Differences in protein and energy metabolism following portal versus systemic administration of insulin in diabetic dogs.

AIMS/HYPOTHESIS: In non-diabetic people, insulin levels in the liver are two-fold higher than those in the systemic circulation. In contrast, patients with type 1 diabetes have similar hepatic and systemic insulin levels because insulin is administered peripherally. The aim of this study was to compare the effects of systemic (SI) and pre-portal (PI) insulin administration on energy, glucose and protein metabolism in chronic insulin-dependent ketosis-prone diabetic dogs. MATERIALS AND METHODS: We applied glucose-controlled insulin infusion, indirect calorimetry and stable isotope and radioisotope techniques to measure energy, protein and glucose metabolism. We maintained near-normoglycaemia at identical levels under both study conditions for 20 h. RESULTS: SI was associated with lower oxygen consumption (130+/-13 vs 161+/-8 ml/min), CO(2) production (99+/-10 vs 130+/-8 ml/min), respiratory quotient (0.76+/-0.02 vs 0.81+/-0.01) and energy expenditure (870+/-90 vs 1089+/-60 kcal/24 h) (p<0.05 for all differences). PI increased the respiratory quotient from the insulin-deprived state, whereas SI did not. Glucose kinetics were similar for SI and PI, whereas leucine oxidation (36+/-4 vs 54+/-5 micromol kg(-1) min(-1)) and the fractional synthesis rates of liver tissue protein (0.68+/-0.6 vs 0.83+/-0.07%/h), albumin (0.55+/-0.06 vs 0.68+/-0.4%/h), and fibrinogen (1.73+/-0.23 vs 2.59+/-0.25%/h) were all lower during SI than PI (p<0.05). CONCLUSIONS/INTERPRETATION: The route of insulin administration did not alter glucose metabolism but did affect protein synthesis in the liver. The potential impact of this altered liver protein metabolism on chronic complications needs careful evaluation. A similar decrease in energy expenditure resulting from systemic insulin administration during tight glycaemic control is a potential cause of weight gain.

In vitro stimulation by islet antigen facilitates the detectability of beta-cell reactive cells in diabetes-prone BB/OK rats.

It has been supposed that beta-cell destruction in man and animals is due to autoreactive T-cells. We used the [51Cr]-release assay to identify the presence of beta-cell reactive cells in the spleen of diabetes-prone BB/OK rats before and after diabetes manifestation as well as in long-term normoglycaemic rats with a reduced diabetes risk of 3%. Splenic mononuclear cells (MNCs) obtained from diabetes-resistant LEW.1W and the majority of long-term normoglycaemic BB/OK rats (86.4%) showed no reactivity to pancreatic islets in vitro. In contrast, beta-cell reactive cells were identified in dependence on age in 30.4-65.0% of 75-120 days old normoglycaemic rats and in relation to diabetes duration (1 and 20 days) in 75.0% and 16.0% of diabetic BB/OK rats. Islet antigen-specific stimulation of splenic MNCs, that showed no spontaneous islet-directed reactivity, resulted in a concentration-dependent activation of cytolytically reactive cells in BB/OK but not in LEW.1W rats. Splenic MNCs derived from all diabetic, from 82.4% of young normoglycaemic and from 46.2% of long-term normoglycaemic BB/OK rats developed an islet-directed reactivity in vitro. Phenotyping of MNCs showed a significant increase of activated IL2R+ T-lymphocytes in diabetic BB/OK rats, but without any correlation to their cytolytic potential in the [51Cr]-release assay. Despite this fact, IL2R+ cells enriched from the pool of MNCs mediated an enhanced [51Cr]-release from islets, indicating their relevance in the beta-cell destruction. These data suggest, that functional reactivity rather than phenotypic characterization of MNCs is useful to identify the existence of beta-cell reactive cells. Furthermore, for screening diabetes risk in young normoglycaemic BB/OK rats besides the detection of beta-cell reactive cells the occurrence of regulatory cells seems to be decisive.

Glucagon-like peptide-1 has no insulin-like effects in insulin-dependent diabetic dogs maintained normoglycemic and normoinsulinemic.

