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S Sandler

Publications and source records attributed to S Sandler.

At least 127 records · Page 7Linked to original sources
PubMed1990

Altered blood flow regulation in autotransplanted pancreatic islets of rats.

Adult rats were partially depancreatized, and approximately 500 islets were isolated from each excised pancreas, maintained in tissue culture for 7 days, and subsequently transplanted back to the same animals beneath the renal capsule. Four weeks after transplantation the animals were anesthetized and given an intravenous injection of 1 ml of either saline, 30% (wt/vol) D-glucose, 30% (wt/vol) D-galactose, DL-propranolol (15 mg/kg body wt) dissolved in saline, or terbutaline (1 mg/kg body wt) dissolved in saline. Five minutes later blood perfusion of the islet grafts and the pancreatic remnant were measured with a microsphere technique. Islet blood flow was also measured in animals with pancreas intact and no islet grafts after administration of saline, glucose, or galactose. These animals demonstrated a significant and preferential increase in islet blood flow after glucose administration, whereas galactose caused a selective decrease in islet blood perfusion. Both whole pancreatic blood flow and islet blood flow in the pancreatic remnant were decreased by terbutaline administration, whereas the other substances had no effect. Blood flow to the transplanted islets was decreased by glucose and galactose, whereas propranolol and terbutaline had no effect compared with the saline-injected animals. These results suggest that blood flow regulation differs between transplanted pancreatic islets, islets in the normal pancreas, and islets in the pancreatic remnant after partial pancreatectomy. Whether this reflects lack of innervation or an altered reactivity of the newly formed blood vessels in islet grafts is presently unknown.

Animals↗
PubMed1990

Reversal of beta-cell suppression in vitro in pancreatic islets isolated from nonobese diabetic mice during the phase preceding insulin-dependent diabetes mellitus.

Insulin-dependent diabetes mellitus (IDDM) is characterized by a progressive autoimmune destruction of the pancreatic beta-cells. One of the best-suited animal models for IDDM is the nonobese diabetic (NOD) mouse. In this investigation pancreatic islets were isolated from female NOD mice aged 5-7, 8-11, and 12-13 wk and examined immediately (day 0) or after 7 d of culture (day 7). The mice showed a progressive disturbance in glucose tolerance with age, and a correspondingly increased frequency of pancreatic insulitis. Islets isolated from the oldest mice often contained inflammatory cells on day 0, which resulted in an elevated islet DNA content. During culture these islets became depleted of infiltrating cells and the DNA content of the islets decreased on day 7. Islets of the eldest mice failed to respond with insulin secretion to high glucose, whereas a response was observed in the other groups. After culture all groups of islets showed a markedly improved insulin secretion. Islets from the 12-13-wk-old mice displayed a lower glucose oxidation rate at 16.7 mM glucose on day 0 compared with day 7. Islet (pro)insulin and total protein biosynthesis was essentially unaffected. In conclusion, islets obtained from 12-13-wk-old NOD mice exhibit an impaired glucose metabolism, which may explain the suppressed insulin secretion observed immediately after isolation. This inhibition of beta-cell function can be reversed in vitro. Thus, there may be a stage during development of IDDM when beta-cell destruction can be counteracted and beta-cell function restored, provided the immune aggression is arrested.

Age Factors↗
PubMed1990

Hyperglycemia-induced B cell toxicity. The fate of pancreatic islets transplanted into diabetic mice is dependent on their genetic background.

