Reversal effects of L-arginine treatment on blood pressure and vascular responsiveness of streptozotocin-diabetic rats.

In the present study, we examined the reversal effects of L-arginine (L-ARG) treatment in vivo on blood pressure and on vascular responsiveness of chronic diabetic rats. Twelve weeks after streptozotocin (STZ) injection, the systolic blood pressures (SBP) of diabetic groups have been found to be significantly higher compared with that of control groups. L-ARG treatment for 4 weeks, begun 12 weeks after the onset of diabetes, induced a significant fall in SBP of diabetic rats. Maximal contractile response and sensitivity (pD(2)value) of the aortae to phenylephrine (PE) were significantly enhanced in diabetic rats compared with control subjects. Treatment of diabetic rats with L-ARG completely reversed the increases in responsiveness and sensitivity of aortae to PE. The relaxation response to acetylcholine (ACh), but not to sodium nitroprusside (SNP), in diabetic aorta has been found to be significantly decreased when compared with control subjects. The in vivo treatment with L-ARG reversed the decreased ACh responses to the control level. Plasma malondialdehyde (MDA) level of diabetic rats was also significantly higher than control subjects. However, L-ARG treatment normalized the increase in MDA level of plasma of diabetic rats. All of the effects of L-ARG treatment were found to be specific for diabetic rats but not control subjects. These results show that L-ARG treatment in vivo has a reversal effect on impaired vascular responses and increased oxidative stress. The present findings also suggest that oxidative stress that occurred in diabetes might cause or contribute to the development of hypertension by affecting vascular reactivity. On the other hand, the lipid peroxidation-lowering effect of L-ARG may account for its beneficial effect on SBP and vascular responsiveness of diabetic rats.

Alpha-lipoic acid treatment ameliorates metabolic parameters, blood pressure, vascular reactivity and morphology of vessels already damaged by streptozotocin-diabetes.

The present study investigated the effects of alpha-lipoic acid treatment (50 mg/kg/day) on the metabolism and vascular condition already damaged by streptozotocin (STZ)-diabetes in rats. Carbohydrate and lipid metabolism, oxidative stress and antioxidant status were assessed in non-diabetic controls, 12-week untreated diabetic and 12-week treated diabetic (untreated for 6 weeks and then treated with alpha-lipoic acid for the last 6 weeks) rats. Blood pressures of rats were measured by tail-cuff method. Vascular reactivity was evaluated in isolated aortic rings. Morphology of aorta was examined by electron microscopy technique. Alpha-lipoic acid treatment effectively reversed body weight, blood glucose, plasma insulin, cholesterol, triglycerides and lipid peroxidation levels of diabetic animals. STZ-diabetes resulted in increased blood pressure, which was partially improved by alpha-lipoic acid treatment. Although the superoxide dismutase (SOD) activity in aortic homogenates was not changed by diabetes or antioxidant treatment, catalase or glutathione peroxidase (GPx) activity significantly increased in untreated diabetic rats. Alpha-lipoic acid treatment improved catalase activity in diabetic aorta. The contractile effect of phenylephrine markedly increased in diabetic rings, which was completely reversed by alpha-lipoic acid treatment. The maximum vasorelaxant response of pre-contracted aortic rings exposed to cumulatively increased concentrations of acetylcholine was unaffected by diabetes or antioxidant treatment. Sodium nitroprusside-induced endothelium-independent relaxations were similar in all experimental groups. Various alterations caused by STZ-diabetes in aorta structure were partially ameliorated by alpha-lipoic acid treatment. The potency of alpha-lipoic acid on the reversal of hypertension by affecting vascular reactivity and morphology as well as general metabolism of diabetic rats confirms the importance of hyperglycemia-induced oxidative stress in the development of diabetes-induced vascular complications and suggests a potential therapeutic approach.

The effects of chronic L-arginine treatment on vascular responsiveness of streptozotocin-diabetic rats.

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 pD2 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.

Calmodulin content and in vitro contractility of duodenum from streptozotocin-induced diabetic rats: effects of insulin therapy and calmodulin antagonism.

