Diagnostic evaluation of the cervical nystagmus in cervical torsion test

The long-term effects of streptozotocin (30-70 mg/kg) were studied on plasma glucose and insulin levels, islet morphology, and glucose-stimulated insulin secretion in rats. In addition, the protective effect of short-term (7 days) insulin treatment on streptozotocin-induced diabetes was examined. Streptozotocin administration at dose levels exceeding 40 mg/kg resulted in a long-term, stable hyperglycemia with no insulin response to glucose at 3 months and with a marked derangement of islet morphology (few insulin cells, accumulation of glucagon cells). In contrast, at 30 and 40 mg/kg, streptozotocin induced a transient diabetes. Thus, the blood glucose levels, being elevated at days 1-7, returned to normal levels within 10 days after streptozotocin administration and the glucose-induced insulin secretion, being absent at day 1, was normal at 3 months. Furthermore, the islet morphology was also normal in these groups at 3 months. Short-term (7 days) insulin treatment normalized the long-term diabetes in rats given 50 mg/kg streptozotocin, but not in rats given 60 or 70 mg/kg streptozotocin. Thus, after insulin treatment, all rats receiving 50 mg/kg streptozotocin returned to normoglycemia within the following 2 weeks, and the glucose-induced insulin secretion was normal after 3 months, as was islet morphology.(ABSTRACT TRUNCATED AT 250 WORDS)     

Roles of prostaglandin E-receptor subtypes in gastric and duodenal bicarbonate secretion in rats

BACKGROUND & AIMS: Receptors activated by prostaglandin (PG) E2 are pharmacologically subdivided into four subtypes (EP1-EP4). The EP-receptor subtype(s) involved in stimulation of gastroduodenal HCO3- secretion in rats were investigated. METHODS: Under urethane anesthesia, a stomach mounted in an ex vivo chamber or a proximal duodenal loop was perfused with saline, and HCO3- secretion was measured using a pH-stat method. RESULTS: Intravenous PGE2 increased HCO3- secretion by the gastroduodenal mucosa; this action was verapamil sensitive and, only in the duodenum, potentiated by isobutylmethyl xanthine (IBMX). Duodenal HCO3- secretion was stimulated by enprostil, sulprostone (EP1/EP3 agonist), misoprostol (EP2/EP3 agonist), and ONO-NT012 (EP3 agonist) but was not affected by butaprost (EP2 agonist) or 17-phenyl-PGE2 (EP1 agonist). Gastric HCO3- secretion was stimulated by sulprostone, enprostil, and 17-phenyl-PGE2 but not by misoprostol, butaprost, or ONO-NT012. SC-51089 (EP1 antagonist) inhibited the HCO3--stimulatory action of sulprostone only in the stomach. IBMX potentiated the HCO3- response to sulprostone in the duodenum, whereas verapamil reduced the response in both the stomach and duodenum. CONCLUSIONS: PGE stimulates HCO3- secretion via different EP-receptor subtypes in the stomach and duodenum: in the stomach, EP1 receptors are linked to Ca2+; in the duodenum, EP3 receptors are coupled with both adenosine 3', 5'-cyclic monophosphate and Ca2+.     

Relationship between nitric oxide and platelet-activating factor in castor-oil induced mucosal injury in the rat duodenum

The modulation of platelet activating factor (PAF) formation in duodenal tissue by nitric oxide (NO) released in response to castor oil was studied in rats pretreated with NG-nitro-L-arginine methyl ester (L-NAME, 6.25-25 mg/kg, i.p.), an inhibitor of NO synthase, NG-nitro-D-arginine methyl ester (D-NAME, 25 mg/kg, i.p.), the inactive enantiomer of L-NAME or isosorbide-5-mononitrate (IMN, 30-90 mg/kg, p.o.), a NO donating compound. Castor oil (2 ml/rat orally) increased PAF production in the rat duodenum 3 h after challenge. L-NAME, but not D-NAME, enhanced the amount of PAF formed by duodenal tissue, while IMN (30-90 mg/kg) counteracted the effects of L-NAME (12.5 mg/kg) and also reduced PAF release in the tissue of rats treated with castor oil. L-NAME 12.5 mg/kg, but not D-NAME, enhanced both macroscopic damage and acid phosphatase release induced by castor oil. These effects were reduced by a PAF antagonist BN 52021 (3-t-Butyl-hexahydro-4, 7b, 11-trihydroxy-8-methyl-9H-1, 7a-epoxymethano-1H, 6aH-cyclopenta [c] furo [2, 3b] furo [3'2':3,4] cyclopenta [1.2-d]furan-5,9,12(4H)trione) 10 and 20 mg/kg i.p. Such findings suggest that endogenous nitric oxide could reduce PAF biosynthesis in castor oil-treated rats.     

