Glucagon-induced insulin secretion in normal diabetic subjects.
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Eight normal subjects and ten diabetic patients were studied to compare the response of plasma insulin to glucagon with that to glucose and tolbutamide. Oral glucose tolerance test, glucagon test and tolbutamide-glucagon test were performed at intervals of several days. In glucose tolerance test, insulin response was reduced in the patients with severe diabetes. Plasma insulin increased and reached the peak 3 min after glucagon injection (glucagon I) in the normal controls, while plasma insulin response was reduced in diabetic patients, especially in the severe diabetics. In the normal controls plasma insulin rose and reached the peak 6 min after the tolbutamide injection and thereafter fell to the initial level. Glucagon injection following tolbutamide (glucagon II) caused the rise in insulin in the control subjects. In diabetics insulin response to either tolbutamide or glucagon I was reduced. Tolbutamide or glucagon II caused a significant difference in plasma insulin response in all the diabetic groups compared with the normal subjects, while glucose or glucagon I showed a significant increment of plasma insulin between the normal subjects and the severe diabetics. These results suggest that injection of tolbutamide as well as glucagon II provides a definite discrimination of insulin response in diabetics from the normal controls. The usefulness of the tolbutamide-glucagon test in the diagnosis of diabetes mellitus was discussed. -- glucose tolerance test; glucagon test; tolbutamide-glucagon test; plasma insulin. (+info)
Antidiabetic activity of the rhizoma of Anemarrhena asphodeloides and active components, mangiferin and its glucoside.
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The antidiabetic activity of the rhizoma of Anemarrhena asphodeloides was investigated in KK-Ay mice, an animal model of genetic type 2 diabetes. The water extract of the rhizoma (AA) (90 mg/kg) reduced blood glucose levels from 570 +/- 29 to 401 +/- 59 mg/dl 7 h after oral administration (p<0.05) and also tended to reduce serum insulin levels in KK-Ay mice. AA-treated KK-Ay mice had significantly reduced blood glucose levels in an insulin tolerance test. Based on these results, the antidiabetic mechanism of AA may be due to decreased insulin resistance. In addition, the active components of AA were confirmed to be mangiferin and its glucoside. (+info)
Diabetogenic effect of cyclosporin A is mediated by interference with mitochondrial function of pancreatic B-cells.
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Treatment of patients after organ transplantation with the immunosuppressive drug cyclosporin A (CsA) is often accompanied by impaired glucose tolerance, thus promoting the development of diabetes mellitus. In the present article we show that 2 to 5 microM CsA diminishes glucose-induced insulin secretion of isolated mouse pancreatic islets in vitro by inhibiting glucose-stimulated oscillations of the cytoplasmic free-Ca(2+) concentration [Ca(2+)](c). This effect is not due to an inhibition of calcineurin, which mediates the immunosuppressive effect of CsA, because other calcineurin inhibitors, deltamethrin and tacrolimus, did not affect the oscillations in [Ca(2+)](c) of the B-cells. The CsA-induced decrease in [Ca(2+)](c) to basal values was not caused by a direct inhibition of L-type Ca(2+) channels. CsA is known to be a potent inhibitor of the mitochondrial permeability transition pore (PTP), which we recently suggested to be involved in the regulation of oscillations. Consequently, CsA also inhibited the oscillations of the cell membrane potential, and it is shown that these effects could not be ascribed to cellular ATP depletion. However, the mitochondrial membrane potential Delta Psi was affected by CsA by inhibiting the oscillations in Delta Psi. Interestingly, the observed reduction in [Ca(2+)](c) could be counteracted by the K(+)(ATP) channel blocker tolbutamide, indicating that the stimulus-secretion coupling was interrupted before the closure of K(+)(ATP) channels. It is concluded that CsA alters B-cell function by inhibiting the mitochondrial PTP. This terminates the oscillatory activity that is indispensable for adequate insulin secretion. Thus, CsA acts on different targets to induce the immunosuppressive and the diabetogenic effect. (+info)
Molecular modelling and 1H-NMR: ultimate tools for the investigation of tolbutamide: beta-cyclodextrin and tolbutamide: hydroxypropyl-beta-cyclodextrin complexes.