The effects of experimental diabetes and insulin treatment on the decreased reactivity of isolated rat duodenum to KCl and calmidazolium, a specific calmodulin antagonist, were examined. After 8 weeks of streptozotocin diabetes, the contractile effect of KCl and the non-competitive antagonistic effect of calmidazolium against KCl on isolated rat duodenum were decreased. Calmodulin levels, as measured by radioimmunoassay, were also found to the decreased in duodenum from streptozotocin-diabetic rats. Neither impaired reactivity to KCl nor decreased calmodulin levels in diabetic rat duodenum were corrected by treatment with insulin (10 IU/kg for 20 days). Following insulin treatment, there was only a partial correction in the antagonistic effect of calmidazolium as shown by the increase in non-competitive antagonist affinity constant.

Duration-dependent changes in calcium responsiveness in the alloxan-diabetic rat intestine.

Disturbances of the gastrointestinal tract that are common in diabetes mellitus seem to be related to intestinal motility. In experimental models of diabetes, decreased calcium sensitivity has been demonstrated in various smooth muscles including those in the gastrointestinal tract. The main purpose of the present study was to examine further the calcium sensitivity in diabetic rat intestine and to understand if changes in the calcium sensitivity occur at an earlier stage of the disease. For this purpose, the effects of potassium and calcium were evaluated on nondepolarized and depolarized duodenum from rats with alloxan diabetes for 1 and 8 weeks and their age-matched controls. To evaluate the calcium sensitivity in rat duodenum, apparent affinity constants (pD2 values) and intrinsic activities (alpha E values) were calculated for every experimental conditions examined in this study. Both values (pD2 and alpha E) for the effects of potassium and calcium on the nondepolarized and depolarized duodenum, respectively, were not changed in 1-week diabetic rats. In contrast, intrinsic activities for the effects of potassium and calcium were found to be significantly decreased (p < 0.001) in the nondepolarized and depolarized duodenum from rats with alloxan diabetes for 8 weeks, whereas apparent affinity constants were not altered in this case. Taking into consideration all these experimental findings, the decreased calcium sensitivity in gastrointestinal tract seems to be closely related to decreased calmodulin levels and may occur at a later stage of diabetes as a linkage to long-term gastrointestinal complications.

Effect of insulin treatment on smooth muscle calmodulin levels in rats with long-term streptozotocin-diabetes.

Altered responses to several agonists have been reported in various smooth muscles from experimentally-diabetic animals suggesting a defective contractile process of smooth muscle. Recently, decreased smooth muscle calmodulin levels have been reported in streptozotocin-diabetic rats. However, the effectiveness of insulin on the decreased calmodulin levels in diabetic rats has not been questioned. Therefore, the present study was designed to examine the effect of insulin on smooth muscle calmodulin levels from streptozotocin-diabetic rats. Calmodulin levels of the smooth muscle were measured by a radioimmunoassay technique. Streptozotocin diabetes caused a significant decrease in tissue calmodulin levels of smooth muscles. Insulin therapy for 20 days did not correct the changes in calmodulin levels of rat smooth muscles, although it normalised blood glucose in streptozotocin-diabetic rats. These findings suggest that the altered smooth muscle calmodulin may contribute the defective contractile responses in diabetes and these changes may be resistant to insulin therapy.

The effects of glyburide and insulin on the decreased beta-adrenergic responsiveness of the gastrointestinal tract in rats with non-insulin-dependent diabetes.

1. Decreased beta-adrenergic responses have been reported in gastro-intestinal tract of rats with diabetes mellitus. Effects of glyburide and insulin on the decreased beta-adrenergic responsiveness of the gastro-intestinal tract due to non-insulin-dependent diabetes were investigated using duodenum, jejunum and ileum from rats which were injected with alloxan in their neonatal periods. 2. Insulin treatment of non-insulin-dependent diabetic rats for 10 days corrected the decreased beta-adrenergic responses of the isolated duodenum, jejunum and ileum confirming the previous results obtained from insulin-dependent diabetic rats. 3. Glyburide treatment alone for 3 weeks also reversed the changes in the gastro-intestinal beta-adrenergic responses of non-insulin-dependent diabetic rats. Combination of glyburide with insulin, however, did not cause an additive or supra-additive interaction in terms of beta-adrenergic sensitivities of the diabetic tissues. 4. The results obtained in the present study strongly suggested that non-insulin-dependent diabetes may cause a decrease in the number of gastro-intestinal beta-adrenoceptors, while glyburide and insulin treatments correct the changes related to beta-adrenoceptors. The effect of insulin on the beta-adrenergic sensitivity of diabetic rat duodenum, jejunum and ileum may occur via a direct mechanism, whereas glyburide seems to be effective on the beta-adrenergic responses through the increases in the insulin secretion and/or in the number of gastro-intestinal insulin receptors.

