Induction of gastric lesions and hypoglycemic response by food deprivation in streptozotocin-diabetic rats

Nutrient induced type 2 and chemical induced type 1 experimental diabetes differently modulate gastric GLP-1 receptor expression

T2DM patients demonstrate reduced GLP-1 receptor (GLP-1R) expression in their gastric glands. Whether induced T2DM and T1DM differently affect the gastric GLP-1R expression is not known. This study assessed extrapancreatic GLP-1R system in glandular stomach of rodents with different types of experimental diabetes. T2DM and T1DM were induced in Psammomys obesus (PO) by high-energy (HE) diet and by streptozotocin (STZ) in Sprague Dawly (SD) rats, respectively. GLP-1R expression was determined in glandular stomach by RT PCR and immunohistomorphological analysis. The mRNA expression and cellular association of the GLP-1R in principal glands were similar in control PO and SD rats. However, nutrient and chemical induced diabetes resulted in opposite alterations of glandular GLP-1R expression. Diabetic PO demonstrated increased GLP-1R mRNA expression, intensity of cellular GLP-1R immunostaining, and frequency of GLP-1R positive cells in the neck area of principal glands compared with controls. In contrast, SD diabetic rats demonstrated decreased GLP-1 mRNA, cellular GLP-1R immunoreactivity, and frequency of GLP-1R immunoreactive cells in the neck area compared with controls. In conclusion, nutrient and chemical induced experimental diabetes result in distinct opposite alterations of GLP-1R expression in glandular stomach. These results suggest that induced T1DM and T2DM may differently modulate GLP-1R system in enteropancreatic axis.

Vulnerability of Gastric Mucosa in Diabetic Rats, Its Pathogenesis and Amelioration by Cuminum cyminum

Various studies have indicated that peptic ulcers occurring during the course of diabetic state are more severe and often associated with complications such as gastrointestinal bleeding. This study is the first attempt to understand the pathogenesis of gastric ulcers occurring during the diabetic state considering alternate biochemical pathways using suitable markers and its amelioration by Cuminum cyminum. In this study, diabetic rats showed a progressive increase in the stomach advanced glycated end products formation, gastric mucosal tumour necrosis factor-α and Thiobarbituric acid reactive substances levels as compared to normal control (nondiabetic) rats. There was decrease in gastric mucosal content, antioxidant enzymes and cellular ATPase enzyme levels of diabetic gastric mucosa when compared to the normal control group. mRNA expression of epidermal growth factor was found to be significantly higher as compared to normal control animals. Further methanol extract of Cuminum cyminum treatment to diabetic animals caused a reduction in blood glucose, and ulcer score when compared to diabetic control rats. It significantly increased gastric mucus content, antioxidant status and cellular ATPase enzyme levels as compared to diabetic control animals. Methanol extract of Cuminum cyminum inhibited advanced glycated end products formation in vitro as well as in vivo.

Possible biochemical effects following inhibition of ethanol-induced gastric mucosa damage by Gymnema sylvestre in male Wistar albino rats

CONTEXT

Gymnema sylvestre (GS) R. Br. (Gymnema) (Asclepiadaceae) has been used from ancient times as a folk medicine for the treatment of diabetes, obesity, urinary disorder, and stomach stimulation.

OBJECTIVE

The present study was designed to investigate the effects of G. sylvestre leaves ethanol extract on gastric mucosal injury in rats.

MATERIALS AND METHODS

Gastric mucosal damage was induced by 80% ethanol in 36 h fasted rats. The effect of G. sylvestre on gastric secretions induced in Shay rats was estimated. In stomach, wall mucus, non-protein sulfhydryl groups (NP-SH), malondialdehyde (MDA), total proteins and nucleic acids levels were estimated. Histopathological changes were observed.