The role of pancreatic B cell dysfunction in the phase preceding clinical onset of insulin-dependent and non-insulin-dependent diabetes mellitus has been much debated. In this investigation, the impact of a prolonged diabetic environment on pancreatic islet B cells transplanted syngeneically under the kidney capsule of C57BL/6 (B6) and C57BL/Ks (BKs) mice was studied. Alloxan-diabetic mice bearing a subcapsular islet graft insufficient to normalize the blood glucose level were rendered normoglycemic by a second intrasplenic islet graft after various period of hyperglycemia to examine the reversibility of hyperglycemia-induced B cell dysfunction. Using a perfusion technique of the graft-bearing, it was found that both strains of mice exhibited a diminished glucose-induced insulin secretion after 6 wk of hyperglycemia, when compared with normoglycemic mice carrying islet grafts. When normoglycemia was restituted by the splenic graft after 4 or 12 wk, there was a normalization of glucose-stimulated insulin secretion in the renal islet grafts in B6 mice, whereas insulin secretion from the grafted BKs islets remained impaired. Morphometric measurements of the islet grafts demonstrated a 50% reduction in the graft volume in diabetic BKs mice after 12 wk, compared with normoglycemic animals, whereas no such decrease was observed in B6 mice. Islet grafts removed from hyperglycemic mice of both strains exhibited diminished insulin mRNA contents, and in the BKs mice there was also a reduced glucose oxidation rate in the islet grafts in vitro. This metabolic dysfunction can only partly be explained by a reduced graft size. The present findings emphasize the genetic constitution as a decisive factor for the survival and function during a period of sustained stress on a limited B cell mass.

Animals↗
PubMed1990

Interleukin-6 affects insulin secretion and glucose metabolism of rat pancreatic islets in vitro.

Recently it has been postulated that interleukin-1 (IL-1) locally released by infiltrating mononuclear cells may destroy the pancreatic B cells during the development of insulin-dependent diabetes mellitus. Since IL-1 is a potent inducer of interleukin-6 (IL-6) in various cells, it is conceivable that IL-6 is a second mediator of the IL-1 action. In the present study the effects of IL-6 alone or in combination with IL-1 were studied on pancreatic islet function in vitro after tissue culture and compared with the effects observed after exposure to IL-1 only. Rat pancreatic islets were cultured in medium RPMI 1640 + 10% calf serum with or without the addition of human recombinant IL-6 (500-5000 pg/ml) for 48 h. The medium insulin accumulation was increased by 40-50% after culture with 500-2000 pg/ml IL-6, but was similar to the controls at 5000 pg/ml. When islets were cultured for 18 h only, also 5000 pg/ml IL-6 stimulated the medium insulin accumulation. IL-6 did not affect the islet insulin content and the rates of islet (pro)insulin and total protein biosynthesis. It inconsistently decreased the islet DNA content. In short-term experiments after 48-h culture with IL-6, there was a dose-dependent inhibition of the glucose-stimulated insulin release. On the other hand, islets cultured with IL-6 (5000 pg/ml) exhibited an elevated glucose oxidation and oxygen uptake, but a lower ATP content at 16.7 mM glucose and an unaffected glucose utilization and glutamine oxidation compared to the controls. This raises the possibility that IL-6 had induced a condition with an increased energy expenditure, resulting in an enhanced mitochondrial metabolism of glucose. Islets cultured with human recombinant IL-1 beta (25 units/ml) showed a strong inhibition of the insulin accumulation in the culture medium and of glucose-stimulated insulin release and a marked decrease in the islet DNA and insulin content. A combination of IL-1 (25 U/ml) + IL-6 (1000 pg/ml) did not alter the inhibitory action of IL-1 alone. The present findings thus show that IL-6 induces a dissociation between insulin secretion and glucose oxidation in islets in vitro. This has not been observed in islets exposed to IL-1, which suggests that IL-6 does not solely mediate the inhibitory effects of IL-1 on islet function.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗
PubMed1990

Interleukin-1 beta depletes insulin messenger ribonucleic acid and increases the heat shock protein hsp70 in mouse pancreatic islets without impairing the glucose metabolism.

