The action of insulin and sugar on the respiratory quotient and metabolism of the heart-lung preparation

XXII.—The Metabolism of the Frog's Isolated Heart

Theories regarding the chemistry of the contraction process in striped muscle have been revolutionised during the last year. The Hill-Meyerhof theory was based on the assumption that the contraction process was due to the liberation of lactic acid by the break-down of glycogen, a non-oxidative reaction, and that the recovery process consisted in the oxidation of part of the lactic acid and the resynthesis of glycogen from the remainder. Meyerhof now believes (1, p. 305) that contraction is produced by the break-down of creatin-phosphoric acid (phosphagen), and that the energy produced by carbohydrate break-down is utilised to resynthesise phosphagen.

Myocardial performance in conscious streptozotocin diabetic rats

Background

In spite of a large amount of studies in anesthetized animals, isolated hearts, and in vitro cardiomyocytes, to our knowledge, myocardial function was never studied in conscious diabetic rats. Myocardial performance and the response to stress caused by dobutamine were examined in conscious rats, fifteen days after the onset of diabetes caused by streptozotocin (STZ). The protective effect of insulin was also investigated in STZ-diabetic rats.

Methods

Cardiac contractility and relaxation were evaluated by means of maximum positive (+dP/dt_max) and negative (-dP/dt_max) values of first derivative of left ventricular pressure over time. In addition, it was examined the myocardial response to stress caused by two dosages (1 and 15 μg/kg) of dobutamine. One-way analysis of variance (ANOVA) was used to compare differences among groups, and two-way ANOVA for repeated measure, followed by Tukey post hoc test, to compare the responses to dobutamine. Differences were considered significant if P < 0.05.

Results

Basal mean arterial pressure, heart rate, +dP/dt_max and -dP/dt_max were found decreased in STZ-diabetic rats, but unaltered in control rats treated with vehicle and STZ-diabetic rats treated with insulin. Therefore, insulin prevented the hemodynamic and myocardial function alterations observed in STZ-diabetic rats. Lower dosage of dobutamine increased heart rate, +dP/dt_max and -dP/dt_max only in STZ-diabetic rats, while the higher dosage promoted greater, but similar, responses in the three groups. In conclusion, the results indicate that myocardial function was remarkably attenuated in conscious STZ-diabetic rats. In addition, the lower dosage of dobutamine uncovered a greater responsiveness of the myocardium of STZ-diabetic rats. Insulin preserved myocardial function and the integrity of the response to dobutamine of STZ-diabetic rats.

Conclusion

The present study provides new data from conscious rats showing that the cardiomyopathy of this pathophysiological condition was expressed by low indices of contractility and relaxation. In addition, it was also demonstrated that these pathophysiological features were prevented by the treatment with insulin.

The computational integrated myocyte: a view into the virtual heart

The presentation outlines an integrative approach for developing a computational model of cardiomyocytes. A modular approach is proposed, and strategies of linking the modules (intermediary metabolism, electrophysiology, and mechanics) of the model are presented. A strong recommendation is given toward an integrated system approach backed by experimental validation.

Insulin inhibits the increased contractile force induced by epinephrine in isolated guinea pig heart muscle

While the mechanism of positive inotropic action of insulin is not yet fully known, glycose, insulin and potassium solution (GIK solution) has been used in cardiopulmonary resuscitation. Catecholamines continue to be the first line drug to increase blood pressure during cardiac arrest. This study was designed to determine the interaction of insulin and epinephrine on guinea pig papillary heart muscle. The mechanical response of papillary muscle isolated from guinea pig ventricle was observed. Epinephrine increased the twitch tension with a mean maximum contractile force of 766.4% of control. Insulin decreased the increased tension induced by epinephrine to 103.8% of control. This blocking phenomena was not influenced by preadministered insulin. Likewise, the effect of epinephrine was not affected by preadministered insulin.

Response of isolated guinea pig myocardium to insulin therapy during normothermia and graded hypothermia

The discovery of insulin in 1922 aroused immediate clinical interest in its use in heart disease. In severe heart failure, insulin release is suppressed by the combined effect of poor pancreatic perfusion and by increased sympathetic activity. In these circumstances, myocardial metabolism of glucose may break down through the deficiency of insulin. Because of this, glucose, insulin and potassium solution (GIK solution) has been used in cardiopulmonary resuscitation. However, its mechanism is not yet fully known. This study was designed to determine the effect of insulin on cardiac muscle at various temperatures. The mechanical response of papillary muscle isolated from guinea pig ventricle was observed under various thermal conditions (23-37 degrees C). Twitch tension was increased by the administration of 0.2 I.U./ml insulin under each thermal condition. In all circumstances, the increase in contractile force was noted about 2 min after the administration of insulin. The effect of insulin on 20 preparations demonstrated the mean maximum contractile force was 226% ( +/- 34 S.D., n = 5) in 37 degrees C, 194% ( +/- 36 S.D., n = 5) in 30 degrees C, 190% ( +/- 30 S.D., n = 5) in 27 degrees C and 200% ( +/- 36 S.D., n = 5) in in 23 degrees C. The differences between different temperatures was not significant. The effect of insulin during depression Na-K pump by high concentration of ouabain (g-strophanthin, 10(-5) M) was also observed. Insulin (0.2 I.U./ml) was administered when the papillary muscle showed no response to electrical stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of insulin on the metabolism of the isolated working rat heart perfused with undiluted rat blood