A pharmacological concentration of glucagon-like peptide-1 (GLP-1) in the insulin-deficient state clearly decreases the blood glucose level. Therefore, this study was designed to evaluate a putatively relevant effect of the gastrointestinal peptide as an adjuvant to insulin replacement therapy. GLP-1 (GLP-1(7-36) amide 10 pmol x kg(-1) x min(-1)) was infused intravenously over 8 hours in nine fasting, C-peptide-negative diabetic dogs. The animals were under normoglycemic control by glucose-controlled insulin infusion (GCII) during the night before and during GLP-1 administration. During the paired control tests, the animals received saline infusion instead of GLP-1. In addition to the insulin infusion rates required to maintain normoglycemia, hormones, metabolites, and the turnover rates for glucose (6-3H-glucose), alanine (U-14C-alanine), and urea (15N2-urea) were measured during the final 2 hours of GLP-1 administration. Circulating plasma GLP-1 levels increased from 3+/-1 to 17+/-7 pmol/L. There was no significant difference in the insulin infusion rate between the experimental and control groups (0.43+/-0.05 v. 0.40+/-0.05 mU x kg(-1) x h(-1), average over the entire interval). Glycemia was maintained at a practically identical level (4.9+/-0.3 v. 4.8+/-0.4 mmol/L). Also, the concentration of plasma insulin-which was not hyperinsulinemic--and pancreatic glucagon remained unaltered. We found no appreciable effect of GLP-1 on glucose production and metabolic clearance, alanine turnover and the formation of glucose from alanine (1.8+/-0.2 v. 1.4+/-0.2 micromol x kg(-1) x min(-1), or the urea production rate as a measure of overall amino acid catabolism (4.1+/-0.4 v. 4.1+/-0.4 micromol x kg(-1) x min(-1)). Thus, no conclusive adjuvant effect of GLP-1 was ascertained in insulin-treated diabetic dogs under normoglycemic control.

Estimation of urea production rate with [15N2]urea and [13C]urea to measure catabolic rates in diabetes mellitus.

For verifying catabolic states in insulin-dependent patients and dogs the method estimating urea production rates with 13C and with doubly 15N labeled urea, respectively, has been established. For a fast steady state of urea tracer dilution, a prime of 600 times the continuous infusion rate had to be injected. Urea was isolated from plasma samples by protein precipitation and cation exchange chromatography with a consecutive derivatization of the dried urea fraction (trimethylsilyl derivatives). The masses of the fragment ions m/z 189 (14N14N), 190 (14N15N) and 191 (15N15N) urea are monitored to estimate the [15N2] urea frequency in the overall body urea pool in mol percent excess (MPE). 1 to 15 ng of derivatized urea were measured efficiently. An excellent correlation between expected standard and measured MPE (r = 0.9977) was achieved from solutions containing 1 to 7% [15N2]urea. The interassay coefficient of variation amounted to < 10% for a [15N2]urea portion of > or = 3%. Normoglycemic diabetic patients who were treated with insulin overnight showed significantly higher urea production compared to healthy controls (9.22 +/- 2.07 vs. 5.4 +/- 0.32 mumol.kg-1.min-1; p < 0.05). Measurements in chronic diabetic dogs proved an increased rate of amino acid catabolism (+20% urea production) in systemic versus portal application of insulin in paired studies. This increased nitrogen load in diabetics may accelerate progression of diabetic nephropathy. Thus, the established stable isotope technique may serve as a sensitive and useful indicator of amino acid catabolism in clinical and experimental research.

Blood glucose lowering and glucagonostatic effects of glucagon-like peptide I in insulin-deprived diabetic dogs.

