Hypophosphatemia and glucose intolerance: evidence for tissue insensitivity to insulin

Although hypophosphatemia is commonly present in diabetics, little is known about its isolated effects on glucose and insulin metabolism. We therefore investigated glucose metabolism in six nondiabetic subjects with chronic hypophosphatemia. When glucose was infused to maintain a constant hyperglycemic level (125 mg per deciliter [6.9 mmol per liter] above basal levels), the glucose infusion rate was 36 per cent less in the hypophosphatemic group than in controls (4.90 +/- 0.34 mg per kilogram of body weight per minute vs. 7.64 +/- 0.37, P < 0.001), although responses to endogenous insulin were similar. When exogenous insulin was infused at a constant rate to maintain an insulin level about 100 microU per milliliter (718 pmol per liter) above basal levels and glucose was infused as necessary to maintain fasting glucose levels, the infusion rate of glucose was 43 per cent lower in the hypophosphatemic group than in controls (3.80 +/- 0.58 mg per kilogram per minute vs. 6.70 +/- 0.33, P < 0.001), although the clearance rate of insulin was similar in both groups. These results indicate that hypophosphatemia is associated with impaired glucose metabolism in both the hyperglycemic and euglycemic states, and that this associated primarily reflects decreased tissue sensitivity to insulin. (N Engl J Med. 1980; 303; 1259-63.).     

Effect of neonatal treatment with MSG (monosodium glutamate) on thyroid of the adult male rats

Percutaneous transluminal angioplasty (PTA) has been well described in the treatment of mesenteric artery stenoses but has met with limited success in ostial lesions. The authors describe a case of a 79-year-old woman diagnosed with chronic mesenteric ischemia associated with a 22-pound weight loss and postprandial pain. The celiac axis and inferior mesenteric artery were occluded. A high-grade, calcified stenosis was present in the proximal superior mesenteric artery. This was treated with primary stent placement using a Palmaz stent deployed from an axillary approach. A brief discussion of mesenteric ischemic and visceral artery PTA is included.     

Taste dimensions of monosodium glutamate (MSG) in a food system: role of glutamate in young American subjects

Fibrosing cholestatic hepatitis is a histological variant of hepatitis B virus infection with a high rate of mortality. We describe a patient who acquired acute hepatitis B virus infection 8 months after renal transplantation. Clinical features of rapidly progressive liver failure, indicated by prolonged prothrombin time (57 seconds) and increased bilirubin (40.4 mg/dL) and ammonia (129 mumol/L) concentrations, were accompanied by an extremely high serum HBV DNA level (2.153 x 10(6) pg/mL). Liver biopsy specimen showed fibrosing cholestatic hepatitis with widespread balloon degeneration of hepatocytes, focal hepatocyte loss, bile stasis, periportal fibrosis, mild lymphocytic infiltration, and strongly positive immunohistochemical staining for hepatitis B surface antigen (HBsAg) and hepatitis B core antigen. Lamivudine therapy suppressed HBV DNA to < 10 pg/mL within 4 weeks, which was followed by gradual recovery of liver function from a state of hepatic precoma. Twenty-four months after the onset of hepatitis, the patient had normal prothrombin time and bilirubin, transaminase, and albumin levels. She remained HBsAg positive and hepatitis B e antigen negative. Renal allograft function was stable, with a creatinine level of 1.52 mg/dL. HBV DNA remained suppressed after 22 months of lamivudine therapy. Our experience shows that fibrosing cholestatic hepatitis and liver failure caused by HBV infection can be successfully treated with lamivudine.     

