Effects of streptozotocin-diabetes on rat intestinal mucin and goblet cells

Intestinal mucin and goblet cells were examined in streptozotocin-diabetic rats and age-matched controls. Mucin (tissue content and secretion) was measured using a highly specific enzyme-linked immunoassay. In contrast to the increased protein to deoxyribonucleic acid ratio, an absolute decrease was observed in the mucin to deoxyribonucleic acid ratio in mucosal homogenates of the diabetic intestine. This was not due to a loss of goblet cells as their numbers per crypt-villus unit increased in diabetic rats (in proportion to the rise in enterocyte numbers and crypt-villus length). Histochemically, goblet cell mucin was unchanged in diabetes. After a 90-min incubation of everted intestinal segments in Krebs' buffer, pH 7.4, at 37 degrees C, the amount of mucin released into the medium was the same in diabetic and control rats when expressed relative to tissue deoxyribonucleic acid. However, secreted mucin represented a significantly larger proportion of the total tissue mucin content in diabetic animals. Thus, to maintain mucin output at normal levels, the rate of mucin secretion is apparently increased in the diabetic intestine, despite (or perhaps causing) a large decrease in the tissue mucin content.     

Experimental streptozotocin-induced diabetes and intestinal glucose metabolism in the rat,in vivo and in vitro

The intestine has a high glycolytic activity, but its metabolic role could be altered in diabetes mellitus. The aim of the present work was to investigate in vivo the glucose retained and the lactate produced by the intestine of normal and diabetic rats and in vitro the effect of different arterial glucose concentrations on glucose utilization and lactate, alanine, and pyruvate production in normal and diabetic rats when the glucose is supplied to the intestine exclusively via the vascular route. In vivo, the normal and diabetic rats retained similar percentages of the arterially supplied glucose (14.7±3.2 and 12.6±2.4, respectively). In vitro, when the preparations were perfused under hyperglycemic conditions, the glucose consumed, as a fraction of the quantity infused, was significantly lower (P<0.05) in the diabetic (247.0±22.8 mol/mmol infused glucose) than in normal (315.0±16.3 mol/mmol infused glucose) rats. The lactate produced was significantly higher in diabetic than in normal rats whether the preparations were perfused under isoglycemic (P<0.01; 1916.4±124.0 vs 1284±67.7 mol/mmol consumed glucose) or hyperglycemic (P<0.05; 1356.4±199.7 vs 898.0±87.3 mol/mmol consumed glucose) conditions. There was significantly (P<0.05) greater alanine release from the diabetic (123.7±21.8 mol/mmol consumed glucose) than from the normal (40.7±10.3 mol/mmol consumed glucose) rat preparations perfused under isoglycemic conditions.     

Altered hypothalamic-pituitary function in the adult female rat with streptozotocin-induced diabetes

Summary Infertility associated with anovulation and loss of regular oestrous cyclicity is a consequence of diabetes mellitus in the rat. In an attempt to define loci of altered function, studies were undertaken to examine various aspects of hypothalamic-pituitary function in rats treated with streptozotocin. Medial basal hypothalamic fragments from adult female diabetic rats contained the same amount of gonadotrophin-releasing hormone but, with depolarization, released slightly but insignificantly (p>0.05) more than did those from control animals. Furthermore, release of luteinizing hormone from pituitaries exposed to hypothalamic gonadotrophin-releasing hormone was not altered by diabetes. Removal of the negative feedback effect of gonadal steroids upon the hypothalamic-pituitary axis produced an increase in luteinizing hormone and follicle stimulating hormone concentrations in the serum of normal rats within 6h (p<0.05), whereas 24h were required for similar increases in diabetic rats. However, the same concentrations of gonadotrophins were found in diabetic and control animals 120h after ovariectomy. The inhibitory action of oestradiol benzoate on the secretion of gonadotrophins was more pronounced in ovariectomized diabetic than in control rats. A 74% depression in serum luteinizing hormone (p<0.01) was produced by 0.5 g oestradiol benzoate per day in diabetic rats, while 5 g was required in control animals. Similar reductions in follicle stimulating hormone concentrations (50%, p<0.05) were obtained by injecting 5 g of the oestrogen into diabetic or 50 g into control rats. Increases in serum prolactin were greater in the control animals however. Although pituitary weights were consistently lower in oestrogen-treated diabetic than in control animals, the luteinizing hormone, follicle stimulating hormone and prolactin contents, on the basis of wet weight of gland, were not different (p>0.05). The positive feedback action of progesterone on release of luteinizing hormone that had been suppressed with oestradiol benzoate was delayed by 3 h and reduced by more than 50% in diabetic compared to control animals (p<0.01). Release of follicle stimulating hormone was also delayed and reduced in the diabetic rats. While several indices of hypothalamic-pituitary function were not greatly altered by streptozotocin-induced diabetes, the enhanced negative and reduced positive-feedback effects of steroids could be responsible for attenuated gonadotrophin surges and loss of cyclicity in diabetic female rats.     