Gastroduodenal mucosal protection

The barrier that protects the undamaged gastroduodenal mucosa from autodigestion by gastric juice is a dynamic multicomponent system. The major elements of this barrier are the adherent mucus gel layer, which is percolated by the HCO3- secretion from the underlying epithelial cells; the epithelial layer itself, which provides a permeability barrier and can rapidly repair superficial damage by a process of cell migration referred to as reepithelization or restitution; and a specially adapted vasculature, which provides a supply of HCO3- for transcellular transport and/or diffusion into the mucus layer. Passive diffusion of intestinal HCO3- into the lumen is particularly important when there is superficial damage resulting in increased leakiness of the mucosal epithelium. The process of reepithelization occurs by the migration of performed cells from gastric pits or duodenal crypts. This process is quite distinct from the wound healing and associated inflammatory response that accompany more severe injury or chronic damage. The adherent mucus gel acts as a physical barrier against luminal pepsin and provides a stable unstirred layer that supports surface neutralization of acid by mucosal HCO3-. Surface neutralization by mucosal HCO3- provides a major mechanism of protection against acid in the proximal duodenum. In the stomach, where luminal acidity can fall to around pH 1, other mechanisms of protection must exist, since the surface pH gradient is reported to collapse when luminal H+ exceeds approximately 10 mM. This collapse of the surface pH gradients may reflect, at least in part, that such studies have been mostly performed on non-acid-secreting mucosa where the supply of HCO3- to the interstitium from the parietal cells will be reduced. However, because the gastric mucosa can withstand prolonged exposure to acid without apparent damage, this implies an intrinsic resistance of the epithelial apical surface. This is amply illustrated within the gastric glands that do not secrete mucus and HCO3- yet are exposed to undiluted pepsin and an isotonic solution of HCl. Bicarbonate and mucus secretions together with mucosal blood flow are under paracrine, endocrine, and neural control. The rate of reepithelialization will depend on local chemotactic factors, adhesion mechanisms, and the creation of an acid/pepsin/irritant-free environment under a protective gelatinous or mucoid cap. If optimal conditions are met, then the rate of reepithelialization appears to depend primarily on the intrinsic properties of the migrating cells themselves rather than control by exogenous mediators.(ABSTRACT TRUNCATED AT 400 WORDS)     

Water extract of Helicobacter pylori inhibits duodenal mucosal alkaline secretion in anesthetized rats

BACKGROUND & AIMS: The pathophysiology behind Helicobacter pylori-induced gastroduodenal dysfunction is incompletely understood. The aim of this study was to investigate if a water extract of H. pylori distorts acid-induced duodenal mucosal alkaline secretion. METHODS: Chloralose-anesthetized rats were prepared for duodenal luminal perfusion and in situ pH-stat titration of mucosal alkaline secretion. RESULTS: Mucosal bicarbonate secretion increased approximately 55%-60% after a 5-minute exposure to 10 mmol/L HCl. This response was absent when water extracts of three strains of H. pylori (protein content, 0.2-20 microg/mL) had been added to the perfusate. Presence of 3 mmol/L L-arginine, but not the stereoisomer D-arginine, in the luminal perfusate reversed the H. pylori extract blockade of acid-induced mucosal alkaline secretion. High-performance liquid chromatography-based analyses showed that the endogenous nitric oxide synthase inhibitor asymmetric dimethyl arginine (ADMA) increased fourfold in duodenal perfusate and fivefold in duodenal tissue after H. pylori extract exposure. In vitro proteolysis of H. pylori extract also resulted in a substantial accumulation of ADMA. Exogenously administered ADMA, giving similar tissue concentrations, inhibited the mucosal alkaline response to acid exposure. CONCLUSIONS: Water extracts of H. pylori inhibit acid-induced mucosal alkaline secretion via interference with mucosal NO synthase.     

