Tolbutamide Injection Research Articles

ATP-gated potassium channels contribute to ketogenic diet-mediated analgesia in mice

Chronic pain is a substantial health burden and options for treating chronic pain remain minimally effective. Ketogenic diets are emerging as well-tolerated, effective therapeutic strategies in preclinical models of chronic pain, especially diabetic neuropathy. We tested whether a ketogenic diet is antinociceptive through ketone oxidation and related activation of ATP-gated potassium (KATP) channels in mice. We demonstrate that consumption of a ketogenic diet for one week reduced evoked nocifensive behaviors (licking, biting, lifting) following intraplantar injection of different noxious stimuli (methylglyoxal, cinnamaldehyde, capsaicin, or Yoda1) in mice. A ketogenic diet also decreased the expression of p-ERK, an indicator of neuronal activation in the spinal cord, following peripheral administration of these stimuli. Using a genetic mouse model with deficient ketone oxidation in peripheral sensory neurons, we demonstrate that protection against methylglyoxal-induced nociception by a ketogenic diet partially depends on ketone oxidation by peripheral neurons. Injection of tolbutamide, a KATP channel antagonist, prevented ketogenic diet-mediated antinociception following intraplantar capsaicin injection. Tolbutamide also restored the expression of spinal activation markers in ketogenic diet-fed, capsaicin-injected mice. Moreover, activation of KATP channels with the KATP channel agonist diazoxide reduced pain-like behaviors in capsaicin-injected, chow-fed mice, similar to the effects observed with a ketogenic diet. Diazoxide also reduced the number of p-ERK+ cells in capsaicin-injected mice. These data support a mechanism that includes neuronal ketone oxidation and activation of KATP channels to provide ketogenic diet-related analgesia. This study also identifies KATP channels as a new target to mimic the antinociceptive effects of a ketogenic diet.

Electrophysiological and neurochemical effects of antidiabetic sulphonylurea tolbutamide in the rat ventral tegmental area and prefrontal cortex

Tolbutamide is an orally administered sulphonylurea, used in the management of non‐insulin‐dependent diabetes mellitus. This class of drug acts on the sulphonyureas receptors(SUR) through blockage of ATP‐regulated K‐channels to release insulin. Some studies have revealed the presence of sulphonylureas binding sites in the substantia nigra. However, there is very little documented data about the presence of these receptors in the ventral tegmental area (VTA) and prefrontal cortex(PFC).Here, using in vivo extracellular single unit recordings, we have investigated the electrophysiological effects of acute intravenous administration of tolbutamide (20mg/kg) on VTA dopamine and PFC pyramidal neurons. We also examined in vitro the effects of this drug on dopamine transporter activity using striatum and tegmental synaptosomes.Adult Sprague Dawley rats were deeply anaesthetised with chloral hydrate (400mg/kg) and urethane (1.5 g/kg) and placed in a stereotaxic instrument for VTA dopamine/GABA and PFC pyramidal neurons recordings, respectively. Appropriately, blood level glucose was monitored with glucometer to avoid hypoglycermia followed by administration with 2ml/kg of 20% glucose subsequent to tolbutamide injection, when necessary. Furthermore, we studied tolbutamide(30μM) effects on striatal synaptosome preparation for dopamine transporter activity through in vitro [3H]‐dopamine radiometric uptake assay technique.In the VTA, administration of tolbutamide induced biphasic effects on the basal activity of most of the dopamine neurons tested: large inhibition (up to 100%) during a relatively short period (1–3 min), caused by hyperpolarisation, followed by a long‐lasting excitatory effect (40% of the baseline activity). Significant increased burst activity was also observed. This initial inhibitory effect was insensitive to a pre‐administration of the dopamine D2 antagonist(eticlopride100μg/kg). Interestingly, presumed GABAergic VTA neurons exhibit only a monophasic significant excitatory effect following tolbutamide administration. In the prefrontal cortex, tolbutamide also induced a monophasic excitatory effect in a dose dependent manner on most of the presumed pyramidal neurons tested. Neurochemical in vitro investigation revealed a statistically significant partial decrease (p<0.05) in specific dopamine synaptosomal uptake at relatively high concentration of tolbutamide (30 μM) an indication of possible direct modulation of dopamine turn‐over.In conclusion, tolbutamide induced a unique biphasic effect in the VTA dopamine neurons. The large but short lasting inhibitory effect is hypothesised to be mediated by GABA interneurons which are found to be immediately activated by the drug. Future works are needed to understand the function of this putative metabolic‐sensitive modulation of dopamine neuronal activity.Support or Funding InformationSelf funded international student, supported by the university bursary department.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Prenatal tolbutamide treatment alters plasma glucose and insulin concentrations and negatively affects the postnatal performance of chickens