Mild insulin resistance during oral glucose tolerance test (OGTT) in women with acne

The purpose of this study was to evaluate serum levels of basal insulin and glucose-stimulated insulin, and to evaluate their correlations with androgen levels in women with acne. Serum levels of total testosterone (T), free testosterone (FT), dihydrotestosterone (DHT), dehydroepiandrosterone sulfate (DHEA-S), sex hormone binding globulin (SHBG), insulin-like growth factor-1 (IFG-1), and immunoreactive insulin (IRI) were measured and compared in thirty women with moderate or severe acne and thirteen healthy controls. Serum FT, DHT and DHEA-S levels in the acne group were significantly higher than those in the control group. In the acne group, there were no significant correlations between insulin or IGF-1 levels and T, FT, DHT and SHBG, despite the positive correlation between insulin and IGF-1. In order to determine the effects of insulin secretion as a dynamic response to an oral glucose tolerance test (OGTT) on serum androgen levels in acne patients, we examined the responses of serum insulin and androgen levels to a 75 g, 2 hour OGTT in the acne group and in the control group. Basal insulin levels were not significantly higher than those in the control group, but the summed insulin levels during the OGTT in the acne group were significantly higher than those in the control group. Serum T and FT levels in the acne group decreased during the OGTT, but these changes were not so significant when compared to normal controls. In conclusion, we tried to demonstrate mild insulin resistance during the OGTT in acne patients. However, postmeal transient hyperinsulinemia does not seem to play an important role in determining hyperandrogenemia in acne patients.     

Portal and peripheral vein insulin responses to intravenous glucose in the rhesus monkey

Catheterization of the portal vein and bilateral femoral veins were performed under general anesthesia in 6 healthy male rhesus monkeys. Four days later, sequential, simultaneous peripheral and portal plasma samples were obtained for glucose and immunoreactive insulin determinations before and after administration of 0.5 Gm. of glucose per kilogram (over a 1-minute period) via the opposite peripheral catheter. Two phases of insulin secretion were noted in both portal and peripheral plasma samples. An immediate early-phase insulin response was noted with a peak response at 1 minute followed by a rapid decline to a nadir at 5 minutes. A second phase of insulin secretion was evident with a peak response at 10 minutes and a subsequent decline to basal levels by 60 minutes. Simultaneous portal vein and peripheral vein glucose concentrations were not significantly different from each other by paired analysis. Thus, in the rhesus monkey peripheral insulin concentrations following intravenous glucose exhibit a biphasic response closely paralleling pancreatic insulin secretion.     

Treatment with protease inhibitors associated with peripheral insulin resistance and impaired oral glucose tolerance in HIV-1-infected patients

BACKGROUND: The use of protease inhibitors in the treatment of HIV-1 infection is associated with the new onset of diabetes mellitus, hyperlipidaemia and lipodystrophy. It is unclear whether these findings are coincidental or whether they reflect a causative effect of protease inhibitors. OBJECTIVE: To evaluate the effect of treatment with protease inhibitors on insulin sensitivity, oral glucose tolerance and serum lipids in HIV-infected patients in order to determine whether treatment with protease inhibitors can cause peripheral insulin resistance. DESIGN: Cross-sectional controlled study in HIV-infected patients treated with protease inhibitors to assess insulin sensitivity, oral glucose tolerance and changes in serum lipids. METHODS: Sixty-seven patients treated with protease inhibitors, 13 therapy-naive patients and 18 HIV-negative control subjects were tested for insulin sensitivity (intravenous insulin tolerance test). In a subgroup of 24 treated patients, oral glucose tolerance was determined. Serum lipids prior to and under treatment with protease inhibitors were compared. RESULTS: Patients on protease inhibitors had a significantly decreased insulin sensitivity when compared with therapy-naive patients (median, 75 and 156 micromol/l/min, respectively; P < 0.001). All treated patients with impaired (n=4) or diabetic (n=9) oral glucose tolerance, and four out of 11 patients with normal glucose tolerance showed peripheral insulin resistance; all therapy-naive patients had normal insulin sensitivity. Treatment with protease inhibitors led to a significant increase in total triglycerides and cholesterol in the 67 treated patients (median increase, 113 and 37 mg/ml, respectively). CONCLUSION: Treatment with protease inhibitors is associated with peripheral insulin resistance, leading to impaired or diabetic oral glucose tolerance in some of the patients, and with hyperlipidaemia. Overall, there is a large variation in the severity and clinical presentation of protease inhibitor-associated metabolic side-effects.     