In order to further characterize the actions of recombinant interleukin-1 beta (rIL-1 beta) on the function of insulin-producing cells, the effects of different concentrations of the cytokine were studied on islets obtained from four different mouse strains (NMRI, NOD, C57BL/6, and C57BL/Ks). For this purpose the islets were exposed to rIL-1 beta (25, 50, or 100 U/ml) for a 48-h period in medium RPMI 1640 containing 10% calf serum and 11.1 mM glucose. In all groups and at the various rIL-1 beta concentrations tested, there was a similar 30-50% inhibition in glucose-induced insulin release, a 70-80% decrease in islet insulin content, and no significant differences in islet DNA content or insulin accumulation in the culture medium. To clarify the mechanisms underlying the decreased islet insulin content, rates of (pro)insulin biosynthesis and insulin messenger RNA (mRNA) contents were determined. Exposure of NMRI and C57BL/6 islets to 50 U/ml rIL-1 beta reduced the (pro)insulin biosynthesis by 40-50% and the insulin mRNA contents by 80-90%. The cytokine also induced an increased cellular content of the heat shock protein hsp70, as measured by western blot analysis, and a decrease in DNA biosynthesis, as measured by [methyl-3H]thymidine incorporation. However, exposure to rIL-1 beta did not decrease islet total protein biosynthesis, glucose oxidation, ATP content, ATP/ADP ratio, cAMP content, or polyamine contents. In conclusion, these data suggest that exposure of mouse islets to rIL-1 beta reduces DNA synthesis, insulin mRNA levels, and the biosynthesis of (pro)insulin, without equally impairing other cellular functions. The mechanisms behind these reductions seem to be different from those observed in rat islets, where a rIL-1 beta-induced impairment of substrate metabolism at the mitochondrial level seems to be related to the decrease of several cellular functions.

Animals↗
PubMed1989

Terbutaline decreases the blood flow of the pancreatic islets but does not reduce the diabetogenic action of streptozotocin in the rat.

Male Sprague-Dawley rats were injected i.v. with either 0.5 ml saline or terbutaline (1 mg/kg body weight) and 5 min later the whole pancreatic blood flow (PBF) and the islet blood flow (IBF) were measured with a microsphere technique. Injection of terbutaline increased the serum insulin concentrations, but had no effect on the serum glucose concentration of the animals. The IBF was decreased by terbutaline by approximately 40%, while the PBF remained unchanged. Furthermore, the diabetogenic action of streptozotocin (SZ; 35 mg/kg bodyweight; i.v.) was not affected by the administration of terbutaline 5 min before the SZ injection. It is concluded that the beta 2-selective adrenoceptor agonist terbutaline selectively decreases the blood flow of the pancreatic islets in spite of its stimulatory effects on the release of insulin. This confirms our previous findings that the IBF and the release of insulin can be dissociated. Moreover, the hyperglycemic action of a single diabetogenic dose of SZ could not be reduced by terbutaline administration despite the reduction in the IBF. This suggests that a decrease in the islet blood flow is not sufficient to prevent the cytotoxicity of SZ.

Animals↗
PubMed1989

Human interleukin-1 beta induced stimulation of insulin release from rat pancreatic islets is accompanied by an increase in mitochondrial oxidative events.

Acute exposure of pancreatic islets to interleukin-1 beta results in an increase in insulin release, while an extension of the exposure time induces a functional suppression and eventually, destruction of the B-cells. We have recently suggested that the interleukin-1 beta induced inhibition of islet function is mediated through an impairment in oxidative metabolism. The aim of the current study was to investigate if the acute, stimulatory effects of interleukin-1 beta on islet function could also be related to changes in the substrate metabolism. For this purpose, rat islets were exposed for 90-120 min to 30 pmol/l human recombinant interleukin-1 beta (biological activity of 2.5 U/ml) and their function and metabolism characterized during this period. The cytokine did not increase insulin release in the presence of 1.7 or 5.5 mmol/l glucose but in both the presence of 16.7 mmol/l glucose or 10 mmol/l leucine + 2 mmol/l glutamine there was a 50% increase in insulin release. Interleukin-1 beta exposure increased the oxidation of D-[U-14C]glucose at 5.5 mmol/l glucose by 25% and at 16.7 mmol/l glucose by 60%. Carbohydrate and amino acid metabolism were further examined in the presence of D-[5-3H]glucose, D-[6-14C]glucose, [1-14C]pyruvate, L-[U-14C]glutamine, L-[U-14C]leucine and L-[1-14C]leucine. There was no difference between control islets and interleukin-1 beta exposed islets in terms of D-[5-3H]glucose utilization or [1-14C]pyruvate decarboxylation, but the oxidation of D-[6-14C]glucose was increased by 64% in the interleukin-1 beta exposed islets.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Decreased cell replication and polyamine content in insulin-producing cells after exposure to human interleukin 1 beta.