RESULTS

G. sylvestre pretreatment at doses of 100, 200 and 400 mg/kg provided 27, 49, and 63% protection against the ulcerogenic effect of ethanol, respectively. Pylorus ligation accumulated 10.24 mL gastric secretions with 66.56 mEq of acidity in control rats. Pretreatment with G. sylvestre significantly inhibited the secretions volume and acidity in dose-dependent manner. Ethanol caused significant depletion in stomach-wall mucus (p < 0.001), total proteins (p < 0.01), nucleic acids (p < 0.001), and NP-SH (p < 0.001) levels. Pretreatment with G. sylvestre showed protection against these depleted levels in dose-dependent manner. The MDA levels increased from 19.02 to 29.22 nmol/g by ethanol ingestion and decreased with G. sylvestre pretreatments in dose-dependent manner.

CONCLUSION

The protective effect of G. sylvestre observed in the present study is attributed to its effect on mucus production, increase in nucleic acid and NP-SH levels, which appears to be mediated through its free radical scavenging ability and/or possible cytoprotective properties.

High sensitivity of gastric mucosa to ulcerogenic effect of indomethacin in rats with diabetes

One week after injection of streptozotocin (60 mg/kg intravenously), rats developed diabetes associated with a significant increase of gastric mucosa sensitivity to the ulcerogenic effect of indomethacin (35 mg/kg subcutaneously). Since potentiation of the ulcerogenic effect of indomethacin was observed only in rats subjected to fasting before drug injection, we hypothesize that this effect was caused by a drop of high glucose level in the blood after fasting.

The effect of dehydroepiandrosterone (DHEA) on renal function and metabolism in diabetic rats

Dehydroepiandrosterone (DHEA) is an endogenous steroid hormone involved in a number of biological actions in humans and rodents, but its effects on renal tissue have not yet been fully understood. The aim of this study is to assess the effect of DHEA treatment on diabetic rats, mainly in relation to renal function and metabolism. Diabetic rats were treated with subcutaneous injections of a 10mg/kg dose of DHEA diluted in oil. Plasma glucose and creatinine, in addition to urine creatinine, were quantified espectophotometrically. Glucose uptake and oxidation were quantified using radioactive glucose, the urinary Transforming Growth Factor β(1) (TGF-β(1)) was assessed by enzyme immunoassay, and the total glutathione in the renal tissue was also measured. The diabetic rats displayed higher levels of glycemia, and DHEA treatment reduced hyperglycemia. Plasmatic creatinine levels were higher in the diabetic rats treated with DHEA, while creatinine clearance was lower. Glucose uptake and oxidation were lower in the renal medulla of the diabetic rats treated with DHEA, and urinary TGF-β(1), as well as total gluthatione levels, were higher in the diabetic rats treated with DHEA. DHEA treatment was not beneficial to renal tissue, since it reduced the glomerular filtration rate and renal medulla metabolism, while increasing the urinary excretion of TGF-β(1) and the compensatory response by the glutathione system, probably due to a mechanism involving a pro-oxidant action or a pro-fibrotic effect of this androgen or its derivatives. In conclusion, this study reports that DHEA treatment may be harmful to renal tissue, but the mechanisms of this action have not yet been fully understood.

Effect of Agaricus blazei Murill on the pulmonary tissue of animals with streptozotocin-induced diabetes

The present study was designed to evaluate the oxidative stress as well as the therapeutic effect of Agaricus blazei Muril (A. Blazei) in rats with streptozotocin-induced diabetes. We used 25 Wistar rats, and DM was induced by injecting streptozotocin (70 mg/Kg i.p.). Agaricus blazei Muril was administered daily starting 40 days after disease onset. A. Blazei was tested as an aqueous extract for its phytochemical composition, and its antioxidant activity in vitro was also evaluated. Lipoperoxidation (LPO), and superoxide dismutase (SOD), catalase, and glutathione peroxidase activities were measured in the pulmonary tissue, as well as the presence of inducible nitric oxide synthase (iNOS), through immunohistochemistry. An anatomopathologic study was also performed. Phytochemical screening of A. Blazei detected the presence of alkaloids and saponins. The extract exhibited a significant antioxidant activity in the DPPH-scavenging and the hipoxanthine/xanthine oxidase assays. Pulmonary LPO increased in diabetic animals (0.43 ± 0.09; P < .001) as compared to the control group (0.18 ± 0.02), followed by a reduction in the A. Blazei-treated group (0.33 ± 0.04; P < .05). iNOS was found increased in the lung in diabetic rats and reduced in the A. Blazei-treated group. The pulmonary tissue in diabetic rats showed oxidative alterations related to the streptozotocin treatment. The A. Blazei treatment effectively reduced the oxidative stress and contributed to tissue recovery.