ACE inhibition by enalaprilate stimulates duodenal mucosal alkaline secretion via a bradykinin pathway in the rat

The effects of enalaprilate on duodenal mucosal alkaline secretion (in situ titration) and mean arterial blood pressure were investigated in chloralose-anesthetized male rats. A bolus injection of enalaprilate (0.7 mg/kg intravenously) increased alkaline secretion by about 60%, and this response was resistant to guanethidine (5 mg/kg intravenously), splanchnicotomy, and vagotomy. Furthermore, angiotensin II infusion (0.25-2.5 microg/kg/hr intravenously) following the administration of enalaprilate failed to influence this response. Bradykinin (10(-6)-10(-4) M) applied topically to the serosal surface of the duodenal segment under study increased dose-dependently the duodenal mucosal alkaline secretion, an effect that could be blocked by the selective bradykinin receptor subtype-2 antagonist HOE140 (100 nmol/kg intravenously). HOE140 also antagonized the response to enalaprilate. These data suggest that enalaprilate increases duodenal mucosal alkaline secretion via a local bradykinin pathway involving receptors of the bradykinin receptor subtype-2 antagonist, rather than by blockade of endogenous angiotensin II or by central autonomic neural regulation.     

Gastric mucosal blood flow response to stress in streptozotocin diabetic rats: regulatory role of nitric oxide

To investigate cytoprotection against mucosal injuries of the stomach in patients with diabetes, we investigated gastric mucosal blood flow (GMBF), its response to a burn stress, and the involvement of nitric oxide (NO) in streptozotocin (STZ) diabetic rats. GMBF was measured by laser-Doppler velocimetry (LDV) and by the hydrogen gas clearance technique (HGC). The steady-state GMBF of STZ rats decreased according to the duration of diabetes, and insulin treatment blocked this decrease. Burn stress caused a rapid decrease in the GMBF. Reduction of the GMBF and gastric mucosal leakage of Evans blue (EB) after the burn stress were greater in the STZ rats than in the controls, but insulin treatment completely blocked this increase in EB leakage in the STZ rats. There was a significant negative correlation between the percent GMBF 3 h after the burn stress and EB leakage at the same time point. In the controls and the insulin-treated STZ rats, N-nitro-L-arginine (L-NNA), an NO synthase inhibitor, enhanced the decrease in postburn GMBF and EB leakage, but was without effect in the STZ rats. These results suggest that NO may be involved in the regulation of GMBF, and that persistent hyperglycemia may impair this regulation. These findings suggest that patients with diabetes have reduced cytoprotection against a variety of gastric mucosal injuries.     

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 delta 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 delta 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.(ABSTRACT TRUNCATED AT 250 WORDS)     

Suppressors of the temperature sensitivity of DNA polymerase alpha mutations in Saccharomyces cerevisiae

We recently showed the involvement of the L-arginine/nitric oxide (NO) pathway in acid-induced duodenal mucosal bicarbonate secretion in rats. The aim of the present study was to confirm this observation in pigs by direct measurements of NO production. Experiments were performed on 16 anaesthetized pigs of both sexes treated with guanethidine (6 mg kg-1, intravenously). A duodenal segment, devoid of pancreaticobiliary influxes, was perfused with saline and the duodenal mucosal bicarbonate secretion was calculated from continuous measurements of pH and PCO2. The perfusate contents of NO and its oxidative product nitrite were determined by chemiluminescence, after reduction of nitrite to NO. Luminal acidification with 30 mM hydrochloric acid increased the output of bicarbonate as well as NO to the perfusate, by 195 +/- 45% and 106 +/- 10%, respectively. These responses to acid were markedly inhibited by adding the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 0.3 mM) to the perfusate. The inhibitory effect of L-NMMA could be reversed by administration of L-arginine (3 mM). The study presents simultaneous measurements of bicarbonate and NO outputs to a duodenal luminal perfusate. The results strongly support the view that the L-arginine/NO pathway is involved in the acid-induced duodenal mucosal bicarbonate secretory response.     