To establish potential effects of glucagon-like peptide I (GLP-I) on blood glucose control in insulin-deficient states, GLP-I [GLP-I(7-36) amide; 10 pmol x kg(-1) x min(-1)] was infused intravenously in six fasting, canine C-peptide-negative, chronically diabetic dogs for 8 h. Blood samples were saved for the analysis of hormones, metabolites, and turnover rates of glucose (6-(3)H-glucose), alanine (U-(14)C-alanine), and urea ((15)N(2)-urea) starting 22 h after the last subcutaneous dose of exogenous insulin. Circulating plasma GLP-I levels rose under infusion from 2.9 +/- 0.8 to 41.4 +/- 10.1 pmol/l. This was efficient to significantly reduce the preexisting diabetic hyperglucagonemia. Since in the utilized model functioning pancreatic beta-cells are lacking, GLP-I had no insulinogenic effect. Compared with control experiments in the same animals receiving saline infusion, glycemia dropped from 20.8 +/- 1.9 to 16.2 +/- 1.0 mmol/l (P < 0.05). This was in parallel to the infusion of GLP-I and was most likely caused by a decrease of elevated glucose production since overall glucose turnover decreased with no alteration in glucose metabolic clearance. Alanine turnover was significantly reduced, obviously reflecting a decline in alanine production in relation to changed muscle glucose uptake under conditions of lower glycemia and overall glucose turnover. There was, however, neither an effect of GLP-I on alanine conversion into circulating glucose nor an effect on urea production rate, indicating unchanged gluconeogenesis from amino acid precursors. We conclude that the blood glucose-lowering effect of GLP-I in an animal model of insulinopenia was shown to be due to a reduction in hepatic glucose output, possibly secondary to reduction in glucagon concentrations leading to decreased glycogenolysis. Whether GLP-I might be therapeutically useful in clinical insulin-deficient diabetes needs to be verified.

Estimation of urea production rate with [(15)n(2)]urea and [(13)c]urea to measure catabolic rates in diabetes mellitus.

Abstract For verifying catabolic states in insulin-dependent patients and dogs the method estimating urea production rates with (13)C and with doubly (15)N labeled urea, respectively, has been established. For a fast steady state of urea tracer dilution, a prime of 600 times the continuous infusion rate had to be injected. Urea was isolated from plasma samples by protein precipitation and cation exchange chromatography with a consecutive derivatization of the dried urea fraction (trimethylsilyl derivatives). The masses of the fragment ions m/z 189 ((14)N(14)N), 190 ((14)N(15)N) and 191 ((15)N(15)N) urea are monitored to estimate the [(15)N(2)]urea frequency in the overall body urea pool in mol percent excess (MPE). 1 to 15 ng of derivatized urea were measured efficiently. An excellent correlation between expected standard and measured MPE (r = 0.9977) was achieved from solutions containing 1 to 7% [(15)N(2)]urea. The interassay coefficient of variation amounted to < 10% for a [(15)N(2)]urea portion of ≥ 3%. Normoglycemic diabetic patients who were treated with insulin overnight showed significantly higher urea production compared to healthy controls (9.22 ± 2.07 vs. 5.4 ± 0.32 µmol·kg(-1) · min(-1); p < 0.05). Measurements in chronic diabetic dogs proved an increased rate of amino acid catabolism (+ 20% urea production) in systemic versus portal application of insulin in paired studies. This increased nitrogen load in diabetics may accelerate progression of diabetic nephropathy. - Thus, the established stable isotope technique may serve as a sensitive and useful indicator of amino acid catabolism in clinical and experimental research.

Effects of the platelet-activating factor antagonist BN 52021 on anti-islet cytotoxicity of mononuclear cells and serum from type 1 (insulin-dependent) diabetic patients.

The effect of platelet-activating factor (PAF) antagonist BN 52021 (0.06-2.5 mM) on the cytotoxic activity of mononuclear cells (MNC) from newly diagnosed type 1 diabetic patients against 51Cr-labeled Langerhans islets from neonatal rats was investigated in a 6-hour cytotoxicity test. A dose-dependent inhibition of anti-islet cytotoxicity by BN 52021 was observed. The suppression of the islet lysis was significant at a concentration of 0.6 mM BN 52021. During a 4-day cell culture, BN 52021 had no inhibitory effect on the antigen-mediated triggering of immunocytes with anti-islet cytotoxicity. The results suggest that the drug is only effective during immunocytolytic reactions of MNC against pancreatic islets. A PAF-independent action of BN 52021 can not be excluded at present.

Beta cell destruction of pancreatic islets transplanted into diabetic BB/OK rats may be reflected by increased antibody-mediated anti-islet cytotoxicity.

