Toshiharu Akiyama

High-fat hypercaloric diet induces obesity, glucose intolerance and hyperlipidemia in normal adult male Wistar rat

There is strong evidence that genetic factors contribute to the development of obesity in humans as well as laboratory animals. Another important factor leading to obesity is an increase in energy intake. However, it is difficult to make normal rats obese by controlling daily food intake. There is no report of normal adult male Wistar rats becoming obese and diabetic on a high-fat diet. The aim of the present study was, therefore, to make normal adult Wistar rats obese by infusing high fat and hypercaloric diet through the cannula without disturbing the free movement and to investigate the influence of an increase in the caloric intake on body weight and glucose metabolism. High-fat hypercaloric diet (360 kcal/kg body wt./day; H group) or control diet (180 kcal/kg body wt./day; C group) was continuously infused into the stomach of normal adult male Wistar rats weighing approximately 300 g through gastric cannulas for 27 days. On day 28 after a 24-h fasting, serum concentrations of aspartate aminotransferase, alanine aminotransferase, total cholesterol, triglyceride, phospholipid, and free fatty acids (FFA) were determined, and intragastric glucose loading test (2 g/kg body wt.) was performed. The average weekly body weight gain in the H group was twice as much as that of the C group (40.0 +/- 2.4 vs. 19.4 +/- 1.9 g/week, P < 0.001). Serum levels of triglyceride, phospholipid, total cholesterol, and FFA were significantly elevated in the H group compared to those in the C group. Liver weight in the H group was significantly higher than that in the C group and showed steatosis. Pancreas weight (-13%) as well as protein (-12%), amylase (-53%) and trypsin content (-26%) were all reduced, whereas pancreatic DNA content was significantly increased in the H group compared to those in the C group. Serum glucose and insulin concentrations before and after glucose loading in the H group were significantly higher than those in the C group. Moreover, the insulin response relative to glucose response in the H group was significantly high compared to that in the C group, indicating the presence of insulin resistance. These results indicate that feeding of high-fat hypercaloric diet makes normal Wistar male adult rat obese associated with hyperlipidemia, hyperinsulinemia, and glucose intolerance.

Troglitazone prevents fatty changes of the liver in obese diabetic rats

Abstract Background and Aims: Troglitazone is a newly developed antidiabetic drug and is indicated to be useful for the treatment of patients with type II diabetes mellitus. Recently, however, it became clear that troglitazone could cause liver dysfunction in some patients. In addition, a relationship between the activation of the peroxisome proliferator‐activated receptor gamma receptor by troglitazone and colon tumorigenesis has been suggested. The present study was undertaken to examine the effects of long‐term administration of troglitazone on the liver and intestine in genetically obese and diabetic Otsuka Long‐Evans Tokushima Fatty (OLETF) and control Long‐Evans Tokushima Otsuka (LETO) rats.

Role of endogenous cholecystokinin and cholecystokinin-A receptors in the development of acute pancreatitis in rats

Recent studies provide significant evidence that Cholecystokinin (CCK) is involved in the induction and development of acute pancreatitis in experimental animals. However, the results obtained with specific CCK-A (peripheral) receptor antagonists are still controversial. The present studies were undertaken to evaluate the involvement of endogenous CCK and the CCK-A receptors in the development of severe acute pancreatitis induced in Otsuka Long-Evans Tokushima Fatty (OLETF) rats that have a selective defect in the CCK-A receptor. Three models of severe acute pancreatitis were induced by retrograde intraductal infusion of 4% sodium taurocholate, by the closed duodenal loop, or by a single intraperitoneal injection of 500 mg/100 g body weight of L-arginine in OLETF rats and control Long-Evans Tokushima Otsuka (LETO) rats. Plasma CCK levels rose up to 4- to 14-fold over the preloading values after the onset of acute pancreatitis in all three models in both groups of rats. However, histologic alterations as well as the magnitudes of increase in serum amylase and lipase activity and the pancreatic wet weight were significantly less in the OLETF rats than those in the LETO rats. In addition, 72 h after the onset of arginine pancreatitis, massive destruction of pancreatic parenchyma with a significant reduction in serum amylase and lipase activities and pancreatic wet weight was observed in the LETO rats, whereas these changes were not seen in OLETF rats. These results suggest that endogenous CCK and CCK-A receptors play a role in the development of severe acute pancreatitis in rats.