The effects of γ-radiation on intestinal motor activity and faecal pellet expulsion in the guinea pig

The effects of whole-body -radiation (10 Gy) on intestinal motor activity was examined in the small and large intestine of the guinea pig 18 hr post irradiation. Neurally mediated relaxations of isolated gut bath preparations were generally unaffected. However, the contractile responses to direct smooth muscle stimulation with the cholinergic muscarinic agonist carbachol or ganglionic stimulation of intrinsic cholinergic motor neurones were significantly increased in the duodenum and colon but not the jejunum. This increased sensitivity to cholinergic stimulation was reflected in an increased contractility and a shift in the concentration-response curves for carbachol. The specificity of radiation actions for cholinergic mediated contractions was further supported by the observation that histamine-evoked contractions were unaffected. In a second series of experiments we examined the effects of -radiation on the rate of pellet expulsion from freshly excised colons. Both colons from irradiated animals and nonirradiated colons exposed to carbachol showed significantly faster rates of pellet expulsion, indicative of increased propulsive motility. Pretreatment of animals with 0.5 mg/kg sc of the 5HT₃ receptor antagonist Granisetron prevented the effect of radiation and reduced the pellet expulsion rate to below normal. These results indicate that gastrointestinal motility disturbances seen in organ-bath preparations of the intestine from rats exposed to whole-body -radiation may be related to an increased sensitivity of the cholinergic muscarinic system.     

Acid Secretory Changes in Streptozotocin-Diabetic Rats

We examined gastric acid secretion in response to various stimuli in streptozotocin (STZ) induced diabetic rats and characterized the alteration of acid secretory responses in diabetic conditions. Animals were injected STZ (70 mg/kg, intraperitoneally) and used after five weeks of diabetes with blood glucose >350 mg/dl. Under urethane anesthesia, the experiment was performed in a chambered stomach or a whole stomach preparation, and the 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 intravenous infusion of either histamine (4 mg/kg/hr), pentagastrin (60 g/kg/hr), or carbachol (20 g/kg/hr) or by intraluminal application of peptone solution (4%), or vagal electrical stimulation (2 msec, 3 Hz, 0.5 mA). In normal rats, acid secretion was increased in response to either histamine, pentagastrin, carbachol, peptone, or electrical vagal stimulation. In STZ diabetic rats, however, changes in acid secretion varied depending on the stimuli; the acid response to histamine remained unchanged, but the responses to vagal electrical stimulation or pentagastrin and carbachol were significantly decreased or enhanced, respectively, as compared to normal rats. Likewise, the acid response to peptone was also markedly enhanced in STZ-diabetic rats, and this response was significantly blocked by atropine and YM022 (a CCK_B/gastrin antagonist) as well as famotidine in both normal and diabetic rats. Both pentagastrin and carbachol increased the luminal release of histamine in normal rats, and these responses were significantly augmented in STZ-diabetic rats. The altered acid response and histamine release induced by pentagastrin in STZ diabetic rats were partially reversed by daily injection of insulin. These results suggest that STZ-diabetic rats showed different changes in gastric acid secretion in response to various stimuli. 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.     