Anal pressure in experimental diabetes

PURPOSE

Diabetes mellitus is a metabolic endocrine disorder that affects many systems, the gastrointestinal system often being among the affected systems. This experimental study work was designed to demonstrate altered anal sphincter pressures in an experimental model of diabetes mellitus (DM).

MATERIALS AND METHODS

Male Wistar rats (mean weight = 250 g) were used and randomized in two groups (n = 10): CO = control and DM. DM was induced by administering a single dose of streptozotocin. Glycemic levels were measured at the start (time = 0) and end (time = 60) of the experiment and anorectal manometry at the end.

RESULTS

DM rats presented a significant increase in glycemia at day 60 (DM = 407.14 +/- 73.76) as compared to the control group (time 0 = 175.7 +/- 18.62 and time 60 = 198.04 +/- 28.66). Anorectal manometry showed a significant decrease in anal pressure in the DM group at day 60 (DM = 34.2 +/- 4.97) as compared to the CO group at the same time (CO = 67.4 +/- 2.06), with P < 0.01 and P < 0.001 (Student's t test).

CONCLUSIONS

The results suggest that DM, due to the high glycemic levels, lead to alterations such as anal sphincter hypotony, which may cause complications such as fecal incontinence.

Pharmacological evaluation of membrane-moderated transdermal system of glipizide

1. Membrane-moderated transdermal systems of glipizide were prepared using drug-containing carbopol gel (drug reservoir) and ethyl cellulose, as well as Eudragit RS-100, Eudragit RL-100 (Rohm Pharma, Darmstadt, Germany) and ethylene vinyl acetate (EVA; 2, 9 and 19% vinyl acetate content) rate-controlling membranes, and were subsequently evaluated in vitro (drug content and drug permeation studies) and in vivo (acute and long-term hypoglycaemic activity, effect on glucose tolerance, biochemical and histopathological studies, skin irritation test and pharmacokinetic studies in mice). 2. The drug content of the systems was found to be more than 99%. Variations in drug permeation patterns were observed among the formulations containing different rate-controlling membranes. 3. The system with the EVA (19% vinyl acetate) rate-controlling membrane was selected for in vivo experiments. This transdermal system produced better improvement with respect to hypoglycaemic activity, glucose tolerance and tested biochemical, histopathological and pharmacokinetic parameters all compared with oral administration and exhibited negligible skin irritation. 4. The transdermal system successfully prevented severe hypoglycaemia in the initial hours and it was also effective for chronic application.

Alterações gastrointestinais no diabetes mellitus: estresse oxidativo e fluxo sangüíneo da artéria mesentérica - estudo experimental

RACIONAL: Os sintomas gastrointestinais são freqüentes no diabetes mellitus e podem estar relacionados com o estresse oxidativo, que é definido pelo desequilíbrio entre os sistemas pró-oxidante e o antioxidante. OBJETIVO: Avaliar algumas das alterações gastrointestinais no modelo de diabetes mellitus, como o estresse oxidativo no estômago e no fígado de animais diabéticos e o fluxo sangüíneo na artéria mesentérica superior em diferentes tempos de estudo. MATERIAL E MÉTODOS: Os parâmetros utilizados para verificar o estresse oxidativo no fígado e no estômago foram a mensuração da lipoperoxidação, através das técnicas das substâncias reativas ao ácido tiobarbitúrico e da quimiluminescência e a avaliação da atividade das enzimas antioxidantes catalase, superóxido dismutase e glutationa transferase. Utilizaram-se ratos machos Wistar, pesando entre 250-350 g, que foram divididos em quatro grupos: grupo I - 7 dias de diabetes, grupo II- 30 dias de diabetes, grupo III - 60 dias de diabetes e grupo IV - 90 dias de diabetes. O diabetes foi induzido por administração de estreptozotocina 70 mg/kg intraperitonialmente. RESULTADOS: Houve aumento significativo na lipoperoxidação no estômago e no fígado de animais diabéticos somente no tempo de 90 dias. No estômago, foi encontrada significativa diminuição na atividade das enzimas antioxidantes catalase e glutationa transferase. No fígado, somente a enzima glutationa transferase apresentou diminuição significativa. Houve aumento no fluxo da artéria mesentérica superior dos animais diabéticos com 90 dias, quando comparados aos animais-controle. CONCLUSÕES: É possível supor que o aumento no estresse oxidativo no estômago e no fígado e a alteração no fluxo sangüíneo da artéria mesentérica superior sejam influenciados pelo tempo de diabetes e pela hiperglicemia encontrada nos animais estudados, o que determinaria as alterações gastrointestinais.

