Coronary nitric oxide production controls cardiac substrate metabolism during pregnancy in the dog

The aim of this study was to examine the role of nitric oxide (NO) in the control of cardiac metabolism at 60 days of pregnancy (P60) in the dog. There was a basal increase in diastolic coronary blood flow during pregnancy and a statistically significant increase in cardiac output (55 +/- 4%) and in cardiac NOx production (44 +/- 4 to 59 +/- 3 nmol/min, P < 0.05). Immunohistochemistry of the left ventricle showed an increase in endothelial nitric oxide synthase staining in the endothelial cells at P60. NO-dependent coronary vasodilation (Bezold-Jarisch reflex) was increased by 20% and blocked by N(G)-nitro-l-arginine methyl ester (l-NAME). Isotopically labeled substrates were infused to measure oleate, glucose uptake, and oxidation. Glucose oxidation was not significantly different in P60 hearts (5.4 +/- 0.5 vs. 6.2 +/- 0.4 micromol/min) but greatly increased in response to l-NAME injection (to 19.9 +/- 0.9 micromol/min, P < 0.05). Free fatty acid (FFA) oxidation was increased in P60 (from 5.3 +/- 0.6 to 10.4 +/- 0.5 micromol/min, P < 0.05) and decreased in response to l-NAME (to 4.5 +/- 0.5 micromol/min, P < 0.05). There was an increased oxidation of FFA for ATP production but no change in the respiratory quotient during pregnancy. Genes associated with glucose and glycogen metabolism were downregulated, whereas genes involved in FFA oxidation were elevated. The acute inhibition of NO shifts the heart away from FFA and toward glucose metabolism despite the downregulation of the carbohydrate oxidative pathway. The increase in endothelium-derived NO during pregnancy results in a tonic inhibition of glucose oxidation and reliance on FFA uptake and oxidation to support ATP synthesis in conjunction with upregulation of FFA metabolic enzymes.     

Effects of adenosine, exercise, and moderate acute hypoxia on energy substrate utilization of human skeletal muscle

Glucose metabolism increases in hypoxia and can be influenced by endogenous adenosine, but the role of adenosine for regulating glucose metabolism at rest or during exercise in hypoxia has not been elucidated in humans. We studied the effects of exogenous adenosine on human skeletal muscle glucose uptake and other blood energy substrates [free fatty acid (FFA) and lactate] by infusing adenosine into the femoral artery in nine healthy young men. The role of endogenous adenosine was studied by intra-arterial adenosine receptor inhibition (aminophylline) during dynamic one-leg knee extension exercise in normoxia and acute hypoxia corresponding to ～3,400 m of altitude. Extraction and release of energy substrates were studied by arterial-to-venous (A-V) blood samples, and total uptake or release was determined by the product of A-V differences and muscle nutritive perfusion measured by positron emission tomography. The results showed that glucose uptake increased from a baseline value of 0.2 ± 0.2 to 2.0 ± 2.2 μmol·100 g(-1)·min(-1) during adenosine infusion (P < 0.05) at rest. Although acute hypoxia enhanced arterial FFA levels, it did not affect muscle substrate utilization at rest. During exercise, glucose uptake was higher (195%) during acute hypoxia compared with normoxia (P = 0.058), and aminophylline had no effect on energy substrate utilization during exercise, despite that arterial FFA levels were increased. In conclusion, exogenous adenosine at rest and acute moderate hypoxia during low-intensity knee-extension exercise increases skeletal muscle glucose uptake, but the increase in hypoxia appears not to be mediated by adenosine.     

Application of tracers in studying free fatty acid metabolism of various organs in vivo.

A few selected examples are given of the application of radio-labeled fatty acids in studying substrate utilization under in vivo conditions. The flux of free fatty acids (FFA) may be calculated by the constant infusion technique of Armstrong et al. using either labeled palmitic or oleic acid. Utilization of FFA by the myocardium is conveniently studied by the constant infusion of 14C-labeled palmitate or oleate. The extraction ratio of these two fatty acids is very similar both in the case of myocardium and of several other tissues investigated. Using this technique not only the removal and oxidation of FFA may be calculated but also competition between the major substrates (FFA, lactate, ketone bodies) can be studied. Arterial FFA concentration, rate of coronary blood flow, and myocardial work are mentioned as some of the important factors influencing the rate of myocardial FFA utilization. The study of skeletal muscle metabolism employing labeled fatty acids is of great importance since release as well as uptake of FFA takes place across most muscle beds and thus net arteriovenous differences may be misleading. A somewhat similar situation also exists in the splanchnic region. Labeled fatty acids have also been utilized to investigate both the oxidation of FFA and their incorporation into brain lipids. Both the uptake and release of FFA may be followed in the adipose tissue by the use of labeled palmitate or oleate.     