To examine the relationship of insulin and glucose, broiler embryos were subjected to acute or prolonged hypoglycemia during the late embryonic phase by, respectively, injecting once (at embryonic day [ED] 16 or 17) or on 3 consecutive days (ED 16, 17, and 18) with tolbutamide (80 μg/g embryo weight), a substance that stimulates insulin secretion from the pancreas. After 1 tolbutamide injection, a prolonged (32 h) decrease of plasma glucose and a profound acute increase in plasma insulin were observed. The 3 consecutive tolbutamide injections induced hypoglycemia for 4 days (from ED 16 to ED 19). The postnatal performance after 3 consecutive tolbutamide injections in broiler embryos was also investigated. Body weight was lower in tolbutamide-treated chickens from hatch to 42 d compared with sham (P = 0.001) and control (P < 0.001) chickens. Feed intake was lower in the tolbutamide group from hatch to 42 d as compared with sham (P = 0.007) and control (P = 0.017) animals. In addition, at 42 d, plasma glucose concentrations, after an insulin injection challenge (50 μg/kg body weight), were higher in tolbutamide-treated chickens compared with the sham and the control group as were their basal glucose levels (P value of group effect <0.001). In conclusion, tolbutamide treatment during the late embryonic development in broilers resulted in prolonged hypoglycemia in this period and negatively influenced the posthatch performance.

Glucose intolerance in thiamine-deficient rats.

Abstract The mechanism of glucose intolerance in thiamine-deficient rats has been examined. Deficient rats showed marked glucose intolerance. However, the hypoglycaemic effect of insulin (1 i.u. kg−1, i.p.) was similar in the deficient, pair-fed and normal groups, though somewhat weaker in the normal group than in the other two groups. After injection of tolbutamide (40 mg kg−1, i.p.), the hypoglycaemic effects in the three groups were the same. Tyramine (10 mg kg−1, s.c.) restored the impaired glucose tolerance of deficient rats to normal, but not that of alloxan diabetic rats. Furthermore, tyramine did not restore the intolerance of deficient rats pretreated with alloxan. These results suggest that the main factor causing glucose intolerance in the deficient rats may be suppressed insulin secretion.

Sulphonylurea physicochemical-pharmacokinetic relationships in the pancreas and liver

This study examined the physicochemical-pharmacokinetic relationships for the sulphonylureas in the perfused rat pancreas and liver. Multiple indicator dilution studies were conducted with bolus injections of tolbutamide, chlorpropamide, gliclazide, glipizide, glibenclamide and glimepiride, and a reference marker albumin, in the perfused pancreas and liver. Individual solute pharmacokinetics were analysed using nonparametric moment analysis and nonlinear regression assuming a physiologically based pharmacokinetic model. All solutes had similar shaped outflow concentration-time profiles in both the pancreas and liver, but varied in extraction. Negligible drug extraction was evident in the pancreas. Hepatic extraction ranged from 0.03 (tolbutamide) to 0.52 (glibenclamide) and could be related to solute lipophilicity and perfusate protein binding. The sulphonylurea mean transit times in both the pancreas and liver varied four- and ninefold respectively and were related to the lipophilicity and perfusate protein binding of the drug. The permeability surface area product of sulphonylureas from the perfusate into the organs were greater in the liver and were mainly determined by lipophilicity (pancreas, r2=0.89; liver, r2=0.80). The distribution of the sulphonylureas in both the perfused pancreas and perfused liver was dependent on their lipophilicity and perfusate protein binding. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2807–2821, 2009

Plasma glucose response after intravenous injection of tolbutamide in insulin-treated type I and type II diabetic patients.

