Unloaded heart in vivo replicates fetal gene expression of cardiac hypertrophy.

The cardiac response to increased work includes a reactivation of fetal genes. The response to a decrease in cardiac work is not known. Such information is of clinical interest, because mechanical unloading can improve the functional capacity of the failing heart. We compared here the patterns of gene expression in unloaded rat heart with those in hypertrophied rat heart. Both conditions induced a re-expression of growth factors and proto-oncogenes, and a downregulation of the 'adult' isoforms, but not of the 'fetal' isoforms, of proteins regulating myocardial energetics. Therefore, opposite changes in cardiac workload in vivo induce similar patterns of gene response. Reactivation of fetal genes may underlie the functional improvement of an unloaded failing heart.

Changes in citric acid cycle flux and anaplerosis antedate the functional decline in isolated rat hearts utilizing acetoacetate.

To determine the temporal relationship between changes in contractile performance and flux through the citric acid cycle in hearts oxidizing acetoacetate, we perfused isolated working rat hearts with either glucose or acetoacetate (both 5 mM) and freeze-clamped the tissue at defined times. After 60 min of perfusion, hearts utilizing acetoacetate exhibited lower systolic and diastolic pressures and lower cardiac outputs. The oxidation of acetoacetate increased the tissue content of 2-oxoglutarate and glutamate and decreased the content of succinyl-CoA suggesting inhibition of citric acid cycle flux through 2-oxoglutarate dehydrogenase. Whereas hearts perfused with either acetoacetate or glucose were similar with respect to their function for the first 20 min, changes in tissue metabolites were already observed within 5 min of perfusion at near-physiological workloads. The addition of lactate or propionate, but not acetate, to hearts oxidizing acetoacetate improved contractile performance, although inhibition of 2-oxoglutarate dehydrogenase was probably not diminished. If lactate or propionate were added, malate and citrate accumulated indicating utilization of anaplerotic pathways for the citric acid cycle. We conclude that a decreased rate of flux through 2-oxoglutarate dehydrogenase in hearts oxidizing acetoacetate precedes, and may be responsible for, contractile failure and is not the result of decreased cardiac work. Further, anaplerosis play an important role in the maintenance of contractile function in hearts utilizing acetoacetate.

Coenzyme A sequestration in rat hearts oxidizing ketone bodies.

Previous studies have indicated that ketone body-mediated contractile failure in rat hearts is due to inhibition of 2-oxoglutarate dehydrogenase, and it has been speculated that this inhibition is due to the sequestration of intramitochondrial CoA as acetoacetyl-CoA and acetyl-CoA. These studies were performed to determine whether oxidation of acetoacetate by isolated rat heart mitochondria results in a fall in intramitochondrial nonesterified CoA [CoASH] and whether increasing the available CoA improves contractile performance in hearts oxidizing acetoacetate. The oxidation of acetoacetate by isolated rat heart mitochondria resulted in depressed state 3 respiration as well as in a decrease in [CoASH]. Increasing the tissue content of CoASH in perfused hearts by providing the precursors for CoA relieved inhibition of 2-oxoglutarate dehydrogenase and improved the contractile performance of isolated working hearts. In contrast, the addition of carnitine increased the tissue content of CoASH but did not improve function. These findings suggest the presence of two different pools of CoASH. We conclude that ketone body-mediated inhibition of 2-oxoglutarate dehydrogenase is due to decreased intramitochondrial CoASH and that this inhibition of the citric acid cycle is a plausible mechanism for concomitant contractile failure.

Preferential oxidation of glycogen in isolated working rat heart.

We tested the hypothesis that glycogen is preferentially oxidized in isolated working rat heart. This was accomplished by measuring the proportion of glycolytic flux (oxidation plus lactate production) specifically from glycogen which is metabolized to lactate, and comparing it to the same proportion determined concurrently from exogenous glucose during stimulation with epinephrine. After prelabeling of glycogen with either 14C or 3H, a dual isotope technique was used to simultaneously trace the disposition of glycogen and exogenous glucose between oxidative and non-oxidative pathways. Immediately after the addition of epinephrine (1 microM), 40-50% of flux from glucose was directed towards lactate. Glycogen, however, did not contribute to lactate, being almost entirely oxidized. Further, glycogen utilization responded promptly to the abrupt increase in contractile performance with epinephrine, during the lag in stimulation of utilization of exogenous glucose, suggesting that glycogen serves as substrate reservoir to buffer rapid increases in demand. Preferential oxidation of glycogen may serve to ensure efficient generation of ATP from a limited supply of endogenous substrate, or as a mechanism to limit lactate accumulation during rapid glycogenolysis.