Portal and peripheral blood immunoreactive insulin concentrations after glucose infusion during gastrectomy

We evaluated portal and peripheral blood immunoreactive insulin concentrations (IRI) after glucose infusion in patients undergoing gastrectomy. Seventy-four patients were divided into following two groups: 68 received 25g glucose infusion in an hour (glucose group), and the remainder received no glucose (control group). Portal blood IRI level in glucose group was about thirty-fold higher than that in control group. However, peripheral blood IRI did not correlate with portal blood IRI in glucose group. In addition, significant negative correlation between portal blood IRI and blood glucose was observed in glucose group. Our results reveal that adequate pancreatic insulin secretion occurs after glucose infusion during gastrectomy, but peripheral blood IRI does not reflect this pancreatic insulin secretion. The results also suggest that blood glucose may be regulated by the liver under these conditions.     

Evaluation of glucose metabolic disorder: insulin resistance and insulin receptors in critically ill children

OBJECTIVE: To explore the pathogenesis of glucose metabolic disorder and insulin resistance in critically ill children under severe stress. METHODS: To test glucose, lactate, glucagon, insulin, c-peptide, cortisol levels in 50 critically ill children. While we measured 125I-insulin binding to erythrocytes of 13 critically ill children who had hyperglycemia and hyperinsulinemia. Glucose and lactate were measured biochemically. Insulin, c-peptide, cortisol and glucagon were determined by RIA. Erythrocytes insulin receptor was detected by insulin radioreceptor assay. RESULTS: Glucose, lactate, insulin, c-peptide, glucagon, cortisol, insulin/glucose, insulin/glucagon ratio in patients were higher than those in normal controls (P < 0.05). As compared with normal controls, the maximum 125I-insulin bound and insulin receptor number per cell were significantly lower (P < 0.01). But there was no difference of mean value in receptor affinity (P > 0.05). CONCLUSIONS: Hyperglycemia is common in critically ill children during stress, which may be attributed to hormones disturbance and tissure insulin resistance. Insulin receptor defect due to comprehensive factors was one of the important causes for insulin resistance. The blood glucose level can be used as an predicting index in ICU.     

Rilmenidine normalizes fructose-induced insulin resistance and hypertension in rats

OBJECTIVE: The aim of this study was to determine the effects of rilmenidine (an antihypertensive drug that lowers blood pressure by decreasing sympathetic outflow) in an animal model of hypertension associated with insulin resistance, i.e. rats fed on a high-fructose diet. DESIGN: Wistar rats were fed for 4 weeks either on a standard diet (S group) or on a high-fructose diet (F group; 34.5% fructose). In half of the rats in the F group, rilmenidine (1 mg/kg per day) was added to the drinking water for the last 2 weeks of the diet (FR group). RESULTS: Body weight gain was higher in the F than in the S rats (66+/-8g versus 45+/-8g, P< 0.05), but was prevented by rilmenidine treatment (32+/-2g). Arterial systolic blood pressure was increased in F rats (162+/-2 versus 155+/-2 mmHg, P< 0.05), rilmenidine reduced this value to normal (149+/-3 mmHg). Glucose tolerance, glucose turnover rate, and insulin secretion were not modified by the diet or by the drug. However, during a euglycemic hyperinsulinemic clamp, glucose utilization was lower (10+/-1 versus 14+/-1.5 mg/min per kg; P< 0.05) and hepatic glucose production higher (1+/-0.01 versus 0 mg/min per kg, P< 0.01) in F than in S rats. These changes in insulin action were totally abolished by rilmenidine. CONCLUSIONS: These data demonstrate that rilmenidine can ameliorate the deleterious effects of a high-fructose diet, i.e. weight gain, hypertension, and resistance to the effects of insulin.     