Effects of tetraprenylacetone on pancreatic exocrine secretion and acute pancreatitis in two experimental models in rats

SummaryThe effects of tetraprenylacetone (TPN), an acyclic polyisoprenoid with antiulcer actions, on pancreatic exocrine secretion, and its preventive and therapeutic effects on acute pancreatitis in two experimental models were studied in rats. Intraduodenal administration of TPN (0, 100, 200 and 400 mg/kg/h) caused dose-dependent increases in pancreatic juice and bicarbonate output without increasing protein output and plasma cholecystokinin (CCK) concentrations. TPN-stimulated pancreatic exocrine secretion was completely abolished by antisecretin serum but it was not by CCK receptor antagonist loxiglumide (50 mg/kg/h). In acute pancreatitis induced by four subcutaneous injections of 20 μg/kg cerulein at hourly intervals over, 3 h, TPN (400 mg/kg) given by an oral route either 1 h before the first cerulein injection or immediately after the last injection significantly reduced the increases in serum amylase and lipase activities and pancreatic wet wt. Pretreatment with TPN caused histologic improvements, whereas posttreatment failed to ameliorate histologic alterations. In severe type of acute pancreatitis induced by retrograde intraductal injection of 1.0 mL/kg of 4% sodium taurocholate, TPN exerted no apparent beneficial effects on biochemical and histologic alterations of acute pancreatitis. It is concluded that TPN given by an oral route stimulates pancreatic exocrine secretion through an increase in endogenous secretin release and causes beneficial effects on the experimental model of mild acute pancreatitis in rats.

Pharmacological profile of TP-680, a new cholecystokininA receptor antagonist

1 The pharmacological characteristics of a newly developed serine derivative (R)‐1‐[3‐(3‐carboxypyridine‐2‐yl)thio‐2‐(indol‐2‐yl)carbonylamino]propionyl‐4‐diphenylmethyl‐piperazine (TP‐680), a cholecystokinin type A (CCKA) receptor antagonist, were studied and compared with those of MK‐329 and loxiglumide. 2 TP‐680 showed approximately 2 and 22 times greater selectivity for peripheral CCKA receptors relative to brain CCK (CCKB) receptors than MK‐329 and loxiglumide, respectively, when IC50 values for inhibition of [125I]‐CCK‐8 binding in isolated acini and cerebral cortex were compared. 3 TP‐680 was approximately 17 times less potent than MK‐329, but was 106 times more potent than loxiglumide in inhibiting 100 pM CCK‐8‐stimulated amylase release from rat pancreatic acini. The antagonism produced by TP‐680 was specific for CCK in that the effects of other receptor secretagogues or agents bypassing receptors were not altered. 4 TP‐680 caused a parallel rightward shift of the dose‐response curve for CCK‐8‐stimulated amylase release as did MK‐329 and loxiglumide. However, in contrast to MK‐329 and loxiglumide, TP‐680 suppressed the maximal responses of CCK‐8‐induced amylase release in a concentration‐dependent fashion, indicating that TP‐680 is an unsurmountable antagonist. 5 Repeated washing of acini after a 30 min treatment with TP‐680 restored the responsiveness but not the sensitivity, causing a residual inhibition on the action of CCK‐8. 6 The addition of loxiglumide prior to or together with application of TP‐680 protected CCK receptors from unsurmountable and irreversible antagonism by TP‐680. 7 Our results indicate that TP‐680 is a potent and the most selective CCKA receptor antagonist for the pancreas reported to date.

Characterization of a new cholecystokinin receptor antagonist FK480 in in vitro isolated rat pancreatic acini.