Compartmentation of hexokinase in rat heart. A critical factor for tracer kinetic analysis of myocardial glucose metabolism.

Radiolabeled analogues of 2-deoxyglucose are widely used to trace glucose metabolism in cell cultures, whole organs, and intact animals, although kinetic differences in transport and phosphorylation between these compounds and glucose exist. The present studies were undertaken to determine the effects of insulin stimulation on the phosphorylation of 2-deoxyglucose compared to glucose in the intact, saline-perfused working rat heart. Rates of glucose utilization determined from tritiated glucose differed from rates estimated from the accumulation of [14C]2-deoxyglucose in a nonconstant manner when comparing rates in the absence or presence of physiologic levels of insulin (13 microU/ml). The fraction of monophosphorylated hexoses that was accounted for by [14C]2-deoxyglucose 6-phosphate was dramatically decreased in hearts perfused in the presence of insulin. Additionally, hexokinase activity associated with the mitochondrial fraction of tissue extracts was increased in hearts stimulated by insulin. While this redistribution of hexokinase to the mitochondria did not affect the apparent affinity constant for glucose, hexokinase bound to mitochondria exhibited an 8.5-fold decrease in the affinity for 2-deoxyglucose when compared with hexokinase present in the cytosolic fraction. The findings are consistent with an insulin-mediated preferential uptake and phosphorylation of glucose compared to deoxyglucose. The results also imply that the redistribution of hexokinase and the differential effect of insulin on its affinity for tracer and tracee are responsible for changes in the "lumped constant" (i.e., the correction factor used to equate 2-deoxyglucose to glucose uptake). These changes must be taken into account when regional myocardial glucose metabolism is assessed by the 2-deoxyglucose method.

Alterations of myocardial amino acid metabolism in chronic ischemic heart disease.

Arteriovenous differences (A-V) of all naturally occurring amino acids, lactate, and oxygen were measured simultaneously with coronary sinus blood flow (CSBF) in 8 normal subjects and 11 patients with coronary artery disease at rest and during pacing stress. Mean values for CSBF and myocardial oxygen consumptions (MVO2) for the two groups were similar at rest and during pacing, although mean CSBF and MVO2 increased significantly in both groups in the paced as compared to the rest state. Alanine (ala) was the only amino acid released by the myocardium, while only glutamic acid(glu) demonstrated uptake. Mean A-V ala was negative at rest in the control and coronary disease groups (-4.8+/-3.8 vs. -22.0+/-3.0 nmol/ml, respectively), but was significantly more negative in the coronary group (P less than 0.001) and not statistically different than zero in the normals. A-V ala became significantly negative with pacing in the normals (-10.0+/-4.3 nmol/ml), remained unchanged in the coronary group (-23.0+/-2.9 nmol/ml), and was significantly more negative in the coronary group (P less than 0.05). Calculation of data on the basis of net ala flux ([A-V] X [CSBF X hematocrit]) yielded similar results as that obtained with A-V differences. A-V glu was significantly positive in normals (27.7 +/- 8.9 nmol/ml, P less than 0.01) and coronary patients (59.9 +/- 8.9 nmol/ml, P less than 0.01) at rest but significantly greater in the latter group (P less than 0.001). With pacing, A-V glu remained significantly greater than zero in coronary patients (35.3 +/- 6.3 nmol/ml) and decreased to zero in the normals (4.3 +/- 11.8 nmol/ml). Calculation of net glu flux (nmol/min) at rest yielded data similar to that based on A-V difference. With pacing, net glu flux in the coronary patients did not decrease due to the augmentation of CSBF. No relation between A-V glu or ala and CSBF, MVO2 or A-V lactate was noted. The data demonstrate that specific alterations of myocardial amino acid metabolism characterize patients with chronic ischemic heart disease.