To estimate the residual beta-cell function, plasma glucose and C-peptide response to an intravenous injection of tolbutamide were observed in seven Type I (insulin dependent) and nine Type II (non-insulin dependent) diabetic patients on insulin therapy. Fasting plasma glucose in the patient was controlled below 11 mmol/l by conventional insulin therapy, and 1 g of tolbutamide was intravenously injected. In the serum C-peptide response following tolbutamide injection, seven of nine Type II diabetics showed the peak values of serum C-peptide more than 0.3 nmol/l from 20 min to 60 min after the load, and Type I diabetics gained the peak values less than 0.3 nmol/l except one patient. The decrease of plasma glucose within 60 min after tolbutamide injection was more than 20% of the basal level in eight of nine Type II diabetics, and in all of seven Type I diabetics the decrease did not exceed 15%. Both serum C-peptide and plasma glucose after tolbutamide load responded differently between Type I and Type II diabetics on insulin therapy, and it was thought that tolbutamide load-glucose response test may be a useful method to estimate the residual beta-cell function in the diabetics.

G-allele of Intronic rs10830963 inMTNR1BConfers Increased Risk of Impaired Fasting Glycemia and Type 2 Diabetes Through an Impaired Glucose-Stimulated Insulin Release

OBJECTIVEGenome-wide association studies have identified several variants within the MTNR1B locus that are associated with fasting plasma glucose (FPG) and type 2 diabetes. We refined the association signal by direct genotyping and examined for associations of the variant displaying the most independent effect on FPG with isolated impaired fasting glycemia (i-IFG), isolated impaired glucose tolerance (i-IGT), type 2 diabetes, and measures of insulin release and peripheral and hepatic insulin sensitivity.RESEARCH DESIGN AND METHODSWe examined European-descent participants in the Inter99 study (n = 5,553), in a sample of young healthy Danes (n = 372), in Danish twins (n = 77 elderly and n = 97 young), in additional Danish type 2 diabetic patients (n = 1,626) and control subjects (n = 505), in the Data from the Epidemiological Study on the Insulin Resistance Syndrome (DESIR) study (n = 4,656), in the North Finland Birth Cohort 86 (n = 5,258), and in the Haguenau study (n = 1,461).RESULTSThe MTNR1B intronic variant, rs10830963, carried most of the effect on FPG and showed the strongest association with FPG (combined P = 5.3 × 10−31) and type 2 diabetes. The rs10830963 G-allele increased the risk of i-IFG (odds ratio [OR] 1.64, P = 5.5 × 10−11) but not i-IGT. The G-allele was associated with a decreased insulin release after oral and intravenous glucose challenges (P < 0.01) but not after injection of tolbutamide. In elderly twins, the G-allele associated with hepatic insulin resistance (P = 0.017).CONCLUSIONSThe G-allele of MTNR1B rs10830963 increases risk of type 2 diabetes through a state of i-IFG and not through i-IGT. The same allele associates with estimates of β-cell dysfunction and hepatic insulin resistance.

Studies of Association of Variants Near the HHEX, CDKN2A/B, and IGF2BP2 Genes With Type 2 Diabetes and Impaired Insulin Release in 10,705 Danish Subjects

