calcimycin and Obesity

The effect of insulin-resistance syndrome on vascular function has been examined in isolated basilar arteries using the obese Zucker rat (OZR) and age-matched lean littermate controls (lean Zucker rat; LZR) at 36 weeks of age. The OZR showed significantly reduced oral glucose tolerance and increased body weight, blood pressure, proteinuria, plasma levels of triglycerides, cholesterol, and insulin compared with the LZR. The contractile response to serotonin was significantly increased in the OZR. Furthermore, contractions to serotonin in LZR but not OZR were enhanced in the presence of the nitric oxide synthase inhibitor Nomega-nitro-L-arginine methyl ester (NAME). Relaxations to acetylcholine (ACh), histamine, and A23187 were significantly reduced in precontracted arteries from the OZR. In the presence of NAME, histamine responses were significantly reduced whereas ACh and A23187 responses were almost abolished. Relaxations to free-radical nitric oxide (NO) and papaverine were not different in arteries from the OZR, even though responses to sodium nitroprusside were reduced in the OZR. Western blot and immunofluorescent quantitative analyses of eNOS content in cerebral microvessel fractions and basilar artery preparations, respectively, were not significantly different between OZR and LZR. The results suggest impairment in endothelial function resulting in reduced NO function in the basilar artery from the OZR.

Topics: Acetylcholine; Animals; Basilar Artery; Biogenic Amines; Calcimycin; Endothelium, Vascular; Female; Hemodynamics; Insulin Resistance; Metabolism; Muscle Relaxation; Muscle, Smooth; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Nitroprusside; Obesity; Papaverine; Rats; Rats, Zucker

The JCR:LA-corpulent rat is a unique animal model of human vascular disease that exhibits a profound insulin resistance, vasculopathy, and cardiovascular dysfunction. We tested the hypothesis that the defects affect endothelial and smooth muscle function of the coronary microvasculature as well as cardiac contractility. Coronary, myocardial and aortic function were assessed in obese (homozygous for the cp gene, cp/cp) and lean (heterozygous or homozygous normal, +/?) littermates aged 7 and 18 weeks.. Coronary endothelial relaxation was examined in isolated perfused hearts by determining the effect of bradykinin (0. 1-1000 nmol l(-1)) on coronary perfusion pressure (CPP), myocardial mechanical function was evaluated in terms of left-ventricular developed pressure (LVDevP), and aortic relaxation with the endothelium-dependent agonist, A 23187 (1-1000 nmol l(-1)).. In rats aged 7 weeks, bradykinin reduced CPP from 133+/-1 mmHg to 43+/-1 mmHg (-67%) in lean rats, but only to 64+/-3 mmHg (-52%) in corpulent rats (n=6, P<0.05). Similar differences were found in rats aged 18 weeks (n=8). Inhibition of NO synthase with N(G)-nitro-L-arginine (L-NNA; 0.2 mmol l(-1)) impaired, and tetrahydrobiopterin (0.1 mmol l(-1)), a NO synthase cofactor, restored relaxation in cp/cp rats. Spermine/NO equally reduced CPP in both groups (-58%). Mechanical function was similar in lean and corpulent rats, aortic endothelial relaxation was attenuated by approximately 30% and aortic smooth muscle function was normal (7 weeks) or improved (18 weeks) in the cp/cp genotype.. These results suggest that (i) there is a specific impairment of NO-mediated relaxation of the coronary resistance vessels in the JCR:LA-corpulent rat that is not associated with impaired baseline myocardial contractility, and (ii) exogenous tetrahydrobiopterin reversed the relaxation defects that are part of the vascular complications typical for the insulin resistance syndrome.

