ucn-1028-c and Hyperglycemia

Isoflurane activates vascular adenosine triphosphate sensitive potassium (K(ATP)) channels, and may induce vasodilation. In the present study, we investigated whether hyperglycemia modifies isoflurane activation of vascular K(ATP) channel.. We used a cell-attached patch-clamp configuration to test the effects of isoflurane on K(ATP) channel activity in vascular smooth muscle cells (VSMCs) after incubation for 24 h in medium containing normal glucose (NG, 5.5 mM D-glucose), L-glucose (LG, 5.5 mM D-glucose plus 17.5 mM L-glucose), or high glucose (HG, 23 mM D-glucose). Superoxide levels in aortas were measured by the lucigenin-enhanced chemiluminescence technique.. Isoflurane-induced open probabilities were significantly reduced in VSMCs from arteries incubated in HG (0.06 +/- 0.01) compared with NG (0.17 +/- 0.02; P < 0.05) and LG (0.15 +/- 0.02; P < 0.05). Pretreatment of VSMCs with protein kinase C (PKC) inhibitors, calphostin C and PKC inhibitor 20-28, greatly reduced HG inhibition of isoflurane-induced K(ATP) channel activity. In addition, a PKC activator, PMA, mimicked the effects of HG. Superoxide release was significantly increased in arteries incubated in HG (18.3 +/- 11.5 relative light units (RLU) x s(-1) x mg(-1); P < 0.05 versus NG). Coincubated with polyethylene glycol-superoxide dismutase (250 U/mL), a cell-permeable superoxide scavenger, greatly reduced the HG-induced increase of superoxide, but failed to reduce HG inhibition of isoflurane-induced K(ATP) channel activity.. Our results suggest that the metabolic stress of hyperglycemia can impair isoflurane-induced vascular K(ATP) channel activity mediated by excessive activation of PKC. This could impede the coronary vasodilation response to isoflurane, causing ischemia or hypoxia in patients with perioperative hyperglycemia.

Topics: Anesthetics, Inhalation; Animals; Cells, Cultured; Enzyme Activators; Free Radical Scavengers; Glucose; Hyperglycemia; Isoflurane; KATP Channels; Male; Membrane Potentials; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Naphthalenes; Polyethylene Glycols; Protein Kinase C; Protein Kinase Inhibitors; Rats; Rats, Wistar; Signal Transduction; Superoxide Dismutase; Superoxides; Tetradecanoylphorbol Acetate; Time Factors; Vasodilation

Recently, we demonstrated in vivo effects of acutely induced hyperglycemia, diabetes and mannitol infusions on rat mesenteric microcirculation concerning leukocyte-endothelial-cell interaction (Schäffler et al. EJCI 28: 886-893, 1998).. In this study we have investigated the possible involvement of the protein kinase C (PKC) and p38 MAP kinase cascade as signal transducing elements during hyperglycemic and osmotic stress in an in vivo rat model.. Acutely induced hyperglycemia resulted in a significant increase in leukocyte adhesion. This effect could be mimicked by mannitol. Both PKC and p38 MAP kinase were involved in the effects mediated by glucose and mannitol. Acutely induced hyperglycemia resulted in a significant increase in leukocyte emigration. This effect could be imitated by mannitol. However, PKC and p38 MAP kinase were only involved under osmotic stimulation. The hyperglycemia-induced reduction in leukocyte rolling velocity seemed to be a glucose-specific effect, since mannitol did not influence leukocyte rolling velocity. This glucose effect on leukocyte rolling velocity was mediated by an activation of the PKC/p38 MAP kinase cascade. Both hyperglycemia and osmotic stimuli alone were able to reduce venular shear rate without recruitment of the p38 MAP kinase cascade. The observed reduction of shear rate seems to be mediated only by the osmotic effects of glucose via activation of the PKC system.. The observed effects of glucose on adhesion, emigration and shear rate are due to osmotic effects. The PKC/MAP kinase cascade is involved as a signal transducing component. The reduction of leukocyte rolling velocity is a glucose-specific effect, mediated by the activation of both the PKC and the p38 MAP kinase cascade. Venular shear rate and leukocyte emigration can be influenced by glucose and mannitol due to different regulation mechanisms. It is concluded, that isoform-specific inhibitors of PKC and specific MAP kinase inhibitors represent a potential drug target for preventing microvascular dysfunction in diabetes.

Topics: Animals; Capillaries; Cell Adhesion; Diabetic Angiopathies; Diuretics, Osmotic; Enzyme Inhibitors; Glucose; Hyperglycemia; Imidazoles; Leukocytes; Male; Mannitol; MAP Kinase Signaling System; Microcirculation; Mitogen-Activated Protein Kinases; Naphthalenes; Osmotic Pressure; p38 Mitogen-Activated Protein Kinases; Protein Kinase C; Pyridines; Rats; Rats, Sprague-Dawley; Water-Electrolyte Balance

We have reported that plasma adrenomedullin (AM) in hyperglycemic patients was significantly increased compared with normal volunteers. In this report we examined the effects of hyperglycemia on AM expression in the vasculature, the main site of AM production. AM mRNA level in the aorta was higher in the diabetic rats than in the control rats. AM mRNA level and protein kinase C (PKC) activity in cultured vascular smooth muscle cells (VSMC) increased as the glucose concentration in the medium changed from 100mg/dl to 450mg/dl. PKC inhibitors blocked this increase of AM mRNA. Similar osmotic change with mannitol had no effect on AM expression. We conclude that (1) hyperglycemia increases vascular AM expression through PKC-dependent pathway, and (2) the elevated plasma AM in hyperglycemic patients originates from the glucose induced vascular AM expression. We propose the possible role of AM in the pathogenesis of diabetic vascular complications.

Topics: Adrenomedullin; Amino Acid Sequence; Animals; Aorta; Diabetic Angiopathies; Hyperglycemia; Male; Muscle, Smooth, Vascular; Naphthalenes; Peptides; Protein Kinase C; Rats; Rats, Sprague-Dawley; RNA, Messenger; Staurosporine