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A structural study of the inclusion compound of tolbutamide (TBM) with beta-cyclodextrin (beta-CD) and hydroxypropyl-beta-cyclodextrin (HP-beta-CD) was attempted by means of 1H-nuclear magnetic resonance (1H-NMR) experiments and computer molecular modelling. To establish the stoichiometry and stability constant of the beta-CD:TBM complex, the continuous variation method was used. The presence of true inclusion complexes between TBM and beta-CD or HP-beta-CD in solution was clearly evidenced by the 1H-NMR technique. Changes in chemical shifts of H-3 and H-5 protons, located inside the CD cavity, associated with variations in the chemical shifts of TBM aromatic protons provided clear evidence of inclusion complexation, suggesting that the phenyl moiety of the drug molecule was included in the hydrophobic cavity of CDs. This view was further supported by the observation of intermolecular NOEs between TBM and beta-CD and by the aid of a molecular modelling program, which established the most probable structure of the complex. The molecular graphic computation confirmed that the minimum energy, positioning TBM relative to beta-CD, occurs when the aromatic ring of TBM is included within the beta-CD cavity by its wider side, leaving the aliphatic chain externally, which is in good agreement with the results of 1H-NMR studies. (+info)
Opioid receptor modulation of a metabolically sensitive ion channel in rat amygdala neurons.
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We have used single-channel patch-clamp recordings to study opiate receptor effects on freshly dissociated neurons from the rat amygdalohippocampal area (also called the posterior nucleus of the amygdala), an output nucleus of the amygdala implicated in appetitive behaviors. Dissociated cells included a distinct subpopulation that was 30-40 micrometer in diameter, multipolar or pyramidal in shape, and immunoreactive for neuron-specific enolase, mu opioid receptors, and galanin. In whole-cell perforated-patch recordings, these cells responded to low concentrations of mu opioid agonists with a hyperpolarization. In cell-attached single channel recordings, these cells expressed a large variety of K(+)-permeable ion channels, including 20-100 pS inward rectifiers and 150-200 pS apparent Ca(2+)-activated K(+) channels, none of which appeared sensitive to the presence of opioid drugs. In contrast, a 130 pS inwardly rectifying channel was selectively activated by mu opioid receptors in this same subpopulation of cells and was active only in the presence of opioid agonists, and inhibited in the presence of antagonists. Channels identical to the 130 pS channel in conductance and voltage sensitivity were activated in the absence of opioids, when the cells were treated with glucose-free medium or with the metabolic inhibitor rotenone. The sulfonylurea drug tolbutamide inhibited 130 pS channel openings elicited by opioids. Thus, a subpopulation of amygdala projection neurons expresses a metabolically sensitive ion channel that is selectively modulated by opiate receptors. This mechanism may allow opioid neurotransmitters to regulate ingestive behaviors, and thus, opiate drugs to influence reward pathways. (+info)
Phenotyping of individual pancreatic islets locates genetic defects in stimulus secretion coupling to Niddm1i within the major diabetes locus in GK rats.
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The major diabetes quantitative trait locus (Niddm1), which segregates in crosses between GK rats affected with spontaneous type 2-like diabetes and normoglycemic F344 rats, encodes at least two different diabetes susceptibility genes. Congenic strains for the two subloci (Niddm1f and Niddm1i) have been generated by transfer of GK alleles onto the genome of F344 rats. Whereas the Niddm1f phenotype implicated insulin resistance, the Niddm1i phenotype displayed diabetes related to insulin deficiency. Individual islets from 16-week-old congenic rats were characterized for insulin release and oxygen tension (pO(2)). In the presence of 3 mmol/l glucose, insulin release from Niddm1f and Niddm1i islets was approximately 5 pmol. g(-1). s(-1) and pO(2) was 120 mmHg. Similar recordings were obtained from GK and F344 islets. When glucose was raised to 11 mmol/l, insulin release increased significantly in Niddm1f and F344 islets but was essentially unchanged in islets from GK and Niddm1i. The high glucose concentration lowered pO(2) to the same extent in islets from all strains. Addition of 1 mmol/l tolbutamide to the perifusion medium further increased pulsatile insulin release threefold in all islets. The pulse frequency was approximately 0.4 min(-1). alpha-Ketoisocaproate (11 mmol/l) alone increased pulsatile insulin release eightfold in islets from Niddm1f, Niddm1i, and control F344 rats but had no effect on insulin release from GK islets. These secretory patterns in response to alpha-ketoisocaproate were paralleled by reduction of pO(2) in Niddm1f, Niddm1i, and control F344 islets and no change of pO(2) in GK islets. The results demonstrate that Niddm1i carries alleles of gene(s) that reduce glucose-induced insulin release and that are amenable to molecular identification by genetic fine mapping. (+info)
Application of the PKCYP-test to predict the amount of in vivo CYP2C11 using tolbutamide as a probe.
