Vanadium is an oral insulin-mimetic agent that diminishes hyperglycemia, improves beta-cell insulin store and secretory function, and can reverse the diabetic state chronically after withdrawal from treatment. As food restriction has been reported to enhance insulin sensitivity and reduce insulin demand, we assessed the contribution of a reduced food intake to the glucose lowering and beta-cell protective effects of vanadium. Streptozotocin (STZ)-diabetic rats were untreated (D) or administered vanadyl sulfate in the drinking water (DT) at one week prior to and for 5 weeks following the administration of STZ. An additional group was pair-fed (DP) with an equal amount of food as that consumed by the DT group. Shortly after the induction of diabetes, hyperglycemic D rats demonstrated a significant rise in plasma insulin to levels that initially exceeded that of the controls. This was followed by a steady reduction over several weeks, suggesting a gradual depletion of functional beta-cells. Both vanadium treatment and pair-feeding abolished the insulin hypersecretory response following STZ administration. Glucose lowering was enhanced in DT animals when administered higher concentrations of vanadium, despite no further reduction in food intake, and all DT animals (10/10) were normoglycemic by 5 weeks. Mean pancreatic insulin content in DT rats was improved fourfold and was associated with a greater number of granulated beta-cells. Conversely, food restriction only modestly improved glycemia and the pancreatic insulin store and, unlike DT, DP rats remained highly glucoseintolerant. At 5 weeks of diabetes, fed circulating glucose and insulin levels were strongly correlated (P=0.0002) in the D and DP groups, supporting the notion that glucose lowering with food restriction is dependent on improved plasma insulin levels. A separate correlation was observed in DT animals within a lower range of plasma insulin, suggesting that vanadium, unlike food restriction, reduced plasma glucose by enhancing insulin sensitivity. Thus, vanadium preserves beta-cells in STZ-diabetes at least partially by abolishing the insulin hypersecretory response and the eventual exhaustion of residual insulin stores following a moderate dose of STZ. This property of vanadium would appear to be useful in the treatment of prediabetic and newly diagnosed insulin-dependent diabetes mellitus.

Keywords matrix metalloproteinase; insulin resistance; hypertension; endothelial dysfunction; fructose; heat shock protein 90 ---------------------------------------------------------------- Received BACKGROUND AND PURPOSEInsulin resistance is often found to be associated with high blood pressure. We propose that in insulin-resistant hypertension, endothelial dysfunction is the consequence of increased activity of vascular MMP-2. As MMP-2 proteolytically cleaves a number of extracellular matrix proteins, we hypothesized that MMP-2 impairs endothelial function by proteolytic degradation of endothelial NOS (eNOS) or its cofactor, heat shock protein 90 (HSP90). EXPERIMENTAL APPROACHWe tested our hypothesis in bovine coronary artery endothelial cells and fructose-fed hypertensive rats (FHR), a model of acquired systolic hypertension and insulin resistance. KEY RESULTSTreatment of FHRs with the MMP inhibitor doxycycline, preserved endothelial function as well as prevented the development of hypertension, suggesting that MMPs impair endothelial function. Furthermore, incubating endothelial cells in vitro with a recombinant MMP-2 decreased NO production in a dose-dependent manner. Using substrate cleavage assays and immunofluorescence microscopy studies, we found that MMP-2 not only cleaves and degrades HSP90, an eNOS cofactor but also co-localizes with both eNOS and HSP90 in endothelial cells, suggesting that MMPs functionally interact with the eNOS system. Treatment of FHRs with doxycycline attenuated the decrease in eNOS and HSP90 expression but did not improve insulin sensitivity. CONCLUSIONS AND IMPLICATIONSOur data suggest that increased activity of MMP-2 in FHRs impairs endothelial function and promotes hypertension. Inhibition of MMP-2 could be a potential therapeutic strategy for the management of hypertension. AbbreviationsPKB, protein kinase B; Ang II, angiotensin II; APMA, p-aminophenyl mercuric acetate; BCAE cells, bovine coronary artery endothelial cells; Con A, concanavalin A; EGFR, epidermal growth factor receptor; EGM, endothelial growth medium; FHR, fructose hypertensive rat HSP90, heat shock protein 90; ISI, insulin sensitivity index; L-NAME, N G -nitro-L-arginine methyl ester; PE, phenylephrine; SMA, superior mesenteric artery; TIMP, tissue inhibitor of MMP BJP British Journal of Pharmacology

A series of imidazo[1,2-alpha]pyrazine derivatives was synthesized by condensation of alpha-halogenocarbonyl compounds and aminopyrazines. Various compounds resulted from competitive reactions or reagent isomerization and demonstrated in vitro uterine-relaxing and in vivo antibronchospastic activities. On isolated atria, 5-bromoimidazo-[1,2-alpha]pyrazine showed positive chronotropic and inotropic properties; the latter was associated with an increase in the cyclic AMP tissue concentration. Potentiation of the isoproterenol positive inotropic effect of 5-bromoimidazo[1,2-alpha]pyrazine and the lack of blockade of the 5-bromoimidazo[1,2-alpha]pyrazine positive inotropic effect by propranolol suggested phosphodiesterase-inhibiting properties.

The ultrastructural changes in the left ventricles of rabbits with alloxan (100 mg/kg i.v.)-induced diabetes were examined. Injection of alloxan resulted in a diabetic state characterized by increased hemoglobin glycosylation, blood and urine glucose and a significant depression of serum insulin levels. Electron microscopic examination of 10-week diabetic hearts revealed a spectrum of abnormalities ranging from mild to severe. Cardiac muscle cells in diabetic hearts showed some myofibrillar damage and varying degrees of contraction. The most prominent findings, however, were alterations in the mitochondria. Swollen and fragmented mitochondria containing amorphous dense bodies were evident upon electron microscopic examination. The cristae in the mitochondria appeared distorted and in some cases were completely lysed. A marked increase in lipid droplets and glycogen granules was also apparent. In addition, the sarcoplasmic reticulum was dilated and contained varying degrees of electron-dense material. These ultrastructural alterations suggest that the cardiomyopathy observed in alloxan-induced diabetic rabbits could be due to alterations in the vasculature or may be secondary to a number of metabolic alterations previously reported in this model.

Ventricular hypertrophy and hypothyroidism are each characterized by impaired cardiac muscle relaxation and sarcoplasmic reticulum (SR) calcium uptake activity. A previous report also showed that hypothyroidism does not reverse ventricular hypertrophy (left-to-right ventricular weight ratios) of spontaneously hypertensive rats (SHR). We characterized the effects of thyroidectomy of 8 wk duration on relaxation of ejecting hearts and on SR calcium uptake activity from SHR and nonhypertrophic Wistar-Kyoto rat (WKY) controls. Relaxation was quantified by plotting maximum left ventricular pulse pressure (Pmax) vs. the area under the falling phase of the left ventricular pressure wave at three different pressure loads. Ventricles of euthyroid SHR were characterized by impaired relaxation and depressed SR calcium uptake activity compared with those of euthyroid WKY, confirming earlier studies. Thyroidectomy reduced ventricular relaxation and SR calcium uptake activities to about the same extent in SHR and WKY strains so that these measurements were most depressed in the SHR hypothyroid group. When all groups were considered, the extent of mechanical relaxation ex vivo and the rate of SR calcium uptake in vitro were well correlated.