Vascular reactivity in diabetes mellitus

Attenuation of store-operated Ca2+ entry and enhanced expression of TRPC channels in caudal artery smooth muscle from Type 2 diabetic Goto-Kakizaki rats

1. Previously, we found that Ca(2+) entry from the extracellular space via alpha(1)-adrenoceptor-activated, Ca(2+)-permeable channels, but not voltage-gated Ca(2+) channels, is impaired in endothelium-denuded caudal artery smooth muscle from Type 2 diabetic Goto-Kakizaki (GK) rats. In the present study, we investigated the impairment of Ca(2+) entry mechanisms via Ca(2+)-permeable channels from the extracellular space in response to alpha(1)-adrenoceptor stimulation (cirazoline) in endothelium-denuded caudal artery strips isolated from GK rats. 2. The contraction of caudal artery strips from GK rats in response to the sarcoplasmic reticulum Ca(2+)-ATPase inhibitor cyclopiazonic acid (10 micromol/L), which causes depletion of Ca(2+) stores and subsequent store-operated Ca(2+) (SOC) entry, was significantly depressed compared with that of Wistar rats (maximal force 0.023 +/- 0.004 vs 0.058 +/- 0.005 mN/mg tissue wet weight, respectively). These results suggest that receptor-activated Ca(2+) entry through SOC channels is impaired in caudal artery smooth muscle in GK rats. 3. The classic transient receptor potential (TRPC) channels, which constitute SOC and receptor-operated cation channels, play an important role in Ca(2+) regulation. Therefore, we investigated the mRNA and protein expression of TRPC channels in caudal artery smooth muscle from Wistar and GK rats using reverse transcription-polymerase chain reaction and immunoblotting. 4. Expression of TRPC1, TRPC3 and TRPC6 mRNA and protein was found in Wistar rats. However, in GK rats, in addition to the expression of these TRPC channels, mRNA and protein expression of TRPC4 was found. The expression of TRPC1 and TRPC6, but not TRPC3, was increased approximately twofold in GK rats compared with Wistar rats. 5. These results suggest that changes in TRPC channel expression may be responsible, in part, for the dysfunction of receptor-mediated Ca(2+) entry in caudal artery smooth muscle of GK rats.

Impairment of α1-adrenoceptor-mediated contractile activity in caudal arterial smooth muscle from type 2 diabetic Goto-Kakizaki rats

1. In the present study, we compared the responsiveness of de-endothelialized caudal artery smooth muscle strips, isolated from Type 2 diabetic Goto-Kakizaki (GK) and normal Wistar rats, to alpha(1)-adrenoceptor stimulation (cirazoline) and membrane depolarization (K(+)). 2. The contractile and myosin 20 kDa light chain (LC(20)) phosphorylation responses to 0.3 micromol/L cirazoline of caudal artery strips isolated from 12-week-old GK rats were significantly reduced compared with those of age-matched Wistar rats, whereas the contractile and LC(20) phosphorylation responses to 60 mmol/L K(+) were unaltered. 3. Stimulation of fura 2-AM-loaded strips from GK rats with 0.3 micromol/L cirazoline induced a significantly smaller rise in [Ca(2+)](i) (by approximately 20%) compared with that in strips from Wistar rats, whereas comparable Ca(2+) transients were evoked by K(+) in both. 4. Using quantitative polymerase chain reaction, no significant differences were detected in the mRNA expression of alpha(1A)-, alpha(1B)- and alpha(1D)-adrenoceptor subtypes between GK and Wistar rats. 5. Cirazoline (1 micromol/L)- and caffeine (20 mmol/L)-induced contractions in the absence of extracellular Ca(2+) were unaltered in GK rats, suggesting that the release of Ca(2+) from the sarcoplasmic reticulum in response to cirazoline does not differ between GK and Wistar rats. 6. The results of the present study suggest that Ca(2+) entry from the extracellular space via alpha(1)-adrenoceptor-activated, Ca(2+)-permeable channels, but not via membrane depolarization and voltage-gated L-type Ca(2+) channels, is impaired in caudal artery smooth muscle of GK rats.