Interleukin 1 (IL-1) has been suggested to cause the islet B cell destruction occurring during the development of insulin-dependent diabetes mellitus. One mechanism by which B cell loss can be compensated for is via de novo formation of new cells through replication. In the present study the replicatory activity of cells in isolated rat pancreatic islets and in the insulin-producing cell line RINm5F has been assessed by [3H]thymidine incorporation methods after exposure to 1-25 U/ml of human recombinant IL-1 beta (rIL-1 beta). In the rat islets [3H]thymidine incorporation was decreased by 20% 5 h after exposure to 25 U/ml rIL-1 beta. A similar inhibition was also observed in islets exposed to 2.5 and 12.5 U/ml rIL-1 beta. In the RINm5F cells there was a dose-dependent inhibition of the cell replication to approximately 50% of the controls in cells exposed to 25 U/ml rIL-1 beta for 48 h. This was also accompanied by an increased cell death, as measured by trypan blue inclusion (controls 13% and rIL-1 beta treated cells 25%). The insulin content of the RINm5F cells was reduced by about 40% after a 48-h exposure to 25 U/ml rIL-1 beta. When the exposure of the RINm5F cells to rIL-1 beta was decreased to 24 h there was no increased cell death, but a reduced replicatory activity was still observed. rIL-1 beta decreased the cellular content of the polyamines spermidine and spermine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Aspects of pancreatic islet transplantation in diabetes mellitus.

The justification for pancreatic or islet transplantation in diabetes mellitus is to halt progression of diabetic vascular complications. Although this goal has so far not been achieved, technical progress in transplanting the whole or segmental, vascularized pancreas has been remarkable. However, the operation is complicated and not without risk; immune rejection is furthermore a major problem, and the availability of suitable organs is limited. Transplantation of isolated pancreatic islet grafts, i.e. isolated islets or fetal pancreas, has therefore emerged as an attractive alternative. Iso-, allo- or xenografts of such preparations have been found to reverse diabetes in experimental animals. Only a minor operation is required and islets, although highly immunogenic, may be accessible to immunomodulation in vitro in order to decrease or abolish the allograft rejection and prevent cells from becoming targets for the autoimmune assault. However, problems and difficulties have emerged in this context also. Thus, islets are extremely difficult to isolate from the adult human pancreas. Such glands, be they adult or fetal, are not easily available, and clinical trials have so far remained without documented success. Considerable efforts are being made to overcome the difficulties encountered in islet transplantation. Attempts are being made to improve the techniques for preparation of clean and viable islets and to understand critical factors in the cellular interactions between the graft and the host after transplantation. Factors of importance in this context are the nutritional requirements of the graft and the vascularization process at the site of implantation. In order to provide unlimited access to cells with a high potential for insulin production and adaptive growth in the diabetic recipient, ongoing research is also directed towards methods for preparation of porcine fetal and adult islets suitable for xenotransplantation. The obvious problems involved in immune rejection of the grafted tissue are being investigated with respect both to the possibility of immunomodulation of the graft in vitro, the design of new immunosuppressive drugs, and the possibility of immuno-isolation of the insulin-producing cells with the aid of artificial membranes.

