Myocardial Phosphorylase Research Articles

Metabolic effects of acarbose administration in normal and diabetic rats

The effect of acarbose on cardiac and hepatic metabolism was investigated in normal and diabetic rats. Groups of rats were fed one of the three following diets for 7 days: (1) ground Purina chow, (2) ground Purina chow fortified with raw corn starch and sucrose, and (3) the above high carbohydrate diet, with added acarbose (40 mg/100 g food). At the end of the dietary period the rats were decapitated, and a sample of liver tissue was removed and frozen in liquid nitrogen. The heart was extirpated for subsequent perfusion by the Langendorff technique. Increases in liver and heart glycogen produced by the high carbohydrate diet in the normal rats were prevented completely when acarbose was incorporated into the food. In diabetic animals, liver glycogen was uniformly lower than normal, irrespective of the diet or the presence of acarbose. With animals fed the control diet, cardiac glycogen was higher in diabetic than in normal rats. The high carbohydrate diet caused a lowering of heart glycogen in diabetic rats and this reduction in glycogen content was reversed by including acarbose in the diet. Effects of isoproterenol on myocardial phosphorylase a activity were determined in hearts from normal and diabetic rats given one of the three diets. The high carbohydrate diet decreased the enzymatic response to the catecholamine in hearts from both normal and diabetic animals, and this phenomenon was prevented by the presence of acarbose in the diet. In diabetic rats fed any of the three diets, the activation of cardiac phosphorylase by isoproterenol was greatly accentuated. Measurements of heart uridine kinase showed that the activity of this enzyme was lower than normal in hearts from diabetic rats given either the control or the high carbohydrate diet. The presence of acarbose in the latter diet resulted in a significant decrease in cardiac uridine kinase activity in hearts from normal rats. The results of this study demonstrate the effectiveness of acarbose in modulating tissue metabolism in normal and diabetic animals.

Catecholamine-thyroid hormone interaction on myocardial ornithine decarboxylase.

Myocardial phosphorylase alpha activity responds to stimulation by catecholamines and thyroid hormone. In hyperthyroidism this enzyme is supersensitive to beta-adrenergic stimulation and blockade, indicating that its increased activity is an indirect effect of thyroid hormone. Myocardial ornithine decarboxylase (ODC) activity also responds to catecholamine and thyroid hormone stimulation. In the present studies, we sought to determine whether ODC shares the responses of phosphorylase alpha in hyperthyroidism. As opposed to euthyroid rats, isoproterenol acutely inhibited myocardial OCD activity in hyperthyroid rats. Timolol (60 mg/kg) injected immediately before the isoproterenol blocked this paradoxical inhibitory effect, defining it as beta-adrenergic. When timolol (100 mg/kg), distributed over a 24-h period, was administered during the 3 days of triiodothyronine (T3) administration, it blocked the T3 stimulation of myocardial OCD activity by 35%. However, timolol affected weight gain of the hyperthyroid rats. When fasted rats were used, timolol was without effect on T3-induced myocardial ODC stimulation. Timolol was also without effect on T3-induced stimulation of hepatic ODC or on T3-induced cardiomegaly. Timolol did decrease the T3-induced tachycardia. In summary, in the hyperthyroid heart, 1) isoproterenol paradoxically inhibits myocardial ODC activity and 2) timolol, when food intake is not a variable, is without effect. We conclude that the effect of thyroid hormone on myocardial ODC is not mediated by change in catecholamine sensitivity. Thus the behavior of phosphorylase alpha does not represent a general enzymatic phenomenon.

Glycogenolysis during anoxia in aged mouse heart.

Myocardial glycogen mobilization in response to anoxia has been studied in open-chested C57Bl/6NCrl male mice 6 and 24 months of age. During the 1st minute without oxygen, old animals utilized glycogen more rapidly than did young animals. However, during the 2nd minute of anoxia, young animals continued to utilize cardiac glycogen, whereas old animals did not. A direct correlation was noted between glycogen utilization and activation of myocardial phosphorylase activity (A+B forms). Moreover total myocardial phosphorylase declined during anoxia in old animals while showing no significant change in their younger counterparts. This age-related defect in glycogen mobilization suggests altered tolerance to anoxia in aged animals. The inability to mobilize myocardial glycogen may stem from the existence of an altered form of phosphorylase or from an altered environment in the aged heart.