Altered alpha-adrenergic responses of vas deferens to noradrenaline and tyramine from rats with short- and long-term alloxan diabetes.

1. Functional and morphological abnormalities in vas deferens have been reported by both experimental and clinical studies as a cause of genital function abnormalities in diabetic males. 2. In the present study, contractile effects of noradrenaline and tyramine in isolated vas deferens from rats with short- and long-term alloxan diabetes were investigated by comparing with those from control rats. For this purpose, intrinsic activities (alpha E value) and apparent affinity constants (pD2 value) for contractile effects of noradrenaline and tyramine in the isolated rat vas deferens were calculated in normal rats and rats with short- and long-term alloxan diabetes. 3. Apparent affinity constants for contractile effects of noradrenaline in the isolated rat vas deferens were increased depending on both short- and long-term alloxan diabetes. By contrast, apparent affinity constants for contractile effects of tyramine in the isolated rat vas deferens were attenuated due to both short- and long-term alloxan diabetes. Intrinsic activities for both noradrenaline- and tyramine-induced contractions of rat vas deferens, however, were increased due to short-term diabetes and decreased due to long-term diabetes. 4. Experimental findings obtained in this study indicate that vas deferens preparations from rats with short- and long-term alloxan-induced diabetes exhibit altered alpha-adrenergic responsiveness depending on time elapsed. While short-term alloxan diabetes causes enhanced alpha-adrenergic responses in the rat vas deferens, the long-term diabetes decreases the responses in this tissue.

Vanadate treatment reverses gastrointestinal complications in the streptozotocin-diabetic rats.

1. Insulin-like effects of vanadium compounds have been reported in various experimental conditions. Effects of vanadate on the decreased beta-adrenergic responsiveness of the rat duodenum due to streptozotocin diabetes were investigated to determine its influence on diabetic gastro-intestinal complications as well as its effects on the carbohydrate metabolism. 2. Administration of sodium orthovanadate to streptozoticin-diabetic rats in drinking water (0.7 mg/ml) for 4 weeks resulted in an improvement of carbohydrate metabolism noticed by increased serum levels of insulin and decreased blood levels of glucose as reported in previous studies. 3. Vanadate treatment of streptozotocin-diabetic rats also corrected the diabetic changes in the beta-adrenergic responsiveness of the rat duodenum to salbutamol suggesting a beneficial effect on the diabetic complications of rat gastro-intestinal tract. The same treatment with vanadate did not cause any alteration in the beta-adrenergic responsiveness of isolated duodenum from non-diabetic rats. 4. From the findings obtained, it is concluded that vanadate possesses an insulin-like effect on the beta-adrenergic responsiveness of the rat gastro-intestinal tract. Since vanadate treatment did not alter the beta-adrenergic responses of isolated duodenum from non-diabetic rats it seems likely that the insulin-like effect of vanadate is dependent on increased responsiveness of the gastrointestinal tract to circulating insulin.

Effect of short and long term streptozotocin diabetes on smooth muscle calmodulin levels in the rat.

Diabetes mellitus is a metabolic disease associated with certain complications which have also been demonstrated in the experimental models of this disease. Altered responses to several agonists have been reported in various smooth muscles from alloxan or streptozotocin diabetic animals. Since these reports revealed a defect in the contractile process of smooth muscles from experimentally-induced diabetes, short and long term effects of diabetes on calmodulin levels in the smooth muscles of aorta, trachea, vas deferens and duodenum were investigated using streptozotocin diabetic rats. In spite of the fact that most of the reports have demonstrated the defective contractions in long term diabetic rats, short term effect (for 1 week) of diabetes on calmodulin levels in the smooth muscles of aorta, trachea, vas deferens and duodenum was also investigated in the present study using streptozotocin diabetic rats to understand whether the changes in calmodulin dependent contractile process begin at an earlier stage of the disease. Tissue calmodulin levels of the smooth muscles were measured by the radioimmunoassay technique using a [125I]-labeled kit. Although rats injected with streptozotocin exerted the characteristics of diabetes such as polyuria, polydipsy, polyphagy and elevated blood glucose levels, unchanged calmodulin levels were found in the rats with short term streptozotocin diabetes. In contrast, long term streptozotocin diabetes (for 8 weeks) was found to cause a significant decrease in tissue calmodulin levels of these four smooth muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of insulin on the decreased beta-adrenergic responses of duodenum and atrium isolated from streptozotocin diabetic rats.