Neonatal rat pancreatic islets can be affected in vitro by ADCC mediated by serum and mononuclear cells from diabetic BB/OK rats or complement-dependent antibody-mediated cytotoxicity (C'AMC) of BB rat serum as revealed by enhanced 51Cr-release. Using a syngeneic islet transplantation system in BB/OK rats this study addressed the question whether the destruction of islets of Langerhans in vivo is reflected by the appearance of ADCC or C'AMC in vitro. The frequency of the appearance of enhanced anti-islet ADCC in newly diagnosed diabetic BB/OK rats amounted to 33% whereas ADCC was not detectable in long-term diabetic rats with a diabetes duration in a range between 50 and 90 days. After transplantation of syngeneic islets beneath the kidney capsule of long-term diabetic BB/OK rats held without immunosuppression the destruction of the islet graft and the persistence of hyperglycaemia was accompanied by an increase of anti-islet ADCC in 66.6% of the animals. While only 18.7% of the long-term diabetic BB/OK rats showed C'AMC against islet cells before transplantation this frequency raised after transplantation and 62.8% of the animals exhibited increased C'AMC within a period of 21 days but with a pronounced individual variability of the time-course. Increased anti-islet cytotoxicity (ADCC or C'AMC) parallels newly initiated or reactivated beta-cell destruction after transplantation and thus seems to reflect this process.

Autologous mixed lymphocyte reaction in newly diagnosed type-1 diabetes.

The autologous mixed lymphocyte reaction (AMLR) represents activation, proliferation and differentiation of T cells in response to signals from autologous non-T cells. Deteriorations in AMLR have been reported in many autoimmune diseases and in diseases with a derangement in T cell regulatory function. We have studied AMLR in 23 newly diagnosed Type-1 diabetic patients and 32 healthy subjects. T and non-T cells were purified by rosetting mononuclear cells with sheep erythrocytes and separating the rosetted T cells from the nonrosetted non-T cells by density gradient centrifugation. Purity of T-lymphocytes isolated was 90% as determined by indirect immunofluorescent analysis with monoclonal antibodies. Proliferation of lymphocytes was measured in response to phytohaemagglutinin and of concanavalin A in a lymphocyte transformation test. In the present study, a deficient AMLR is demonstrated in patients with newly diagnosed Type-1 diabetes. Our data provide evidence for an aberrant immune regulation at the time of diabetes manifestation. The deficient AMLR may represent the in-vitro expression of an in-vivo process against pancreatic cells.

Ciamexone suppressed anti-islet ADCC of mononuclear cells and serum from type 1 (insulin-dependent) diabetic patients.

ADCC (Antibody-dependent cellular cytotoxicity) against xenogenic islets has frequently been found in newly diagnosed Type 1 (insulin-dependent) diabetics suggesting that when combined with autologous serum in vitro, the destruction of islet cells caused by mononuclear cells (MNC) reflects islet destruction in vivo. In this study the ability of Ciamexone to suppress the anti-islet ADCC in vitro was investigated. We selected both ADCC positive and ADCC negative subjects from a group of Type 1 diabetics. The targets, islets from neonatal rats, were incubated for one hour with the probands serum. The ADCC was then measured by the 51Cr-release of the serum-treated islets after a 6h-incubation with MNC of the same donor. Results both with and without co-incubation of Ciamexone were compared. Ciamexone does not influence the spontaneous 51Cr-release from neonatal rat islets treated with the probands serum but significantly suppresses the anti-islet ADCC. The fact that Ciamexone suppresses anti-islet ADCC may explain its possible effectiveness in Type 1 diabetes.

Persistence of anti-islet ADCC after manifestation of type-1 (insulin-dependent) diabetes.

ADCC (antibody-dependent cellular cytotoxicity) against xenogenic islets in vitro has frequently been found with mononuclear blood cells and heat inactivated autologous serum from newly diagnosed Type-1 diabetics. Anti-islet ADCC, as measured by enhanced 51Cr-release of islets after a 6h-incubation, leads to functional alteration of islets such as a decrease in insulin content and in leucine incorporation. In a follow-up investigation over at least three years it was demonstrated that anti-islet ADCC in vitro disappears, if there is no more C-peptide secretion in vivo. Furthermore, anti-islet ADCC has also not been found in long-term Type-1 diabetics who had no C-peptide secretion but an acutely stimulated immune system due to infectious diseases. An acute immunocytolytic process against pancreatic beta cells in vivo seems to be the precondition for anti-islet ADCC in vitro.