Immunogold studies of monomeric elements from the globular domain (NC1) of type IV collagen in renal basement membranes during experimental diabetes in the rat

Summary The protein A-gold immunocytochemical technique was applied to reveal the monomeric elements M1, M2^* and M3 from the non-collagenous globular domain (NC1) of type IV collagen over various renal basement membranes from control and long-term streptozotocin-induced diabetic rats. This study includes the basement membranes of the proximal tubule, the Bowman's capsule and the glomerulus as well as the extracellular matrix of the mesangium. The labellings obtained were confined to basement membrane material. The quantitative analysis demonstrated changes in labelling intensities and distribution between tissues from normal and diabetic animals. Increased labelling intensities were observed for M1 and M2^* monomers in all the basement membranes studied except for the mesangial matrix which remained unchanged. In addition, the labelling for M1 monomers, present on the endothelial side of the glomerular basement membrane of control animals, was found to be distributed throughout the entire thickness of the basement membrane of diabetic animals. In contrast, neither the intensity of the labelling, nor the distribution of M3 monomers were altered in diabetic animals. Since M1 monomers are markers of the 1(IV) and 2(IV) chains of type IV collagen while M2^* and M3 mark 3(IV) and 4(IV) chains respectively, the present results demonstrate changes in the nature of the collagenous elements of basement membranes during diabetes. Furthermore, the results indicate that the 3(IV) and the 4(IV) chains are not necessarily present in the same molecule. The modifications of the collagenous elements of the basement membranes during diabetes must alter the structural characteristics of these matrices which in turn might influence their functional properties.     

Coordinated Muc2 and Muc3 mucin gene expression in Trichinella spiralis infection in wild-type and cytokine-deficient mice

Mucin hypersecretion is an important component of the immune response to gastrointestinal nematode infection. Two discrete types of mucin proteins exist in the mouse intestine, secretory Muc2 and membrane-bound Muc3. We examined Muc2 and Muc3 expression in wild-type mice and mice lacking gamma interferon receptor (IFNR–/–), tumor necrosis factor receptor 1 (TNFR1–/–) and interleukin 4 (IL4–/–) infected with Trichinella spiralis. Infected wild-type mice demonstrated significant goblet cell hyperplasia and increased mucin glycoprotein. In situ hybridization showed this was accompanied by increases in Muc2 and Muc3 mRNA. Total intestinal mucin protein and Muc2 and Muc3 mRNA levels were also significantly increased in cytokine-deficient mice. These data demonstrate the coordinated up-regulation of two types of mucin genes in response to T. spiralis infection and may form the basis of an innate mucosal response independent of IFN-, TNF, and IL-4.     

Stress proteins in colorectal mucosa

Stress (heat shock) proteins are ubiquitous intracellular proteins that can be inducedin vitro by physiological stress events that occur during inflammation. We have used an indirect immunoperoxidase method to locate 60-kDa stress proteins in biopsies taken from normal and inflamed colorectal mucosa. An anti-60-kDa monoclonal antibody (ML30) produced specific staining of surface epithelial cells localized to the site of the Golgi apparatus. In ulcerative colitis, there was an increased concentration of this stress protein compared with controls (P0.002) and also with a small group of active Crohn's colitis (P0.01), but no relationship between its concentration and disease activity. All biopsies also showed staining of goblet cells by ML30, suggesting a possible cross-reaction with mucin; electroblotting of crude but not purified mucin showed a faint 60-kDa band with ML30. We conclude that the 60-kDa stress protein is present in normal colorectal epithelial cells and is markedly inducedin vivo in ulcerative colitis. Further, we suggest that since the 60-kDa protein functions as a molecular chaperone, it may associate with colonic mucin aiding in its synthesis and/or secretion.V.R. Winrow is supported by The Arthritis and Rheumatism Council for Research.     

Cyclooxygenase-2 mediates mucin secretion from epithelial cells of lipopolysaccharide-treated canine gallbladder

