calcimycin and Hyperinsulinism

To investigate underlying mechanisms responsible for the impaired nitric oxide (NO)-dependent vascular relaxation in the insulin-resistant state, we examined production of both NO and superoxide anion radical (O2-) and those modulating factors in aortas obtained from normal (CTR), insulin-treated (INS), or high fructose-fed (FR) rats. FR rats showed insulin resistance with endogenous hyperinsulinemia, whereas INS rats showed normal insulin sensitivity. Only FR aortic strips with endothelium elicited impaired relaxation in response to either acetylcholine or calcium ionophore A23187. Endothelial NO synthase (eNOS) activity and its mRNA levels were increased only in vessels from INS rats (P < 0.001), whereas eNOS activity in FR rats was decreased by 58% (P < 0.05) when compared with CTR rats. NO production from aortic strips stimulated with A23187 was significantly lower in FR than CTR rats. In contrast, A23187-stimulated O2- production was higher (P < 0.01) in FR than CTR rats. These differences were abolished when aortic strips were preincubated in the media including (6R)-5,6,7,8-tetrahydrobiopterin (BH4), an active cofactor for eNOS. Furthermore, as compared with CTR rats, aortic BH4 contents in FR rats were decreased (P < 0.001), whereas the levels of 7,8-dihydrobiopterin, the oxidized form of BH4, were increased, with opposite results in INS rats. These results indicate that insulin resistance rather than hyperinsulinemia itself may be a pathogenic factor for decreased vascular relaxation through impaired eNOS activity and increased oxidative breakdown of NO due to enhanced formation of O2- (NO/O2- imbalance), which are caused by relative deficiency of BH4 in vascular endothelial cells.

Topics: Acetylcholine; Animals; Aorta, Thoracic; Ascorbic Acid; Biopterins; Blood Glucose; Blood Pressure; Calcimycin; Endothelium, Vascular; Fructose; Hyperinsulinism; In Vitro Techniques; Insulin; Insulin Resistance; Isometric Contraction; Male; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroprusside; Rats; Rats, Sprague-Dawley; RNA, Messenger; Superoxides; Transcription, Genetic; Vasodilation

Impairment of nitric oxide-dependent vascular relaxation is a characteristic feature of the insulin-resistant state. To understand those mechanisms, we examined imbalance of O2-/NO production in aortic endothelial cells obtained from high fructose-fed, exogenous hyperinsulinemic, and control rats. Aortic segments from both high fructose-fed and insulin-treated rats produced a 4-fold more O2- than control rats evaluated by a chemiluminescence method. The O2- production in the aortas of both high fructose-fed and insulin-treated rats was mediated through activation of NADH/NADPH oxidase. In isometric tension studies, high fructose vessels with endothelium elicited impaired relaxation in response to acetylcholine or a calcium ionophore A23187 when compared with control rats, whereas these impaired vascular responses were not found in insulin-treated rats. Furthermore, endothelial constitutive NO synthase activity was increased in vessels from insulin-treated rats, but decreased in vessels from high fructose-fed rats. These results indicate that relative excess of O2- production through activation of NADH/NADPH oxidase over NO generation in endothelial cells may contribute to impaired endothelial-dependent relaxation in insulin-resistant state.

Topics: Acetylcholine; Animals; Calcimycin; Endothelium, Vascular; Free Radicals; Fructose; Hyperinsulinism; In Vitro Techniques; Indomethacin; Insulin; Insulin Resistance; Luminescent Measurements; Male; Models, Cardiovascular; Muscle, Smooth, Vascular; Nitric Oxide; Phenylephrine; Rats; Rats, Sprague-Dawley; Superoxides; Vasodilation

Insulinopenic diabetes is known to produce endothelial dysfunction. This dysfunction could arise from either hyperglycemia or inadequate insulin. It is not known whether endothelial dysfunction occurs when hyperglycemia is present with elevated insulin levels. In this study, we utilized an experimental model of hyperglycemia with hyperinsulinemia to investigate latent endothelial dysfunction. Rats were continuously infused with glucose or saline for 72 h to achieve peak plasma glucose concentrations of approximately 25 mM. Plasma insulin rose by 12-fold in glucose-infused rats. No significant differences in serum electrolyte concentration were noted between control and glucose-infused rats after 72 h. Blood pressure was not altered by this intervention. Aortic rings taken from control rats relaxed to the endothelium-dependent vasodilators, acetylcholine and A-23187, and to the endothelium-independent vasodilator, nitroglycerin. Relaxation to acetylcholine but not to A-23187 or nitroglycerin was impaired in glucose-infused rat aortic rings. Incubation in vitro with either indomethacin or superoxide dismutase did not restore the impaired relaxation to acetylcholine in rings taken from glucose-infused rats. Thus hyperglycemia with hyperinsulinemia selectively impairs receptor-dependent, endothelium-dependent relaxation. These studies suggest that elevated glucose may be a common pathway leading to endothelial dysfunction in insulin-dependent diabetes mellitus and hyperglycemia-induced insulin resistance.

Topics: Acetylcholine; Animals; Aorta; Calcimycin; Endothelium, Vascular; Hyperglycemia; Hyperinsulinism; Male; Nitroglycerin; Rats; Rats, Sprague-Dawley; Vasodilation; Vasodilator Agents

Genetically obese Zucker rats share several abnormalities with obese patients: inheritance of the obesity, hyperinsulinemia, hypertriglyceridemia. Because alterations in membrane fatty acid composition and in prostaglandin synthesis can be involved in the genesis of the cardiovascular complications of obesity, cardiac prostaglandins and phospholipid fatty acid composition were compared in obese and lean animals. Obese cardiac tissues produced smaller amounts of prostacyclin, thromboxane A2 and PGE2 than lean (p less than 0.01). The cyclooxygenase pathway and the activation of phospholipase by the calcium ionophore A 23187 were not altered. Phospholipid fatty acid composition of obese tissues was abnormal: the amount of stearic, arachidonic, docosapentaenoic and cervonic acids was decreased, whereas the amount of linoleic acid, the precursor of arachidonic acid, was doubled. It is concluded that obesity in Zucker rats is associated with alteration of cardiac arachidonic acid metabolism and that the alterations associated with obesity can be studied in this rat strain.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Calcimycin; Fatty Acids; Hyperinsulinism; Male; Membrane Lipids; Myocardium; Obesity; Prostaglandins; Rats; Rats, Zucker