A broadening view of recombinational DNA repair in bacteria

The role of the cholinergic and peptidergic pathways in the impairment of gastric motility associated with diabetic gastroparesis was assessed at the postsynaptic level using isolated fundus smooth muscle strips. Maximal contractile responses to carbachol and galanin were significantly decreased in fundus strips isolated from rats rendered diabetic by a single intraperitoneal injection of streptozotocin (STZ, 70 mg/kg) 1, 4 and 8 weeks before experiments. We also observed notable decrements in the slopes and Hill's coefficients without conspicuous changes in the EC50 of the respective galanin concentration-response curves measured in strips obtained from STZ animals after 4 and 8 weeks. L-NAME reversed the above-mentioned alterations in an L-arginine-sensitive manner in STZ rats after 4 weeks but not in STZ rats after 8 weeks. The blood plasma nitrite/nitrate levels in STZ animals after 4 and 8 weeks were increased by 44.6 and 61.9%, respectively. Ca2+-independent nitric oxide synthase activity in gastric fundus strips and stomach corpus mucosa from STZ rats after 4 weeks was markedly enhanced by 37.4 and 31.9%, respectively, suggesting an enhanced nitric oxide production. In vivo insulin treatment prevented diabetes-induced alterations in smooth muscle contractility. We conclude that the smooth muscle dysfunction evoked by experimental diabetes causing diminished contractions of fundus strips to carbachol and galanin is at least partly due to the increased nitric oxide synthesis.     

Early and late post-ischaemic recovery of contractile function is affected to different degrees by isoflurane and halothane in the anaesthetized rabbit model

We took advantage of the partial protection exerted by suitable dosages of nicotinamide against the beta-cytotoxic effect of streptozotocin (STZ) to create a new experimental diabetic syndrome in adult rats that appears closer to NIDDM than other available animal models with regard to insulin responsiveness to glucose and sulfonylureas. Among the various dosages of nicotinamide tested in 3-month-old Wistar rats (100-350 mg/kg body wt), the dosage of 230 mg/kg, given intraperitoneally 15 min before STZ administration (65 mg/kg i.v.) yielded a maximum of animals with moderate and stable nonfasting hyperglycemia (155 +/- 3 vs. 121 +/- 3 mg/dl in controls; P < 0.05) and 40% preservation of pancreatic insulin stores. We also evaluated beta-cell function both in vitro and in vivo 4-9 weeks after inducing diabetes. In the isolated perfused pancreas, insulin response to glucose elevation (5-11 mmol/l) was clearly present, although significantly reduced with respect to controls (P < 0.01). Moreover, the insulin response to tolbutamide (0.19 mmol/l) was similar to that observed in normal pancreases. Perfused pancreases from diabetic animals also exhibited a striking hypersensitivity to arginine infusion (7 mmol/l). In rats administered STZ plus nicotinamide, intravenous glucose tolerance tests revealed clear abnormalities in glucose tolerance and insulin responsiveness, which were interestingly reversed by tolbutamide administration (40 mg/kg i.v.). In conclusion, this novel NIDDM syndrome with reduced pancreatic insulin stores, which is similar to human NIDDM in that it has a significant response to glucose (although abnormal in kinetics) and preserved sensitivity to tolbutamide, may provide a particularly advantageous tool for pharmacological investigations of new insulinotropic agents.     

Pancreatic beta-cell regeneration after 48-h glucose infusion in mildly diabetic rats is not correlated with functional improvement

We investigated the effect of glucose infusion on beta-cell regeneration in rats made mildly diabetic by a single injection of low dosage (35 mg/kg) streptozotocin (STZ). Nondiabetic (ND) and STZ rats were submitted to a 48-h glucose infusion (hyperglycemia approximately 22 mmol/l in both groups: ND and STZ hyperglycemic-hyperinsulinemic [ND HG-HI and STZ HG-HI rats]). Before infusion, beta-cell mass was 65% lower in STZ rats than in ND rats (2.0 +/- 0.02 vs. 5.5 +/- 0.6 mg), 1.6-fold increased in ND HG-HI rats (8.7 +/- 1.7 mg), and 2.7-fold increased in STZ HG-HI rats (5.4 +/- 0.9 mg). In ND HG-HI rats, beta-cell enlargement was related to an increase in beta-cell responsiveness to nutrient secretagogues both in vivo and in vitro, whereas in STZ HG-HI rats, no significant improvement in insulin secretion could be noticed. To determine the respective role of hyperglycemia and hyperinsulinemia on beta-cell area changes, ND and STZ rats were submitted to a 48-h hyperinsulinemic-euglycemic clamp. No modification of beta-cell mass was detected in either group. In conclusion, 48-h superimposed hyperglycemia was enough to restore beta-cell mass previously reduced by STZ injection. This effect seemed to be due to hyperglycemia rather than hyperinsulinemia alone. The data stress the dissociation between beta-cell regeneration and improvement in islet function in diabetic rats. Our model seems suitable for studying factors that can improve the plasticity and function of the pancreas in NIDDM.     