Glibenclamide transdermal patches: Physicochemical, pharmacodynamic, and pharmacokinetic evaluations

In the present study, matrix type transdermal patches containing glibenclamide were prepared using different ratios of ethyl cellulose (EC)/polyvinylpyrrolidone (PVP) and Eudragit RL-100 (ERL)/Eudragit RS-100 (ERS) by solvent evaporation technique. The possible drug and polymer interaction was studied by infrared spectroscopy, differential scanning calorimetry, and HPTLC analysis. All the prepared formulations were subjected to physicochemical studies (thickness, weight variation, drug content, moisture content and uptake, and flatness), in vitro release and in vitro permeation studies through mouse skin. The results suggested that there was no interaction between drug and polymers. Variations in drug release/permeation profiles among the formulations studied were observed. The microphotographs obtained by scanning electron microscopy showed the formation of pores on the surface of the patches after in vitro skin permeation studies. Based on physicochemical and in vitro skin permeation studies, the formulations with EC:PVP (3:2) and ERL:ERS (4:1) were selected for in vivo experiments. The hypoglycemic activity of the patches in comparison with oral glibenclamide administration was studied for acute (24 h) and long-term (6 weeks) effect in both normal and streptozotocin-induced diabetic mice. Various biochemical parameters (serum levels of high-density lipoprotein-cholesterol, triglycerides, total cholesterol, alanine transaminase, aspertate transaminase, urea, and creatinine and liver protein and glycogen content) and histopathological (liver, pancreas and stomach) studies were carried out in diabetic mice after treating for 6 weeks. The patches were subjected to skin irritation test (by both visual observation and histopathological evaluation), oral glucose tolerance test and pharmacokinetic evaluation in mice. The results revealed that the patches successfully prevented the severe hypoglycemia in the initial hours, which is the major side effect associated with oral route. The patches maintained similar effect during long-term treatment also. The transdermal systems produced better improvement with all the tested biochemical parameters compared to oral administration. They produced improved repair of the tissues after diabetes induced tissue injury and exhibited negligible skin irritation. The pharmacokinetic evaluation showed that the patches could maintain almost steady-state concentration of drug within the pharmacologically effective range for prolonged period of time. The better in vivo performance of the transdermal patches of glibenclamide in comparison with oral administration could be due to day-to-day glycemic control on long-term application.

Enhancement of peptone-induced gastric acid secretion in streptozotocin-induced diabetic rats

We compared the acid secretory response to peptone in normal and streptozotocin-induced diabetic rats. Animals were injected with streptozotocin and used after 5 weeks of diabetes with blood glucose levels of >350 mg/dl. Under urethane anesthesia, 2 ml peptone solution (2-8%) was instilled in the stomach through an acute fistula every 30 min. Peptone increased acid secretion in a concentration-dependent manner in normal rats, the maximal response being obtained at 8%. Likewise, the increased acid response was observed in diabetic rats, yet the maximal response observed at 4% was significantly greater than that in normal rats. In both cases, this response was inhibited potently by famotidine as well as YM-022 (a CCKB antagonist) and partially inhibited by atropine. Peptone increased luminal histamine and plasma gastrin levels in both normal and diabetic rats, and the former response was significantly greater in diabetic animals. The altered acid secretion and histamine output in diabetic rats were reverted by insulin treatment. Pentagastrin- but not histamine-induced acid secretion was also increased in diabetic rats. We conclude that peptone-induced acid secretion is increased in diabetic conditions. This phenomenon is insulin-dependent and associated with an enhanced release of histamine but not with an increased sensitivity of the parietal cells.