Regulation of exogenous and endogenous glucose metabolism by insulin and acetoacetate in the isolated working rat heart. A three tracer study of glycolysis, glycogen metabolism, and glucose oxidation.

Myocardial glucose use is regulated by competing substrates and hormonal influences. However, the interactions of these effectors on the metabolism of exogenous glucose and glucose derived from endogenous glycogen are not completely understood. In order to determine changes in exogenous glucose uptake, glucose oxidation, and glycogen enrichment, hearts were perfused with glucose (5 mM) either alone, or glucose plus insulin (40 microU/ml), glucose plus acetoacetate (5 mM), or glucose plus insulin and acetoacetate, using a three tracer (3H, 14C, and 13C) technique. Insulin-stimulated glucose uptake and lactate production in the absence of acetoacetate, while acetoacetate inhibited the uptake of glucose and the oxidation of both exogenous glucose and endogenous carbohydrate. Depending on the metabolic conditions, the contribution of glycogen to carbohydrate metabolism varied from 20-60%. The addition of acetoacetate or insulin increased the incorporation of exogenous glucose into glycogen twofold, and the combination of the two had additive effects on the incorporation of glucose into glycogen. In contrast, the glycogen content was similar for the three groups. The increased incorporation of glucose in glycogen without a significant change in the glycogen content in hearts perfused with glucose, acetoacetate, and insulin suggests increased glycogen turnover. We conclude that insulin and acetoacetate regulate the incorporation of glucose into glycogen as well as the relative contributions of exogenous glucose and endogenous carbohydrate to myocardial energy metabolism by different mechanisms.

Clock genes in the heart: characterization and attenuation with hypertrophy.

We investigated whether the heart, like other mammalian organs, possesses internal clocks, and, if so, whether pressure overload-induced hypertrophy alters the clock mechanism. Clock genes are intrinsically maintained, as shown by rhythmic changes even in single cells. Clocks are believed to confer a selective advantage by priming the cell for the expected environmental stimulus. In this way, clocks allow anticipation, thereby synchronizing responsiveness of the cell with the timing of the stimulus. We have found that in rat heart all mammalian homologues of known Drosophila clock genes (bmal1, clock, cry1, cry2, per1, per2, per3, dbp, hlf, and tef) show circadian patterns of expression and that the induction of clock output genes (the PAR [rich in proline and acidic amino acid residues] transcription factors dbp, hlf, and tef) is attenuated in the pressure-overloaded hypertrophied heart. The results expose a new dynamic regulatory system in the heart, which is partially lost with hypertrophy. Although the target genes of these PAR transcription factors are not known in the heart, the results provide evidence for a diminished ability of the hypertrophied heart to anticipate and subsequently adapt to physiological alterations during the day.

Intrinsic diurnal variations in cardiac metabolism and contractile function.

Diurnal variation of cardiac function in vivo has been attributed primarily to changes in factors such as sympathetic activity. No study has investigated previously the intrinsic properties of the heart throughout the day. We therefore investigated diurnal variations in metabolic flux and contractile function of the isolated working rat heart and how this related to circadian expression of metabolic genes. Contractile performance, carbohydrate oxidation, and oxygen consumption were greatest in the middle of the night, with little variation in fatty acid oxidation. The expression of all metabolic genes investigated (including regulators of carbohydrate utilization, fatty acid oxidation, and mitochondrial function) showed diurnal variation, with a general peak in the night. In contrast, pressure overload-induced cardiac hypertrophy completely abolished this diurnal variation of metabolic gene expression. Thus, over the course of the day, the normal heart anticipates, responds, and adapts to physiological alterations within its environment, a trait that is lost by the hypertrophied heart. We speculate that loss of plasticity of the hypertrophied heart may play a role in the subsequent development of contractile dysfunction.

Reversal of intramyocellular lipid accumulation by lipophagy and a p62-mediated pathway.