Trp64Arg mutation of beta 3-adrenergic receptor and insulin sensitivity in subjects with glucose intolerance

We investigated the relationship between the Trp64Arg mutation in the beta 3-adrenergic receptor gene and insulin sensitivity, which was evaluated by the euglycemic-hyperinsulinemic-clamp technique, in 54 patients with impaired glucose tolerance (IGT) or non-insulin dependent diabetes mellitus (NIDDM) who were not receiving insulin therapy. The frequencies of Trp/Trp, Trp/Arg, and Arg/Arg genotypes in the patients were 63.0, 33.3, and 3.7%, respectively, which did not differ significantly from those of the 227 controls (67.0, 33.3, and 3.7%, respectively, which did not differ significantly from those of the 227 controls (67.0, 31.3, and 1.8%, respectively). The mean glucose infusion rate of the 34 patients with Trp/Trp did not differ from that of the 18 patients with Trp/Arg (4.3 +/- 2.2 and 5.3 +/- 2.4 mg/kg/min, respectively); while that of the 2 patients with Arg/Arg was 11.5 mg/kg/min. There were no differences in the BMI or fat distribution in the abdomen between each genotype of patients, although the frequency of the Arg64 allele tended to increase with body mass index (BMI) in the control subjects under 60 years of age, which suggests that the mutation is involved in weight gain.     

Sex specific action of insulin on the glucose metabolism of lymphatic tissue of rats and humans (author's transl)

Glucose metabolism of lymphoid cells isolated from thymus and spleen of Wistar rats, weighing 140-150 g, was found to be sensitive to insulin. The influence of insulin on glucose uptake by isolated cells from both lymphoid tissues displayed a significant sex specificity. Insulin at 0.1-10 nmol/1 stimulated glucose uptake of cells from male rats, whereas in cells from females, inhibition of glucose uptake was observed. However, lactate production was enhanced in lymphoid cells of both sexes. Cortisol (100 nmol/1) displayed a significant anti-insulin action on glucose uptake and lactate release by thymocytes of male rats. In contrast, in cells from females, cortisol and insulin both exhibited an inhibitory action on glucose uptake, whereas the hormones were found to antagonise lactate production. The sex specific stimualtory influence of insulin on glucose uptake by thymocytes of male rats was reversed and the hormone became inhibitory when animals were castrated. The action of insulin on glucose uptake was also shown to be age-dependent. In experiments with rats weighing either about 10 g or 40 g, sex-specific effects on glucose influx were found, that were similar to those of rats weighing 140-150 g. However, stimulation of glucose uptake was found with thymocytes from rats of both sexes weighing about 80 g. Comparable results were obtained with isolated thymocytes from immature humans (2 months-10 years old). Incubation of thymocytes from males with insulin (10 nmol/1) stimulated glucose uptake and lactate release, whereas insulin caused an inhibition of glucose uptake and an enhancement of lactate production in thymocytes from female. Age dependence and sex specificity of insulin action on glucose metabolism in lymphoid cells and tissues may explain the contradictory results reported by other authors.     

Increased intestinal glucose absorption and postprandial hyperglycaemia at the early step of glucose intolerance in Otsuka Long-Evans Tokushima Fatty rats

Otsuka Long-Evans Tokushima Fatty (OLETF) rats are reported to be obese Type II (non-insulin-dependent) diabetic rats with insulin resistance and impaired insulin secretion. To investigate the contribution of intestinal glucose absorption to postprandial hyperglycaemia, we determined the plasma xylose concentrations after an 0.8 g/kg oral xylose load which was used as a test of small intestinal glucose absorption in 6-week-old OLETF rats and weight-matched Long-Evans Tokushima Otsuka (LETO) rats. An oral glucose tolerance test showed that OLETF rats developed hyperglycaemia at 60 and 90 min after the glucose load, though the fasting plasma glucose concentration, insulin concentration and insulin-induced in vivo glucose utilization rate were similar. Consistently, in an oral D-xylose loading test, the peak concentration of plasma xylose in OLETF rats was increased by 58.7% compared with that of LETO rats (p < 0.005). The disappearance rate of plasma xylose concentrations after intravenous xylose loading did not differ between the two strains. Co-treatment with 0.4 g/kg phlorizin, a specific inhibitor of sodium-dependent glucose transporter 1 (SGLT1), abolished both plasma glucose and xylose concentrations after the loads. Morphological studies showed that both the small intestinal wet weight and surface area were 30% larger in the OLETF rats than in the LETO rats. Furthermore, the SGLT1 mRNA content of OLETF rats also increased compared with LETO rats. These results suggest that an increased SGLT1 expression concomitant with intestinal hypertrophy in OLETF rats is partly associated with postprandial hyperglycaemia before the onset of insulin resistance and hyperinsulinaemia.     

