mPa.s), and small intestinal digestibility coefficient of starch was significantly (P < 0.01) greater (0.584 vs. 0.861) relative to values in birds fed the low metabolizable energy wheat diet alone. Although the protein digestibility coefficient also increased from 0.689 to 0.745, the difference was not significant. Weight gain and feed efficiency of birds fed the low metabolizable energy wheat+enzyme equaled those of controls. The enzyme product significantly (P < 0.01) increased the solubilization of non-starch polysaccharides within the gastrointestinal tract of birds fed both types of wheat diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma lipids and large bowel volatile fatty acids in pigs fed on white rice, brown rice and rice bran.

Adult male pigs were fed on a diet containing (% of energy) fat 25 starch 55 from white rice and providing 20 g fibre/pig d (diet WR). In two other groups rice bran was added to the diet to provide 43 g fibre/d. One group received the diet unmodified (diet RB), but in another (diet RO) heat-stabilized unrefined rice oil replaced the palm oil. In a further group brown rice replaced white rice and provided 37 g fibre/pig per d (diet BR). Plasma cholesterol concentrations were similar with diets WR, RB and BR. With diet RO the concentration was significantly lower than with diets WR and BR but was not different from diet RB. Plasma high-density-lipoprotein-cholesterol and plasma triacylglycerols were unaffected by diet. In all groups, digesta mass rose from the caecum to the proximal colon but fell in the distal colon. Diet WR gave the lowest digesta mass while diet BR gave a significantly higher mass along the large bowel length. RB- and RO-fed pigs had equal masses of digesta which were intermediate between BR- and WR-fed pigs at all sampling sites. Pools of individual and total volatile fatty acids (VFA) in the proximal large bowel were unaffected by diet. Pools of total and individual VFA in the median and distal colon were lowest with diets WR and RB and significantly higher with diet BR. In these regions of the colon pools of acetate in RO-fed pigs did not differ from those in the BR-fed group but were higher than in other groups. However, pools of propionate and butyrate with the RO diet were significantly lower than with diet BR and the same as with diets WR and RB. Portal venous VFA concentrations were unaffected by diet. The higher large bowel digesta masses and VFA with diet BR may reflect the escape of starch from the small intestine.

A viscous fibre (methylcellulose) lowers blood glucose and plasma triacylglycerols and increases liver glycogen independently of volatile fatty acid production in the rat.

1. Adult male rats were maintained on diets containing 80 g methylcellulose/kg of low (25 cP), medium (400 cP) and high (1500 cP) viscosity. 2. After 10 d, the viscosity of stomach and caecal contents was found to have increased in proportion to that of the dietary fibre. Concentrations of volatile fatty acids in caecal digesta were lowest with the high-viscosity fibre but acetate was the major acid present with all three diets. Acetate was the only acid found in significant quantities in hepatic portal venous plasma and concentrations of this acid were unaffected by diet. 3. Concentrations of glucose in arterial blood were low with the medium- and high-viscosity diets while the content of liver glycogen was high. These effects of fibre were not directly on glucose absorption as the intestines were net removers of the hexose at the time of sampling. 4. Hepatic lipogenesis and plasma triacylglycerol concentrations were both higher in rats fed on the low-viscosity fibre. Plasma cholesterol concentrations, hepatic cholesterol synthesis and faecal bile acid excretion were not altered by dietary fibre viscosity. 5. We conclude that the effects of dietary fibre on carbohydrate absorption and storage and fatty acid synthesis are a function of the viscosity of the fibre in solution, high viscosity slowing the digestion and absorption of nutrients in the small intestine. Large-bowel microbial fermentation is not of direct significance to these events. In contrast, effects of fibre polysaccharides on sterol metabolism seem not to be related to their rheological properties.

Inhibition by insulin of ethanol-induced hyperglycaemia in perfused livers from fed rats.

Livers from fed male rats were perfused with homologous whole blood and infused with ethanol and insulin. Ethanol raised hepatic glucose output by enhancing gluconeogenesis from perfusate lactate and amino acids. Ketogenesis and the ratio [3-hydroxy butyrate]/[acetoacetate] were also raised. Insulin, infused alone, lowered blood glucose, ketogenesis and total serum amino acids and when added with ethanol opposed the metabolic effects of the latter. Ethanol did not affect serum fatty acids but their concentrations were raised by insulin.