We have previously observed the reversal of lipid droplet deposition in skeletal muscle of morbidly obese patients following bariatric surgery. We now investigated whether activation of autophagy is the mechanism underlying this observation. For this purpose, we incubated rat L6 myocytes over a period of 6 days with long-chain fatty acids (an equimolar, 1.0 mM, mixture of oleate and palmitate in the incubation medium). At day 6, the autophagic inhibitor (bafilomycin A1, 200 nM) and the autophagic activator (rapamycin, 1 µM) were added separately or in combination for 48 h. Intracellular triglyceride (TG) accumulation was visualized and quantified colorimetrically. Protein markers of autophagic flux (LC3 and p62) and cell death (caspase-3 cleavage) were measured by immunoblotting. Inhibition of autophagy by bafilomycin increased TG accumulation and also increased lipid-mediated cell death. Conversely, activation of autophagy by rapamycin reduced both intracellular lipid accumulation and cell death. Unexpectedly, treatment with both drugs added simultaneously resulted in decreased lipid accumulation. In this treatment group, immunoblotting revealed p62 degradation (autophagic flux), immunofluorescence revealed the colocalization of p62 with lipid droplets, and co-immunoprecipitation confirmed the interaction of p62 with ADRP (adipose differentiation-related protein), a lipid droplet membrane protein. Thus the association of p62 with lipid droplet turnover suggests a novel pathway for the breakdown of lipid droplets in muscle cells. In addition, treatment with rapamycin and bafilomycin together also suggested the export of TG into the extracellular space. We conclude that lipophagy promotes the clearance of lipids from myocytes and switches to an alternative, p62-mediated, lysosomal-independent pathway in the context of chronic lipid overload (*P<0.05, **P<0.01, ***P<0.001, ****P<0.0001).

Metabolic gene expression in fetal and failing human heart.

BACKGROUND: Previous studies suggest that the failing heart reactivates fetal genes and reverts to a fetal pattern of energy substrate metabolism. We tested this hypothesis by examining metabolic gene expression profiles in the fetal, nonfailing, and failing human heart. METHODS AND RESULTS: Human left ventricular tissue (apex) was obtained from 9 fetal, 10 nonfailing, and 10 failing adult hearts. Using quantitative reverse transcription-polymerase chain reaction, we measured transcript levels of atrial natriuretic factor, myosin heavy chain-alpha and -beta, and 13 key regulators of energy substrate metabolism, of which 3 are considered "adult" isoforms (GLUT4, mGS, mCPT-I) and 3 are considered "fetal" isoforms (GLUT1, lGS, and lCPT-I), primarily through previous studies in rodent models. Compared with the nonfailing adult heart, steady-state mRNA levels of atrial natriuretic factor were increased in both the fetal and the failing heart. The 2 myosin heavy chain isoforms showed the highest expression level in the nonfailing heart. Transcript levels of most of the metabolic genes were higher in the nonfailing heart than the fetal heart. Adult isogenes predominated in all groups and always showed a greater induction than the fetal isogenes in the nonfailing heart compared with the fetal heart. In the failing heart, the expression of metabolic genes decreased to the same levels as in the fetal heart. CONCLUSIONS: In the human heart, metabolic genes exist as constitutive and inducible forms. The failing adult heart reverts to a fetal metabolic gene profile by downregulating adult gene transcripts rather than by upregulating fetal genes.

Energy metabolism in reperfused heart muscle: metabolic correlates to return of function.

An important question in energy metabolism of the reperfused, previously ischemic myocardium is whether the return of a normal tissue adenosine triphosphate (ATP) content is a prerequisite for normal rates of oxygen consumption (that is, ATP turnover) and cardiac function. To study this problem, isolated working rat hearts were perfused with bicarbonate saline solution containing glucose (10 mM) at near physiologic work load. After 20 minutes, hearts were made totally ischemic by clamping the aortic and atrial lines for 5, 10 or 20 minutes and then were reperfused for another 10 minutes. Heart rate, aortic pressure, cardiac output and myocardial oxygen consumption were measured continuously. Adenine nucleotides, phosphocreatine, glycogen and the products of glycolysis were determined in freeze-clamped tissue extracts. Functional recovery was assessed by return of aortic pressure and oxygen consumption to preischemic values. Time required for return of function after reperfusion was 90 seconds after 5 minutes and 124 seconds after 10 minutes of ischemia. No recovery was observed after 20 minutes of ischemia. Tissue ATP content decreased significantly at the end of 5 (-38%) and 10 (-56%) minutes of ischemia and did not increase significantly at return of aortic pressure and oxygen consumption to preischemic values. Glycogen stores decreased by more than 50% at the end of 10 minutes of ischemia and did not normalize on recovery. In contrast to ATP or glycogen, the phosphocreatine content decreased to even lower levels at the end of ischemia, but returned to levels higher than the control level after recovery from 5 to 10 minutes of ischemia in association with return of function.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of technetium-99m teboroxime tomography with automated quantitative coronary arteriography and thallium-201 tomographic imaging.

