The effect of insulin on pyruvate dehydrogenase interconversion in heart muscle of alloxan-diabetic rats

Analysis of pyruvate dehydrogenase expression in embryonic mouse brain: localization and developmental regulation

Brain malformations and neurological dysfunctions are often seen in pyruvate dehydrogenase (PDH) deficient patients. To understand these clinical presentations, we have analyzed the localization and developmental expression of PDH in the embryonic mouse nervous system. Immunostaining was performed to localize PDH E1 alpha protein. PDH activities were measured before and after activation. PDH E1 alpha mRNA levels were quantitated by reverse transcriptase-polymerase chain reaction. Abundant PDH E1 alpha protein was localized in the central nervous system and other neural tissues in embryos at embryonic day (E) 11 onwards. The PDH activity was very low in E9 brain and it increased continuously until the end of gestation. The proportion of active form of PDH increased significantly in E15 brain. Analysis of the PDH E1 alpha mRNA showed that only the X-linked form of the gene was transcribed. The overall mRNA level of E9 brain was approximately 93% of the adult value. It decreased gradually during embryogenesis. A large increase took place at the end of gestation. The mRNA level of PDH was approximately 100 times higher than that of the acetoacetyl-CoA thiolase gene. These results suggest that PDH E1 alpha transcripts of E9 brain are not translated at a high level. The appearance of PDH activity and its increase during E11 and E15 are mainly due to increased levels of translation and activation of PDH. Increased PDH activity at the end of gestation is attributed to an increase in transcription. Our data to a large extent explain pathological presentations in PDH E1 alpha deficient patients with congenital brain disorders.

Ex vivo effect of insulin on normal and diabetic rat hearts hypoperfused with norepinephrine

The effect of ex vivo insulin on contractile and energy metabolism dysfunctions was examined during hypoperfusion (0.6 ml/min per g heart weight) with 10(-6) M norepinephrine in isolated non-diabetic and streptozotocin-diabetic rats hearts. Insulin (2 mU/min per g heart weight) was infused for 15 min before as well as during 60-min hypoperfusion. Insulin significantly reduced the elevated diastolic tension in diabetic hearts (from 3.8 to 0.7 delta g), but not in non-diabetic hearts (from 1.4 to 1.2 delta g). Insulin partly improved the ATP decrease in the subendocardium of the left ventricle of the diabetic hearts (from 3.5 to 10.2 mumol/g dry weight) but did not affect non-diabetic hearts (from 6.9 to 6.8 mumol/g dry weight). Insulin also partly improved the creatine phosphate decrease and the inorganic phosphate increase in diabetic hearts only. Lactate accumulation was greater in non-diabetic than in diabetic hearts, even in the presence of insulin (77 vs. 45 mumol/g dry weight). The results indicate that acute intracoronary application of insulin in diabetic hearts improves hypoperfusion with norepinephrine injury to a level above that of non-diabetic hearts, but does not improve a less severe injury in non-diabetic hearts.

Biochemical abnormalities in the heart of rats fed a sucrose-rich diet: is the low activity of the pyruvate dehydrogenase complex a result of increased fatty acid oxidation?

We have previously shown that normal Wistar rats fed for 3 weeks with an isocaloric sucrose-rich (63%) diet (SRD) develop high levels of plasma free fatty acids and increased triacylglycerol content in the myocardium. We are now reporting that these changes are accompanied by remarkably low levels of the active form of the pyruvate dehydrogenase complex (PDHa; mean +/- SEM, 37.2% +/- 3.7% of the total activity) when compared with levels found in hearts donated by control rats fed the standard chow diet (STD; 71.0% +/- 2.8%; P less than .01). Increased concentrations of both long-chain acyl-CoA (0.21 +/- 0.03 v 0.06 +/- 0.01 mumol.g dry weight-1 found in STD; P less than .01) and acetyl-CoA (0.17 +/- 0.05 v 0.09 +/- 0.01 found in STD; P less than .01), as well as a relative decrease in coenzyme A (CoASH) (0.21 +/- 0.02 v 0.32 +/- 0.05 from STD; P = NS), resulting in an increased acetyl-CoA/CoASH ratio (0.80 +/- 0.13 v 0.29 +/- 0.03 in STD; P less than .01) may have stimulated the PDH kinase, leading in turn to an inactivation of the PDH complex. The above enzymatic and metabolic changes in the in situ heart of SRD-fed rats were still present after perfusing them for 35 minutes with a Krebs-Henseleit buffer containing 11 mmol/L glucose as the only exogenous substrate.(ABSTRACT TRUNCATED AT 250 WORDS)

