Biomedical subjects

M C Griswold

Publications and source records attributed to M C Griswold.

4 recordsLinked to original sources

PubMed1999

Resistance of endothelium-dependent relaxation to elevation of O(-)(2) levels in rabbit carotid artery.

Endogenous superoxide anion (O(-)(2)) interferes with the bioactivity of nitric oxide (NO) in endothelium-dependent arterial relaxation (EDR). Using the lucigenin chemiluminescence assay, we measured O(-)(2) in the thoracic and abdominal aortas and the carotid artery of rabbits to determine whether ambient O(-)(2) varies among the three arteries and differentially diminishes the effect of NO. Basal levels of O(-)(2) were significantly higher in carotid arteries than in the thoracic aorta [23 +/- 6.1 vs. 3.9 +/- 1.4 chemiluminescence units (CU); P < 0.05], whereas EDR in response to ACh (10(-8)-10(-5) M) was not significantly different on ANOVA. After treatment with the superoxide dismutase (SOD) inhibitor diethyldithiocarbamate (DDC; 10 mM), O(-)(2) levels were significantly elevated, becoming greater in the carotid artery and abdominal aorta than in the thoracic aorta (185 +/- 31.2 and 202 +/- 40.3 vs. 89 +/- 18 CU; P < 0.05). DDC significantly reversed EDR in the thoracic aorta but not in the carotid artery; at 10(-6) M ACh, the decrease seen with DDC was 48 +/- 6.2 vs. 6.8 +/- 8.0% of maximal relaxation in the thoracic aorta and carotid artery, respectively. In the thoracic aorta, exogenous SOD reversed the inhibition of EDR caused by DDC. Moreover, DDC/O(-)(2)-resistant EDR in the carotid artery was ablated by the addition of nitro-L-arginine methyl ester (300 microM; P < 0.05), an NO synthase inhibitor, consistent with peroxynitrite or an O(-)(2)-resistant NO donor being involved in carotid relaxation. Indeed, exogenous peroxynitrite caused similar relaxation of the carotid artery and thoracic aorta, which was unaffected by DDC. Our studies show a greater production of nitrite and O(-)(2) per unit area by the carotid artery, suggesting a greater amount of their product peroxynitrite. These findings support the hypothesis that peroxynitrite is the relaxing agent that resists high O(-)(2) in the carotid artery.

Acetylcholine↗

PubMed1998

Vascular action of the hypoglycaemic agent gliclazide in diabetic rabbits.

ATP-dependent potassium channel blockers used as hypoglycaemic agents may have effects on vascular disease in diabetes mellitus beyond their effect on blood glucose control. This study was designed to determine the effects of treatment with gliclazide on the isolated abdominal aorta of diabetic rabbits in which endothelium-dependent relaxation is impaired by a mechanism involving oxygen-derived free radicals. After induction of diabetes with alloxan, there was no effect of gliclazide (10 mg x kg(-1) day(-1) orally) on blood glucose or insulin levels over a 6 week period. Hence, this permitted an examination of the vascular effects of gliclazide in diabetic rabbits exclusive of metabolic effects. Acetylcholine- and nitric oxide-induced relaxation in aortae from rabbits treated with or without gliclazide were measured in the absence or presence of the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine (L-NAME). Diabetes was associated with significant impairment of acetylcholine-induced endothelium-dependent relaxation of the abdominal aorta which was not significant in diabetic rabbits treated with gliclazide in vivo. Aortae from diabetic rabbits studied in the presence of L-NAME showed an exaggerated contraction to acetylcholine which was prevented in rabbits treated with gliclazide. Gliclazide treatment did not affect the response to acetylcholine of normal rabbit aorta, and gliclazide when added in vitro had no effect on the response of diabetic rabbit aorta, suggesting that the effect of gliclazide was specific to the abnormality arising with diabetes and was not due to an acute effect of the drug. These data indicate that gliclazide, aside from either a direct antioxidant action or an effect on insulin or glucose levels, may ameliorate diabetic endothelial cell dysfunction.

Acetylcholine↗

PubMed1998

Evidence that additional mechanisms to cyclic GMP mediate the decrease in intracellular calcium and relaxation of rabbit aortic smooth muscle to nitric oxide.