Diabetes Mellitus↗
PubMed1989

Survival and B-cell function of mouse pancreatic islets maintained in culture after concomitant exposure to streptozotocin and nicotinamide.

It has recently been suggested from experiments performed on isolated pancreatic islets in vitro, that streptozotocin (SZ) may exert a progressive damage to the islet B-cells. It may be that this damaging effect is not dependent on the acute activation of the enzyme poly(ADP-ribose) synthetase, and a subsequent depletion of the islet NAD content. In the present study we have exposed mouse pancreatic islets in vitro to 2.2 mM SZ for 30 min at 37 degrees C, in the presence or absence of 10 mM nicotinamide, an inhibitor of poly(ADP-ribose) synthetase and examined the islet function immediately (Day 0) or after six days of culture (Day 6). Nicotinamide protected the islets against an inhibition of the glucose-stimulated insulin release on day 0 and against a SZ-induced loss in islet number and islet insulin content on day 6. However, on day 6 the islets incubated with SZ in the presence of nicotinamide showed an inhibition of the insulin release comparable to that observed in islets treated with SZ in the absence of nicotinamide. Furthermore, on day 0 nicotinamide counteracted a SZ-induced impairment of islet glucose oxidation, whereas on day 6 islets incubated with SZ both in the absence or presence of nicotinamide showed a similar and more markedly impaired oxidation of glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Effects of streptozotocin exposure in vitro on the replication and repair of DNA in fetal rat pancreatic islet cells.

It was recently proposed that the role for poly(ADP-ribose) synthetase during DNA repair was exerted via a depletion of cellular NAD in order to slow down energy-requiring processes in the cell, notably DNA replication. This would enable the cell to more efficiently repair damaged DNA. In the present study fetal rat pancreatic islet cells were exposed to 2.2 mM streptozotocin (SZ). Using [3H]thymidine labeling and autoradiographic techniques, it was found that cellular nuclear silver grain counts, an index of DNA repair synthesis, were doubled after SZ exposure. However, autoradiographically measured DNA replication remained unaffected. Cellular NAD + NADH contents were reduced by 60% in the SZ-treated islets. Estimates of the poly(ADP-ribose) synthetase activity showed that this was doubled in islets exposed to SZ. Immediately after the SZ treatment the islets exhibited a 35% reduction in insulin secretion in response to 16.7 mM glucose. Taken together, the present findings do not favor the suggested role for poly(ADP-ribose) synthetase during DNA repair. Rather we observed an increased activity of this enzyme, a lowered cellular NAD + NADH content, and an increased rate of DNA repair synthesis concomitant with an unchanged DNA replicative rate in the SZ-exposed islets.

Animals↗
PubMed1989

Effects of porcine pancreastatin on secretion and biosynthesis of insulin and glucose oxidation of isolated rat pancreatic islets.

The effects of porcine pancreastatin were studied on insulin secretion induced by glucose and nonnutrient stimuli, insulin biosynthesis, and glucose oxidation of cultured rat islets. Pancreastatin (100 nM) significantly suppressed, by 32-52%, the insulin response to 27, 16.7, 11, and 5.5 mM but not to 50 mM glucose, whereas 10 nM pancreastatin inhibited insulin release significantly only at 11 and 5.5 mM glucose. Pancreastatin (10 and 100 nM) also suppressed release induced by 20 mM arginine (by 26 and 30%) as well as by 1 microgram/ml of glibenclamide (by 56 and 72%, respectively). Pancreastatin (10 and 100 nM) furthermore inhibited insulin release induced by 0.1 mM 3-isobutyl-1-methylxanthine (IBMX) (by 40 and 61%, respectively) and 1.0 mM IBMX (by 44 and 76%, respectively). Neither glucose oxidation nor overall insulin biosynthesis in islets was significantly affected by pancreastatin, although a slight but significant enhancement of biosynthesis was noted at 1.7 mM glucose in the presence of 100 nM pancreastatin. In conclusion, these data demonstrate that porcine pancreastatin suppresses glucose-induced insulin response from isolated rat islets in a competitive manner. This effect seems not to be exerted through a suppression of (pro)insulin biosynthesis or glucose metabolism in the islets, and thus the effect mediated by pancreastatin must be on a step distal to the coupling between islet glucose metabolism and insulin secretion. The relatively strong inhibition by the peptide of IBMX-induced insulin release suggests that it acts on the cAMP system of islet B cells.