In the present study, we aimed to validate the type 2 diabetes susceptibility alleles identified in six recent genome-wide association studies in the HHEX/KIF11/IDE (rs1111875), CDKN2A/B (rs10811661), and IGF2BP2 (rs4402960) loci, as well as the intergenic rs9300039 variant. Furthermore, we aimed to characterize quantitative metabolic risk phenotypes of the four variants. The variants were genotyped in the population-based Inter99 cohort (n = 5,970), the ADDITION Study (n = 1,626), a population-based sample of young healthy subjects (n = 377), and in additional type 2 diabetic case (n = 2,111) and glucose-tolerant (n = 521) subjects. The case-control studies involved a total of 4,089 type 2 diabetic patients and 5,043 glucose-tolerant control subjects. We validated association of variants near HHEX/KIF11/IDE, CDKN2A/B, and IGF2BP2 with type 2 diabetes. Interestingly, in middle-aged people, the rs1111875 C-allele of HHEX/KIF11/IDE strongly associated with lower acute insulin response during an oral glucose tolerance test (P = 6 x 10(-7)). In addition, decreased insulin release following intravenous tolbutamide injection was observed in young healthy subjects (P = 0.02). Also, a reduced insulin release was observed for the CDKN2A/B rs10811661 T-allele after both oral and intravenous glucose challenges (P = 0.001 and P = 0.009, respectively). We validate that variants in the proximity of the HHEX/KIF11/IDE, CDKN2A/B, and IFG2BP2 loci associate with type 2 diabetes. Importantly, variations within the HHEX/KIF11/IDE and CDKN2A/B loci confer impaired glucose- and tolbutamide-induced insulin release in middle-aged and young healthy subjects, suggesting a role for these variants in the pathogenesis of pancreatic beta-cell dysfunction.

Th-P15:176 Association of lipoprotein(A) with coronariography pattern in young survivors of myocardial infarction (MI)

This study examined the physicochemical-pharmacokinetic relationships for the sulphonylureas in the perfused rat pancreas and liver. Multiple indicator dilution studies were conducted with bolus injections of tolbutamide, chlorpropamide, gliclazide, glipizide, glibenclamide and glimepiride, and a reference marker albumin, in the perfused pancreas and liver. Individual solute pharmacokinetics were analysed using nonparametric moment analysis and nonlinear regression assuming a physiologically based pharmacokinetic model. All solutes had similar shaped outflow concentration-time profiles in both the pancreas and liver, but varied in extraction. Negligible drug extraction was evident in the pancreas. Hepatic extraction ranged from 0.03 (tolbutamide) to 0.52 (glibenclamide) and could be related to solute lipophilicity and perfusate protein binding. The sulphonylurea mean transit times in both the pancreas and liver varied four- and ninefold respectively and were related to the lipophilicity and perfusate protein binding of the drug. The permeability surface area product of sulphonylureas from the perfusate into the organs were greater in the liver and were mainly determined by lipophilicity (pancreas, r2 = 0.89; liver, r2 = 0.80). The distribution of the sulphonylureas in both the perfused pancreas and perfused liver was dependent on their lipophilicity and perfusate protein binding. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2807–2821, 2009

Acute insulin responses to calcium and tolbutamide do not differentiate focal from diffuse congenital hyperinsulinism.

Congenital hyperinsulinism (CHI) is related to two main histological pancreas anomalies: focal adenomatous hyperplasia and diffuse beta-cell hypersecretion. Pharmacological tests to measure acute insulin responses (AIR) to peripheral i.v. injections of glucose, calcium, and tolbutamide have been reported as potential means to distinguish between these histological forms. In patients with defects in ATP-sensitive potassium channels, tolbutamide will fail to induce insulin release in affected portions of the pancreas, whereas calcium gluconate will enhance insulin release through spontaneously active voltage-gated Ca(2+) channels. Consequently, in focal CHI patients, calcium should promote AIRs from the lesion, whereas tolbutamide should act to promote insulin secretion from the healthy region of the pancreas (outside the focal hyperplasia). We therefore studied AIRs to calcium and tolbutamide stimulation tests in 16 children with focal (n = 9) or diffuse (n = 7) CHI before pancreatic surgery. We found hypervariable AIRs to glucose and calcium stimulation in both focal and diffuse CHI patients. AIRs to tolbutamide stimulation were found modest in focal CHI patients, which might account for beta-cell quiescence in the healthy portion of the pancreas of these patients. We conclude that AIRs to calcium and tolbutamide stimulation tests are not sufficient to differentiate the focal from the diffuse CHI patients.