Comparison of local and systemic effects of insulin on myocardial glucose extraction in ischemic heart disease

Physiological increases in circulating insulin level significantly increase myocardial glucose uptake in vivo. To what extent this represents a direct insulin action on the heart or results indirectly from reduction in circulating concentrations of free fatty acids (FFA) is uncertain. To examine this, we measured myocardial glucose, lactate, and FFA extraction in 10 fasting men (ages 49-76 yr) with stable coronary artery disease during sequential intracoronary (10 mU/min, coronary plasma insulin = 140 +/- 20 microU/ml) and intravenous (100 mU/min, systemic plasma insulin = 168 +/- 26 microU/ml) insulin infusion. Basally, hearts extracted 2 +/- 2% of arterial glucose and extracted 27 +/- 6% of FFA. Coronary insulin infusion increased glucose extraction to 5 +/- 3% (P < 0.01 vs. basal) without changing plasma FFA or heart FFA extraction. Conversion to intravenous infusion lowered plasma FFA by approximately 50% and heart FFA extraction by approximately 75%, increasing heart glucose extraction still further to 8 +/- 3% (P < 0. 01 vs. intracoronary). This suggests the increase in myocardial glucose extraction observed in response to an increment in systemic insulin concentration is mediated equally by a reduction in circulating FFA and by direct insulin action on the heart itself. Coronary insulin infusion increased myocardial lactate extraction as well (from 20 +/- 10% to 29 +/- 9%, P < 0.05), suggesting the local action may include stimulation of a metabolic step distal to glucose transport and glycolysis.     

No in vitro effects of fatty acids on glucose uptake, lipolysis or insulin signaling in rat adipocytes.

Elevated plasma levels of free fatty acids (FFA) can produce insulin resistance in skeletal muscle tissue and liver and, together with alterations in beta-cell function, this has been referred to as lipotoxicity. This study explores the effects of FFAs on insulin action in rat adipocytes. Cells were incubated 4 or 24 h with or without an unsaturated FFA, oleate or a saturated FFA, palmitate (0.6 and 1.5 mM, respectively). After the culture period, cells were washed and insulin effects on glucose uptake and lipolysis as well as cellular content of insulin signaling proteins (IRS-1, PI3-kinase, PKB and phosphorylated PKB) and the insulin regulated glucose transporter GLUT4 were measured. No significant differences were found in basal or insulin-stimulated glucose uptake in FFA-treated cells compared to control cells, regardless of fatty acid concentration or incubation period. Moreover, there were no significant alterations in the expression of IRS-1, PI3-kinase, PKB and GLUT4 following FFA exposure. Insulin's ability to stimulate PKB phosphorylation was also left intact. Nor did we find any alterations following FFA exposure in basal or cAMP-stimulated lipolysis or in the ability of insulin to inhibit lipolysis. The results indicate that oleate or palmitate does not directly influence insulin action to stimulate glucose uptake and inhibit lipolysis in rat fat cells. Thus, lipotoxicity does not seem to occur in the fat tissue itself.     