Effect of lymphocytes and serum from probands before and after manifestation of type 1 (insulin-dependent) diabetes on rat islets in vitro.

In a two-year follow-up study neonatal rat islets have been shown to be affected in vitro by lymphocytes and complement-inactivated serum obtained from newly diagnosed Type 1 (insulin-dependent) diabetic patients and probands who are at high risk for developing the disease. The effect was measured by 51Cr-release of the islets treated with the proband's serum after a 6 h-incubation with lymphocytes of the same donor. Nineteen newly diagnosed diabetic patients, 23 persons at risk and 11 control probands were studied. There was no appreciable cytotoxic activity in the control probands (with one exception) and in 7 out of the 19 newly diagnosed diabetics. Five of the diabetes-susceptible probands developed diabetes mellitus during the investigation period. Anti-islet cytotoxicity of lymphocytes was found in these individuals at least 8 months before diagnosis of Type 1 diabetes. The cytotoxic effect disappeared at various time intervals after disease manifestation. Islet cytotoxicity was intermittently found with lymphocytes from further 13 probands at risk, sometimes for more than one year. Our data indicate that mononuclear cells from probands who are at high risk for developing Type 1 diabetes can exert cytotoxicity on xenogenic neonatal islets in the presence of their own serum.

Phagocytic activity of blood cells in diabetic risk probands and newly diagnosed type 1 diabetics.

The phagocytic activity of granulocytes and mononuclear blood cells was compared in probands at risk for insulin-dependent Type 1 diabetes mellitus and in newly diagnosed diabetics before and during short-term insulin treatment. Healthy persons without family history of Type 1 diabetes were used as controls. Furthermore, the relationship between phagocytic activity and the proportion on monocytes in the granulocyte- and mononuclear blood cell fractions was estimated. The phagocytic activity of the mononuclear cells from the risk subjects was reduced. This observation suggests that defective phagocytosis might be important in the pathogenesis of Type 1 diabetes. But the phagocytic activity of mononuclear cells from newly diagnosed diabetics was not severely impaired and was fully normal under insulin treatment. We found no differences in the phagocytic activity of the granulocytes between patients and healthy probands. The proportion of monocytes in the mononuclear cell fraction was significantly enhanced in newly diagnosed diabetics and remained high throughout the 6-month period of insulin therapy. We assume that the increased monocyte level and the phagocytic activity of mononuclear cells in diabetics are not related to each other. But the increased monocyte level could also be interpreted as a compensatory reaction against the impaired phagocytic activity observed in the risk probands.

Genetic control of diabetes induction by complete Freund's adjuvant combined with subdiabetogenic doses of streptozotocin in Lewis rats--evidence for transient cytotoxicity against beta cells.

The non-specific activation of the immune system by administration of complete Freund's adjuvant (CFA) was examined in two congenic Lewis rat strains LEW. 1A (RT1a) and LEW. 1W (RT1u) as a possible mean of amplification of the specific immune response, directed to pancreatic beta cells induced by multiple non-diabetogenic injections of streptozotocin (STZ). Rats were given intraperitoneally 0.5 ml CFA and 1 day later 25 mg/kg body weight STZ. This combined treatment was repeated twice at weekly intervals. Control groups received vehicle, STZ or CFA only with the same doses and at the same times. Only CFA/STZ-treated rats developed a persisting hyperglycaemia (greater than 15 mmol/l glucose) namely 3/18 (17%) LEW. 1W and 47/76 (62%) LEW. 1A rats. The pancreatic insulin content in these hyperglycaemic rats was reduced by 96.6% in LEW. 1A rats and by 93% in LEW. 1W rats measured 8 weeks after the last CFA/STZ treatment. The response to CFA indicated by an increase of number of peripheral leucocytes and relative spleen weight gain at 7 days after CFA administration, was higher in LEW. 1A rats compared with those of LEW. 1W rats. Spleen cells harvested 72 h/48 h after the first and second CFA/STZ administration showed a cytotoxic reaction to isolated syngeneic islets as measured by 51Cr-release in vitro. Control rats receiving vehicle, STZ or CFA only showed no cellular anti-islet cytotoxicity. The anti-islet cytotoxicity of spleen cells was only transient and disappeared after the third CFA/STZ administration. Anti-islet cytotoxic antibodies were not detectable in this short-term study.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell-mediated immune reactions against islets of Langerhans in diabetes-prone BB rats.