Effect of dietary docosahexaenoic acid on the endothelium-dependent vasorelaxation in diabetic rats

1. The aim of the present study was to investigate the responses to acetylcholine (ACh; 3 nmol/L-30 micromol/L) and sodium nitroprusside (SNP; 3 nmol/L-30 micromol/L) of precontracted aortic rings from diabetic rats supplemented with docosahexaenoic acid (DHA). 2. Diabetes was induced by streptozotocin (STZ; 55 mg/kg). Diabetic and sham rats were fed, over a period of 8 weeks, either control diet or a DHA-supplemented diet. Aortic endothelial fatty acid composition was analysed by gas chromatography. The involvement of endothelial-derived nitric oxide (NO) and cyclo-oxygenase (COX) metabolites in response to ACh was assessed using the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (100 micromol/L) and the COX inhibitor indomethacin (1 micromol/L), respectively. 3. The DHA-supplemented diet induced a small increase in n-3 polyunsaturated fatty acids (PUFA; P < 0.001) owing to the incorporation of DHA in the endothelial cells of sham animals (1.6 +/- 0.2% in the DHA group compared with traces in the control group; P < 0.001) and diabetic animals (1.3 +/- 0.2% in the DHA group compared with traces in control group; P < 0.001), without a decrease in n-6 PUFA, despite a small decrease in arachidonic acid content (P < 0.05). Diabetes did not modify the incorporation of DHA in endothelial cells, but did significantly increase the arachidonic acid content (0.6 +/- 0.0 vs 0.4 +/- 0.1% in control group in the STZ and sham groups, respectively; P < 0.001). Acetylcholine-induced relaxation was significantly reduced in STZ groups compared with the sham groups (P < 0.001) and the DHA-supplemented diet did not modify these effects. In contrast, neither the DHA-supplemented diet nor diabetes affected the aortic relaxation induced by SNP. N(G)-Nitro-L-arginine methyl ester strongly inhibited the relaxant effects of ACh in the sham groups (P < 0.001) and abolished ACh-induced relaxation in the STZ groups (P < 0.001). The diet did not modify these effects. In the presence of indomethacin, the relaxation induced by ACh was decreased in the sham groups (P < 0.01), but not in the STZ groups. The DHA-supplemented diet did not have any effect on these responses. 4. In conclusion, these results suggest that, in the present study, the endothelial dysfunction occurring in the rat model of STZ-induced diabetes is associated with modifications of both the synthesis of COX derivatives and NO metabolism and is not affected by dietary supplementation with DHA.

Noncardiac pulmonary, endocrine, and renal preoperative evaluation of the vascular surgical patient

Patients who have vascular disease who are to undergo an operation are at risk for developing perioperative and postoperative complications caused by coexisting diseases. A comprehensive preoperative evaluation is critical in identifying these coexisting diseases, and the anesthetic plan might require modification. This article focuses on important aspects of the pulmonary, endocrine (diabetes), and renal systems during the preoperative evaluation of the vascular surgical patient.

Glucose-Dependent Enhancement of Spontaneous Phasic Contraction Is Suppressed in Diabetic Mouse Portal Vein: Association with Diacylglycerol-Protein Kinase C Pathway

We investigated portal vein (PV) contractility in diabetes using a mouse model (ob/ob mouse) of spontaneous noninsulin-dependent diabetic mellitus. Spontaneous phasic contraction in control mice (C57Bl) was increased in the presence of the thromboxane A(2) analog 9,11-dideoxy-11alpha, 9alpha-epoxymethanoprostaglandin F(2)alpha (U46619) in a time- and concentration-dependent manner. This response was enhanced under high glucose conditions (22.2 mM). Diacylglycerol (DG) was synthesized from glucose and was not affected by phospholipase C (PLC) inhibition under resting conditions in normal glucose. Inhibition of DG-induced PKC activation with 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo-(2,3-alpha)pyrrolo(3,4-c)-carbazole (Gö6976), a calcium-dependent protein kinase C (PKC) inhibitor, was only observed under normal glucose conditions. High glucose levels enhanced PLC-independent DG formation followed by an induction of total phosphatidylinositol turnover via calcium-independent PKC activation in C57Bl mice. In ob/ob mice, the high glucose-induced enhancement of PV contraction in response to U46619 was suppressed. These findings suggest that these differences are associated with long-term exposure of tissue to a hyperglycemic state. Under high glucose conditions, DG derived from glucose fell below 50% in C57Bl mice. Moreover, the DG-related calcium-independent PKC was desensitized in ob/ob mice. These results suggest that suppression of the glucose-induced enhancement of PV contraction involves both a decrease in glucose-derived DG formation and reduction of the glucose sensitivity of DG-related PKC.