Calmodulin Overexpression Causes Ca2+-Dependent Apoptosis of Pancreatic β Cells, Which Can Be Prevented by Inhibition of Nitric Oxide Synthase

We investigated the mechanism of β-cell loss in transgenic mice with elevated levels of β cell calmodulin. The transgenic mice experienced a sudden rise in blood glucose levels between 21 and 28 days of age. This change was associated with development of severe hypoinsulinemia and loss of β cells from the islets. Ultrastructural analysis revealed that compromised granule formation and apoptotic changes in the transgenic β cells preceded the onset of hyperglycemia. Intraperitoneal injection of tolbutamide, an antidiabetic sulfonylurea, decreased blood glucose levels but increased the number of apoptotic β cells. Finally, injection of transgenic mice with Nω-nitro-l-arginine methyl ester, which inhibits nitric oxide synthase activity, prevented hyperglycemia and lessened the changes in number and size of β cells. Because immunofluorescent staining revealed preferential distribution of neural nitric oxide synthase in pancreatic β cells, we speculate that overexpression of calmodulin sensitizes the β cells to Ca2+-dependent activation of neural nitric oxide synthase, which mediates apoptosis.

Genetic variability of the SUR1 promoter in relation to beta-cell function and Type II diabetes mellitus.

We aimed to examine the promoter of SUR1 for genetic variation and to determine if variants were associated with Type II (non-insulin-dependent) diabetes mellitus or measures of beta-cell function. We examined 465 bp upstream of the ATG site in 46 Type II diabetic patients and 15 glucose tolerant control subjects by SSCP-heteroduplex analysis. We identified an a --> t substitution 437 bp upstream of the ATG site. The allelic frequency was similar in 455 unrelated Type II diabetic patients and in 203 glucose tolerant control subjects matched for age (0.036, [95 % CI 0.019-0.053] vs 0.034 [95 % CI 0.009-0.059]; p = 0.92). Among the glucose tolerant subjects there were no differences between non-carriers (n = 189) and carriers (n = 14) of the variant in fasting values or 30 min values of plasma glucose and serum insulin during an oral glucose tolerance test. In a study of 233 glucose tolerant offspring of and spouses to Danish Caucasian Type II diabetic patients, non-carriers (n = 193) and carriers (n = 37) of the -437 a/t polymorphism did not differ in glucose or tolbutamide stimulated insulin response during an intravenous glucose tolerance test with intravenous tolbutamide injection [AUCs-insulin (0-8) min, 2290 +/- 1660 vs 2308 +/- 1935 pmol/l x min and AUCs-insulin(20-30 min), 3113 +/- 2033 vs. 3393 +/- 2830 pmol/l x min, respectively]. We have identified a novel a/t polymorphism of the SUR1 gene promoter which is not associated with Type II diabetes mellitus or measures of beta-cell function. Previous reported non-functional variants of SUR1 associated with Type II diabetes mellitus still need to be accounted for.

The K121Q variant of the human PC-1 gene is not associated with insulin resistance or type 2 diabetes among Danish Caucasians.

The human plasma-cell membrane differentiation antigen-1 (PC-1) has been shown to inhibit insulin receptor tyrosine kinase activity. Recently, a K121Q polymorphism in the human PC-1 gene was found in a Sicilian population and was shown to be strongly associated with insulin resistance. The objectives of the present investigation were to examine in the Danish Caucasian population whether the K121Q variant was associated with type 2 diabetes or, in glucose-tolerant subjects, with impaired whole-body insulin sensitivity. We genotyped 404 Danish type 2 diabetic patients and found that the allele frequency of the variant was 0.14 (95% CI 0.12-0.16), whereas the allele frequency was 0.16 (95% CI 0.13-0.19) among 237 matched glucose-tolerant control subjects (P = 0.6). In the control subjects, there were no significant differences among wild-type, heterozygous, or homozygous subjects in regard to 1) serum insulin and plasma glucose levels at fasting, 60 min, or 120 min during an oral glucose tolerance test (OGTT) or 2) the estimates of insulin resistance obtained from the homeostasis model assessment (HOMA). Furthermore, we investigated the impact of the variant in 2 other Danish population samples that comprised 356 young healthy subjects and 226 glucose-tolerant offspring of type 2 diabetic probands, respectively. In all of the study populations, the polymorphism was not associated with an altered insulin sensitivity index as estimated from an intravenous glucose tolerance test in combination with an intravenous injection of tolbutamide. In addition, among the 226 offspring, the variations in serum insulin and serum C-peptide responses measured during an OGTT were not related to the PC-1 genotype. In conclusion, the K121Q polymorphism of the human PC-1 gene is not associated with type 2 diabetes or insulin resistance among Danish Caucasians.