Interstitial muscle insulin and glucose levels in normal and insulin-resistant Zucker rats

Tumour angiogenesis (antifactor VIII-related antigen antibody), p53 overexpression (DO-1) and proliferative activity (MIB-1) were immunohistochemically analysed for the prediction of long-term survival in 113 patients with squamous cervical carcinoma. The median follow-up time was 82 months (range 72-99). In early stages (IB-IIA), neovascularisation was significantly related to tumour size. Significantly more patients in stage IIA had high tumour vascularity compared to stage IB (P < 0.01) but no significant difference was found between early and advanced stages (IIB-IVB) of cervical carcinoma. p53 overexpression was correlated to the stage of disease (P < 0.01). No relationship was found between tumour angiogenesis, p53 overexpression or MIB-1 and pelvic lymph node metastases, histological subtype or differentiation. Tumours with more than 50% p53 overexpression was significantly correlated with survival in the univariate analysis, but no independent predictive value was found. It is concluded that immunohistochemically detectable p53 overexpression as measured by DO-1 and proliferative activity as measured by MIB-1 seems of no clinical value for the prediction of long-term survival in squamous cervical carcinoma. The predictive value of tumour angiogenesis for survival outcome has still to be determined in squamous cervical carcinoma.     

Antazoline increases insulin secretion and improves glucose tolerance in rats and dogs

In vivo effects of an imidazoline devoid of alpha2-adrenoceptor antagonistic properties, antazoline, on insulin secretion and glycemia were investigated both in fasted rats and dogs. In both species, antazoline (1.5 mg/kg i.v.) transiently increased insulinemia without affecting basal plasma glucose levels. In contrast, during an i.v. glucose tolerance test, antazoline markedly potentiated insulin release and thus increased the glucose disappearance rate. In rats, during an oral glucose tolerance test, the intragastric administration of antazoline (1.5 mg/kg) clearly enhanced insulin secretion and reduced hyperglycemia. In dogs provided with a venous pancreatico-duodenal bypass, antazoline (0.5 mg/kg i.v.) induced an immediate and transient increase in insulin and somatostatin but not in glucagon pancreatico-duodenal outputs. In conclusion, intravenously and orally administered, the imidazoline antazoline is able to stimulate insulin secretion in vivo and improve glucose tolerance. The imidazoline compounds could therefore have a potential therapeutic relevance as new antihyperglycemic insulinotropic agents.     