The intact pancreatic islet can be destroyed by antibody-dependent cell-mediated cytotoxicity (ADCC). T cell-mediated cytotoxicity (CMC) might additionally be important in the pathogenesis of IDDM. However, in vitro alterations of islets due to CMC have so far not been demonstrated. For the evaluation of the cytotoxic attack caused by ADCC and CMC against the islets in the development of IDDM we used a BB rat line with a high incidence of the disease (dp BB/OK). Cytotoxicity tests were carried out on autologous and on nonsyngeneic islets with mononuclear spleen cells and serum from non-diabetic BB rats of different ages. The cytotoxic action of the mononuclear cells was quantified by the specific 51Cr-release from the islets after pretreatment with serum. It was found that an anti-islet cytotoxicity appears with a peak incidence between 40 and 60 days of age. The frequency of cytotoxicity in vitro was related to the incidence of diabetes as normally observed in this rat line. Furthermore, it was shown that both autologous, allogeneic and xenogeneic islets can be destroyed by mononuclear spleen cells and serum of dp BB/OK rats.--The frequency and the strength of anti-islet cytotoxicity in vitro were higher in these dp BB/OK animals than in a control group of non-diabetes prone BB/PhiK rats. There was an association between cytotoxic 51Cr-release in the positive assays and a reduction in the hormone content of pancreatic islets.--This report provides evidence of cell-mediated immune damage of islets during the prediabetic state of BB rats suggesting that both CMC and ADCC are involved in islet cell killing.

Measurement of insulin during isolation and purification from animal pancreas. A comparison of radioimmunoassay, radioreceptor assay and in-vivo bioassay.

For the purpose of monitoring the yield of the insulin extraction procedure from animal pancreas three methods of insulin determination were compared, i.e. the mouse convulsion test, a radioreceptor assay (RRA) on rat fat cells and a radioimmunoassay (RIA) which was especially laid out for high insulin concentrations. In samples containing actually insulin in general all three methods provided comparable results. Notable differences were only found in proinsulin-containing material. Because of its simplicity and high reproducibility as well as the good agreement of its results with those obtained with the other assays, the RIA turned out to be the most suitable assay. On the other hand, the RRA should be useful in detecting molecular differences between the investigated insulin-like preparations and standard insulin.

Effect of antibody-mediated crosslinking of insulin on its bioactivity and receptor binding.

Precipitating anti-insulin antibodies or anti-insulin IgG/anti-IgG complexes bind insulin in a highly aggregated form and thus should preferably be capable of inducing receptor aggregation, which has recently been suggested to be a precondition for insulin bioactivity. We, therefore, studied the influence of antibody-mediated crosslinking of insulin on the glucose conversion into CO2 in rat fat cells and glycogen synthesis in rat liver cells. As far as possible receptor-bound insulin was measured in parallel. Insulin bound to antibodies with low insulin precipitating capacity had no or little bioactivity and receptor reactivity on fat cells. The bioactivity, however, could be restored in part by addition of a second antibody. On liver cells, second antibody-mediated crosslinking of insulin-antibody complexes resulted in an enhancement of receptor reactivity, and insulin bioactivity of such crosslinked immune complexes was demonstrable. An insulin-precipitating antiserum was shown to form insulin-antibody complexes with significant bioactivity in fat cells which correlated with their receptor binding. In each case antibodies had no or little effect in the absence of insulin. Our data suggest that insulin neutralization by antibodies can be compensated by crosslinking the insulin-antibody complexes or by formation of big complexes precipitating by themselves. This is probably due to the induction of receptor aggregation.

The frequency of islet cell surface antibodies and antibody-dependent cell-mediated cytotoxicity (ADCC) of mononuclear cells in HLA-typed patients with high diabetes risk.