Improvement of hypoperfusion with norepinephrine injury by ex vivo insulin in isolated diabetic rat hearts

Effects of insulin on contractile and energy metabolic dysfunctions during hypoperfusion (2 ml/min/g heart wt., 60 min) with 10(-6) M norepinephrine were studied in paced hearts isolated from streptozotocin-diabetic rats. Insulin (2 mU/min/g heart wt.) was infused 20 min before and during hypoperfusion (pre-treated group) or 30 min after the onset of hypoperfusion (post-treated group). Hearts in the non-treated group were hypoperfused without insulin and other hearts in the control group were not hypoperfused. In the non-treated group, resting contractile force (CF) and resting left ventricular pressure (LVP) were significantly elevated to maximum levels within 30 min after hypoperfusion and these elevations were restored in the pre-treated group but not in the post-treated group. Developed CF was depressed in the non-treated group and improved significantly in the pretreated group but not in the post-treated group. Developed LVP was depressed in the non-treated group, and depression was slightly larger in the pre-treated group. In the non-treated group, ATP and creatine phosphate contents in the left ventricle significantly decreased. Decreases in ATP and creatine phosphate contents in the inner layer were partially restored in the pre-treated group but not in the post-treated group. Lactate significantly increased in the non-treated group and increased even further in the insulin treated groups. These results indicate that contractile dysfunction during hypoperfusion with norepinephrine is improved by pre-treated insulin, as is partial recovery of energy metabolism.

Influence of insulin and glucose on pyruvate catabolism in perfused rat hindlimbs

The effects of insulin and glucose on the oxidative decarboxylation of pyruvate in isolated rat hindlimbs was studied in non-recirculating perfusion with [1-14C]pyruvate. Insulin increased the calculated pyruvate decarboxylation rate in a concentration-dependent manner. At supramaximal insulin concentrations, the calculated pyruvate decarboxylation rate was increased by about 40% in perfusions with 0.15-1.5 mM-pyruvate. Glucose up to 20 mM had no effect. In the presence of insulin and low physiological pyruvate concentrations (0.15 mM), glucose increased the calculated pyruvate oxidation. This effect was abolished by high concentrations of pyruvate (1 mM). The data provide evidence that in resting perfused rat skeletal muscle insulin primarily increased the activity of the pyruvate dehydrogenase complex. The effect of glucose was due to increased intracellular pyruvate supply.

Parallel stimulation by Ca2+ of inotropism and pyruvate dehydrogenase in perfused heart

The effects of extracellular Ca2+ (0.375-3.75 mM) on pyruvate oxidation and active form of the pyruvate dehydrogenase complex (PDCa) were quantitated in perfused guinea pig hearts in relation to inotropism, hydraulic work performance, and myocardial oxygen uptake (MVO2). The effects of afterload and norepinephrine (NE), alone or combined with the Ca2+ channel blocker D 600, were also examined. Hearts utilized 1-5 mM pyruvate in presence of 5 mM DL-3-hydroxybutyrate as substrates. Pyruvate oxidation and MVO2 increased essentially in parallel regardless of whether inotropism and energy metabolism were stimulated by increasing the Ca2+ concentration [( Ca2+]), the NE concentration [( NE]), or the afterload. PDCa activity was also directly related to [Ca2+], [NE], and afterload, respectively. Elevated [Ca2+] failed, however, to stimulate pyruvate oxidation and PDCa activity when MVO2 was held constant by an appropriate decrease in afterload at constant preload. Compound D 600, theophylline, and dibutyryl adenosine 3',5'-cyclic monophosphate also produced parallel alterations in cardiac mechanics, pyruvate oxidation, and MVO2. The striking proportionality between PDCa parameters, MVO2, and cardiac mechanics during the various alterations in cellular Ca2+ metabolism seemed to suggest that the observed Ca2+ stimulation of the PDC might be mainly secondary to increased myocardial energy utilization and myocyte respiration. Evidence for an additional direct effect of Ca2+ on the intact PDC system was not obtained.