Obesity and insulin resistance in human growth hormone transgenic rats

A line of transgenic rats (heterozygotes) carrying a chimeric gene comprising a regulatory portion of murine whey acidic protein and a structural portion of human GH (hGH) genes developed severe obesity with age. To characterize physiological mechanisms that lead to fat accumulation, an array of parameters related to obesity were studied. Blood hGH levels were continuously low, endogenous rat GH secretion was suppressed, and the pulsatility in peripheral GH levels was absent. Plasma glucose, insulin, triglyceride, and FFA levels in the male transgenic rats significantly exceeded those in nontransgenic littermates at 12 and 17 weeks, but not at 7 weeks, of age. All symptoms except hyperlipidemia were restored to normal by treatment with an antidiabetic agent, thiazolidinedione (troglitazone), for 1 week from 17 weeks of age. As phenotypic expression of obesity was already evident before aberration of physiological parameters, it was assumed that animals had a condition in which obesity or hyperlipidemia caused hyperinsulinemia. Gene expression and enzymatic activity of lipoprotein lipase in the adipose tissue in the transgenic rats were not different from those in normal rats. In contrast, the gene expression level of glycerol-3-phosphodehydrogenase was markedly elevated, suggesting that glycerol synthesis was much enhanced in the adipocytes of the transgenic rats. In an i.p. glucose tolerance test, the transgenic rats were not hyperglycemic at 7 weeks of age; however, the animal became hyperglycemic at 15-17 weeks of age. Finally, treatment with recombinant hGH for 1 week to produce pulsatile secretion reduced the size of epididymal and kidney fat pads and restored normal weight gain. These observations suggest that continuously low peripheral GH levels with the lack of pulsatile secretion resulted in obesity and noninsulin-dependent diabetes mellitus.     

Effect of physical training on insulin response to intravenous glucose in male peripubertal rats

This study was undertaken to evaluate the effects of regular endurance-type exercise (i.e., swimming) on glucose tolerance and glucose-stimulated insulin response (GSIR) in 55- and 90-day-old peripubertal male rats. Intravenous glucose tolerance tests (0.5 g/kg) were done in four groups of male Sprague-Dawley rats: two groups of trained (TR; 55- and 90-day-old) and two groups of age- and weight-matched untrained (UNTR) rats. The UNTR rats were subjected to a continuous food restriction to maintain body weights equal to those of the TR rats. Rats were received in our laboratory after weaning at 21 days of age and were evaluated 48 h after the last exercise bout. No significant differences in body weights were found between TR and UNTR rats, at the age of either 55 or 90 days. A significant (P < 0.01) decrease in the mean integrated area under the glucose and insulin curves was observed in TR compared with UNTR groups in 55- as well as 90-day-old rats. These results indicate that exercise training in male rats improves the glucose tolerance and GSIR before and during puberty (21-90 days) independently of a reduction in body weight gain.     

Limitations to exercise- and maximal insulin-stimulated muscle glucose uptake

The hypothesis of this investigation was that insulin and muscle contraction, by increasing the rate of skeletal muscle glucose transport, would bias control so that glucose delivery to the sarcolemma (and t tubule) and phosphorylation of glucose intracellularly would exert more influence over glucose uptake. Because of the substantial increases in blood flow (and hence glucose delivery) that accompany exercise, we predicted that glucose phosphorylation would become more rate determining during exercise. The transsarcolemmal glucose gradient (TSGG; the glucose concentration difference across the membrane) is inversely related to the degree to which glucose transport determines the rate of glucose uptake. The TSGG was determined by using isotopic methods in conscious rats during euglycemic hyperinsulinemia [Ins; 20 mU/(kg. min); n = 7], during treadmill exercise (Ex, n = 6), and in sedentary, saline-infused rats (Bas, n = 13). Rats received primed, constant intravenous infusions of trace 3-O-[3H]methyl-D-glucose and [U-14C]mannitol. Then 2-deoxy-[3H]glucose was infused for the calculation of a glucose metabolic index (Rg). At the end of experiments, rats were anesthetized, and soleus muscles were excised. Total soleus glucose concentration and the steady-state ratio of intracellular to extracellular 3-O-[3H]methyl-D-glucose (which distributes on the basis of the TSGG) were used to calculate ranges of possible glucose concentrations ([G]) at the inner and outer sarcolemmal surfaces ([G]im and [G]om, respectively). Soleus Rg was increased in Ins and further increased in Ex. In Ins, total soleus glucose, [G]om, and the TSGG were decreased compared with Bas, while [G]im remained near 0. In Ex, total soleus glucose and [G]im were increased compared with Bas, and there was not a decrease in [G]om as was observed in Ins. In addition, accumulation of intracellular free 2-deoxy-[3H]glucose occurred in soleus in both Ex and Ins. Taken together, these data indicate that, in Ex, glucose phosphorylation becomes an important limitation to soleus glucose uptake. In Ins, both glucose delivery and glucose phosphorylation influence the rate of soleus glucose uptake more than under basal conditions.     