Insulin-like growth factor binding protein-1 induces insulin release in the rat

Injections of human insulin-like growth factor binding protein (hIGFBP-1) are reported to induce hyperglycemia in the rat, suggesting that IGFBP-1 acutely regulates glucose homeostasis. We now report the effects on glucose and insulin levels of administering recombinant (r) hIGFBP-1. In a series of studies, normal and streptozotocin (STZ) diabetic male Wistar rats (180-210 g), fasted for 6 or 16 h, were injected with rhIGFBP-1 (i.v., 80-500 microg/rat). rhIGFBP-1 did not affect blood glucose acutely but did stimulate insulin release in normal rats (5 min post injection; PBS, 103.5 +/- 8.5; rhIGFBP-1 (500 microg), 166.8 +/- 15.7; rhIGFBP-1 (100 microg); 151.4 +/- 14.1% initial). rhIGFBP-1 pretreatment, in normal and diabetic rats, reduced the hypoglycemic response to rhIGF-I (diabetic rats after 20 min: PBS, 103.4 +/- 11.4; BP-1 (500 microg) +/- rhIGF-I (50 microg), 97.6 +/- 3.6; rhIGF-I, 48.2 +/- 4.3% initial) but did not affect the hypoglycemic response to des(1-3)IGF-I or insulin (0.5 U/kg). These studies show that rhIGFBP-1 causes insulin release, has a minimal effect on blood glucose, and inhibits the hypoglycemic effect of rhIGF-I. These data suggest that endogenous IGF-I tonically suppresses insulin secretion and imply that aberrant IGFBP levels or reduced IGF-I bioactivity may lead to chronic hyperinsulinemia.     

Phosphatidylcholines as mediators of adaptive cytoprotection of the rat duodenum

BACKGROUND/AIMS: Surfactant phospholipids impede diffusion of acid through the gastric mucus, but their relevance in the defense of the duodenum against luminal acid is not known. METHODS: Duodenal resistance to acid was tested in anesthetized rats by instillation of HCl using a tube implanted in the proximal duodenum. The effects of a detergent (Brij 35; Sigma, St. Louis, MO) and a lipid mixture flushed through the luminal surface on duodenal resistance to acid were studied. The lipid content in the mucus and the effects of acid, prostaglandins, and indomethacin on the lipid layer were also analyzed. RESULTS: Instillation of 100 mumol HCl or 5 micrograms/kg 16,16-dimethyl prostaglandin E2 increased resistance to acid, preventing duodenal lesions induced by 500 mumol HCl. However, 100 mumol HCl or 16,16-dimethyl prostaglandin E2 did not prevent lesions induced by 500 mumol HCl in rats undergoing perfusions with 5% Brij 35. Indomethacin suppressed acid-induced protection. A mixture of tripalmitin and dipalmitoyl-phosphatidylcholine protected against 500 mumol HCl, and the effect was also observed in rats receiving indomethacin. Finally, 100 mumol HCl increased the phosphatidylcholine content in the duodenal mucus but not in rats receiving 5% Brij 35 or indomethacin. CONCLUSIONS: Surface-active phospholipids are critical for adaptive cytoprotection to acid in the rat duodenum.     

