Islet cell function in gold thioglucose-induced obesity in mice

Heart metabolic disturbances in cardiovascular diseases

Myocardial function depends on adenosine triphosphate (ATP) supplied by oxidation of several substrates. In the adult heart, this energy is obtained primarily from fatty acid oxidation through oxidative phosphorylation. However, the energy source may change depending on several factors such as substrate availability, energy demands, oxygen supply, and metabolic condition of the individual. Surprisingly, the role of energy metabolism in development of cardiac diseases has not been extensively studied. For instance, alterations in glucose oxidation and transport developed in diabetic heart may compromise myocardial performance under conditions in which ATP provided by glycolysis is relevant, such as in ischemia and reperfusion. In some cardiac diseases such as ischemic cardiomyopathy, heart failure, hypertrophy, and dilated cardiomyopathy, ATP generation is diminished by derangement of fatty acid delivery to mitochondria and by alteration of certain key enzymes of energy metabolism. Shortage of some co-factors such as L-carnitine and creatine also leads to energy depletion. Creatine kinase system and other mitochondrial enzymes are also affected. Initial attempts to modulate cardiac energy metabolism by use of drugs or supplements as a therapeutic approach to heart disease are described.

Experimental obesity: a homeostatic failure due to defective nutrient stimulation of the sympathetic nervous system

The basic hypothesis of this review is that studies on models of experimental obesity can provide insight into the control systems regulating body nutrient stores in humans. In this homeostatic or feedback approach to analysis of the nutrient control system, we have examined the afferent feedback signals, the central controller, and the efferent control elements regulating the controlled system of nutrient intake, storage, and oxidation. The mechanisms involved in the beginning and ending of single meals must clearly be related to the long-term changes in fat stores, although this relationship is far from clear. Changes in total nutrient storage in adipose tissue can arise as a consequence of changes in the quantity of nutrients ingested in one form or another or a decrease in the utilization of the ingested nutrients. A change in energy intake can be effected by increased size of individual meals, increased number of meals in a 24-hour period, or a combination of these events. Similarly, a decrease in utilization of these nutrients can develop through changes in resting metabolic energy expenditure which are associated with one of more of the biological cycles such as protein metabolism, triglyceride for glycogen synthesis and breakdown, or maintenance of ionic gradients for Na+ + K+ across cell walls. In addition, differences in energy expenditure related to the thermogenesis of eating or to the level of physical activity may account for differences in nutrient utilization.

The activity of the pyruvate dehydrogenase complex in heart and liver from mice during the development of obesity and insulin resistance

The amount of pyruvate dehydrogenase in the active form (PDHa) was increased 1.7-fold compared with controls in heart muscle of mice 1 week after induction of obesity with a single injection of gold-thioglucose. At 4 weeks post injection, the amount of PDHa was decreased to 32% of control, a value which was observed in later stages of the obesity syndrome. In contrast, liver PDHa was increased and remained at an increased activity during the development of obesity. Despite normal post-prandial serum insulin contents, liver membrane insulin-receptor numbers were decreased 1 week after gold-thioglucose injection, and there was no change in receptor affinity. The decrease in heart PDHa in the obese animals was reversed by a single dose of 2-tetradecylglycidic acid, but this inhibitor of mitochondrial fatty acid oxidation did not affect liver PDHa in these animals. These early and diverse changes in PDHa argue for a multifactorial aetiology in the development of the whole-body insulin resistance seen in older gold-thioglucose-treated obese animals.

Proportion of active dephosphorylated pyruvate dehydrogenase complex in heart and isolated heart mitochondria is decreased in obese hyperinsulinaemic mice

The proportion of active, dephosphorylated, pyruvate dehydrogenase complex was decreased in the mouse heart by obesity (by 56%), and this decrease in enzyme activity persisted during preparation and extraction of heart mitochondria. Phosphorylation and inactivation of pyruvate dehydrogenase may be a major factor in mediating the inhibitory effects of obesity on glucose oxidation in muscle, and this may represent an important mechanism in the development and/or expression of cellular insulin-resistance.