Technetium-99m (Tc-99m) teboroxime is a new perfusion tracer that is highly extracted and rapidly cleared by the myocardium. To determine the feasibility of Tc-99m teboroxime imaging in the diagnosis of patients with suspected coronary artery disease, 30 patients underwent single photon emission computed tomography imaging with Tc-99m teboroxime (25.2 +/- 1 mCi) at peak exercise and again 60 min later at rest. All patients underwent either a thallium stress test (n = 26) or automated quantitative coronary arteriography (n = 25), or both, without intervening revascularization or infarction. Images were reviewed by two investigators who had no knowledge of clinical data. Coronary lesions with greater than or equal to 50% diameter narrowing by quantitative coronary arteriography were considered significant. Both thallium and Tc-99m teboroxime detected disease in all patients with two or three vessel disease. One vessel disease was detected with Tc-99m teboroxime in 9 of 10 patients and with thallium in 8 of 10 (p = NS). In patients without angiographically significant disease. Tc-99m teboroxime demonstrated normal perfusion in six of eight patients and thallium in three of five (p = NS). Overall, when presence or absence of disease detected by Tc-99m teboroxime or thallium was compared with quantitative coronary arteriography, there was no difference between Tc-99m teboroxime and thallium. These results suggest that Tc-99m teboroxime is comparable to thallium as an imaging agent. The rapid biologic half-life, 5.3 min, allows studies to be completed in 60 to 90 min.

Metabolic aspects of programmed cell survival and cell death in the heart.

Normal cardiac function requires a tight interaction between metabolism, contractile function and gene expression. The main perturbation challenging this equilibrium in vivo is ischemia, which alters energy flux through the control of key enzymes. The review highlights metabolic imprints and energetic aspects of programmed cell survival, programmed cell death, and of necrosis. When sustained and severe, ischemia leads to a total collapse of energy transfer, to the accumulation of metabolic endproducts, and to the development of myocardial necrosis. When moderate, ischemia results in a coordinated cellular response including enhanced anaerobic glucose metabolism, a modification of cardiac gene expression, and the development of specific mechanisms for programmed cell survival (preconditioning, stunning, hibernation). Repetitive stress results in a decrease of contractile function, a downregulation of gene expression and an impairment of energy transfer, which eventually cause the heart to fail. When the failing heart becomes energy-depleted, the programs of cell survival are no longer operational and programmed cell death ensues. To define the point of departure from programmed cell survival to cell death remains a major challenge.

Mitochondrial metabolism and substrate competition in the aging Fischer rat heart.

OBJECTIVE: The objective was to examine mitochondrial oxidative metabolism of long chain fatty acids and to compare it with glucose uptake and the generation of pressure-volume work in hearts from mature and aged rats. METHODS: Hearts from mature (8 to 15 months of age) and old (28 to 30 months) Fischer 344 rats were perfused as working hearts with either 10 mM glucose or glucose plus 1 mM oleic acid (2% bovine serum albumin) and rates of glucose extraction were determined. Hearts were subjected to a stepwise increase in work load. In separate experiments, mitochondria were isolated from mature and old rat hearts and assayed for respiratory function, carnitine exchange, carnitine palmitoyltransferase activities, and phospholipid content. RESULTS: Although there were no differences in peak work attained between the mature and old rats in the presence of either glucose alone or glucose plus oleic acid, glucose utilisation was significantly decreased by oleate in the mature animals only. No significant changes in either glutamate or succinate (+rotenone) supported respiration were found in heart mitochondria isolated from old rats compared with mature animals. In agreement with prior studies with the Wistar rat model of aging, significant decrements in the rates of palmitoylcarnitine oxidation and carnitine exchange were apparent in the old Fischer animals. A significant lowering of heart mitochondrial carnitine palmitoyltransferase I activity was also found in the old animals. A decrease in the amounts of carnitine loaded in mitochondria from old animals is consistent with reduced carnitine content in both mitochondria and whole hearts from aged Wistar and Fischer rats. A significant (23%) reduction in heart mitochondrial cardiolipin content from 30 month old Fischer rats suggests that this phospholipid may also contribute to the lower rates of carnitine and acylcarnitine transport across the mitochondrial inner membrane. CONCLUSION: The limitation in the delivery of fatty acyl units to beta oxidation as measured in isolated heart mitochondria from old rats has a physiological correlate in the intact heart. The well documented suppression of glucose oxidation by fatty acids seen in the adult rat heart is not seen in old hearts, supporting the in vitro finding of decreased oxidation of palmitoylcarnitine with senescence.