Biliary mucin was regarded as a major contributing factor in formation of pigment stones as well as cholesterol ones. The aim of this study was to elucidate the mechanism of biliary mucin secretion in canine gallbladder epithelial (CGBE) cells treated by lipopolysaccharides (LPS) with special reference to cyclooxygenase (COX) -2. Confluent CGBE cells were incubated with following compounds for 8, 12, and 24 hr: (1) serum-free medium, (2) serum-free medium containing LPS (100 m/ml), (3) serum-free medium containing LPS (100 m/ml) with NS-398 (10 M), and (4) serum-free medium containing LPS (100 m/ml) with indomethacin (10 M). Mucin assay and western blots for COX-1 and COX-2 were performed. Production of PGE₂, and cAMP was also measured. Mucin secretion increased with time. At 12 hr, mucin secretion increased to 200% of control (from 100 ± 5 to 200±45%, P < 0.05). LPS treatment significantly stimulated the COX-2 expression (P < 0.05). The productions of PGE₂ and cAMP were increased from 299±68 to 524±163 pg/mg (P < 0.05) and from 0.2±0.1 to 0.92±0.4 pmol/ml (P < 0.05), respectively. NS-398, which completely inhibited COX-2 expression, significantly suppressed the level of PGE₂ and cAMP as well as mucin secretion (P < 0.05). Indomethacin, which partially inhibited COX-2 expression, suppressed the production of PGE₂, but not cAMP and mucin secretion. In conclusion, our results suggested that the PGE₂ induced by COX-2 might play a role in mucin secretion from the gallbladder epithelium through the increment of cAMP.     

Evidence for a Nonneural Electrogenic Effect of Cholera Toxin on Human Isolated Ileal Mucosa

Cholera toxin-induced intestinal secretion inintact rats requires a functioning myenteric plexus. Theaim of this investigation was to determine whetherneural elements were essential for cholera toxin to produce a secretory effect in human isolatedileum. Mucosal preparations were mounted in Ussingchambers. Cholera toxin was applied apically andshort-circuit current monitored for 3 hr, at which point forskolin was given. Cholera toxin (10g/ml) induced a tetrodotoxin-insensitive increase inshort-circuit current in muscle-stripped preparations ofhuman ileum. The increase was not additive with the action of forskolin (25 M). Cholera toxinexerts a marked nonneural secretory effect in humanileal mucosa in vitro , probably by the same mechanismas forskolin, namely elevation of cyclic AMP.     

Repetitive in vivo treatment with human recombinant interleukin-1β modifies Beta-cell function in normal rats

Summary It is unknown whether interleukin-1 exerts a bimodal effect on Beta-cell function in vivo, and whether interleukin-1 has a diabetogenic action in normal animals. We therefore studied: (a) acute effects 2 h after an intraperitoneal bolus injection of 4 g of recombinant human interleukin-1 per kg body weight on blood glucose, plasma levels of insulin, glucagon and corticosterone in Wistar Kyoto rats, either untreated or pre-treated with 4 g/kg of interleukin-1 daily for 3 or 5 days; (b) the cumulative effects of repetitive intraperitoneal injections of 4 g/kg interleukin-1 on blood glucose, glucose tolerance, plasma levels of insulin, glucagon and corticosterone, pancreatic insulin content and pancreatic ultrastructure; and (c) blood glucose and plasma concentrations of insulin, glucagon and corticosterone 10 h after the last of five intraperitoneal injections of interleukin-1, at which time point the inhibitory effect of short-term interleukin-1 exposure on insulin secretion reaches its nadir in vitro. A single injection of 4 g/kg of interleukin-1 caused a slight, but significant lowering of blood glucose 2 h after interleukin-1 injection with no significant changes in plasma insulin and in spite of increases in plasma glucagon and corticosterone. A lowering of blood glucose 2 h after interleukin-1 administration was reproduced with 40, but not 0.4 g/kg of interleukin-1, and was also seen in interleukin-1 pre-treated rats. Two hours after the fifth injection of interleukin-1, intraperitoneal glucose tolerance was impaired with elevated plasma insulin and corticosterone levels and increased pancreatic insulin content, indicating a state of insulin resistance. Blood glucose levels significantly increased time-dependently 4–10 h after the third and fifth injection of interleukin-1, and diabetic values (blood glucose >11.0 mmol/l) were observed 6 and 10 h after the fifth injection of interleukin-1. Ten hours after the fifth injection of interleukin-1, diabetic blood glucose levels were observed together with a 50% reduction in plasma insulin concentration. Ultrastructural examination showed no signs of Betacell lysis. In conclusion, interleukin-1 has bimodal effects on glucose homeostasis in vivo, a slight lowering of the blood glucose followed by impaired glucose tolerance and later by diabetic blood glucose levels. Two hours after the last of five daily injections of interleukin-1 impaired glucose tolerance is primarily caused by a state of insulin resistance, whereas diabetic blood glucose levels are associated with inhibition of insulin secretion. Thus, interleukin-1 causes a diabetic state in normal animals, but it remains to be demonstrated that administration of interleukin-1 to normal animals leads to permanent diabetes due to Beta-cell destruction.     