Biochemical and pharmacologic characteristics of a newly developed benzodiazepine derivative (S)-N-[l-(2-fluorophenyl)-3,4,6,7-tetrahydro-4-oxo-pyrrolo-[3,2,1 -jk] [1,4]benzodiazepine-3-yl]-lH-indole-2-carboxamide (FK480) as a cholecystokinin (CCK) receptor antagonist were examined in the isolated rat pancreatic acini and compared with those of MK-329 and loxiglumide. FK480, MK-329, and loxiglumide inhibited CCK octapeptide (CCK-8)-stimulated amylase release and binding of [125I]CCK-8 in a concentration-dependent manner, with a half-maximal inhibition (ID50) at 1.30 ± 0.12 n M, 1.33 ± 0.21 nM, and 1.27 ± 0.23 μM, respectively, for amylase release, and 0.40 2 0.06 nM, 0.68 ± 0.08 n M, and 0.38 ± 0.03 μM, respectively, for [125I]CCK-8 binding. The antagonism was competitive in nature because these three compounds caused a parallel rightward shift of the dose-response curve for CCK-8-stimulated amylase secretion, without altering the maximal increase. The antagonism produced by FK480 was specific for CCK in that the effects of other receptor secretagogues or agents bypassing receptors were not altered. FK480 not only prevented but also reversed CCK-&stimulated amylase release. This compound caused a residual inhibition of the action of CCK-8. When acini were preincubated with 100 nM FK480 for 30 min, the subsequent dose-response curve to CCK-8 was shifted 10-fold toward higher concentration. Similar results were obtained with MK-329 but not with loxiglumide. FK480 appeared to be bound to the receptors on acinar cells in a slowly dissociating state. These results demonstrate that FK480 is a potent, competitive, and specific antagonist of CCKs stirnulatory action on the exocrine pancreas.

Supramaximal CCK and CCh concentrations abolish VIP potentiation by inhibiting adenylyl cyclase activity

Exocrine pancreatic secretion stimulated by vasoactive intestinal polypeptide (VIP), which acts through the adenylyl cyclase-cAMP pathway, is potentiated by stimulation with other secretagogues such as CCK and carbachol (CCh). However, the potentiating effect is abolished by the same secretagogues at supramaximal concentrations. In the present study, we examined the mechanisms by which supramaximal concentrations of CCK octapeptide (CCK-8) or CCh reduce the VIP-induced potentiation of amylase secretion from isolated rat pancreatic acini. VIP-stimulated amylase secretion was potentiated by submaximal stimulatory concentrations of CCK-8 and CCh but was reduced by the same reagents at higher concentrations. Supramaximal concentrations of CCK-8 or CCh also reduced forskolin-induced potentiation of amylase release but did not reduce that induced by 8-bromo-cAMP. Moreover, supramaximal concentrations of CCK-8 or CCh inhibited VIP-stimulated intracellular cAMP production as well as adenylyl cyclase activity. 12- O-tetradecanoylphorbol 13-acetate (TPA) also reduced the magnitude of the potentiation of amylase release caused by VIP plus CCK-8 or CCh, although TPA itself decreased neither VIP-stimulated adenylyl cyclase activity nor intracellular cAMP accumulation. These results indicate that supramaximal concentrations of CCK-8 and CCh reduce the potentiating effect of VIP and forskolin on amylase secretion by inhibiting the adenylyl cyclase activity. In addition, protein kinase C is suggested to be partly implicated in this inhibitory mechanism. The mechanisms that lead to such inhibition may be interlinked but distinct from each other.

Effects of Mci-727 on Pancreatic Exocrine Secretion and Acute Pancreatitis in Two Experimental Rat Models

The effects of a newly developed compound having antiulcer action, (Z)-2-(4-methylpiperazin-1-yl)-1-[4-(2-phenyl-ethyl)phenyl]-ethanone oxime hydrochloride monohydrate (MCI-727), on pancreatic exocrine secretion were studied in anesthetized rats and evaluated its preventive and therapeutic effects on acute pancreatitis in two experimental rat models. Intraduodenal administration of MCI-727 [25, 50, or 100 mg/kg body weight (wt)] stimulated a dose-dependent increase in pancreatic juice and bicarbonate output without increasing the protein output or plasma cholecystokinin concentration. MCI-727-stimulated pancreatic exocrine secretion was completely abolished by antisecretin serum but not by the cholecystokinin receptor antagonist loxiglumide (50 mg/kg body wt/h) or cholinergic receptor antagonist atropine (100 μg/kg body wt/h). In rats with acute pancreatitis induced by four subcutaneous injections of 20 μg/kg body wt cerulein at hourly intervals over 3 h, MCI-727 administered orally at a dose of 100 mg/kg body wt 30 min before the first cerulein injection significantly reduced the increases in serum amylase and lipase activity and pancreatic wet weight and induced improvements in the results of histologic examination. Moreover, when given 30 min before and 90 min after the first cerulein injection, MCI-727 had even more dramatic protective effects on all these parameters. In addition, even when administered immediately after the last cerulein injection, MCI-727 effectively ameliorated all these alterations of acute pancreatitis. However, MCI-727 had no apparent beneficial effects on the biochemical and histologic alterations of acute pancreatitis in the severe form induced by retrograde intraductal injection of 1.0 ml/kg body wt of 4% sodium taurocholate. These findings suggest that oral administration of MCI-727 stimulates pancreatic exocrine secretion by endogenous secretin release and that it has therapeutic as well as preventive effects on mild forms of acute pancreatitis in rats.