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) decreases glutamate uptake in cultured astrocytes

The deleterious effect of the parkinsonian neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on dopaminergic neurons of the substantia nigra is well established. In addition, increased glutamatergic drive to basal ganglia output nuclei is considered a likely contributor to the pathogenesis of Parkinson's disease. One possibility for the increased excitatory tone may be related to an impairment in glutamate uptake. As astrocytes possess efficient transport mechanisms for both MPTP and glutamate, we have examined the effect of this agent on D-aspartate uptake into these cells. Treatment of cultures with 50 microM MPTP for 24 h decreased uptake by 39%. Kinetic analysis revealed that this effect was due to a 35% decrease in Vmax with no change in the Km. Treatment with deprenyl, a monoamine oxidase B inhibitor, produced a complete reversal of MPTP-induced uptake inhibition, but was ineffective following exposure of cells to the MPTP metabolite, 1-methyl-4-phenylpyridinium (MPP+). Removal of MPTP from cultures resulted in a complete restoration of glutamate uptake after 24 h. These results show that MPTP reversibly compromises glutamate uptake in cultured astrocytes, which is dependent on the conversion of MPTP to MPP+. Such findings suggest that the glutamate transporter in astrocytes plays an important role in MPTP-induced neurotoxicity and possibly in parkinsonism.     

Cellular characterization of pituitary adenoma cell line (AtT20 cell) transfected with insulin, glucose transporter type 2 (GLUT2) and glucokinase genes: insulin secretion in response to physiological concentrations of glucose

We investigated the mechanisms of insulin secretion by transfecting into a pituitary adenoma cell line (AtT20) a combination of genes encoding human insulin (HI), glucose transporter type 2 (GLUT2) and glucokinase (GK), followed by studying the characteristics of these cells. In static incubation, a cell line transfected with insulin gene alone (AtT20HI) secreted mature human insulin but this was not in a glucose-dependent manner. Other cell lines transfected with insulin and GLUT2 genes (AtT20HI-GLUT2-3) or with insulin and GK genes (AtT20HI-GK-1) secreted insulin in response to glucose concentrations of only less than 1 mmol/l. In contrast, cell lines transfected with insulin, GLUT2 and GK genes (AtT20HI-GLUT2-GK-6, AtT20HI-GLUT2-GK-7 and AtT20HI-GLUT2-GK-10) showed a glucose-dependent insulin secretion up to 25 mmol/l glucose. Glucose utilization and oxidation were increased in AtT20HI-GLUT2-GK cell lines but not in AtT20HI, AtT20HI-GLUT2-3 and AtT20HI-GK-1 cells at physiological glucose concentrations, compared with AtT20 cells. Diazoxide, nifedipine and 2-deoxy glucose suppressed (p < 0.05) glucose stimulated insulin secretion in AtT20HI-GLUT2-GK-6 cells. Glibenclamide, KCl or corticotropin releasing factor (CRF) stimulated (p < 0.05) insulin secretion both in AtT20HI and AtT20HI-GLUT2-GK-6 cells. Insulin secretion stimulated by glibenclamide, KCl or CRF was further enhanced by the addition of 25 mmol/l glucose in AtT20HI-GLUT2-GK-6 cells but not in AtT20HI cells. In perifusion experiments, a stepwise increase in glucose concentration from 5 to 25 mmol/l stimulated insulin secretion in AtT20HI-GLUT2-GK cell lines but the response lacked a clear first phase of insulin secretion. Our results suggest that both GLUT2 and glucokinase are necessary for the glucose stimulated insulin secretion in at least rodent cell lines, and that other element(s) are necessary for a biphasic insulin secretion typically observed in beta cells.