Prevention of diabetic glomerulopathy in streptozotocin diabetic rats by insulin treatment

Summary A single antibody radioimmunoassay has been used to measure albumin excretion in 3 groups of female Wistar rats. Two groups had Streptozotocin diabetes and were treated daily with insulin for 6 months. In one of the diabetic groups good glycaemic control was attempted and throughout the 6 months plasma glucose levels were fairly close to normal (92 ± 33 mg/100 ml at 2300 h and 186 ± 9 mg/100 ml at 0800 h). In the other diabetic group poor control was intended and the group had consistent high plasma glucose levels (576 ± 89 mg/100 ml and 460 ± 43 mg/100 ml). The third group was a non-diabetic control group. — Albumin excretion was measured on two occasions: before the induction of diabetes and after 6 months of diabetes. The geometric mean albumin excretion increased from 0.38 to 2.56 mg/24 h in the 18 non-diabetic controls. In the 20 diabetic rats in good control the geometric mean albumin excretion increased from 0.37 to 1.58 mg/ 24 h (NS compared with controls) and in the group of 22 rats in poor control albumin excretion increased from 0.35 to 6.54 mg/24 h. — The increase in albumin excretion in rats in poor control differed significantly both from that of the non-diabetic controls (2p = 0.023) and from that of the well-controlled diabetic rats (2p = 0.00011).     

Prevention of diabetic glomerulopathy in streptozotocin diabetic rats by insulin treatment

Summary Glomerular basement membrane thickness (GBMT) has been measured in streptozotocin diabetic rats treated with insulin. The study included 3 groups of 8 rats each: 1) a well-controlled group of diabetic rats under insulin treatment with a plasma glucose level reasonable close to normal values, 2) a poorly-controlled group also under insulin treatment with constant high plasma glucose values, and 3) an age and weight matched non-diabetic control group. After 6 months of diabetes, GBMT was measured applying an intercept method on 3 glomerular cross sections from each of the 24 animals. The measurements showed that mean GBMT was 132.2. nm in the non-diabetic control rats and 131.6 nm in the well-controlled diabetic rats. In the poorly-control-led group the mean GBMT was 140.4 nm, i.e. statistically significantly increased when compared to each of the two other groups, 2p=0.022 and 0.012 respectively.The results demonstrate that good blood glucose control in rats preserves normal GBMT.     

Effect of base precursors on water and electrolyte transport during oral hydration solution perfusion in secreting rat intestine

In situ steady-state, single-pass small intestine perfusions in rats were carried out to compare the effect of the bicarbonate and citrate World Health Organization oral rehydration solutions and a base precursor-free solution on intestinal water and electrolyte transport after inducing intestinal secretion with purified heat-stableEscherichia coli enterotoxin. When toxin was not perfused, the rates of water, sodium, and bicarbonate absorption were significantly greater from the bicarbonate-containing solution than from the citrate or base precursor-free solutions. Chloride absorption was greater from the base precursor-free solution, but this might reflect the higher chloride concentration of the perfusate. When toxin was perfused, there was no significant difference among the solutions in the rates of water, potassium, or chloride absorption. Sodium absorption occurred at significantly greater rates from both the bicarbonate and the base precursorfree solutions than from the citrate solution. Base precursor-containing solutions may not provide any advantage over a base precursor-free solution in stimulating water and sodium absorption in 5-cyclic guanosine monophosphate mediated acute diarrhea.The Wellcome Research Unit is supported by the Wellcome Trust, London, UK, in association with the Christian Medical College Hospital, Vellore.     

