Alterations in hepatic fine structure after chronic exposure of rats to dexamethasone

Glucocorticoids produce whole body insulin resistance with changes in cardiac metabolism

Insulin resistance is viewed as an insufficiency in insulin action, with glucocorticoids being recognized to play a key role in its pathogenesis. With insulin resistance, metabolism in multiple organ systems such as skeletal muscle, liver, and adipose tissue is altered. These metabolic alterations are widely believed to be important factors in the morbidity and mortality of cardiovascular disease. More importantly, clinical and experimental studies have established that metabolic abnormalities in the heart per se also play a crucial role in the development of heart failure. Following glucocorticoids, glucose utilization is compromised in the heart. This attenuated glucose metabolism is associated with altered fatty acid supply, composition, and utilization. In the heart, elevated fatty acid use has been implicated in a number of metabolic, morphological, and mechanical changes and, more recently, in "lipotoxicity". In the present article, we review the action of glucocorticoids, their role in insulin resistance, and their influence in modulating peripheral and cardiac metabolism and heart disease.

Consequences of treatment with dexamethasone in rats on the susceptibility of total plasma and isolated lipoprotein fractions to copper oxidation

According to the oxidative hypothesis of atherosclerosis, a hyperoxidizability of lipoproteins could favor the development of the atherosclerotic process. Besides, it has been recently reported that models of elevated very-low-density-lipoprotein (VLDL) levels in rats resulted in an increased susceptibility of these VLDL to oxidation. Treatment with dexamethasone classically induces an increase in plasma VLDL concentration. The aim of our study was thus to assess the effects of a treatment with dexamethasone in rats on the susceptibility to copper oxidation, both on total plasma and on isolated lipoproteins. Male Sprague-Dawley rats aged three months were treated with a daily intraperitoneal injection of dexamethasone (1.5 mg per kg) for five days (DEX group), whereas control rats were fed ad libitum (AL group). In order to take into account the decrease of food intake induced by dexamethasone treatment, a group of pair-fed rats was constituted (PF group). These rats had the same food intake as rats of the DEX group and were treated with a daily isovolumic intraperitoneal injection of NaCl for 5 d. After 5 d treatment, rats were fasted overnight, then killed, and blood was collected on EDTA. Low-density lipoproteins (VLDL + LDL) and high-density lipoproteins (HDL) were isolated by ultracentrifugation. A copper oxidation was conducted both on total plasma and on isolated lipoproteins. As expected, after treatment with dexamethasone, plasma exhibited increased triglyceride and glucose levels. Similarly, VLDL + LDL of rats from the DEX group were enriched with triglycerides, when compared with VLDL + LDL of the other two groups of rats. Our major finding was a marked increase in the susceptibility of total plasma of the DEX group to copper oxidation, in comparison with the other two groups of rats. This oxidizability was assessed by the maximal level of oxidation products absorbing at 234 nm and classically considered to be conjugated dienes (7.46+/-0.70 micromol L(-1) in the DEX group vs. 3.36+/-0.40 and 2.05+/-0.60 micromol L(-1) in the AL and PF groups, respectively). Nevertheless, this higher oxidizability was not observed in the isolated lipoprotein fractions, as shown by the formation of lipid peroxidation products such as conjugated dienes, thiobarbituric-acid reactive substances, hydroperoxides, 7-ketocholesterol, and dienals. This is not in agreement with other models of hypertriglyceridemia that have been reported to induce a hyperoxidizability of lipoproteins in rats. Our results led us to hypothesize that other plasma components such as proteins could be involved in this susceptibility to oxidation. Indeed, the severe protein catabolism induced by dexamethasone treatment could support this hypothesis, by forming protein components that are more susceptible to oxidation, as shown by an increased carbonyl formation upon plasma copper oxidation.