Animals↗
PubMed1989

Effects of (-)15-deoxyspergualin on pancreatic islet B-cell function in vitro and on the development of diabetes after multiple low dose streptozotocin administration.

The effects of (-)15-deoxyspergualin (15-DS), a newly described immunosuppressive drug, have been investigated on diabetes induced in mice treated with multiple low-dose streptozotocin (multiple SZ). Male C3D2F1 mice were treated with either intraperitoneal injections of saline or 15-DS (2.5 mg/kg body weight) for a total of 10 days, starting during the first day of SZ administration (5 days; 40 mg/kg body weight). On day 14, 15-DS-treated animals were still normoglycaemic, whilst on day 21 there was only a partial reduction in the hyperglycaemia compared to that found in the saline treated animals receiving SZ. 15-DS did not prevent hyperglycaemia in the long run (day 35-63). Furthermore, morphological examinations of pancreatic glands suggested that the insulitis in the pancreatic islets was delayed in the 15-DS-treated animals. In control experiments mice were treated with 15-DS+ the vehicle for SZ. This regimen did not hamper the glucose homeostasis of the animals. In vitro effects of 15-DS were also examined. Isolated islets from C3D2F1 mice were cultured at different concentrations of 15-DS (0.1-10.0 mg/l). After one week in culture, islet insulin release, islet insulin and DNA content were measured. The islets looked fluffy after culture at the higher 15-DS concentrations (4.0-10.0 mg/l) and at 10 mM almost all of the islets disappeared. A dose-dependent reduction of glucose-stimulated insulin release could also be seen. In other experiments islets were exposed to SZ and subsequently cultured in the presence of 0.5 mM 15-DS, however, 15-DS could not prevent the reduction in insulin release due to SZ exposure. Since 15-DS influences macrophage functions, the presently observed protective effects against the multiple SZ-treatment could reflect a reduced local interleukin-1 production in the islet vicinity. Alternatively, a lowered interleukin-1 secretion could prevent the activation of other immune cells involved in the destruction of B-cells.

Animals↗
PubMed1989

Studies on the mechanisms causing inhibition of insulin secretion in rat pancreatic islets exposed to human interleukin-1 beta indicate a perturbation in the mitochondrial function.

