No abstract

No abstract

In the present study, we examined the effects of chronic L-arginine treatment on plasma insulin levels and systolic blood pressure (SBP) in fructose-fed (F) rats. Fructose feeding resulted in hyperinsulinemia and elevated blood pressure when compared with that in controls (plasma insulin, 311.3+/-11.4 v control 164.4+/-11.8 pmol/L, P < .05; SBP, 135.4+/-4.2 v control 105.5+/-1.3 mm Hg, P < .05). L-arginine treatment of fructose-hypertensive rats prevented the development of hyperinsulinemia and hypertension (plasma insulin, 200.1+/-7.5 pmol/L; P < .05 compared with that in F rats; SBP, 108.0+/-0.9 mm Hg; P < .05 compared with F rats). However, treatment with L-arginine did not influence any of these parameters in control rats. Statistical analysis of the data of plasma insulin level and SBP, revealed a significant correlation between these two variables. On the other hand, L-arginine treatment of F rats prevented the increased glucose and insulin concentrations in response to oral glucose challenge. L-arginine treatment also prevented the decrease in insulin sensitivity of F rats. These results indicate that L-arginine treatment is able to prevent fructose-induced hypertension and hyperinsulinemia. Our data also suggest a strong relationship between hyperinsulinemia and hypertension in this hypertensive rat model. Therefore, the antihypertensive effect of L-arginine could be, at least in part, the result of the restoration of plasma insulin levels by its vasodilator ability to increase blood flow to insulin sensitive tissues.

There have been several attempts published in the literature related with orally effective insulin formulations, which are increasing in popularity. Some of the results indicate that it is possible to reduce blood glucose level by orally administered liposomal insulin formulations, but there is general need to understand the mechanism and effective components of the liposome formulations. In our study, liposomal insulin formulations were prepared using insulin (Humulin R) or protamine- containing insulin (Humulin N) with cholesterol, dipalmitoyl phosphatidylcholine (egg) (DPPC)-cholesterol mixture, and mucoadhesive agent (methyl cellulose, MC)-added DPPC-cholesterol mixture. A tablet formulation of insulin was also prepared. Formulations of liposomal insulin were introduced to mice and rats orally and reduced blood glucose levels were observed. The composition of phospholipid (DPPC, cholesterol and MC mixture) was found to be quite effective in reducing blood glucose levels. The pH of the solution and the presence of the protamine sulfate were found to be important. The application site was also found to be important because liposomal insulin formulations administered through the mouth or esophagus resulted in reduced blood glucose levels. Reduced blood glucose levels were also observed when tablet formulations of insulin were administered to rats orally.

In this study, the protective effects of L-arginine treatment in vivo on vascular reactivity of streptozotocin (STZ)-induced 12-week-old diabetic rats were examined. Loss of weight, polydipsia, polyphagia, hyperglycemia, hypoinsulinemia, and elevated levels of plasma cholesterol and triglyceride were observed in diabetic rats. L-arginine treatment (1 mg/mL in drinking water) did not significantly affect these metabolic and biochemical abnormalities. Plasma malondialdehyde (MDA) levels in untreated diabetic rats were also significantly higher than untreated controls. However, L-arginine treatment prevented the increase in MDA level of plasma of diabetic rats. Contractile responses, but not sensitivity to noradrenaline (NA), were significantly increased in diabetic rats compared to controls. Treatment of diabetic rats with L-arginine completely prevented the increase in NA responses. Relaxation response to acetylcholine (ACh), but not to sodium nitroprusside (SNP), in diabetic aorta has been found to be significantly decreased as compared with controls. However, there were no significant differences in pD 2 values of acetylcholine in either of the groups. L-arginine treatment increased the ACh responses to the control level. All effects of L-arginine on vascular reactivity were found to be specific for diabetic rats and not controls. These results suggest that functional abnormalities occurred in aorta from diabetic rat might at least in part result from L-arginine deficiency, and the lipid peroxidation-lowering effect of L-arginine may account for its protective effect on vascular reactivity of diabetic rats.