Population-based modeling to demonstrate extrapancreatic effects of tolbutamide.

Tolbutamide is used increasingly as an investigative tool in in vivo studies of the physiology of glucose tolerance. Its hypoglycemic effect in nondiabetic subjects is widely variable, reflecting possible variability in its pharmacokinetics, an insulinergic response, an extrapancreatic effect of the drug, or the hypoglycemic effect of insulin itself. Using population-based modeling, we have investigated the kinetics and dynamics of tolbutamide and assessed covariates in two groups of healthy subjects. The results indicate a high variability in insulinergic effect, measured by the area under of the curve of insulin (0-60 min), in response to tolbutamide injection (coefficient of variation = 29-96%). However, it appears that impaired insulin sensitivity is compensated by higher insulin secretion in response to tolbutamide. Thus the hypoglycemic effect of high insulin secretion is minimal in insulin-resistant subjects. Application of the model indicated that tolbutamide has appreciable extrapancreatic effects mediated by prolongation of the residence time of insulin in a remote effect and by enhancement of glucose effectiveness. An effect in increasing the insulin sensitivity index is also possible but could not be confirmed statistically for all groups of subjects studied. These observations may explain inconsistencies between the results of tolbutamide and insulin injection in the frequently sampled intravenous glucose tolerance test and call for further study of insulin- vs. tolbutamide-modified frequently sampled intravenous glucose tolerance tests in the assessment of the insulin sensitivity and glucose effectiveness indexes.

Regulation by tolbutamide and diazoxide of the electrical activity in mouse pancreatic beta-cells recorded in vivo.

1. The glucose-dependence of beta-cell electrical activity and the effects of tolbutamide and diazoxide were studied in anaesthetized mice. 2. In untreated animals there was a direct relationship between glycaemia and the burst pattern of electrical activity. Animals with high glucose concentration showed continuous electrical activity. The application of insulin led to a steady decrease in blood glucose concentration and a transition from continuous to oscillatory activity at 7.7+/-0.1 mM glucose (mean+/-s.d.) and a subsequent transition from oscillatory to silent at 4.7+/-0.6 mM glucose. 3. At physiological blood glucose concentrations the electrical activity was oscillatory. The injection of tolbutamide (1800 mg kg[-1]) transformed this oscillatory pattern into one of continuous electrical activity. The increased electrical activity was associated with a decrease in blood glucose concentration from 7.1+/-0.9 (control) to 5.5+/-1.0 mM (10 min after tolbutamide injection). The effects of tolbutamide are consistent with a direct blocking effect on the K(ATP) channel that leads to membrane depolarization. 4. The injection of diazoxide (6000 mg kg[-1]) hyperpolarized the cells and transformed the oscillatory pattern into a silent one. This is consistent with a direct stimulant effect by diazoxide on the K(ATP) channel. The use of tolbutamide or diazoxide correspondingly led to the lengthening or shortening of the active phase of electrical activity, respectively. This indicates that in vivo, such activity can be modulated by the relative degree of activation or inhibition of the K(ATP) channel. 5. These results indicate that under physiological conditions, tolbutamide and diazoxide have direct and opposite effects on the electrical activity of pancreatic beta-cells, most likely through their action on K(ATP) channels. This is consistent with previous work carried out on in vitro models and explains the drugs hypo- and hyperglycaemic effects.

Amino acid polymorphisms in the ATP-regulatable inward rectifier Kir6.2 and their relationships to glucose- and tolbutamide-induced insulin secretion, the insulin sensitivity index, and NIDDM.