Effects of coronary sinus pressure elevation on coronary blood flow distribution in dogs with normal preload

Coronary sinus pressure (Pcs) elevation shifts the diastolic coronary pressure-flow relation (PFR) of the entire left ventricular myocardium to a higher pressure intercept. This finding suggests that Pcs is one determinant of zero-flow pressure (Pzf) and challenges the existence of a vascular waterfall mechanism in the coronary circulation. To determine whether coronary sinus or tissue pressure is the effective coronary back pressure in different layers of the left ventricular myocardium, the effect of increasing Pcs was studied while left ventricular preload was low. PFRs were determined experimentally by graded constriction of the circumflex coronary artery while measuring flow using a flowmeter. Transmural myocardial blood flow distribution was studied (15-micron radioactive spheres) at steady state, during maximal coronary artery vasodilatation at three points on the linear portion of the circumflex PFR both at low and high diastolic Pcs (7 +/- 3 vs. 22 +/- 5 mmHg; p less than 0.0001) (1 mmHg = 133.322 Pa). In the uninstrumented anterior wall the blood flow measurements were obtained in triplicate at the two Pcs levels. From low to high Pcs, mean aortic (98 +/- 23 mmHg) and left atrial (5 +/- 3 mmHg) pressure, percent diastolic time (49 +/- 7%), percent left ventricular wall thickening (32 +/- 4%), and percent myocardial lactate extraction (15 +/- 12%) were not significantly changed. Increasing Pcs did not alter the slope of the PFR; however, the Pzf increased in the subepicardial layer (p less than 0.0001), whereas in the subendocardial layer Pzf did not change significantly. Similar slopes and Pzf were observed for the PFR of both total myocardial mass and subepicardial region at low and high Pcs. Subendocardial:subepicardial blood flow ratios increased for each set of measurements when Pcs was elevated (p less than 0.0001), owing to a reduction of subepicardial blood flow; however, subendocardial blood flow remained unchanged, while starting in the subepicardium toward midmyocardium blood flow decreased at high Pcs. This pattern was similar for the uninstrumented anterior wall as well as in the posterior wall. Thus as Pcs increases it becomes the effective coronary back pressure with decreasing magnitude from the subepicardium toward the subendocardium of the left ventricle. Assuming that elevating Pcs results in transmural elevation in coronary venous pressure, these findings support the hypothesis of a differential intramyocardial waterfall mechanism with greater subendo- than subepi-cardial tissue pressure.     

Relationship between fatty acid and glucose utilization in Ehrlich ascites tumor cells

Glucose greatly increased total free fatty acid (FFA) esterification by Ehrlich ascites tumor cells. However, the FFA concentration of the cells was not altered. Less exogenous FFA was oxidized to CO(2) at any given extracellular FFA:albumin molar ratio when glucose was available, but increasing amounts of radioactive CO(2) were produced as the FFA:albumin molar ratio was raised, even in the presence of glucose. It is suggested that glucose, by providing either energy or an excess of triose acceptor for fatty acid esterification, stimulated FFA uptake only indirectly, by increasing the utilization of FFA subsequent to initial uptake from the medium, i.e., by increasing the turnover rate of the cellular FFA pool. Availability of glucose decreased the oxidation of endogenous lipid radioactivity and the depletion of endogenous lipid ester radioactivity. Most of the radioactivity utilized was derived from phospholipids, and depletion of phospholipid radio-activity was spared when glucose was available. Depletion of cellular total lipid ester also was spared in the presence of glucose. Availability of FFA did not decrease total glucose uptake or its oxidation to CO(2). Glucose utilization by these cells appears not to be regulated by FFA availability in the manner that Randle and coworkers described for muscle.     

Regional metabolic rate of exogenous glucose in the isoprenaline and dobutamine stimulated canine myocardium as estimated by the 2-deoxy-d[1-14C]glucose method

The effect of β-adrenoceptor stimulation by isoprenaline and dobutamine on the transmural distribution pattern of regional myocardial metabolic rate of exogenous glucose (RMMRGlc) was studied in the anesthetized closed chest dog using the 2-deoxy-d[1-¹⁴C]glucose method. In a previous series a lumped constant (LC) value of 0.93 ± 0.47 (1 SD) was measured for [¹⁴C]2-deoxyglucose in the canine myocardium. In the control group (N = 12) RMMRGlc was significantly higher in the subendocardial layer of the left ventricular free wall than in both the middle and subepicardial layer, where it was quite evenly distributed (P ⩽ 0.05). With i.v. dobutamine (N = 8) RMMRGlc was significantly lower in the midportion of left ventricular free wall than in the subepicardial layer (P ⩽ 0.05), but it was not different from the inner wall section. Significant differences between the subepicardial and subendocardial portions of the left ventricular free wall could not be found, either. In the isoprenaline group (N = 9) no transmural gradients of RMMRGlc were observed in the left ventricular myocardium. In all groups, both the interventricular septum and the right ventricular free wall exhibited homogeneous distribution patterns of RMMRGlc.It is concluded that transmural distribution patterns of exogenous glucose utilization probably reflect corresponding gradients in energy demands of the left ventricular wall. Redistribution of RMMRGlc in the isoprenaline and dobutamine groups may result from altered working conditions, a change in local inotropic state of the left ventricular myocardium, or from regional differences in the proportions of substrate utilization, and from regional differences in adrenoceptor density.     

