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M Vranic

Publications and source records attributed to M Vranic.

At least 91 records · Page 5Linked to original sources
PubMed1990

Paradoxical reduction in pancreatic glucagon with normalization of somatostatin and decrease in insulin in normoglycemic alloxan-diabetic dogs: a putative mechanism of glucagon irresponsiveness to hypoglycemia.

In alloxan-diabetic (A-D) dogs, plasma glucagon does not increase when glycemia is decreased by insulin. Therefore, as in insulin-dependent diabetes mellitus (IDDM), increased glucose utilization is not matched by an increase in hepatic production. To explore further the abnormal effects of insulin on regulation of pancreatic glucagon, we studied content and morphology of pancreatic hormones in six normal (N) dogs, five hyperglycemic A-D (HD) dogs, and in four A-D dogs where normoglycemia was maintained by insulin (ND). Morphometric measurement of islets and of immunocytochemically localized A cells (glucagon) were performed by an image analysis system. In normal pancreas, islets of tail and body were bigger in size (tail = 4850 +/- 376 microns 2, body = 3256 +/- 198 microns 2), than the head (2009 +/- 207 microns 2). Glucagon content was 331 +/- 50 micrograms with a mean concentration of 8.5 +/- 0.9 micrograms/g in N dogs, and did not change in HD dogs (422 +/- 34 micrograms, 9.3 +/- 0.4 micrograms/g). With normoglycemia, glucagon content decreased by 5-fold (p less than 0.001). Morphometry indicated that, although A cell area per islet increased (2.7-fold), islet number decreased (70%), explaining the unchanged glucagon content in HD dogs. This decrease in islet number can also justify the dramatic glucagon decrease in ND dogs. Despite the 70% decrease in islet numbers in HD dogs, pancreatic somatostatin increased 3-fold (9.93 +/- 3.3 to 30.6 +/- 7.2 micrograms), indicating that its islet content was augmented 10-fold. Somatostatin content returned to normal with normoglycemia. Pancreatic insulin content in HD dogs was negligible (55 +/- 23 micrograms) when compared with that in N dogs (5500 micrograms) and it did not increase with normoglycemia. The distinct but markedly diminished insulin and proinsulin peaks in HD dogs nearly disappeared in ND dogs. Thus, in alloxan-diabetic HD dogs, 70% of islets are destroyed. A marked increase in glucagon in residual islets can explain the unchanged islet size despite the absence of B cells; however, the percent increase of somatostatin is larger than that of glucagon. Normoglycemia 1) normalizes somatostatin content, 2) further diminishes insulin and proinsulin synthesis presumably due to lack of hyperglycemic stimulus, and 3) paradoxically decreases pancreatic glucagon content 5-fold below its normal level. We hypothesize that with normalization of plasma insulin, glucagon content in each islet normalizes, but because of destruction of most islets, pancreatic glucagon content becomes extremely low.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Differential effects of IGF-I and insulin on glucoregulation and fat metabolism in depancreatized dogs.

The effects of equipotent glucose-lowering doses of insulinlike growth factor I (IGF-I) and insulin on tracer-determined glucose kinetics and several metabolites were compared in 14 experiments (7 in each group) in fasted, totally depancreatized dogs. This model prevented variations in insulin secretion induced by IGF-I and permitted evaluation of the effects of IGF-I on extrapancreatic glucagon. Steady-state moderate hyperglycemia (9.9 +/- 0.2 mM) was maintained by a subbasal intraportal infusion of insulin (1.29 +/- 0.17 pmol.kg-1.min-1). This was continued throughout the experiment, allowing evaluation of IGF-I effects on insulin clearance. Human recombinant IGF-I or insulin was given intravenously as a primed infusion for 90 min, followed by a 50-min recovery period. The dose of IGF-I was a 2.6-nmol/kg bolus plus 57.4 pmol.kg-1.min-1. The insulin dose required to induce the same plasma glucose decline as IGF-I (44 +/- 6 vs. 43 +/- 5%, NS) was 9-12 times lower (0.06-nmol/kg bolus + 6.4 +/- 0.6 pmol.kg-1.min-1). However, the mechanism of this decline differed with IGF-I and insulin; glucose production was much less suppressed (25 +/- 9 vs. 42 +/- 11%, P less than 0.001) and glucose utilization was more stimulated (68 +/- 18 vs. 38 +/- 19%, P less than 0.05) with IGF-I.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Bioenergetic changes during contraction and recovery in diabetic rat skeletal muscle.