Kir6.2 is an inwardly rectifying potassium channel that is expressed in pancreatic beta-cells and cardiac and skeletal muscle. Expressed together with the high-affinity sulphonylurea receptor, it reconstitutes a sulphonylurea- and also ATP-sensitive potassium channel resembling the native beta-cell channel. The objective of this study was to search for mutations in the Kir6.2 gene that might be associated with NIDDM or related to altered insulin secretion, insulin action, or glucose metabolism in healthy subjects. Using polymerase chain reaction-single-strand conformation polymorphism analysis (PCR-SSCP) on genomic DNA from 69 Danish NIDDM patients and 66 matched control subjects, we report the finding of three missense polymorphisms in otherwise conserved codons and three silent polymorphisms in the gene encoding Kir6.2: codon 23 (GAG/AAG), Glu-->Lys; codon 190 (GCT/GCC), Ala-->Ala; codon 267 (CTC/CTG), Leu-->Leu; codon 270 (CTG/GTG), Leu-->Val; codon 337 (ATC/GTC), Ile-->Val; codon 381 (AAG/AAA), Lys-->Lys. The codon 23 and codon 337 amino acid polymorphisms were always coupled. The allelic frequencies of the polymorphisms were similar in NIDDM patients and control subjects. The amino acid polymorphisms were not associated with altered insulin secretion after intravenous glucose or tolbutamide injections or with altered glucose effectiveness in a phenotype study of 346 young healthy subjects. However, carriers of the maximal load of amino acid variants, the compound homozygous codon 23/337 and heterozygous codon 270, had on average a 62% higher insulin sensitivity index (P = 0.006), compared with noncarriers. We conclude that a combination of common Kir6.2 amino acid variants may contribute to the genetic background behind the large variation of the insulin sensitivity index in the general population.

Insulin and glucagon secretion in goats ( Capra hircus Linnæus) exposed to cold

Cold exposure significantly decreased the insulin response to the intravenous injection of arginine, butyrate and tolbutamide, and tended to reduce the response to glucose in goats. The glucagon responses to these test materials were not different between warm and cold environments. Intravenous phentolamine infusion tended to increase, and propranolol infusion decreased insulin secretion more effectively in the cold than in the warm environment. It is concluded that cold exposure decreases insulin secretion in response to a variety of stimuli in goats.

Reduced pancreatic insulin release and reduced peripheral insulin sensitivity contribute to hyperglycaemia in cystic fibrosis

Traditional opinion holds that patients with cystic fibrosis (CF) develop impaired glucose tolerance or diabetes due to insulinopenia caused by fibrosis of the pancreas. However, studies on the dynamics of insulin secretion and peripheral insulin action have yielded conflicting results. We studied 18 patients with CF (9 male, 9 female, age 15-29 years) and 17 healthy control subjects (8 male, 9 female, 20-32 years). Oral glucose tolerance tests and combined i.v.-glucose-tolbutamide-tests were performed on separate days in fasting subjects. Bergman's "Minimal Model" was used to quantitate both peripheral insulin sensitivity (SI) and insulin-independent glucose disposal (glucose effectiveness; SG). Based on National Diabetes Data Group criteria, 4 patients were classified as diabetic (22%; CF-DM), 3 patients (17%) had impaired glucose tolerance (CF-IGT) while glucose metabolism was normal in 11 patients (61%; CF-NGT). Irrespective of the degree of glucose tolerance, the insulin response to oral glucose was not reduced but delayed, up to 60 min in the CF-IGT/DM group. First-phase insulin release (0-10 min) after i.v.-glucose was significantly lower in CF patients (29% of healthy controls; P < 0.0001), with no difference between the CF-NGT and CF-IGT/DM groups. Insulin release following tolbutamide injection was only marginally reduced in CF patients (64% of controls). In contrast, SI was significantly reduced in the subgroup of CF patients with abnormal glucose metabolism (CF-IGT/DM: 0.97 +/- 0.16 x 10(-4) l/min/pmol; control group: 1.95 +/- 0.25; P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The opposing effects of insulin and hyperglycemia in modulating amino acid metabolism during a glucose tolerance test in lean and obese subjects