1. Decreased beta-adrenergic responses have been reported in both gastro-intestinal tract and atrium of experimentally-induced diabetic rats. The present study was undertaken to investigate in vitro effects of insulin on decreased beta-adrenergic responses of the duodenum and atrium from streptozotocin-diabetic rats. 2. Insulin incubation (16.67 micrograms/ml) in bathing medium for 5 hr enhanced the decreased beta-adrenergic responses in the diabetic rat duodenum, but not those in the diabetic atrium. Incubation of bovine insulin with anti-bovine insulin antibody in the test-tube inhibited the improving effect of insulin on the decreased beta-adrenergic responses of diabetic rat duodenum. 3. In vitro treatment with the same dose of bovine insulin in bathing medium caused a decrease in the beta-adrenergic responses of the atria from both non-diabetic and diabetic rats. Anti-bovine insulin antibody also abolished the inhibitory effect of insulin on the rat atria. 4. These results strongly suggest that the experimental diabetes affects beta-adrenergic responsiveness of the rat gastro-intestinal tract through a different mechanism from that of the rat myocardium.

Basal and histamine-induced gastric acid secretion in alloxan diabetic rats.

1. Effects of alloxan-induced diabetes on the rat gastric acid secretion were investigated using a number of biostatistical models described earlier. 2. Histamine-induced gastric acid secretion was found to be decreased in alloxan-diabetic rats when compared with their age-matched controls. 3. Basal acid secretion was also decreased depending on experimentally-induced diabetes. 4. The above results strongly suggest that alloxan-induced diabetes depresses vagal activity and H2-receptor activity in the stomach.

The effects of glyburide and insulin on the cardiac performance in rats with non-insulin-dependent diabetes mellitus.

1. The effects of glyburide were studied on the myocardial contractile force and heart rate in the atria isolated from non-diabetic and non-insulin-dependent diabetic rats (diabetic). 2. In order to examine the myocardial changes in the alloxan model of non-insulin-dependent diabetes, atrial functions of 11-week old diabetic rats were evaluated by comparing with the atria from their age-matched controls. 3. Diabetic atria were found to possess an increased contractile force and reduced inotropic responses to isoprenaline as a consequence of non-insulin-dependent diabetes induced by neonatal alloxan injection. 4. However, no significant change was observed in the heart rate of diabetic atria in response to isoprenaline when compared with controls. 5. Since apparent affinity constant (pD2 value) calculated for the inotropic response of diabetic atria to isoprenaline was also reduced, it might be suggested that non-insulin-dependent-diabetes causes a decrease in the beta-adrenoceptor affinity of the rat atria. 6. Glyburide treatment (5 mg/kg/day per os) for 3 weeks was able to improve the reduced responsiveness of rat atria due to non-insulin-dependent diabetes as well. The results obtained in this study indicated that glyburide possesses an improving effect on the decreased beta-adrenergic responses of rat atria with non-insulin-dependent diabetes mellitus.

Beta-adrenergic responsiveness of the gastrointestinal tract in diabetic rats.

Recently, decreased gastrointestinal beta-adrenergic responses in experimental diabetes have been demonstrated. Gastrointestinal responses to beta-adrenoceptor agonists are impaired in both insulin-dependent and non-insulin-dependent diabetic rat. Insulin treatment improves the impaired gastrointestinal beta-adrenergic responsiveness of diabetic rats. The improvement seen with insulin treatment on beta-adrenergic responsiveness is closely related to protein biosynthesis. The decreased beta-adrenergic responses in diabetic rat gastrointestinal tract seem to result from a decrease in the number of beta-adrenoceptors. It is most likely that the decreased gastrointestinal beta-adrenergic responsiveness is related to an impairment in the turnover of beta-adrenoceptors as a consequence of diabetes and that insulin has a beneficial effect on the impaired receptor turnover.