Working rat hearts were perfused with either buffer or with defibrinated, undiluted rat blood dialyzed to remove vasoconstrictor factors. With precautions taken for sterility in the preparation of the perfusate and the apparatus, hearts were obtained which were stable as judged by stroke rate and cardiac output. In these hearts, cardiac output and coronary flow averaged 46.0 and 1.7 ml/g heart per min, respectively. Perfusion with erythrocyte-free buffer depressed cardiac output by 30%, while coronary flow averaged 8.8 ml/g of heart per min. The mean stroke rate of blood-perfused hearts was 300 beats/min but only 240 beats/min during buffer perfusion. In blood-perfused hearts, insulin did not alter stroke rate but significantly lowered coronary flow. The hormone caused a transient increase in cardiac output in hearts perfused with buffer. Insulin did not alter glucose uptake in buffer-perfused hearts but increased lactate release in perfusions with blood. Both serum fatty acids and triacylglycerol fatty acids were significant metabolic fuels in hearts perfused with undiluted blood. The preparation described would appear to be potentially useful for the study of myocardial metabolism in vitro.

Termination of cardiopulmonary bypass facilitated by insulin

A 61-year old woman with severe coronary artery disease underwent three-vessel coronary bypass surgery. Difficulty was encountered in terminating cardiopulmonary bypass, but there was dramatic improvement following the administration of intravenous insulin. The use of insulin to facilitate termination of cardiopulmonary bypass is discussed.

Insulin therapy for depressed myocardial contractility after prolonged ischemia

Insulin was administered to two patients whose diminished myocardial contractility made it difficult to terminate cardiopulmonary bypass. In both instances, bypass was successfully terminated shortly after the insulin injection. These clinical observations led to experiments under the controlled conditions provided by the isolated, working rat heart preparation. The recovery of contractility after 30 minutes of severe ischemia was assessed in all 11 control and 11 insulin-treated hearts. Myocardial performance, as judged by the product of heart rate and peak systolic blood pressure, was significantly greater in the insulin-treated hearts. These clinical observations and experimental findings suggest the need for more extensive study of the potential value of insulin in treating depressed contractility after prolonged myocardial ischemia.

Positive inotropic action of insulin on piglet heart

This study was designed to investigate changes in cardiac performance during hypoglycemia produced by the administration of insulin in the newborn piglet. With heart rate, aortic pressure, and aortic flow held constant, the treated group demonstrated a pronounced positive inotropic response manifested by an increase of dP/dt max to 138% of control values. Central nervous system function and beta adrenergic activity were excluded from the preparation by ligation of the brachiocephalic vessels and administration of practolol. For reasons discussed, it is unlikely that the findings can be ascribed to glucagon contamination. Therefore, the increase in contractility presumably resulted from a direct effect of insulin upon the myocardium. Clinical and laboratory data suggest that the resistance of the neonate to hypoxia is modified by glycogen stores. Insulin is known to increase glycogen synthesis, and this effect might be expected to augment myocardial resistance to hypoxia. Under the conditions of these experiments, however, pretreatment with insulin had no demonstrable influence on the rate of deterioration of cardiac function during hypoxia. The mechanism of cardiac stimulation by insulin is unknown but may involve calcium fluxes.

The Effect of Digoxin on the Intermediary Metabolism of the Heart as Measured by Glucose-C 14 Utilization in the Intact Dog

Administration of a therapeutic dose level of digoxin in the intact dog resulted in an augmentation of the glucose utilization of the myocardium accompanied by a greatly increased rate of glycolytic and oxidative activity. The contribution of glucose to the total metabolism of the heart was increased, and the utilization of noncarbohydrate substrates was decreased. These metabolic changes occurred in the absence of changes in the dynamic functions of the heart, indicating that the metabolic alterations were due to a primary effect of the drug rather than an effect secondary to an altered state of cardiac activity.

Pathological changes in the heart, skeletal musculature and liver in rabbits treated with insulin in shock dosage

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