Food deprivation depletes gastric mucus glycoprotein in streptozotocin-induced diabetic rats

Fasting causes gastric mucosal damage in streptozotocin (STZ)-induced diabetic rats, but its pathogenic mechanism remains to be elucidated. The aim of the present study was to investigate the alteration of gastric mucosal mucin, one of the gastric defensive factors against the development of such damage. Diabetes was induced in rats by intravenous injection of STZ (65 mg/kg). The experiments were performed using 4-week STZ-diabetic rats with blood glucose levels above 350 mg/dl. The amount of gastric mucus glycoprotein was determined by gel filtration, and the distribution of neutral and acidic mucins in the stomach epithelium was examined by histochemical analysis. In normal rats, 24-h fasting neither affected the gastric mucin content nor caused any macroscopic gastric mucosal injury. In contrast, starvation significantly reduced the amount of total gastric mucus glycoprotein prior to the formation of mucosal lesions in the STZ-diabetic rats. Nine hours after food deprivation, the gastric damage developed in about 70% of the diabetic rats, the amount of mucus glycoprotein markedly decreased, and both the neutral and acidic mucins diminished in the epithelium. Taken together, in STZ-diabetic rats, fasting by itself depletes gastric mucus glycoprotein, and this depletion may be involved in the pathogenic mechanism of the formation of gastric mucosal lesions.

Fasting induces impairment of gastric mucosal integrity in non-insulin-dependent diabetic (db/db) mice

BACKGROUND

Although diabetic patients often have gastrointestinal complications, the gastric mucosal function in diabetes has not been well documented.

AIM

To investigate the effect of fasting on the gastric mucosa in C57BL/KsJ-db +/+ db (db/db) mice, genetically non-insulin-dependent diabetic animals.

METHODS

Blood glucose levels, gastric mucosal morphology, and the amount of gastric mucin were examined before and after 18 h of fasting with free access to water in db/db mice and their non-diabetic littermates (db/m).

RESULTS

Although 18 h of fasting reduced the blood glucose levels of both db/db and db/m mice, fasting decreased the amount of gastric adherent mucin and caused haemorrhagic gastric lesions only in db/db mice. After fasting, oral administration of ethanol induced much more severe gastric damage in db/db than in db/m mice. The above fasting-induced gastric damage such as haemorrhagic lesions, loss of the mucin, and the increased sensitivity to ethanol worsened as the duration of diabetes became longer. Glucose ingestion in drinking water during the fasting counteracted the fall in blood glucose and prevented the decrease in the amount of gastric mucin and the formation of gastric mucosal lesions in db/db mice.

CONCLUSION

These findings indicate that fasting-induced glucose deficit causes gastric mucosal lesions and increases the susceptibility of gastric mucosa to noxious agents owing to the loss of mucus glycoprotein in db/db mice. Prolonged diabetes is likely to augment the severity of fasting-induced impairment of the gastric mucosal function.

Gastric acid secretion in streptozotocin-diabetic rats--different responses to various secretagogues