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Previous reports have shown that the determination of drug metabolism capacity can be made by the pharmacokinetic estimation of the quantity of cytochrome P450 (CYP) in vivo (PKCYP-test), in which an apparent liver-to-blood free concentration gradient in vivo (qg) is introduced, which is useful for evaluating fluctuations of CYPIA2 in rats. The aim of the present study was to examine the application of the PKCYP-test to evaluate the quantity of in vivo CYP2C11 by using tolbutamide as a probe, to confirm its validity using a physiologically-based pharmacokinetic rat model. Rats treated with carbon tetrachloride (CCl4-treated rats) were used as a model for low levels of CYP2C11 in the liver. In CCl4-treated rats, the total body clearance (CLtot) of tolbutamide and the amount of CYP2C11 fell to about a quarter and a third of that in control rats, respectively. The time-course of tolbutamide concentrations in serum in control rats could be simulated by a physiologically-based pharmacokinetic model. In CCl4-treated rats, take into consideration the qg value of control rats, the level of CYP2C11 was accurately predicted by the PKCYP-test, and the time-course of tolbutamide concentrations in serum could be predicted by the same physiologically-based pharmacokinetic model. In conclusion, we have shown that the PKCYP-test can be used to predict levels of CYP2C11. It was also demonstrated that the qg and amount of CYP are useful parameters in the PKCYP-test by constructing a physiologically-based pharmacokinetic model which was applied to the PKCYP-test. (+info)
In vitro evaluation of valproic acid as an inhibitor of human cytochrome P450 isoforms: preferential inhibition of cytochrome P450 2C9 (CYP2C9).
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AIMS: To evaluate the potency and specificity of valproic acid as an inhibitor of the activity of different human CYP isoforms in liver microsomes. METHODS: Using pooled human liver microsomes, the effects of valproic acid on seven CYP isoform specific marker reactions were measured: phenacetin O-deethylase (CYP1A2), coumarin 7-hydroxylase (CYP2A6), tolbutamide hydroxylase (CYP2C9), S-mephenytoin 4'-hydroxylase (CYP2C19), dextromethorphan O-demethylase (CYP2D6), chlorzoxazone 6-hydroxylase (CYP2E1) and midazolam 1'-hydroxylase (CYP3A4). RESULTS: Valproic acid competitively inhibited CYP2C9 activity with a Ki value of 600 microM. In addition, valproic acid slightly inhibited CYP2C19 activity (Ki = 8553 microM, mixed inhibition) and CYP3A4 activity (Ki = 7975 microM, competitive inhibition). The inhibition of CYP2A6 activity by valproic acid was time-, concentration- and NADPH-dependent (KI = 9150 microM, Kinact=0.048 min(-1)), consistent with mechanism-based inhibition of CYP2A6. However, minimal inhibition of CYP1A2, CYP2D6 and CYP2E1 activities was observed. CONCLUSIONS: Valproic acid inhibits the activity of CYP2C9 at clinically relevant concentrations in human liver microsomes. Inhibition of CYP2C9 can explain some of the effects of valproic acid on the pharmacokinetics of other drugs, such as phenytoin. Co-administration of high doses of valproic acid with drugs that are primarily metabolized by CYP2C9 may result in significant drug interactions. (+info)