Shift in metabolic substrate uptake by the heart during development of alloxan-induced diabetes

Inhibition of endothelial nitric oxide (NO) synthase (eNOS) is associated with an increase in glucose uptake by the heart. We have already shown that Type I diabetes also causes a decrease in eNOS protein expression and altered NO control of both coronary vascular resistance and oxygen consumption. Therefore, we predict that the increase in plasma glucose and the reduction in eNOS during diabetes together would result in a large increase in cardiac glucose uptake. Arterial (A) and coronary sinus (C) plasma levels of glucose, free fatty acid (FFA), beta-hydroxybutyric acid (beta-HBA), and lactate were measured, and myocardial uptake was calculated before and at week 1, 2, 3, and 4 of alloxan-induced diabetes. The heart of healthy dogs consumed FFA (19.2 +/- 2.6 microeq/min) and lactate (19.7 +/- 3.4 micromol/min). Dogs in the late stage of diabetes (at week 4) had elevated arterial beta-HBA concentrations (1.6 +/- 0.7 micromol/l) that were accompanied by an increased beta-HBA uptake (0.3 +/- 0.2 micromol/min). In contrast, myocardial lactate (-4.8 +/- 3.0 micromol/min) and FFA uptake (2.5 +/- 1.9 microeq/min) were significantly reduced in diabetic animals. Despite a marked hyperglycemia (449 +/- 25 mg/dl), the heart did not take up glucose (-7.9 +/- 4.1 mg/dl). Our results indicate significant changes in the myocardial substrate utilization in dogs only in the late stage of diabetes, at a time when myocardial NO production is already decreased.     

Subendocardial and subepicardial pressure-flow relations in the rat heart in diastolic and systolic arrest

Ischemic heart disease is more apparent in the subendocardial than in subepicardial layers. We investigated coronary pressure-flow relations in layers of the isolated rat left ventricle, using 15 microm microspheres during diastolic and systolic arrest in the vasodilated coronary circulation. A special cannula allowed for selective determination of left main stem pressure-flow relations. Arterio-venous shunt flow was derived from microspheres in the venous effluent. We quantitatively investigated the pressure-flow relations in diastolic arrest (n=8), systolic arrest at normal contractility (n=8) and low contractility (n=6). In all three groups normal and large ventricular volume was studied. In diastolic arrest, at a perfusion pressure of 90 mmHg, subendocardial flow is larger than subepicardial flow, i.e., the endo/epi ratio is approximately 1.2. In systolic arrest the endo/epi ratio is approximately 0.3, and subendocardial flow and subepicardial flow are approximately 12% and approximately 55% of their values during diastolic arrest. The endo/epi ratio in diastolic arrest decreases with increasing perfusion pressure, while in systole the ratio increases. The slope of the pressure-flow relations, i.e., inverse of resistance, changes by a factor of approximately 5.3 in the subendocardium and by a factor approximately 2.2 in the subepicardium from diastole to systole. Lowering contractility affects subendocardial flow more than subepicardial flow, but both contractility and ventricular volume changes have only a limited effect on both subendocardial and subepicardial flow. The resistance (inverse of slope) of the total left main stem pressure-flow relation changes by a factor of approximately 3.4 from diastolic to systolic arrest. The zero-flow pressure increases from diastole to systole. Thus, coronary perfusion flow in diastolic arrest is larger than systolic arrest, with the largest difference in the subendocardium, as a result of layer dependent increases in vascular resistance and intercept pressure. Shunt flow is larger in diastolic than in systolic arrest, and increases with perfusion pressure. We conclude that changes in contractility and ventricular volume have a smaller effect on pressure-flow relations than diastolic-systolic differences. A synthesis of models accounting for the effect of cardiac contraction on perfusion is suggested.     