Effects of moderate hypertension on cardiac function and metabolism in the rabbit.

To study the early effects of hypertension on the heart, we examined isolated hearts from rabbits with slowly developing hypertension of up to 64 weeks in duration after unilateral nephrectomy and renal artery stenosis. Normotensive animals kept under identical conditions served as controls. Mean arterial blood pressure rose from 83 to 155 mm Hg in the hypertensive group of longest duration, but the ratio of left ventricular weight to body weight was not different between the experimental and control groups. Although left ventricular hypertrophy was not present, left ventricular peak systolic pressure of perfused hearts was significantly higher in hypertensive than in normotensive hearts. Furthermore, while in hypertensive hearts the left ventricular end-diastolic volume was increased, the peak systolic pressure did not respond to an increase in left ventricular end-diastolic volume. Functional changes were accompanied by metabolic changes in the left ventricle. Rates of glucose utilization were increased and rates of ketone body utilization were decreased in hypertensive hearts. Activities of key enzymes of carbohydrate metabolism (phosphorylase, hexokinase, phosphofructokinase, and lactate dehydrogenase) were increased, while those of ketone body metabolism (3-oxoacid-CoA transferase, acetoacetyl-CoA synthase) were decreased and those of the citric acid cycle (citrate synthase, 2-oxoglutarate dehydrogenase) were not different between groups. In summary, moderate hypertension for a period of more than 1 year resulted in functional and metabolic changes of the left ventricle in hypertensive animals that were already manifest at 8 weeks of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertension and atherosclerosis in cholesterol-fed rabbits. Part 1. Mild, two-kidney, one-clip Goldblatt hypertension treated with enalapril.

Ten groups of New Zealand white rabbits were used to study the effects of mild, chronic two-kidney, one-clip hypertension (HT) and long-term antihypertensive therapy on atherogenesis. Five groups were fed a normal diet (ND) over the 8-month study period; 2 groups, one of which was given enalapril, remained normotensive (NT) throughout the study. Of the 3 HT groups, one was hypertensive for 7 months; the blood pressures of the other groups were normalized after 2 months with enalapril, or by removal of the clipped kidney. The other 5 groups were similar except that they were fed at 0.1% cholesterol diet (CD). The results showed that: neither mild chronic HT nor abrupt, short-term HT exacerbated atherogenesis in the CD-animals; although fibromuscular vascular lesions were present in the aorta of normal-diet, HT animals no atheroma was observed; enalapril therapy had no effect on atherogenesis; enalapril therapy reduced the total weight and the cholesterol and triglyceride content of the aorta of the ND groups regardless of blood pressure history; the aortic triglyceride content, but not the cholesterol content, of the CD group, was reduced by enalapril; and although heart size was unaffected by either diet or blood pressure levels, the mitochondria volume per unit volume of the left ventricle was reduced in both NT-ND and HT-CD groups treated with enalapril.

Hypertension and atherosclerosis in cholesterol-fed rabbits. II. One-kidney, one clip Goldblatt hypertension treated with nifedipine.