Effect of lithium on gastro-intestinal complications in alloxan-diabetic rats.

1. Decreased beta-adrenergic and serotonergic responses have been reported in gastro-intestinal tract of experimentally diabetic rats. Effects of lithium on the decreased beta-adrenergic and serotonergic responsiveness of the gastro-intestinal tract due to diabetes were investigated using gastric fundus strips and proximal duodenum from alloxan diabetic rats. 2. A 6-day treatment with lithium chloride (2 mEq/kg i.p. in saline) normalized the decreased gastro-intestinal responses of the alloxan-diabetic rats, whereas the lithium treatment did not affect the elevated blood glucose levels due to experimental diabetes. 3. Furthermore, the lithium treatments of control and alloxan-diabetic rats did not alter the relaxing effect of manganese chloride on the isolated duodenum. 4. These results strongly suggest that the improving effect of lithium is not related to adenylate cyclase activation and may be as a consequence of its direct action on the diabetic gastro-intestinal smooth muscles.

Beneficial effect of insulin on the decreased gastrointestinal beta-adrenergic responses in streptozotocin-diabetic rats: a contributing role of protein biosynthesis.

The beneficial effect of insulin on the decreased gastrointestinal beta-adrenergic responses in experimentally diabetic rats has been reported. The effects of streptozotocin-induced diabetes and insulin on the isolated rat duodenum, precontracted with bethanechol, were examined in the absence and in the presence of protein synthesis inhibitors in isometric conditions. Streptozotocin-induced diabetes caused a decrease of the beta-adrenergic responses of the rat duodenum. In vitro insulin treatment corrected the decreased beta-adrenergic responses of rat duodenum due to streptozotocin-induced diabetes. In the presence of protein synthesis inhibitors, actinomycin D or cycloheximide, the beneficial effect of insulin on the decreased intestinal beta-adrenergic responses was significantly inhibited. These findings suggest that the beneficial effect of insulin in the rat duodenum might be related to a new receptor synthesis.

Evaluation of contraction time and recovery period as a parameter in the calcium antagonistic action on the K(+)-depolarized rat duodenum.

Verapamil, nifedipine, phentolamine, tolazoline, gentamicin and neomycin inhibited calcium-induced contractions of K(+)-depolarized duodenum of rat by shifting the concentration-response curves to the right. Non-competitive inhibitions were observed with trifluoperazine, lidoflazine, procaine and tetracaine. Lanthanum behaved as a partial agonist in this preparation, while nitroprusside was ineffective. Contraction times in the presence of the antagonists and recovery time of the Ca2+ responses after the removal of the antagonists from the bathing medium were evaluated. From the findings, it is suggested that the contraction time and the time required for tissue recovery after removal of a Ca2+ antagonist are parameters making K(+)-depolarized rat duodenum a potential tool for the evaluation of the pharmacological effects of Ca2+ antagonists.

Biostatistical modeling of the effect of intravenous histamine-infusion on the rat gastric acid secretion.

In this study, a variety of linear and nonlinear biostatistical models of regression were tested to evaluate the histamine-induced gastric acid secretion using the lumen-perfusion model in the rat. Among the linear, parabolic, and polynomial models tested, 3rd- and 4th-order polynomial models of regression exerted best correlations between the time and histamine-induced gastric acid secretion. In order to avoid undulatory behaviors in the regression curves, we conducted the polynomial regression analysis up to 5th order.

Decreased beta-adrenergic responses of rat small intestine due to non-insulin-dependent diabetes.

Relaxing responses to salbutamol of duodenum, jejunum and ileum isolated from alloxan-induced non-insulin-dependent diabetic rats were investigated by means of pharmacodynamic analysis using pD2 (apparent receptor affinity) and alpha E (intrinsic activity) values. beta-Adrenergic responses of these three intestinal parts of diabetic rats were found to be significantly decreased when compared to controls. The decreased responses may be attributable to a decrease in the number of beta-adrenergic receptors. The gastro-intestinal manifestations reported in diabetic patients are possibly linked to the occurrence of a decrease in beta-adrenergic receptors. Furthermore, this model seems to be useful for the investigations of gastro-intestinal complications resulting from non-insulin-dependent diabetes.