Phosphorus nuclear magnetic resonance (31P-NMR) spectroscopy was used to assess the effects of hypoinsulinemia on skeletal muscle during contraction in vivo. Five groups of rats were studied: age-matched (CONA) and weight-matched (CONW) nondiabetic controls; rats given streptozotocin 21 days before study (UD); diabetic rats treated with insulin for 21 days (ITD); and insulin-treated diabetic rats with insulin treatment withheld for 72 h before study (IWD). Both UD and IWD had similar alterations in plasma substrate concentrations and an impairment in the rate of glycogen resynthesis after the stimulation protocol compared with ITD, CONA, and CONW. Pyruvate oxidation was decreased by 30-40% in mitochondria isolated from gastrocnemius of the UD group, whereas no significant decrease was observed for mitochondria from the IWD (or ITD) group(s). In UD, maintenance of gastrocnemius muscle isometric twitch tension at 1 Hz required exaggerated decreases in phosphocreatine (PCr) concentration and pH; at 5 Hz, muscle performance declined significantly, and intracellular pH decreased to lower values than observed for the control groups; during recovery, no impairment of PCr resynthesis was observed. We conclude that in skeletal muscle of UD 1) at 1 Hz there is an increased reliance on glycolytic mechanisms of ATP resynthesis and 2) at 5 Hz force failure may occur because of the decreased rate of pyruvate utilization.

Animals↗
PubMed1989

Phlorizin-induced normoglycemia partially restores glucoregulation in diabetic dogs.

The plasma concentration of glucagon (IRG), catecholamines, and hepatic glucose production (Ra) were followed in insulin-induced hypoglycemia in dogs before (normal) and at 14-21 and again at 89-119 days after the injection of alloxan (diabetic). Some diabetic dogs were also tested when euglycemia was restored by phlorizin. In the normal state plasma IRG and epinephrine were raised by a factor of 3 and 15, respectively. Ra increased in two phases, an early peak (350% basal) was followed by a plataeu at about twice basal. In diabetes, irrespective of its duration, plasma IRG was decreased in hypoglycemia, and the rise in plasma epinephrine was significantly reduced. Ra remained unchanged. In phlorizin-treated euglycemic diabetic dogs plasma IRG fell, and the response in plasma epinephrine remained blunted. There was no early rise in Ra, but the same elevated plateau was reached at the same time as in normal animals. In conclusion, the following is observed in diabetic dogs. 1) The sensitivity of alpha-cells to insulin is maintained, but that to hypoglycemia is lost. The concentration of plasma catecholamines is raised less than in normals. With no increase in plasma glucagon this rise is not sufficient to increase Ra. 2) Restoration of euglycemia with phlorizin does not restore normal IRG and epinephrine responses to hypoglycemia but restores the delayed increase of Ra. Thus the restoration of euglycemia in severely diabetic dogs partially restores the responses of the liver, but not of the alpha-cell or sympathetic discharge, to hypoglycemia.

Animals↗
PubMed1989

Decrease in glucose transporter number in skeletal muscle of mildly diabetic (streptozotocin-treated) rats.