Effect of the fatty acid oxidation inhibitor 2-tetradecylglycidic acid on pyruvate dehydrogenase complex activity in starved and alloxan-diabetic rats

Intravenous administration of the fatty acid oxidation inhibitor 2-tetradecylglycidic acid had no effect on the proportion of pyruvate dehydrogenase complex in the active form in heart, diaphragm or gastrocnemius muscles or in liver, kidney or adipose tissue of fed normal rats. The compound reversed the effect of 48h starvation (which decreased the proportion of active complex) in heart muscle, partially reversed the effect of starvation in kidney, but had no effect in the other tissues listed. The compound failed to reverse the effect of alloxan-diabetes (which decreased the proportion of active complex) in any of these tissues. In perfused hearts of fed normal rats, 2-tetradecylglycidate reversed effects of palmitate (which decreased the proportion of active complex), but it had no effect in the absence of palmitate. In perfused hearts of 48h-starved rats the compound increased the proportion of active complex to that found in fed normal rats in the presence or absence of insulin. In perfused hearts of diabetic rats the compound normalized the proportion of active complex in the presence of insulin, but not in its absence. Palmitate reversed the effects of 2-tetradecylglycidate in perfused hearts of starved or diabetic rats. Evidence is given that 2-tetradecylglycidate only reverses effects of starvation and alloxan-diabetes on the proportion of active complex in heart muscle under conditions in which it inhibits fatty acid oxidation. It is concluded that effects of starvation and alloxan-diabetes on the proportion of active complex in heart muscle are dependent on fatty acid oxidation. Insulin had no effect on the proportion of active complex in hearts or diaphragms of fed or starved rats in vitro. In perfused hearts of alloxan-diabetic rats, insulin induced a modest increase in the proportion of active complex in the presence of albumin, but not in its absence.

The effect of 5-methylpyrazole-3-carboxylate and nicotinic acid on abnormalities of carbohydrate metabolism in alloxan-diabetic rat muscle

The administration of the antilipolytic agents sodium nicotinate (1 mmole/kg i.p.) or sodium 5-methylpyrazole-3-carboxylate (0.5 or 1.0 mmole/kg i.p.) to alloxan-diabetic rats produced a significant reduction in the plasma concentration of free fatty acids and a slight reduction in blood glucose concentration. The concentrations in the freeze-clamped heart of citrate , acetyl CoA, Glucose-6-phosphate and fructose-6-phosphate were increased in untreated alloxan-diabetic rats relative to normoglycaemic controls. Treatment of alloxan-diabetic rats with the antilipolytic agents or insulin (60 U/kg i.p.) lowered these increased concentrations of metabolites in the heart. Treatment of the diabetic rats with the antilipolytic agents also produced an increase in the activity of pyruvate dehydrogenase in heart, but only treatment with 5-methylpyrazole-3-carboxylate had a significant effect on the activity of the enzyme in freeze-clamped soleus muscle.

Pyruvate dehydrogenase complex activity in normal and deficient fibroblasts

Pyruvate dehydrogenase complex (PDC) activity in human skin fibroblasts appears to be regulated by a phosphorylation-dephosphorylation mechanism, as is the case with other animal cells. The enzyme can be activated by pretreating the cells with dichloroacetate (DCA), an inhibitor of pyruvate dehydrogenase kinase, before they are disrupted for measurement of PDC activity. With such treatment, the activity reaches 5-6 nmol/min per mg of protein at 37 degrees C with fibroblasts from infants. Such values represent an activation of about 5-20-fold over those observed with untreated cells. That this assay, based on [1-(14)C]pyruvate decarboxylation, represents a valid measurement of the overall PDC reaction is shown by the dependence of (14)CO(2) production on the presence of thiamin-PP, coenzyme A (CoA), Mg(++), and NAD(+). Also, it has been shown that acetyl-CoA and (14)CO(2) are formed in a 1:1 ratio. A similar degree of activation of PDC can also be achieved by adding purified pyruvate dehydrogenase phosphatase and high concentrations of Mg(++) and Ca(++), or in some cases by adding the metal ions alone to the cell homogenate after disruption. These results strongly suggest that activation is due to dephosphorylation. Addition of NaF, which inhibits dephosphorylation, leads to almost complete loss of PDC activity. Assays of completely activated PDC were performed on two cell lines originating from patients reported to be deficient in this enzyme (Blass, J. P., J. Avigan, and B. W. Ublendorf. 1970. J. Clin. Invest. 49: 423-432; Blass, J. P., J. D. Schuman, D. S. Young, and E. Ham. 1972. J. Clin. Invest. 51: 1545-1551). Even after activation with DCA, fibroblasts from the patients showed values of only 0.1 and 0.3 nmol/min per mg of protein. A familial study of one of these patients showed that both parents exhibited activity in fully activated cells about half that of normal values, whereas cells from a sibling appeared normal. These results demonstrate the inheritance nature of PDC deficiency, and that the present assay is sufficient to detect the heterozygous carriers of the deficiency. Application of the same procedures to fibroblasts obtained from 16 individuals who were believed to have normal PDC activities showed a range from about 2-2.5 nmol/min per mg protein for adults to 5-6 nmol/min per mg protein for cells from infants.