Effects of very mild versus overt diabetes on vascular haemodynamics and barrier function in rats

Summary Rats injected i. p. with a single dose of nicotinamide (250 mg/kg) 15 min prior to i.v. injection of streptozotocin (65 mg/kg) develop a very mild form of diabetes characterized by slight elevations of plasma glucose, increased levels of HbA₁, and reduced insulin secretion in response to an i.v. glucose tolerance test. These rats gain weight normally and they are not hyperphagic, glycosuric, or polyuric. The effects of this very mild form of diabetes vs overt streptozotocin diabetes of three months duration on regional vascular ¹³¹I-albumin clearance, blood flow (assessed by 15 m ⁸⁵Sr-microspheres), and renal filtration function were examined in male Sprague-Dawley rats. Plasma glucose levels of rats with mild diabetes were 7.4±0.9 (mean±SD) (mmol/l) vs 6.5±0.6 for control rats and 31.3±6.0 for overtly diabetic rats. HbA₁ levels were increased 1.4 fold in mildly diabetic and 2.3 fold in overtly diabetic rats. Vascular clearance of ¹³¹I-albumin was markedly increased in ocular tissues (anterior uvea, retina, and choroid), sciatic nerve, aorta, new (subcutaneous) granulation tissue, and kidney of both diabetic groups, although increases in overtly diabetic rats exceeded those in the mildly diabetic group (2.2–4.6 times control animals vs 1.6–3.3 times, respectively). Likewise, both overt and very mild diabetes markedly increased glomerular filtration rate (1.8 times and 1.2 times control animals, respectively), urinary excretion of endogenous albumin (9 times and 4 times) and IgG (15 times and 4 times), as well as regional blood flow in the anterior uvea, choroid, and sciatic nerve. Increases in tissue sorbitol levels were much larger in overtly diabetic rats (generally 10–20 times control animals) than in mildly diabetic rats (1.5–3 times controls). myo-Inositol levels were significantly decreased only in lens and sciatic nerve of overtly diabetic rats. These observations indicate that even very mild diabetes is associated with vascular functional changes which develop more slowly than in overtly diabetic rats, but are disproportionately large (in view of the minimal increases in glycaemia and tissue polyol levels) compared to those in overtly diabetic rats.     

The effect of hyperthyroidism on gastric emptying rates and pancreatic exocrine and biliary secretion in man

Malabsorption and diarrhea in hyperthyroidism has been attributed in part to an increased rate of gastrointestinal transit as measured with barium sulfate suspension. Data are unavailable on the effect of hyperthyroidism on gastric emptying rates of normal food and pancreatic enzyme secretion. These functions have been studied in 4 hyperthyroid patients and compared to results obtained when treatment achieved euthyroidism. Pancreatic trypsin secretion was half the euthyroid level in the hyperthyroid state. No significant change in bile salts occurred, although there was a tendency for a greater proportion of dihydroxy bile salts while hyperthyroid. Gastric emptying rates of a mixed fat, protein, and carbohydrate liquid meal were normal. Similarly the gastric emptying rate of a beef stew plus chicken liver meal was normal. We conclude that in hyperthyroidism gastric emptying rates of physiologically active food is normal. Pancreatic enzyme secretion is depressed in hyperthyroidism and may contribute to maldigestion.Supported by the Medical Research Service of the Veterans Administration and Apprenticeships for Carrer Exploration (KML).     

Nitric oxide-mediated neurotransmission is attenuated in the anococcygeus muscle from diabetic rats

Summary The effect of STZ-induced diabetes of 8-weeks duration was examined on nitric oxide-mediated neurotransmission in the rat anococcygeus muscle. In the presence of noradrenergic blockade and raised tissue tone, relaxant responses to nerve stimulation (0.5–5 Hz, for 10 s), sodium nitroprusside (5 and 10 nmol/l) and nitric oxide (1 and 3 mol/l) were significantly reduced in anococcygeus muscles from diabetic rats compared to responses from control rats (p <0.05). In contrast, relaxations to papaverine (3 and 10 mol/l were not reduced in tissues from diabetic rats. The nitric oxide synthesis inhibitor NOLA (100 mol/l) abolished relaxant responses to nerve stimulation but had no effect on responses to any of the relaxant agents used. Exposure to NOLA at 10 mol/l reduced stimulation-induced relaxations; this reduction was significantly greater in tissues from the diabetic group than from the control group (p <0.05), probably as a consequence of the smaller relaxant responses in muscles from diabetic rats. Contractile responses to nerve stimulation (1–10 Hz, for 10 s), but not noradrenaline (0.03–30 mol/l), were significantly greater in anococcygeus muscles from diabetic rats than from control rats (p <0.05). NOLA (100 mol/l) significantly enhanced stimulation-induced contractions (p <0.05), however the enhancement was significantly less in tissues from diabetic rats (p <0.05). The results suggest that STZ-induced diabetes impairs smooth muscle reactivity to nitric oxide in the rat anococcygeus muscle.Abbreviations STZ Streptozotocin - NOLA N^G-nitro-l-arginine - NANC nonadrenergic noncholinergic - ANOVA analysis of variance     