Good growth despite very low levels of insulin-like growth factors

1. The antioxidant thioctic acid (TA) has been used in the treatment of diabetic neuropathy and recent studies have suggested that TA also has pancreatic and peripheral effects that improve glucose transport and metabolism. In the present study, the metabolic effects of TA were evaluated in rodent models of insulin resistance (fructose-fed Sprague-Dawley rat) and insulin deficiency (streptozotocin (STZ)-induced diabetic rat). Oral and intravenous glucose tolerance tests (OGTT and IVGTT, respectively) were performed in conscious rats after treatment with 50 mg/kg per day TA or vehicle for 5 days. 2. Fructose feeding for 7 days induced insulin resistance and impaired glucose tolerance and hypertriglycerideaemia. Treatment of fructose-fed rats with TA had no significant effect on fasting or stimulated glucose levels or on fasting triglyceride concentrations (e.g. the area under the curve for glucose (AUCglu) following OGTT was 1233 +/- 67 and 1284 +/- 59 in fructose-fed rats treated with either TA (n = 12) or vehicle (n = 12), respectively). Similarly, TA had no significant effect on IVGTT profiles in fructose-induced insulin resistance. 3. Low-dose STZ (80 mg/kg, i.p., over 2 days) induced hyperglycaemia, but TA had no significant glucose-lowering effects in STZ-diabetic rats (AUCglu (OGTT) following oral administration was 5507 +/- 27 and 5450 +/- 27 in TA (n = 12) and vehicle-treated (n = 12) rats, respectively). Nor did pretreatment with TA affect the diabetogenic response to STZ. 4. In contrast with previous in vitro studies reporting favourable metabolic effects of TA, the present study shows that after short-term oral therapy there are no significant improvements in glucose tolerance in rodent models of insulin resistance and insulin deficiency. Thioctic acid is unlikely to be of therapeutic benefit as an anti-diabetic drug in clinical practice.     

Gastroduodenal bicarbonate secretion: pharmacological modulation and contribution to mucosal protection

Bicarbonate secretion from the surface epithelial cells of the gastroduodenal mucosa is an active process depending upon the tissue metabolism and plays an important role as the first line of defense in mucosal protection in collaboration with the mucus gel. This secretion is regulated by humoral and neural factors as well as endogenous prostaglandins (PGs) and is considered to be intracellularly mediated by cyclic AMP in the duodenum and by cyclic GMP in the stomach. Ca2 also acts as an intracellular mediator in this process. This bicarbonate secretion is markedly increased in response to luminal acid, mediated by PGs and neural factors including capsaicin-sensitive sensory nerves, and the impairment of this response is involved in the pathogenesis of various duodenal ulcer models induced by cysteamine, nonsteroidal antiinflammatory drugs and stress. The mechanisms underlying the mucosal protection by HCO3 secretion is two fold; One is the direct neutralization of H + in the lumen, and the other is the establishment of a pH gradient across the mucus gel aided by the physico-chemical property of the mucus. However, the cellular mechanisms of HCO3 secretion, including the receptors, the mediators and the signal transduction pathway have been poorly understood. The establishment of a method for preparing isolated epithelial cells and the probe for HCO3 secretion in isolated cells is required to further elucidate the mechanism of HCO3 secretion.     

Effect of a non-sulphonylurea hypoglycaemic agent, KAD-1229 on hormone secretion in the isolated perfused pancreas of the rat

1. We examined the cooperative effect of a newly synthesized oral hypoglycaemic agent, KAD-1229 with glucose on insulin, glucagon and somatostatin secretion in the isolated perfused pancreas of the rat. 2. KAD-1229 stimulated concentration-dependently the first phase of insulin secretion without the second phase in the presence of 2.8 mM glucose, while it stimulated both the first and the second phase of insulin release in the presence of 5.6 mM glucose. It was confirmed that the first phase of insulin release is depolarization-induced release with no other additional signal transduction. 3. KAD-1229 also enhanced insulin release evoked by 16.7 mM glucose, a concentration known to inhibit the ATP-sensitive K+ current completely. 4. A low concentration (2.8 mM) of glucose stimulated somatostatin release transiently, while a higher concentration (16.7 mM) of glucose exerted a sustained stimulation. KAD-1229 stimulated somatostatin secretion in a concentration-dependent manner irrespective of glucose concentrations. 5. When glucagon release was stimulated with 2.8 mM glucose, KAD-1229 inhibited this hypoglycaemia-induced glucagon secretion. 6. When pancreata from rats pretreated with streptozotocin (STZ) 60 mg kg-1 were perfused, the basal secretion of glucagon was markedly elevated, and the glucagon response to the low glucose was abolished. Further, the insulin and somatostatin responses to KAD-1229 were largely attenuated. KAD-1229 showed transient enhancement followed by inhibition of the glucagon release from the STZ-pretreated rat pancreas. 7. We conclude that KAD-1229 stimulates insulin and somatostatin release, while it inhibits glucagon release following transient stimulation.     