1. The role of cyclic GMP in the ability of nitric oxide (NO) to decrease intracellular free calcium concentration [Ca2+]i and divalent cation influx was studied in rabbit aortic smooth muscle cells in primary culture. In cells stimulated with angiotensin II (AII, 10(-1) M), NO (10(-10) - 10(-6) M) increased cyclic GMP levels measured by radioimmunoassay and decreased [Ca2+]i and cation influx as indicated by fura-2 fluorimetry. 2. Zaprinast (10(-4) M), increased NO-stimulated levels of cyclic GMP by 3-20 fold. Although the phosphodiesterase inhibitor lowered the level of [Ca2+]i reached after administration of NO, the initial decreases in [Ca2+]i initiated by NO were not significantly different in magnitude or duration from those that occurred in the absence of zaprinast. 3. The guanylyl cyclase inhibitor, H-(1,2,4) oxadiazolo(4,3-a) quinoxallin-1-one (ODQ, 10(-5) M), blocked cyclic GMP accumulation and activation of protein kinase G, as measured by back phosphorylation of the inositol trisphosphate receptor. ODQ and Rp-8-Br-cyclic GMPS, a protein kinase G inhibitor, decreased the effects of NO, 10(-10) - 10(-8) M, but the decrease in [Ca2+]i or cation influx caused by higher concentrations of NO (10(-7) - 10(-6) M) were unaffected. Relaxation of intact rabbit aorta rings to NO (10(-7) - 10(-5) M) also persisted in the presence of ODQ without a significant increase in cyclic GMP. Rp-8-Br-cyclic GMPS blocked the decreases in cation influx caused by a cell permeable cyclic GMP analog, but ODQ and/or the protein kinase G inhibitor had no significant effect on the decrease caused by NO. 4. Although inhibitors of cyclic GMP, protein kinase G and phosphodiesterase can be shown to affect the decrease in [Ca2+]i and cation influx via protein kinase G, these studies indicate that when these mechanisms are blocked, cyclic GMP-independent mechanisms also contribute significantly to the decrease in [Ca2+]i and smooth muscle relaxation to NO.

1-Methyl-3-isobutylxanthine↗

PubMed1997

Reduced responsiveness of hypercholesterolemic rabbit aortic smooth muscle cells to nitric oxide.

The response to nitric oxide of intracellular free Ca2+ levels, measured by fura 2 fluorimetry, and cyclic GMP, measured by RIA, was evaluated on smooth muscle cells of the thoracic aorta in primary culture from normal and cholesterol-fed rabbits. Relaxation to acetylcholine and nitric oxide was also determined in isolated rings of aorta. After 10 weeks of high-cholesterol diet, the intact aorta relaxed less to both acetylcholine and nitric oxide. In cultured cells from hypercholesterolemic rabbits, intracellular Ca2+ oscillated, and the mean Ca2+ levels were approximately twofold greater than in normal aortic cells. Nitric oxide failed to affect basal Ca2+ in either cell type. The peak and sustained rise in intracellular Ca2+ induced by angiotensin II (10(-7) mol/L) were similar in the two cell types. However, nitric oxide (10(-10) to 10(-6) mol/L) decreased the sustained Ca2+ levels to a significantly smaller extent in cells from cholesterol-fed rabbits. In addition, in cells from hypercholesterolemic rabbits, nitric oxide added before angiotensin II inhibited to a smaller degree the transient increase in intracellular free Ca2+ caused by angiotensin II in the nominal absence of extracellular Ca2+, as well as the increase in Ca2+ associated with the addition of extracellular Ca2+. Measurements of fura 2 quenching caused by Mn2+ influx confirmed that nitric oxide inhibited the entry of extracellular divalent cations significantly less in cells from hypercholesterolemic rabbits. Basal levels of cyclic GMP were significantly less than normal, and nitric oxide increased levels of cyclic GMP to a significantly smaller degree in cells from cholesterol-fed rabbits. These data indicate a substantial resistance to nitric oxide action in aortic smooth muscle cells of cholesterol-fed rabbits. This observation is consistent with the notion that resistance of smooth muscle cells to nitric oxide contributes to abnormal endothelium-dependent vasodilation during hypercholesterolemia and can play a role in the pathogenesis of atherosclerosis.

Animals↗