Impaired myocardial metabolic reserve and substrate selection flexibility during stress in patients with idiopathic dilated cardiomyopathy

Under resting conditions, the failing heart shifts fuel use toward greater glucose and lower free fatty acid (FFA) oxidation. We hypothesized that chronic metabolic abnormalities in patients with dilated cardiomyopathy (DCM) are associated with the absence of the normal increase in myocardial glucose uptake and maintenance of cardiac mechanical efficiency in response to pacing stress. In 10 DCM patients and 6 control subjects, we measured coronary flow by intravascular ultrasonometry and sampled arterial and coronary sinus blood. Myocardial metabolism was determined at baseline, during atrial pacing at 130 beats/min, and at 15 min of recovery by infusion of [(3)H]oleate and [(13)C]lactate and measurement of transmyocardial arteriovenous differences of oxygen and metabolites. At baseline, DCM patients showed depressed coronary flow, reduced uptake and oxidation of FFA, and preferential utilization of carbohydrates. During pacing, glucose uptake increased by 106% in control subjects but did not change from baseline in DCM patients. Lactate release increased by 122% in DCM patients but not in control subjects. Cardiac mechanical efficiency in DCM patients was not different compared with control subjects at baseline but was 34% lower during stress. Fatty acid uptake and oxidation did not change with pacing in either group. Our results show that in DCM there is preferential utilization of carbohydrates, which is associated with reduced flow and oxygen consumption at rest and an impaired ability to increase glucose uptake during stress. These metabolic abnormalities might contribute to progressive cardiac deterioration and represent a target for therapeutic strategies aimed at modulating cardiac substrate utilization.     

Intramyocardial pressure and coronary extravascular resistance

Intramyocardial pressure is an indicator of coronary extravascular resistance. During systole, pressure in the subendocardium exceeds left ventricular intracavitary pressure; whereas pressure in the subepicardium is lower than left ventricular intracavitary pressure. Conversely, during diastole, subepicardial pressure exceeds both subendocardial pressure and left ventricular pressure. These observations suggest that coronary flow during systole is possible only in the subepicardial layers. During diastolic, however, a greater driving pressure is available for perfusion of the subendocardial layers relative to the subepicardial layers. On this basis, measurements of intramyocardial pressure contribute to an understanding of the mechanisms of regulation of the phasic and transmural distribution of coronary blow flow.     

Comparison of metabolism of free fatty acid by isolated perfused livers from male and female rats.

Livers from normal, fed male and female rats were perfused with different amounts of [1-14C]oleate under steady state conditions, and the rates of uptake and utilization of free fatty acid (FFA) were measured. The uptake of FFA by livers from either male or female rats was proportional to the concentration of FFA in the medium. The rate of uptake of FFA, per g of liver, by livers from female rats exceeded that of the males for the same amount of FFA infused. The incorporation by the liver of exogenous oleic acid into triglyceride, phospholipid, and oxidation products was proportional to the uptake of FFA. Livers from female rats incorporated more oleate into triglyceride (TG) and less into phospholipid (PL) and oxidation products than did livers from male animals. Livers from female rats secreted more TG than did livers from male animals when infused with equal quantities of oleate. The incorporation of endogenous fatty acid into TG of the perfusate was inhibite) by exogenous oleate. At low concentrations of perfusate FFA, however, endogenous fatty acids contributed substantially to the increased output of TG by livers from female animals. Production of 14CO2 and radioactive ketone bodies increased with increasing uptake of FFA. The partition of oleate between oxidative pathways (CO2 production and ketogenesis) was modified by the availability of the fatty acid substrate with livers from either sex. The percent incorporation of radioactivity into CO2 reached a maximum, whereas incorporation into ketone bodies continued to increase. The output of ketone bodies was dependent on the uptake of FFA, and output by livers from female animals was less than by livers from male rats. The increase in rate of ketogenesis was dependent on the influx of exogenous FFA, while ketogenesis from endogenous sources remained relatively stable. The output of glucose by the liver increased with the uptake of FFA, but no difference due to sex was observed. The output of urea by livers from male rats was unaffected by oleate, while the output of urea by livers from females decreased as the uptake of FFA increased. A major conclusion to be derived from this work is that oleate is not metabolized identically by livers from the two sexes, but rather, per gram of liver, livers from female rats take up and esterify more fatty acid to TG and oxidize less than do livers from male animals; livers from female animals synthesize and secrete more triglyceride than do livers from male animals when provided with equal quantities of free fatty acid.     