Liver microsomal Δ6 and Δ5 linoleic acid desaturation in female BB rats

Summary Rat liver microsomal 6 and 5 desaturation are defective in experimental diabetes, but this defect is correctable with insulin treatment. Rat liver fatty acid composition and 6 and 5 desaturation were studied in the spontaneously diabetic adult female Bio-Breeding (BB) rat. Control Wistar rats and BB rats (4 weeks of diabetes), that received insulin (1 IU·100 g body weight^–1·day^–1), were killed 20 h after the last insulin injection. 6 and 5 desaturase activities were estimated from the incubation of liver microsomes with (1-¹⁴C) 18:2, n–6 or (2-¹⁴C) 20:3, n–6, respectively, and the fatty acid composition of the liver and microsomal liver lipids were investigated. Under experimental conditions 6 and 5 desaturase activities were unchanged in the BB rats when compared to the control rats. Impairment of the liver fatty acid composition of diabetic BB rats is not consistent with normal desaturase activity and may be explained by factors other than desaturation disturbance.     

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

Overnight fasting causes hemorrhagic lesions in the stomach of streptozotocin (STZ)-induced diabetic rats, but the pathogenetic mechanism remains unknown. The present study was performed to investigate the pathogenesis of such lesions developed in STZ-diabetic rats after starvation, mainly in relation to blood glucose changes. A single injection of STZ (70 mg/kg, intraperitoneally) induced hyperglycemic conditions one week after the administration, and high blood glucose levels (BGL: >350 mg%) remained up to three weeks later. The STZ-diabetic rats developed gastric lesions with the marked reduction of BGL after 18 hr of fasting, depending upon the duration of diabetes; the lesion score and BGL reduction in the 3-week-old STZ rats were 32.0±7.8 mm and >250 mg/100 ml, respectively. Acid secretion in the pylorus-ligated rats was not significantly changed in the STZ-induced diabetic conditions for the initial two weeks but slightly decreased at three weeks when compared with normal rats. Fasting of normal rats for 18 hr did not cause either BGL reduction or any lesion in the stomach. In the 3-week-old STZ animals, the severity of gastric lesions increased with the duration of fasting (4–18 hr) and was again closely associated with the degree of BGL reduction. These lesions induced by 18 hr of starvation in 3-week-old STZ rats were significantly inhibited by pretreatment with insulin (4 units/rat/day) for the last one week to maintain BGL within normal ranges or by intravenous infusion of 25% glucose during fasting period. Both of these treatments significantly prevented BGL reduction in response to fasting. These results suggest that gastric lesions induced in STZ-diabetic rats by fasting are insulin-sensitive and may be associated with a profound hypoglycemic response to food deprivation.     

On the mechanism of glucose protection against alloxan toxicity

Summary The modifying effects of some sugars and amino acids on the diabetogenic action of alloxan were studied in mice. The severity of diabetes was assessed by measuring the blood glucose level 48 h after the alloxan injection. In accordance with earlier reports, D-glucose and D-mannose, but not D-galactose, protected against alloxan diabetes. No such effect was observed with D-mannoheptulose, L-alanine, or L-leucine. The protective action of glucose was abolished by prior treatment with mannoheptulose. It is concluded that alloxan and glucose do not compete for a common biochemical site in the- cell membrane. Protection against alloxan toxicity may, however, result from a conformational change in the -cell membrane induced by glucose, glucose transport, or glucose metabolism.Supported by the Swedish Medical Research Council (12x-2288), the Swedish Diabetes Association, and the Medical Faculty in Umeå.