Eight groups of New Zealand white rabbits were used to study the effects of moderate chronic one-kidney, one clip hypertension (HT) and long-term nifedipine therapy on atherogenesis. Four groups were fed a normal diet (ND) over an 8-month study period; two groups, one of which was given nifedipine, remained normotensive (NT) throughout the study. Of the two HT groups, one remained hypertensive for 7 months; the blood pressure of the other group was normalized after 2 months with nifedipine. The other four groups of animals were similarly constructed except that they were fed a 0.1% cholesterol diet (CD). The results showed that: although scattered fibromuscular vascular lesions were present in the aortas of normal-diet, HT animals no atheroma was observed; neither moderate chronic HT nor abrupt, short-term HT exacerbated atherogenesis in the CD-animals; nifedipine therapy had no suppressive effect on either fibromuscular lesions or atherogenesis; nifedipine therapy reduced the aorta weight of the normotensive ND and CD groups; the aortic triglyceride content of both dietary groups was reduced by nifedipine; cholesterol content was unaffected; left ventricular hypertrophy was evident only in HT-untreated groups; and only the weight of the left ventricle of the ND-NT-treated group was significantly reduced, but the mitochondria volume per unit volume of left ventricle myocardial cells was reduced only in the NT-CD group treated with nifedipine. It is concluded that an antihypertensive dosage of nifedipine administered to animals with atherosclerosis does not suppress subsequent atherogenesis.

Kinetic differences and similarities among 3 tracers of myocardial glucose uptake.

UNLABELLED: Two glucose tracer analogs, uniformly labeled [14C]2-deoxyglucose ([U-14C]2DG) and FDG, are widely used to assess myocardial glucose uptake. Despite the similar electron configuration of the fluorine and hydrogen atoms, uptake of the 2 tracer analogs may not be the same because of their different electronegativity. METHODS: To test this hypothesis, we determined glucose uptake in isolated rat hearts simultaneously from the accumulation of [U-14C]2DG radioactivity in the tissue, by continuous monitoring of FDG accumulation with a pair of coincidence detectors and by cumulative release of 3HOH from [2-3H]glucose. A first group of hearts was perfused at physiologic workload with Krebs-Henseleit buffer containing 10 mmol/L glucose; a second group, with the buffer containing 5 mmol/L glucose plus 0.4 mmol/L oleate and 1 mU/mL insulin. Third and fourth groups were subjected to ischemia (i.e., a 75% reduction in coronary flow) and reperfused. For the third group, the buffer contained 5 mmol/L glucose; for the fourth, 5 mmol/L glucose plus 0.4 mmol/L oleate. RESULTS: No difference in the total amount of tracer accumulation in any group was seen between the 2 tracer analogs. The ratio [+/-SD] of [U-14C]2DG to FDG ranged from 0.93+/-0.09 to 1.31+/-0.11. However, both tracer analogs paralleled glucose uptake in the absence of insulin but underestimated glucose uptake significantly in the presence of insulin. Changes in 2DG uptake with ischemia and reperfusion could be detected only with FDG. CONCLUSION: Although uptake of [U-14C]2DG equals uptake of FDG quantitatively, acute changes in 2DG uptake (and, thus, in the tracer-tracee relationship) are detectable only with the fluorine-labeled tracer.

Time course of skeletal muscle glucose uptake during euglycemic hyperinsulinemia in the anesthetized rabbit: a fluorine-18-2-deoxy-2-fluoro-D-glucose study.

Since skeletal muscle has been implicated as the major site of insulin resistance, the purpose of this study was to examine in detail the time course of muscle glucose uptake during the onset and maintenance of euglycemic hyperinsulinemia. Uptake of 18F-2-deoxy-2-fluoro-D-glucose (FDG) by the thigh muscle of an anesthetized rabbit was monitored by a single pair of coincidence photon detectors. Graphical analysis of tissue and plasma radioactivity concentrations was performed to derive fractional rates of FDG phosphorylation continuously. FDG phosphorylation rates were determined during rest (glucose 7 mM, insulin 5-10 microU/ml) and subsequent 5-min intervals under conditions of euglycemic hyperinsulinemia (glucose 6-8 mM; insulin 350-400 microU/ml plasma). FDG phosphorylation did not increase above resting control levels until 5.5 +/- 1.5 min after intravenous insulin administration. After 20-30 min of hyperinsulinemia, FDG phosphorylation and calculated glucose metabolic rates were increased by 50%. At 35-40 min of the clamp in place, there was a second increase in tracer phosphorylation which plateaued at 200% of control (p less than 0.01) and remained at this level for the remainder of the experiment. In conclusion, we have described a method for making rapid, serial estimates of insulin-mediated skeletal muscle glucose uptake. We suggest that appraisal of the time course of glucose uptake with FDG will aid in the understanding of normal and pathophysiologic states of insulin action in vivo.