Effects of perhexiline on myocardial phosphorylase activity, myocardial catecholamine content and heart rate.

A study was conducted on the effects of perhexiline on myocardial phosphorylase activity, myocardial catecholamine content and heart rate. Phosphorylase a activity and heart rate were investigated as an indicator of sympathetic nerve tone in order to clarify the characteristic of perhexiline with regard to the effects on myocardial metabolism in hyperthyroid rats and catecholamine deficient rats. Myocardial catecholamine and phosphorylase a activity were measured by von Euler's method and Cori's method respectively. Conclusion of this study are summarized as follows: 1) Perhexiline reduces the heart rate, and its effect is not always dependent upon the changes in myocardial norepinephrine content. 2) Perhexiline reduces myocardial phosphorylase a activity. It cannot be always said that the reduction is dependent upon the changes in myocardial norepinephrine. 3) Though slightly different from propranolol and dichloroisoproterenol, perhexiline possesses cardiac effects resembling beta-blockers.

Inhibitory effects of desmethylimipramine on the action of thyroxine on cardiac beta-receptors and myocardial phosphorylase.

The influence of chronic administration of desmethylimipramine (DMI) on the actions of thyroxine (T4) on rat heart was studied. Administration od DMI (10 mg/kg, i.p., twice daily) for 7 days did not alter the cardiac beta-adrenergic receptor density or the affinity for (-)[3H]dihydroalprenolol (3H-DHA) but diminished the activation of myocardial phosphorylase produced by isoproterenol. Chronic injections of T4 (500 microgram/rat) for 5 days caused an increase in the number of beta-adrenergic receptors in the heart and potentiated the stimulatory effect of isoproterenol on cardiac phosphorylase alpha activity. When DMI was administered concomitantly with T4, there was no increase in the density of myocardial beta-adrenergic receptors and the T4-induced potentiation of the activation of heart phosphorylase by isoproterenol was abolished. However, simultaneous treatment of the rats with DMI and TR4 did not diminish the positive chronotropic effect of T4. It was concluded that DMI, while not affecting the population of cardiac beta-adrenergic receptors by itself, prevents the increase in these receptors produced by T4 and obviates the T4-induced potentiation of phosphorylase activation by isoproterenol. That the tachycardia caused by T4 persists in hearts in which DMI has impeded the increase in myocardial beta-receptors suggests that the increase in heart rate is not dependent on cardiac beta-adrenergic receptor density.

Age-related alterations in the heat-stability of mouse heart phosphorylase

Myocardial phosphorylase from young and old mice has been examined with respect to its thermal lability properties. It has been shown that phosphorylase from the hearts of old animals is more resistant to heat as compared to the enzyme from young hearts. This increase in thermal stability seems to be correlated with an increase in the less active tetrametric form of the enzymes during aging. Sucrose density centrifugation profiles indicate that upon heating the amount of dimer stays relatively constant in the old heart since the tetramer is probably being broken down into its more active dimeric form. This increase in the tetrameric form of phosphorylase in the old heart may help to explain the increased susceptibility of the old heart to many acute stresses.

Purification and properties of bovine myocardial phosphorylase phosphatase (protein phosphatase C)

Phosphorylase phosphatase was purified to homogeneity from bovine myocardium by the procedure of Brandt et al. ( Brandt, H., Capulong, Z. L., and Lee, E. Y. C., (1975) J. Biol. Chem. 250, 8038–8044). The purified enzyme consists of a single polypeptide chain of M r, 34,800 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The K m for phosphorylase a was 2.9 μ m and at V max, the enzyme had a turnover number of 11.7 mol phosphorylase a (dimer) converted/mol phosphatase/s. Phosphorylated histone and protamine were also substrates for this phosphatase. The K m for histone was 46 μ m (based on incorporated 32P i and at V max a turnover number of 3.3 mol phosphate released/mol phosphatase/s was found. In general, the properties of the bovine phosphorylase phosphatase closely resemble those found for the rabbit liver enzyme.