An intravenous glucose tolerance test (IVGTT) was administered in both lean (n = 9) and obese (n = 14) volunteers to ascertain the importance of the dynamic interactions between insulin and glucose on plasma concentrations of two amino acids known to be primarily used by skeletal muscle, namely leucine and isoleucine, and one amino acid, phenylalanine, which is primarily metabolized by the liver. After a 30-minute basal period, each subject received a bolus injection of glucose (0.3 g/kg IV) followed 20 minutes later by a bolus injection of tolbutamide (300 mg). Blood samples were drawn frequently for 180 minutes after the glucose infusion to determine plasma concentrations of glucose, insulin, leucine, isoleucine, and phenylalanine. Plasma glucose and insulin concentrations during the basal period were increased by 10% and 100%, respectively, in obese compared with lean individuals ( P < .05), whereas phenylalanine, isoleucine, and leucine levels were similar between groups. During the IVGTT, plasma glucose level initially increased by twofold and slowly returned to basal level thereafter, whereas insulin level responded to glucose and tolbutamide infusions in a typical biphasic manner. Plasma leucine and isoleucine levels did not change from basal levels during the first 60 minutes of the IVGTT as hyperglycemic hyperinsulinemia prevailed in both groups. However, when plasma glucose had returned to near-basal levels, plasma leucine and isoleucine levels began to decrease, reaching a plateau of approximately 20% and 35% below basal, and plasma insulin level remained elevated in the lean and obese individuals, respectively. In contrast to the two branched-chain amino acids, phenylalanine level remained unchanged throughout the entire experimental period in both lean and obese subjects. During the IVGTT, a resistance to insulin-mediated glucose and protein metabolism was observed in the obese individuals, as evidenced by elevated glucose to insulin, leucine to insulin, isoleucine to insulin, and phenylalanine to insulin ratios. Therefore, during dynamic changes in plasma insulin and glucose levels, hyperglycemia appears to exert an opposing force to insulin's effect on amino acid and protein metabolism, which may be important during dynamic physiologic conditions such as diabetes, stress, trauma, or mealtime.

Factors determining glucose tolerance in patients with thalassemia major.

To better understand the pathophysiology of glucose intolerance secondary to iron overload in patients with thalassemia major, we performed tolbutamide-modified frequently sampled iv glucose tolerance tests (FSIGTs) in 10 thalassemic patients (6 males and 4 females; 21.7 +/- 1.2 yr old; body mass index, 19.7 +/- 0.6 kg/m2) and 10 healthy controls (5 males and 5 females; 22.4 +/- 1.3 yr; body mass index, 20.6 +/- 0.5 kg/m2). Insulin secretion and action were quantified by application of the minimal model of glucose kinetics and the combined model of insulin and C-peptide kinetics to the FSIGT data. The insulin sensitivity index was significantly lower in thalassemia patients [72 +/- 12 min-1(nmol/mL)] compared to controls [158 +/- 21 min-1(nmol/mL); P = 0.0026]. The integrated insulin response during the FSIGT was significantly greater in thalassemia patients than in controls after tolbutamide injection (P = 0.042). The difference in insulin levels was apparently due to reduced hepatic insulin extraction in thalassemia (78 +/- 2% vs. 68 +/- 3%; P = 0.0251). Seven of the 10 thalassemia patients were studied prospectively at 6-month intervals for 6-12 months. Repeated measures analysis of variance indicated that across a 6-month interval, there was a decrease in the total integrated insulin response (P = 0.002), with no change in insulin sensitivity (P = 0.86). In conclusion, patients with thalassemia major have significant insulin resistance, which may be compensated for by an elevated circulating insulin level. The elevated insulin level in response to tolbutamide appears to be due to reduced hepatic extraction of insulin and not to an enhanced insulin secretory response. Over time, patients with thalassemia experience a reduction in their circulating insulin levels. Persistent insulin resistance along with a progressive reduction in circulating insulin levels may lead to glucose intolerance and diabetes mellitus, which have a high prevalence in patients with thalassemia major.