Topics: Animals; Antioxidants; Aorta, Thoracic; Biopterins; Bradykinin; Calcimycin; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Inhibitors; In Vitro Techniques; Insulin Resistance; Ionophores; Male; Microcirculation; Myocardial Contraction; Nitric Oxide Synthase; Nitroarginine; Obesity; Perfusion; Rats; Rats, Inbred Strains

Free Ca2+ was measured in intracellular stores of individual mouse pancreatic beta-cells using dual-wavelength microfluorometry and the low-affinity Ca2+ indicator furaptra. Controlled permeabilization of the plasma membrane with 4 micromol/l digitonin revealed that 22% of the furaptra was trapped in intracellular nonnuclear compartments. When 3 mmol/l ATP and 200 nmol/l Ca2+ were simultaneously present, this cation rapidly accumulated in the organelle pool, reaching an average concentration of 200-500 micromol/l. Whereas agents affecting the mitochondrial function (5 mmol/l succinate, 2 micromol/l ruthenium red, or 10 micromol/l antimycin A + 2 microg/ml oligomycin) had little effects, the Ca2+-ATPase inhibitor thapsigargin released 92% of the Ca2+ mobilizable with the ionophore Br-A23187. Digital imaging revealed regional differences in the organelle Ca2+. The regions with the highest Ca2+ concentration were particularly responsive to inositol 1,4,5-trisphosphate (IP3). IP3 mobilized Ca2+ in a dose-dependent way with half-maximal and maximal effects at about 1 and 5 micromol/l, respectively. High concentrations of IP3 released about half of the thapsigargin-sensitive Ca2+, but there were no responses to agents known to activate ryanodine receptors, such as 10 mmol/l caffeine, 0.1-1 micromol/l ryanodine, or 1-5 micromol/l cyclic ADP ribose. The results reinforce the concept that mobilization of intracellular Ca2+ in the pancreatic beta-cell is mediated by IP3 receptors rather than ryanodine receptors.

Topics: Animals; Calcimycin; Calcium; Cell Membrane; Cell Membrane Permeability; Digitonin; Enzyme Inhibitors; Fluorescent Dyes; Fura-2; Image Processing, Computer-Assisted; Inositol 1,4,5-Trisphosphate; Intracellular Membranes; Ionophores; Islets of Langerhans; Mice; Mice, Mutant Strains; Mitochondria; Obesity; Oligomycins

1. Insulin resistance is associated with hypertension but the underlying mechanism is unclear. We tested the hypothesis that insulin-induced vasodilatation is impaired in insulin-resistant obese Zucker rats. We studied mesenteric artery (approximately 220 microns diameter) function before the development of hypertension in 3-month old obese Zucker rats and age-matched lean rats. 2. In vessels from lean rats, insulin at concentrations of 50, 500 and 5000 m-units/l attenuated the constriction in response to noradrenaline (50 m-units/l: 8 +/- 3%, P < 0.05; 500 m-units/l: 13 +/- 3%, P < 0.02; 5000 m-units/l: 13 +/- 2%, P < 0.02). 3. Vessels from obese rats failed to show any such response to insulin (2 +/- 6% increase in maximal tension with 5000 m-units/l; not significant), both in the presence and absence of L-arginine (3 mmol/l). 4. Vessels from obese rats showed slight but significant impairment in the vasodilator response to acetylcholine (5 x 10(-8)-10(-4) mol/l) (obese: 64.1 +/- 3.7% relaxation; lean: 77.3 +/- 3.7% relaxation; P < 0.05); however, relaxation in response to A23187 was not significantly different between the phenotypes (obese: 81.3 +/- 10.6% relaxation; lean: 79.1 +/- 9.7% relaxation; not significant). 5. Systolic blood pressure was not significantly different in lean (126 +/- 8 mmHg) and obese (127 +/- 7 mmHg) rats at the time of study (not significant). 6. We conclude that insulin-induced attenuation of noradrenaline-mediated vasoconstriction is impaired in the obese Zucker rat and that this defect precedes and therefore could contribute to the development of hypertension in this insulin-resistant model. The defect in insulin action could reside in the endothelial generation of nitric oxide, as endothelial function is also abnormal.

Topics: Acetylcholine; Animals; Arginine; Calcimycin; Endothelium, Vascular; In Vitro Techniques; Insulin; Insulin Resistance; Ionophores; Male; Mesenteric Arteries; Norepinephrine; Obesity; Rats; Rats, Zucker; Vasoconstriction

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