Effect of ouabain on myocardial metabolic and contractile responses to coronary ligation

The effect of pretreatment with ouabain (40 μg/kg, i.v.) on myocardial metabolic and contractile responses to regional ischemia induced by coronary artery ligation was studied in the canine left ventricle. In control dogs, ischemia increased activity of phosphorylase a and the levels of glucose-6-phosphate and lactate, and decreased the levels of glycogen and phosphocreatine, without affecting the levels of adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate (AMP). Ouabain increased the activity of phosphorylase a. In ouabain-treated dogs, ischemia did not further increase the phosphorylase a activity but it increased the epicardial AMP level. Other metabolic responses to ischemia in ouabain-treated dogs were similar to those in control dogs. In control dogs, myocardial contractile force decreased by about 10% after ischemia, but blood pressure and heart rate remained unchanged. Ouabain increased contractile force by about 32%. In ouabain-treated dogs, ischemia decreased contractile force by about 54% without affecting blood pressure and heart rate. It is concluded that ouabain increases the activity of the myocardial phosphorylase a and that the inotropic action of ouabain can be nullified by coronary artery ligation.

Cardiovascular and metabolic responses to thyroid hormones in animals after sympathectomy or treatment with nerve growth factor

The cardiovascular and metabolic effects of thyroxine (T 4) and triiodothyronine (T 3) were examined in rats and mice with decreased or permanently enhanced adrenergic innervations to the heart. 6-Hydroxydopamine (6-OHDA) and the antiserum to the nerve growth factor (AS) were administered to damage sympathetic fibers; the density of the cardiac adrenergic plexus was increased through the use of the nerve growth factor (NGF). Some animals were additionally adrenal demedullated or treated with N, N-diisopropyl- N′-isoamyl- N′-diethylaminoethylurea (P-286) to reduce circulating catecholamine levels. The results of these experiments showed that the rise in heart phosphorylase a activity produced by thyroid hormones was absent after adrenal demedullation and significantly inhibited after chemical sympathectomy with 6-OHDA. Interference with adrenal medullary function by P-286 in combination with chemical or immunological sympathectomy similarly prevented the hormone-induced activation of myocardial phosphorylase a. While an increase in the density of the peripheral sympathetic fibres to the heart accentuated the tachycardia characteristic of hyperthyroidism, the high metabolic rate which accompanies thyrotoxicosis was unaltered either by proliferation of adrenergic fibres or sympathectomy.

Effect of lanthanum on isoproterenol-induced activation of myocardial phosphorylase.

Effect of lanthanum on isoproterenol-induced activation of myocardial phosphorylase.

Metabolic actions of tyramine and McNeil-A-343 in euthyroid and hyperthyroid rats

Chronic administration of thyroxine to rats produced an elevation in myocardial phosphorylase a activity, and increased heart weight/body weight ratio, cardiac rate and mean arterial blood pressure. Both tyramine and McNeil-A-343 caused a rise in heart phosphorylase a activity in euthyroid rats. In rats pretreated with thyroxine, the increase in enzyme activity caused by tyramine was similar to that obtained in euthyroid animals. An analysis of variance over the entire dose range of tyramine showed that the elevation in cardiac phosphorylase a observed in thyrotoxic animals was not significantly different from controls. It was concluded that thyroxine does not potentiate the stimulatory action of McNeil-A-343 or tyramine on cardiac phosphorylase a activity.

Influence of INPEA, pindolol and propranolol on the chronotropic and metabolic responses to β-adrenergic stimulation in intact rats

A study was made of the effect of isoprenaline given intraperitoneally to rats on the chronotropic effect and the activation of myocardial phosphorylase. Pretreatment with three β-blocking agents: pindolol, propranolol and INPEA was carried out to separate metabolic and chronotropic effects of isoprenaline on heart. Isoprenaline at 0.01–40 mg/kg augmented heart rate, but the activation of phosphorylase started only from the dose of 0.02 mg/kg. Metabolic effect of isoprenaline reached the maximum at a lower dose (0.1 mg/kg) than chronotropic effect of isoprenaline did (1 mg/kg). Pindolol at 0.03 mg/kg, propranolol in doses 0.5–5 mg/kg and INPEA at a dose of 50 mg/kg slowed heart rate but did not influence phosphorylase activity. INPEA in doses 0.5–5 mg/kg, accelerated heart rate, but did not activate myocardial phosphorylase. β-Blocking potency of all three drugs was nearly the same with respect to metabolic and chronotropic response to isoprenaline, but only when measured at the level of 50 per cent of inhibition. 1050 were: pindolol —0.006 mg/kg, propranolol —0.33 mg/kg and INPEA —2.8 mg/kg, however distinct differences between metabolic and chronotropic blockade in other doses of propranolol and INPEA were found. Linear dose dependent β-adrenergic blockade was induced with respect to metabolic and chronotropic effects by pindolol, with respect to chronotropic effect by propranolol and in respect to metabolic effect by INPEA. The blockade of metabolic effect by propranolol and the blockade of chronotropic effect by INPEA occurred abruptly from the zero level to maximal level when the dosage of these drugs was doubled.