Alterations of insulin response to different beta cell secretagogues and pancreatic vascular resistance induced by N omega-nitro-L-arginine methyl ester

1. We studied a possible interplay of pancreatic NO synthase activity on insulin secretion induced by different beta cell secretagogues and also on pancreatic vascular bed resistance. 2. This study was performed in the isolated perfused pancreas of the rat. Blockage of NO synthase was achieved with Nw-nitro-L-arginine methyl ester (L-NAME); The specificity of the antagonist was checked by using its D-enantiomer as well as by substitutive treatments with sodium nitroprusside (SNP) as a NO donor in studies of glucose-induced insulin secretion. 3. Arginine (5 mM) induced a monophasic response which was, in the presence of L-NAME at equimolar concentration, very strongly potentiated and converted into a 13 times higher biphasic one. D-NAME (5 mM) was only able to induce a 3 times higher response, but provoked a similar vasoconstrictor effect. 4. The small biphasic insulin secretion induced by L-leucine (5 mM) was also strongly enhanced, by 8 times, in the presence of L-NAME (5 mM) vs 2 times in the presence of D-NAME (5 mM). 5. beta cell responses to KCl (5 mM) and tolbutamide (0.185 mM) were only slight increased by L-NAME (5 mM) to values not far from the sum of the effects of L-NAME and of the two drugs alone. D-NAME (5 mM) was totally ineffective on the actions of both secretagogues. 6. L-NAME, infused 15 min before and during a rise in glucose concentration from 5 to 11 mM, was able in the low millimolar range (0.1-0.5 mM) to blunt the classical biphasic pattern of beta cell response to glucose and, at 5 mM, to convert it into a significantly greater monophasic one. In contrast, D-NAME (5 mM) was unable to induce similar effects. 7. SNP alone at 3 microM was ineffective but at 30 microM substantially reduced to second phase of insulin response to glucose; however, at both concentrations the NO donor partly reversed alterations in insulin secretion caused by L-NAME (5 mM) and restored a biphasic response.     

Interaction of human retinal RGS with G-protein alpha-subunits

The effects of leptin on insulin secretion from pancreatic islets of Sprague-Dawley rats were examined in vitro. In a basal glucose medium (5.5 mM), insulin secretion from isolated islets was significantly decreased after addition of a recombinant leptin (80 nM) (3.20+/-0.14 nmol/10 islets/h) compared with that before the addition (4.41+/-0.30 nmol/10 islets/h). Although significant leptin suppression of insulin secretion was not observed under a glucose-stimulated (11.1 mM) condition, these results suggest that a negative feedback system may exist between leptin and insulin, which increases the production of leptin from adipose tissues.     

Susceptibility to neonatal streptozotocin-induced diabetes in spontaneously hypertensive rats

We studied the difference in the susceptibility to neonatal streptozotocin (STZ) diabetes between spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). Two-day-old female SHR and WKY were injected intraperitoneally with 75.0 mg/kg of STZ or vehicle for control. Hyperglycemia developed in both strains at 4 days of age, but SHR were more hyperglycemic. Overt hyperglycemia developed in SHR with aging after a partial recovery from initial hyperglycemia at 10 days of age, whereas WKY did not develop significant hyperglycemia except shortly after STZ treatment. Percentage of insulin-positive B cells in total islet cells and pancreatic immunoreactive insulin (IRI) content were measured at 4 days, 10 days, 4 weeks, and 12 weeks of age. B cells per islet and pancreatic IRI content were significantly reduced in STZ-treated groups as compared with control in both SHR and WKY at 4 days of age, but later they increased significantly with aging in both strains. However, the reduction in pancreatic IRI content relative to control was significantly greater in SHR than in WKY from 4 days (-94.5 +/- 3.5%, -84.1 +/- 4.8%; p < 0.01) to 12 weeks (-97.1 +/- 2.1%, -28.0 +/- 2.5%; p < 0.05), and the reduction in B cells per islet was also greater in SHR at 4 weeks of age. These results indicated that the initial destruction of pancreatic B cells induced by STZ was greater, and the following regeneration was less in SHR than in WKY. The association of the susceptibility to neonatal STZ diabetes with the development of genetic hypertension in SHR remained to be elucidated.