We compared gastric acid secretion in response to various stimuli in normal and streptozotocin (STZ)-induced diabetic rats, in an attempt to characterize the alteration of acid secretory response in diabetic conditions. Animals were injected STZ (70 mg x kg(-1), i.p.) and used after 5 weeks of diabetes with blood glucose > 350 mg x dL(-1). Under urethane anesthesia, a rat stomach was mounted on an ex vivo chamber, perfused with saline and acid secretion was measured at pH 7.0 using a pH-stat method and by adding 100 mM NaOH. The acid secretion was stimulated by i.v. infusion of either histamine (4 mg x kg(-1) x h(-1)), pentagastrin (60 microg x kg(-1) x h(-1)) or carbachol (20 microg x kg(-1) x h(-1)) or i.v. injection of YM-14673 (0.3 mg x kg(-1)), an analog of thyrotropin-releasing hormone, or vagal electrical stimulation (2 ms, 3 Hz, 0.5 mA). In normal rats, gastric acid secretion was increased in response to either histamine, pentagastrin, carbachol, YM-14673 or electrical vagal stimulation. In STZ diabetic rats, however, changes in acid secretion varied depending on the stimuli; the acid secretory responses to histamine remained unchanged, those to YM-14673 and vagal electrical stimulation significantly decreased, but the responses to both pentagastrin and carbachol were significantly enhanced as compared to normal rats. Luminal release of histamine in response to both pentagastrin and carbachol was increased in STZ-diabetic rats as compared to normal animals. The altered acid secretory responses in STZ diabetic rats were partially reversed by daily injection of insulin with amelioration of high blood glucose levels. These results suggest that STZ-diabetic rats showed different changes in gastric acid secretory responses to various stimuli; no change in response to histamine, a decrease to both YM-14673 and vagal electrical stimulation and an increase to both pentagastrin and carbachol. The increased acid secretory response may be associated with an enhanced release of mucosal histamine, while the decreased response may be due to vagal neuropathy.

Increased susceptibility of gastric mucosa to ulcerogenic stimulation in diabetic rats--role of capsaicin-sensitive sensory neurons

1. We examined the gastric mucosal blood flow (GMBF) and ulcerogenic responses following barrier disruption induced by sodium taurocholate (TC) in diabetic rats and investigated the role of capsaicin-sensitive sensory neurons in these responses. 2. Animals were injected streptozotocin (STZ: 70 mg kg(-1), i.p.) and used after 5, 10 and 15 weeks of diabetes with blood glucose levels of > 350 mg dl(-1). The stomach was mounted on an ex-vivo chamber under urethane anaesthesia and exposed to 20 mM TC plus 50 mM HCl for 30 min in the presence of omeprazole. Gastric transmucosal potential difference (PD), GMBF, and luminal acid loss (H+ back-diffusion) were measured before and after exposure to 20 mM TC, and the mucosa was examined for lesions 90 min after TC treatment. 3. Mucosal application of TC caused PD reduction in all groups; the degree of PD reduction was similar between normal and diabetic rats, although basal PD values were lower in diabetic rats. In normal rats, TC treatment caused luminal acid loss, followed by an increase of GMBF, resulting in minimal damage in the mucosa. 4. The increased GMBF responses associated with H+ back-diffusion were mitigated in STZ-treated rats, depending on the duration of diabetes, and severe haemorrhagic lesions occurred in the stomach after 10 weeks of diabetes. 5. Intragastric application of capsaicin increased GMBF in normal rats, but such responses were mitigated in STZ diabetic rats. The amount of CGRP released in the isolated stomach in response to capsaicin was significantly lower in diabetic rats when compared to controls. 6. The deleterious influences on GMBF and mucosal ulcerogenic responses in STZ-diabetic rats were partially but significantly antagonized by daily insulin (4 units rat(-1)) treatment. 7. These results suggest that the gastric mucosa of diabetic rats is more vulnerable to acid injury following barrier disruption, and this change is insulin-sensitive and may be partly accounted for by the impairment of GMBF response associated with acid back-diffusion and mediated by capsaicin-sensitive sensory neurons.

Impaired insulin but normal pentagastrin effect on gastric acid secretion in diabetic rats: a role for nitric oxide