Dibutyltin dichloride modifies amylase release from isolated rat pancreatic acini.

Introduction Dibutyltin dichloride (DBTC) is widely used as a stabilizer for polyvinylchloride plastics and is of particular toxicologic interest. Aim To examine the effects of DBTC on pancreatic exocrine function in isolated rat pancreatic acini. Methodology Isolated rat pancreatic acini were incubated with various secretagogues in the presence or absence of DBTC. We investigated the effects of DBTC on amylase release, receptor binding, and protein kinase C (PKC) enzyme activity. Results DBTC reduced cholecystokinin octapeptide (CCK-8)–stimulated and carbamylcholine-stimulated amylase release and the binding of [125I]CCK-8 to isolated rat pancreatic acini. Conversely, DBTC potentiated secretin-stimulated amylase release, although it slightly inhibited [125I]secretin binding to its receptors. In addition, DBTC potentiated amylase release stimulated by vasoactive intestinal peptide, 8-bromoadenosine 3´, 5´-monophosphate (8Br-cAMP) or calcium ionophore A23187, whereas it had no influence on amylase release stimulated by 12-O-tetradecanoylphorbol 13-acetate. The protein kinase C (PKC) inhibitor calphostin C abolished the DBTC-induced potentiation of amylase release stimulated by 8Br-cAMP or A23187. Moreover, DBTC caused a significant translocation of PKC enzyme activity from cytosol to membrane fraction. Conclusions These results indicate that DBTC reduces CCK-8- and carbamylcholine-stimulated amylase release by inhibiting their receptor bindings to pancreatic acini, whereas it potentiates cAMP-mediated amylase release by activating PKC in isolated rat pancreatic acini.

Pharmacologic profile of TS-941, a new benzodiazepine derivative cholecystokinin-receptor antagonist, in in vitro isolated rat pancreatic acini.

We investigated the pharmacologic characteristics of a newly developed benzodiazepine derivative (S)-(-)-N-[2,3-dihydro-2-oxo-5-phenyl-1-[(1H-tetrazol-5-yl)methyl] -1H-1,4-benzodiazepine-3-yl]-2-indolecarboxamide (TS-941), a cholecystokinin type A (CCK-A)-receptor antagonist, in the isolated rat pancreatic acini and compared with those of well-known CCK-A-receptor antagonists, devazepide and loxiglumide. TS-941 inhibited CCK-8-stimulated amylase release concentration dependently, as did devazepide and loxiglumide, with a half-maximal inhibition (IC50) at 78.6 +/- 10.3 nM. TS-941 was approximately 23 times less potent than devazepide (IC50, 3.4 +/- 0.3 nM), but was 50 times more potent than loxiglumide (IC50, 3,966 +/- 544 nM) in inhibiting 100 pM CCK-8-stimulated amylase release from rat pancreatic acini. TS-941 had a fivefold lower selectivity than devazepide for pancreatic CCK (CCK-A) over brain CCK (CCK-B) receptors but fourfold greater than loxiglumide when IC50 values for inhibition of [125I]CCK-8 binding in isolated acini and cerebral cortex were compared. The antagonism produced by TS-941 was specific for CCK in that the effects of other receptor secretagogues or agents bypassing receptors were not altered. TS-941 caused a parallel rightward shift of the entire dose-response curve for CCK-8-stimulated amylase release without altering the maximal increase, as did devazepide and loxiglumide. TS-941, whether added at the beginning or 20 min after the CCK-8 stimulation, inhibited amylase release. TS-941 caused a concentration-dependent residual inhibition of the action of CCK-8. The acini, once incubated with a high concentration of TS-941 (10 microM; 127 times IC50) for 30 min, was 10-fold less sensitive to CCK-8 than the acini preincubated without TS-941, whereas the sensitivity and the responsiveness to CCK-8 stimulation of those incubated with a low concentration of TS-941 (1.0 microM) were similar to the control acini. These results indicate that TS-941 is a potent, competitive, and selective CCK-A receptor antagonist for the pancreas.