Inhibition of free fatty acid mobilization by colchicine

Segments of epididymal adipose tissue from normal male rats were incubated with micromolar concentrations of colchicine for different periods of time up to 4 hr, and the mobilization of free fatty acids (FFA) was measured during a subsequent reincubation. Although pretreatment with colchicine did not alter basal unstimulated FFA release, mobilization of FFA in the presence of epinephrine or theophylline was reduced. However, neither lipolysis, as judged by glycerol production, nor cyclic AMP accumulation was impaired under the same conditions. To assess the possibility that colchicine might limit production of fatty acids by accelerating the entry and metabolism of glucose into adipocytes, the metabolism of glucose by adipose tissue was studied. Pretreatment with colchicine did not affect uptake of glucose nor its oxidation to CO(2), although colchicine-treated tissues did have slightly more [(14)C]glucose incorporated into the glyceride moiety of triglyceride. When adipose tissues pretreated with colchicine were incubated in an albumin-free medium, no reduction in FFA production by colchicine was observed. Because no FFA release occurs in albumin-free media, this experiment suggests that colchicine-induced inhibition of FFA mobilization results from impaired extrusion of FFA from adipose cells.     

Fatty acid kinetics and carbohydrate metabolism during electrical exercise in spinal cord-injured humans

Motor center activity and reflexes from contracting muscle have been shown to be important for mobilization of free fatty acids (FFA) during exercise. We studied FFA metabolism in the absence of these mechanisms: during involuntary, electrically induced leg cycling in individuals with complete spinal cord injury (SCI). Healthy subjects performing voluntary cycling served as controls (C). Ten SCI (level of injury: C5-T7) and six C exercised for 30 min at comparable oxygen uptake rates (approximately 1 l/min), and [1-14C]palmitate was infused continuously to estimate FFA turnover. From femoral arteriovenous differences, blood flow, muscle biopsies, and indirect calorimetry, leg substrate balances as well as concentrations of intramuscular substrates were determined. Leg oxygen uptake was similar in the two groups during exercise. In SCI, but not in C, plasma FFA and FFA appearance rate fell during exercise, and plasma glycerol increased less than in C (P < 0.05). Fractional uptake of FFA across the working legs decreased from rest to exercise in all individuals (P < 0.05) but was always lower in SCI than in C (P < 0.05). From rest to exercise, leg FFA uptake increased less in SCI than in C subjects (14 +/- 3 to 57 +/- 20 vs. 41 +/- 13 to 170 +/- 57 micromol x min(-1) x leg(-1); P < 0.05). Muscle glycogen breakdown, leg glucose uptake, carbohydrate oxidation, and lactate release were higher (P < 0.05) in SCI than in C during exercise. Counterregulatory hormonal changes were more pronounced in SCI vs. C, whereas insulin decreased only in C. In conclusion, FFA mobilization, delivery, and fractional uptake are lower and muscle glycogen breakdown and glucose uptake are higher in SCI patients during electrically induced leg exercise compared with healthy subjects performing voluntary exercise. Apparently, blood-borne mechanisms are not sufficient to elicit a normal increase in fatty acid mobilization during exercise. Furthermore, in exercising muscle, FFA delivery enhances FFA uptake and inhibits carbohydrate metabolism, while carbohydrate metabolism inhibits FFA uptake.     