Significant changes in gastrointestinal function, decreased gastric secretion and motility in particular, are often observed in patients with chronic diabetes. The mechanisms leading to those remain unclear. In these studies we evaluated the gastric acid secretory response to insulin and pentagastrin in normal Wistar and streptozotocin diabetic rats. We also sought to determine the role of nitric oxide (NO) in this process. The animals were anesthetized with sodium pentobarbital. Warm saline was perfused through a polyethylene tube placed in the oesophagus and collected from the duodenum at 10 min intervals. Following a 50 min equilibration period, a bolus intra-jugular infusion of insulin (4.0 U/kg), 2-deoxyglucose (200 mg/kg) or pentagastrin 4.0 (ug/kg) was started and samples of the gastrointestinal perfusate were collected for an additional 80 min. Insulin-stimulated acid secretion peaked 60 min after bolus infusion in normal animals; a response that was significantly decreased in the diabetic rats. Similarly, 2-deoxyglucose-induced glucopenia increased gastric acid secretion to a lower extent in diabetic versus normal rats. The stimulatory response to pentagastrin was prompt and essentially equal in normal and diabetic animals. However, when hypoglycemia was prevented by glucose infusion, insulin did not stimulate gastric acid secretion in normal rats. Further, glucose infusion in these animals actually enhanced the secretory response to pentagastrin. Nitro-L-arginine methyl ester (L-NAME 20 mg/kg i.v.), an inhibitor of NO synthetase, also prevented the secretory response to insulin but not to pentagastrin. Preinfusion of arginine (100 mg/kg i.v.) in diabetic rats restored the gastric secretory response to insulin toward that of normal animals. We conclude that the gastric acid secretory response to insulin, but not to pentagastrin, is decreased in diabetic animals, that this response may operate through a NO mediated mechanism possibly set in motion by central nervous system glucopenia and that this NO-mediated mechanism is attenuated in diabetes.

Impaired duodenal bicarbonate secretion in diabetic rats. Salutary effect of nitric oxide synthase inhibitor

We previously reported the impaired HCO3- secretion and the increased mucosal susceptibility to acid in the duodenum of streptozotocin (STZ)-induced diabetic rats. In this study, we investigated the salutary effect of the NO synthase inhibitor L-NAME (NG-nitro-L-arginine methyl ester) on these changes and compared it with those of insulin. Animals were injected streptozotocin (STZ: 70 mg/kg, ip) and used after 1, 3-4, and 5-6 weeks of diabetes with blood glucose levels of > 300 mg/dL. Under urethane anesthesia the HCO3- secretion was measured in the proximal duodenal loop using a pH-stat method and by adding 10 mM HCl. L-NAME (20 mg/kg x 2) or insulin (4 units/rat) was administered sc for 4-5 weeks, starting 1 week after STZ treatment. The duodenal HCO3- secretory responses to various stimuli such as mucosal acidification (10 mM HCl for 10 min), 16,16-dimethyl prostaglandin E2 (dmPGE2: 10 micrograms/kg, i.v.), and vagal stimulation (0.5 mA, 2 ms, 3 Hz) were significantly decreased in STZ-treated rats, depending on the duration of diabetes. Repeated administration of L-NAME, starting from 1 week after STZ treatment, significantly reduced blood glucose levels toward normal values and restored the HCO3- responses to various stimuli in STZ rats, the effects being similar to those observed after supplementation of insulin. Diabetic rats developed duodenal lesions after perfusion of the duodenum with 150 mM HCl for 4 h, but this ulcerogenic response was significantly inhibited by the repeated treatment with L-NAME as well as insulin. We conclude that L-NAME is effective in ameliorating hyperglycemic conditions in STZ-diabetic rats, similar to insulin, and restores the impaired HCO3- secretion and the increased mucosal susceptibility to acid in diabetic rat duodenums.

Protection by amylin of gastric erosions induced by indomethacin or ethanol in rats

1. The effect of amylin on gastric ulcers induced by oral administration of indomethacin (Indo, 20 mg kg-1 at a dosing volume of 5 ml) or ethanol 50% (EtOH, 1 ml/rat) was investigated in conscious rats. 2. Amylin given intracerebroventricularly (0.22, 0.66 and 2.2 micrograms/rat, i.c.v.) demonstrated a dose-dependent cytoprotective effect against both Indo and EtOH-induced ulcers. In contrast, amylin, given subcutaneously at doses effective in inhibiting acid gastric secretion (2.5, 10 and 40 micrograms kg-1, s.c.), did not show any cytoprotective effect. 3. The interaction between amylin and endogenous nitric oxide (NO) in the maintenance of gastric mucosal integrity was investigated by pretreating the rats with a selective inhibitor of NO-synthesis, NG-nitro-L-arginine methyl ester (L-NAME, 25 and 70 mg kg-1, s.c.). Administration of L-NAME to rats did not significantly increase the degree of the Indo-induced ulcer index and was not able to remove the protective effect of amylin on Indo-induced ulcers, thus excluding a role for endogenous NO in mediating the protective effect of this peptide. 4. To determine whether the cytoprotective effect of amylin was mediated by endogenous prostaglandins, we studied the effect of amylin (2.2 micrograms/rat, i.c.v.) on EtOH- induced ulcers in rats pretreated with Indo (10 mg kg-1, s.c.) to inhibit prostanoid biosynthesis; Indo was injected 30 min before amylin and EtOH after a further 30 min. Pretreatment with Indo did not significantly increase the ulcer index induced by EtOH but counteracted the ability of amylin to prevent the ulcer formation. 5. These findings suggest that amylin exerts a gastroprotective activity that is not strictly related to inhibition of acid gastric secretion and can be partly explained through a prostaglandin-dependent mechanism mediated by receptors for the peptide in the brain. Amylin might be considered as a new brain-gut peptide.