The influence of propranolol, inpea, iproveratril and some 1-naphthylethylamine derivatives on the myocardial phosphorylase activity

The antiarrhythmic or negative inotropic and chronotropic response to drugs may be the result of β-adrenergic blockade or the result of the quinidine-like action. The influence of the cardioactive drugs on the isoprenaline-induced phosphorylase activity in the cardiac muscle is decisive in this respect. The influence of propranolol, INPEA, iproveratril and two 1-naphthylethylamine derivatives on the isoprenaline induced phosphorylase activity was studied. Rat hearts were perfused by the method of Langendorff during 20 min. The compounds were infused alone in the range of 0.5–500 μg doses and also 2 min after 0.1 μg isoprenaline (IP) was injected into the perfusion system. Samples of the muscle were taken 30 sec afterwards and the phosphorylase activity was determined. Control hearts were treated with IP alone. IP increased significantly the phosphorylase activity in cardiac muscle as compared with the control. Propanolol completely prevented the effect of IP on metabolism and reduced the mechanical effect of IP. d(—)N- isopropyl-p- nitrophenyl-ethanolamine d(—) INPEA (5 μ g) and l(+) INPEA (50 μg and 500 μg) were ineffective against the IP-induced stimulation of the heart. d(—)INPEA at 50 and 500 μg reduced the effect of IP on phosphorylase activity and blocked completely the pharmacodynamical action of IP on the heart muscle. α-isopropyl- α-[( N-methyl- N-homoveratryl)- α-aminopropyl]-3,4-dimethoxyphenylace-tonitrile (Iproveratril) at 0.5 and 2.5 μg depressed the cardiac activity but not the mechanical or metabolic effects of IP. N-isopropyl- α-methyl- β-1-naphthylethylamine (S-870) (5 μg) and N-propyl- α-methyl- β-1-naphthylethylamine (S-931) (5 μg) did not influence the phosphorylase activity in the heart or the effects of IP.

Effects of adrenal cortical hormones and thyroxine on phosphorylase activity in muscle.

The open-chest rat preparation was used to investigate the interaction between corticosterone and thyroxine in regulating myo-cardial phosphorylase activity; measurements were also made of heart rate and mean arterial blood pressure. Corticosterone, but not thyroxine, caused an increase in total heart phos-phorylase which was due to a specific increase in the enzyme rather than a general increase in cellular protein. Both corticosterone and thyroxine increased cardiac phosphorylase a activity n i normal rats. The enzymatic and positive chronotropic effects of thyroxine were markedly diminished in adrenalectomized rats; simultaneous administration of corticosterone with thyroxine restored the responses to normal. In thy-roidectomized animals, corticosterone produced less stimulation of heart phosphorylase a than in control rats. When both thyroxine and corti-costerone were given to thyroidectomized animals, the level of phosphorylase a approximated that seen when these hormones were injected into normal ra...

The effects of pyridoxine deficiency on cardiac and brain phosphorylase in mice

The effects of pyridoxine deficiency on phosphorylase (α-1,4-glucan: orthophosphate glucosyltransferase, EC 2.4.1.1) activity in mouse brain and heart muscle have been investigated. In pyridoxine-deficient animals, total and phosphorylase a activities were significantly reduced in both brain and heart tissue ( P < 0.001). In brain tissue the levels of phosphorylase a and total phosphorylase activity were restored to control values by the addition of pyridoxine to the diet of mice previously deprived of the vitamin. However, such supplementation did not completely restore the levels of this enzyme in cardiac tissue. These nutritional studies lend further support to the concept that vitamin B 6 may be a cofactor for brain and myocardial phosphorylase.

444 Dissociation of the augmentation of cardiac contractile force from the activation of myocardial phosphorylase by catecholamines

444 Dissociation of the augmentation of cardiac contractile force from the activation of myocardial phosphorylase by catecholamines