Metabolism of adipose tissue in the fat tail of the sheep in vivo

The metabolism of the large mass of adipose tissue constituting the fat tail of the Syrian sheep has been investigated by measuring arteriovenous concentration (A-V) differences. The tail in situ in the intact anesthetized animal, as well as the isolated tail perfused with blood through a constant flow pump oxygenator, was used. In fed animals, the adipose tissue took up glucose and ketone bodies and released lactate and free fatty acids (FFA), although in some animals uptake of FFA also occurred. After 48-144 hr of fasting, uptake of glucose and ketone bodies continued and the FFA release increased. Total lipid esters and phospholipids were not released even after food had been withheld for 6 days. Insulin increased the A-V difference and the uptake of glucose, and reduced the FFA release. Adrenaline increased the A-V difference and uptake of glucose; the simultaneous increase in serum FFA was not accompanied by an increase in A-V difference for FFA in most experiments, which suggests that this adipose tissue is relatively insensitive to the lipolytic effect of the hormone. The effect of noradrenaline was similar to that of adrenaline. Glucagon hyperglycemia was not accompanied by increase in glucose uptake in most experiments.     

Myocardial blood flow regulation relative to left ventricle pressure and volume in anesthetized dogs

The influence of left ventricle pressure and volume changes on coronary blood flow was investigated in eight anesthetized dogs. Coronary artery pressure-flow relationships were determined at two levels of left ventricular pressure and volume. The distribution of blood flow within the myocardium was also determined when these relationships varied. Reducing left ventricle pressures and volumes increased heart rate. Rate-pressure product, diastolic coronary pressure, myocardial O2 consumption, total, subendocardial and subepicardial flow decreased. Hematocrit and blood gas data were unchanged. The pressure-flow relationships were shifted leftward (p = 0.001) but the range of autoregulation was not altered. At low left ventricle pressures and volumes, the lower coronary artery pressure limit was shifted leftward (from 75 to 45 mm Hg (1 mm Hg = 133.3 Pa)), while total, subendocardial, and subepicardial blood flow did not change compared with the control. Below the lower coronary artery pressure limit, subendocardial but not subepicardial flow decreased, resulting in maldistribution of flow across the left ventricular wall. When coronary pressure was reset between control and the lower coronary artery pressure limit, subendocardial flow was restored. These results show that the lower coronary artery pressure limit can be shifted leftward while the distribution of blood flow across the left ventricular wall is preserved.     

Effect of glucose on the utilization of palmitate 1 14C by rat kidney cortex slices.

The authors studied the effect of glucose on the uptake and utilization of palmitate 1 14C by rat kidney cortex slices. They found that its inhibitory effect on free fatty acid (FFA) uptake was caused by inhibition of the incorporation of 1 14C-labelled palmitate into the total lipids and FFA and by reduced oxidation to 14CO2. Glucose has a regulative function in the utilization of FFA by the kidneys.     

Effect of glucose utilization inhibitor isolated from the serum and urine of patients with chronic renal failure on the free fatty acid metabolism in rat kidney cortex slices.

The authors studied interference by the inhibitor of glucose utilization with free fatty acid (FFA) metabolism in rat kidney cortex slices. They found that FFA uptake by the kidneys, their incorporation into triglycerides (TG) and oxidation to 14CO2 were lower when the inhibitor was present in the incubation medium. The findings show that the inhibitor, as well as inhibiting glucose utilization in various tissues, interferes directly with fat metabolism.     

The Exocyst Complex Regulates Free Fatty Acid Uptake by Adipocytes

The exocyst is an octameric molecular complex that drives vesicle trafficking in adipocytes, a rate-limiting step in insulin-dependent glucose uptake. This study assessed the role of the exocyst complex in regulating free fatty acid (FFA) uptake by adipocytes. Upon differentiating into adipocytes, 3T3-L1 cells acquire the ability to incorporate extracellular FFAs in an insulin-dependent manner. A kinetic assay using fluoresceinated FFA (C12 dodecanoic acid) uptake allows the real-time monitoring of FFA internalization by adipocytes. The insulin-dependent uptake of C12 dodecanoic acid by 3T3-L1 adipocytes is mediated by Akt and phosphatidylinositol 3 (PI3)-kinase. Gene silencing of the exocyst components Exo70 and Sec8 significantly reduced insulin-dependent FFA uptake by adipocytes. Consistent with the roles played by Exo70 and Sec8 in FFA uptake, mCherry-tagged Exo70 and HA-tagged Sec8 partially colocalize with lipid droplets within adipocytes, suggesting their active roles in the development of lipid droplets. Tubulin polymerization was also found to regulate FFA uptake in collaboration with the exocyst complex. This study demonstrates a novel role played by the exocyst complex in the regulation of FFA uptake by adipocytes.