Effect of elevated glucose on cyclic GMP and eicosanoids produced by porcine aortic endothelium.

Abstract

The short-term effects of elevated glucose on cyclic GMP (cGMP) and eicosanoid production in pig aortic endothelial cell monolayers was determined by incubating cells in 5.5 mM or 44 mM glucose for 6 hours. Bradykinin-or A23187-stimulated cGMP production was significantly reduced in cells incubated in 44 mM glucose compared with 5.5 mM glucose. Stimulation of cGMP levels with exogenously added nitric oxide (NO) was also decreased to a similar extent in cells exposed to 44 mM glucose. These data suggest that NO production stimulated by bradykinin or A23187 was unchanged by elevated glucose. Assayed eicosanoids, including 6-ketoprostaglandin (PG) F, o , PGEj, PGF^, and 15(S)-hydroxy-(5Z, 8Z, 11Z, 13£)-eicosatetraenoic acid, stimulated by bradykinin or A23187, were increased in cells exposed to 44 mM glucose. These eicosanoid products formed from exogenously added arachidonic acid did not differ between cells incubated in 5.5 mM or 44 mM glucose. Hyperosmolar concentrations of mannose or sucrose had no effect on cGMP levels but did mimic the effect of elevated glucose on eicosanoid production. These data suggest that hyperglycemia in diabetes may interfere with NO-induced guanylate cyclase activation but not NO production in the endothelium and that increased phospholipase activity, secondary to hyperosmolarity, may account for elevated eicosanoid levels. which has been identified as nitric oxide (NO), 2 stimulates smooth muscle guanylate cyclase to produce cyclic GMP (cGMP) and initiate relaxation. Eicosanoids also produced in the endothelium may act as vasodilators or vasoconstrictors, depending on the vascular bed and species.3 -5 Alterations in the production or action of these substances may explain abnormal endotheliumdependent vasomotor responses in several vascular diseases, including diabetes mellitus, hypertension, and hypercholesterolemia.5 " 7Studies on diabetic rabbit and rat models and human vascular tissue have shown decreased endotheliumdependent relaxations. 10 It is possible that the abnormal relaxation seen in diabetes is due to decreased levels of NO, increased vasoconstrictor eicosanoids, or a

Antioxidant pyrrolidine dithiocarbamate prevents defective bradykinin-stimulated calcium accumulation and nitric oxide activity following exposure of endothelial cells to elevated glucose concentration

“…Since the plateau phase of ionomycin was not altered by glucose, this suggests a defect that is unique to receptor-mediated coupling of intracellular Ca 2+ release and extracellular Ca 2+ entry. As opposed to the findings of defective Ca 2+ i signalling and NO activity by elevated glucose exposure of bovine (this study), porcine [22,23] and rat [24] endothelial cells, other investigators have shown that elevated glucose exposure enhanced basal or agoniststimulated Ca 2+ i signalling in porcine [21] and human umbilical vein endothelial cells [32]. These discrepancies may arise from variances in culturing conditions and media, type of endothelial cells, glucose concentration and exposure time, and/or the conditions of measurement of Ca 2+ i and NO/cyclic GMP.…”

“…Furthermore, the restoration of bradykinin-stimulated [Ca i ] was associated with an improvement in NO activity as judged by the improved cyclic GMP generated in RFL-6 detector cells. This is consistent with a role of Ca Previous studies have shown that elevated glucose decreases agonist-stimulated Ca 2+ i production or NO activity or both in porcine [22,23] and rat endothelial cells [24]. Furthermore, previous exposure of endothelial cells to exogenous reactive oxygen (e. g. peroxides) also diminishes receptor-dependent Ca 2+ i signalling [25±27].…”

The pathophysiological role of prostaglandins in penile erection

“…These studies suggest that there is an increase in the production of vasoconstrictor PGs in diabetic vascular tissue and vessels exposed to elevated glucose, which has been confirmed in radioimmunoassay studies [58]. Furthermore, cultured aortic endothelial cells exposed to elevated glucose produce increased quantities of PGs, such as PGF 2α [59]. These findings indicate that in diabetic conduit vessels, PGs lead to significant vascular dysfunction and may be responsible for the altered smooth muscle reactivity seen under these conditions.…”

A new look at the heart in diabetes mellitus: from ailing to failing

“…In the rat aorta of experimental diabetes, decreased functional NO activity, a diminished response to endothelium-dependent vasodilators and an unchanged response to endothelium-independent vasodilators has been observed [106]. In porcine aortic endothelium, hyperglycaemia has been shown to directly inhibit NO synthase and reduce endothelial cell guanylate cyclase activity [107].…”