To evaluate the significance of ICSA as a prognostic marker for the development of type I diabetes we investigated 66 subjects with first degree relatives of type I (47) and type II (9) diabetes as well as subjects with anamnestical data suggestive of diabetes. Patients were studied for glucose tolerance (oGTT) and IRI-response, ICSA (indirect fluorescence of living rat islet cell suspensions), ADCC (specific 51Cr-release of serum pretreated neonatal rat islets elicited by mononuclear cells) and HLA-antigens. 23 subjects revealed normal glucose tolerance, 17 impaired glucose tolerance and 26 had a prevoius abnormality. The incidence of ICSA varied between 46 and 53 per cent, that of positive ADCC between 22 and 56 per cent, both being highest in subjects with IGT. 87 per cent of all patients revealed diabetes associated HLA-antigens. We found no correlation of ICSA with glucose tolerance, IRI-response, ADCC and HLA-antigens. In conclusion it can be said that ICSA are present in a high percentage in patients with high diabetes risk but their predictive role as a marker for the manifestation must be elucidated in follow-up studies.

Impaired hormonal regulation of lipolysis and the interference with adenosine in adipose tissue from hyperglycemic sand rats in vitro.

Sand rats (Psammomys obesus) developed in response to different food intake various states of hyperglycemia and hyperinsulinism. 12 normo- and 10 hyperglycemic animals were selected by means of a weekly control of plasma glucose and plasma insulin over a period of 12 weeks after separation from the mother. During this time also the development of body weight gain was checked. In both groups of rats the hormonal regulation of glycerol release by incubated adipose tissue was investigated. In any case, the fat tissue from hyperglycemic sand rats showed a lower lipolytic responsiveness to noradrenaline stimulation than that of their normoglycemic controls. This correlates well with previous results in hyperglycemic sand rats in which the catecholamine-stimulated cAMP production was disturbed (Knospe and Köhler 1981). Degradation of released adenosine by addition of adenosine deaminase significantly enhanced the noradrenaline action on glycerol release in both groups of sand rats. Even though the noradrenaline-stimulated lipolytic activity of adipose tissue from normo- and hyperglycemic animals was enhanced in the presence of adenosine deaminase, the hormone resistance of adipose tissue from hyperglycemic sand rats was nevertheless not abolished. The theophylline-mediated adenosine receptor blockade gave further evidence that particularly endogenous adenosine released during incubation of adipose tissue from sand rats inhibited the noradrenaline action on lipolysis. The antilipolytic action of insulin on glycerol release is negligibly low in normoglycemic as well as hyperglycemic sand rats. The degradation of adenosine by adenosine deaminase failed to improve the insulin action. Adenosine addition completely blocked the stimulating effects of noradrenaline on glycerol release.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibody-dependent cell-mediated cytotoxicity of mononuclear cells against Langerhans islets of Wistar rats in normal man and in patients at diabetes risk.

Antibody-dependent cell-mediated cytotoxicity against pancreatic islets was investigated in 13 newly diagnosed insulin-dependent diabetics, in 38 patients at high risk for the disease and in 20 age-matched healthy controls. For this purpose 51Cr-labeled neonatal rat pancreatic islets incubated with the specific anti-rat islet cell antiserum 339 or with serum of the lymphocyte donors were used as targets. The antibody-mediated cytotoxic activity of mononuclear cells was evaluated from the specific chromium release after 6 h exposure of pretreated islets to the effector cells. The specific cytotoxic effect of mononuclear cells from healthy controls on pancreatic islets pretreated with serum is weak. ADCC mediated by the specific antirat islet cell antiserum is significantly increased in 54% of newly diagnosed diabetics as well as in 32% of patients at high risk for insulin-dependent diabetes mellitus. 46% of the newly diagnosed diabetics were also ADCC-positive when their own serum was used for the pretreatment of islets, regardless of whether they were islet cell antibody- or islet cell surface antibody positive or not. Subsets of mononuclear cells (non E-rosette-forming cells, high affinity E-rosette-forming cells, low affinity E-rosette-forming cells) were prepared and their cytotoxic potential was analysed in patients with positive ADCC test results.(ABSTRACT TRUNCATED AT 250 WORDS)