This study aimed at a more detailed characterization of the mechanisms by which interleukin 1 (IL-1) inhibits insulin secretion. For this purpose, isolated rat pancreatic islets were kept in tissue culture for 5 days in medium RPMI 1640 plus 10% calf serum. The islets were subsequently transferred to the same culture medium containing various test substances plus 1% human serum with or without 25 U/ml human recombinant IL-1 beta. After a culture period of 48 h the islet structure was examined in the electron microscope and the islet function studied in short term incubations in the absence of IL-1. Islets exposed to IL-1 showed ultrastructural signs of degeneration in 10-20% of the B cells while such changes were not found in other types of islet cells. An increased number of secondary lysosomes and occasional myelin figures were observed in the B cells exposed to IL-1. These ultrastructural alterations were, however, reversed in islets cultured in cytokine-free medium for 6 days after the IL-1 treatment. In islets cultured in the presence of 11.1 mM glucose only, or 11.1 mM glucose plus 10 mM nicotinamide, 61 mM dimethyl area, 2 micrograms/ml indomethacin, 10 microM 4-bromophenacyl bromide or 10 microM nordihydroguaiaretic acid, 10 microM phenantroline, and 0.1 or 1.0 microgram/ml cyclosporin A, IL-1 reduced the insulin release by 64-85%. Culture at 5.6 mM glucose did not modify the IL-1-induced inhibition of insulin release, whereas a significant protective effect was observed at 28 or 56 mM glucose. The DNA content in IL-1-exposed islets cultured at 11.1 mM glucose was decreased by about 20% but not in islets cultured at other glucose concentrations. The D-[5-3H]glucose utilization at 16.7 mM glucose was unaffected by IL-1, whereas the oxidation of D-[6-14C]glucose was reduced by 50%. The present results suggest that IL-1-induced inhibition of insulin secretion is related to a disturbed mitochondrial function. This effect is not counteracted by a poly(ADP-ribose) synthetase inhibitor, a hydroxyl radical scavenger, an iron chelator, a T lymphocyte-specific immunosuppressive drug, or inhibitors of phospholipase A2 or inhibitors of prostaglandin and leukotriene synthesis. Thus, IL-1-induced inhibition of insulin secretion seems not to be mediated by the same mechanisms as those causing alloxan- or streptozotocin-induced damage of B cells. Furthermore, the action of IL-1 does not appear to be mediated via arachidonic acid metabolism. Glucose affords some protection, probably by enhancing the B cell mitochondrial function.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetophenones↗
PubMed1989

Differential sensitivity to beta-cell secretagogues in cultured rat pancreatic islets exposed to human interleukin-1 beta.

The early stages of insulin-dependent diabetes mellitus are characterized by a selective inability to secrete insulin in response to glucose, coupled to a better response to nonnutrient secretagogues. The deficient glucose response may be a result of the autoimmune process directed toward the beta-cells. Interleukin-1 (IL-1) has been suggested to be one possible mediator of immunological damage of the beta-cells. In the present study we characterized the sensitivity of beta-cells to different secretagogues after human recombinant IL-1 beta (rIL-1 beta) exposure. Furthermore, experiments were performed to clarify the biochemical mechanisms behind the defective insulin response observed in these islets. Rat pancreatic islets were isolated and kept in tissue culture (medium RPMI-1640 plus 10% calf serum) for 5 days. The islets were subsequently exposed to 60 pM human recombinant IL-1 beta during 48 h in the same culture conditions as above and examined immediately after IL-1 exposure. The rIL-1 beta-treated islets showed a marked reduction of glucose-stimulated insulin release. Stimulation with arginine plus different glucose concentrations, and leucine plus glutamine partially counteracted the rIL-1 beta-induced reduction of insulin release. The activities of the glycolytic enzymes hexokinase, glucokinase, and glyceraldehyde 3-phosphate dehydrogenase, were similar in control and IL-1-exposed islets. Treatment with IL-1 also did not impair the activities of NADH+- and NADPH+-dependent glutamate dehydrogenase, glutamate-aspartate transaminase, glutamate-alanine transaminase, citrate synthase, and NAD+-linked isocitrate dehydrogenase. The oxidation of D-[6-14C]glucose and L-[U-14C]leucine were decreased by 50% in IL-1-treated islets. Furthermore, there was a significant decrease in the ratios of [2-14C]pyruvate oxidation/[1-14C]pyruvate decarboxylation and L-[U-14C]leucine oxidation/L-[1-14C]leucine decarboxylation, indicating that IL-1 decreases the proportion of generated acetyl-coenzyme-A residues undergoing oxidation. However, in the presence of IL-1 there was a significant increase in L-[U-14C]glutamate oxidation. These combined observations suggest that exposure to IL-1 induces a preferential decrease in glucose-mediated insulin release and mitochondrial glucose metabolism. This mitochondrial dysfunction seems to reflect an impairment in proximal steps of the Krebs cycle. It is conceivable that the IL-1-induced suppression and shift in islet metabolism can be an explanation for the beta-cell insensitivity to glucose observed in the early phases of human and experimental insulin-dependent diabetes mellitus.

Animals↗