Effects of bis(maltolato)oxovanadium(IV) are distinct from food restriction in STZ-diabetic rats

In association with the insulin-mimetic properties, vanadium and related compounds have been shown to normalize hyperphagia associated with diabetes mellitus. The objective of this study was to clarify the effects of an organic vanadium compound, bis(maltolato)oxovanadium(IV) (BMOV), vs. food restriction on the metabolic abnormalities that occur in diabetes. BMOV was administered daily in drinking water to streptozotocin (STZ)-diabetic rats for 6 wk. Pair-fed groups were fed based on the intake for their respective counterparts from the previous day. Plasma parameters were measured weekly after a carefully controlled 5-h fasting period. BMOV reduced plasma glucose (diabetic = 31.2 +/- 1.9, diabetic treated = 10.2 +/- 1.8, and diabetic pair fed = 34.2 +/- 1.1 mM), triglyceride, and cholesterol levels to normal without a concomitant increase in plasma insulin levels. There was no body weight gain in the diabetic pair-fed group compared with all other groups. BMOV but not pair feeding was effective in preventing the decreased cardiac function observed in STZ-diabetic rats. These data suggest that the glucose-lowering properties of BMOV are independent of the effects of dietary restriction and reinforce the efficacy of BMOV as an effective antihyperglycemic agent.

Failure of the nitric oxide synthase inhibitor to stimulate duodenal bicarbonate secretion in streptozotocin-diabetic rats

We examined the HCO(3)- stimulatory effects of L-NAME (N(G)-nitro-L-arginine methyl ester) in the proximal duodenum of streptozotocin (STZ)-induced diabetic rats and compared with those of 16,16-dimethyl prostaglandin E2 (dmPGE2) and vagal electrical stimulation. Male SD rats were given STZ (70 mg/kg) i.p., and the experiments were done using 1 approximately 6 week STZ-diabetic rats with blood glucose levels of >300 mg/dl. Under urethane anesthesia the HCO(3)- secretion was measured in the proximal duodenal loop using a pH-stat method and by adding 10 mM HCl. Hyperglycemic conditions appeared 1 week after STZ treatment and remained during 6 week-test period. The duodenal HCO(3)- secretory response to L-NAME was significantly decreased in STZ-diabetic rats; the degree of reduction was dependent on the duration of diabetes, and the stimulatory effect disappeared completely in rats after 5 approximately 6 weeks of diabetes. Intravenous administration of L-NAME markedly increased arterial blood pressure with significant decrease in heart rate in normal rats, whereas in STZ-diabetic rats this agent caused only pressor response without any effect on heart rate. STZ-diabetic rats also secreted significantly less amount of HCO(3)- from the duodenum in response to dmPGE2 and vagal electrical stimulation after 5 approximately 6 weeks of diabetes. These all changes observed in STZ-diabetic rats were significantly reversed by daily injection of insulin. These results suggest that 1) L-NAME failed to stimulate duodenal HCO(3)- secretion in STZ-diabetic rats, and 2) impairment of the duodenal HCO(3)- secretory ability in STZ-diabetic conditions is due to both vagal-dependent neuronal dysfunction and decreased sensitivity of the secreting cell.