Diabetes is associated with a decrease in glucose uptake into muscle, the primary tissue responsible for whole body glucose uptake in the fed state. To study the basis of such a decrease we estimated the number of glucose transporters in skeletal muscle membranes from control and streptozotocin (STZ)-treated rats. Animals were injected with 65 mg STZ/kg and were clearly diabetic (hyperglycemic and glycosuric) at 1 week. After an overnight fast, animals were killed, and skeletal muscle from hind limbs were removed and used to prepare plasma membranes and internal membranes. The number of glucose transporters was determined by D-glucose-protectable equilibrium binding of [3H]cytochalasin-B. STZ-treated rats showed a 37% decrease in the number of glucose transporters per mg protein in crude membranes. The decrease was more pronounced in plasma membranes (average 50% decrease) than in the intracellular membranes (32% decrease). The reduction in the number of glucose transporters was specific, since it was not paralleled by changes in other plasma membrane markers or in total protein, although plasma membrane protein decreased by 15% in STZ-treated rats. When total recoveries of transporters were calculated (i.e. picomoles of transporters recovered per g tissue), the number of transporters in the plasma membrane fraction from STZ-treated rats was decreased by 68% relative to that in control animals. In the intracellular membranes and in total crude membranes from diabetic rats the transporters were decreased by 45%. This suggests that in STZ-treated rats there is an overall decrease in the number of glucose transporters, and that the plasma membrane is further specifically depleted of transporters. The decrease in glucose transporter number in the plasma membrane could at least in part be the cause of the diminished glucose uptake in diabetic muscle and for overall drop in total body glucose utilization of this condition.

Animals↗
PubMed1989

Glucose turnover in hyperthyroid patients with normal glucose tolerance.

To determine the diabetogenic effect(s) of thyroid hormones, we simultaneously measured glucose turnover in six hyperthyroid patients and six normal subjects. All had normal fasting blood glucose concentration and oral glucose tolerance test values. We determined hepatic total glucose output (HTGO) and total glucose phosphorylation with [2-3H]glucose and hepatic glucose production (HGP) and irreversible glucose uptake using [6-3H]glucose. The difference between the two turnover rates indicates the extent of hepatic glucose cycling (glucose in equilibrium glucose-6-phosphate). Measurements were made both in the postabsorptive steady state and during a 2-h glucose infusion (11.1 mumol/kg.min). The postabsorptive HTGO and total glucose phosphorylation were increased in the hyperthyroid patients [13.5 +/- 0.8 (+/- SE) vs. 11.3 +/- 0.4 mumol/kg.min; P less than 0.05]. HGP and irreversible glucose uptake also were slightly but not significantly higher. During the glucose infusion, HTGO and HGP were less suppressed in the hyperthyroid patients than in the normal subjects, while the increments in peripheral glucose uptake were normal. In hyperthyroidism, glucose cycling was increased both postabsorptively (2.35 +/- 0.27 vs. 1.17 +/- 0.25 mumol/kg.min; P less than 0.025) and during glucose infusion (2.57 +/- 0.34 vs. 1.31 +/- 0.35 mumol/kg.min; P less than 0.05). We conclude that increases in HTGO and HGP are important features of hyperthyroidism, especially during glucose infusion. The increase in GC indicates increased activities of both glucokinase and glucose-6-phosphatase. The diabetogenic effect of hyperthyroidism, as revealed most markedly by [2-3H]glucose, could be accounted for by augmented glucose production, possibly due to increased glucose-6-phosphatase activity.

Adult↗
PubMed1988

Regulation of glucose turnover during exercise in pancreatectomized, totally insulin-deficient dogs. Effects of beta-adrenergic blockade.

To examine whether glucose metabolic clearance increases and whether catecholamines influence glucose turnover during exercise in total insulin deficiency, 24-h fasted and insulin-deprived pancreatectomized dogs were studied before and during exercise (60 min; 100 m/min; 10% slope) with (n = 8) and without (n = 8) propranolol infusion (PI, 5 micrograms/kg-min). Exercise with or without PI was accompanied by four and fivefold increments in norepinephrine and epinephrine respectively, while glucagon (extrapancreatic) fell slightly. Basal plasma glucose and FFA concentrations and rates of tracer-determined (3[3H]glucose) hepatic glucose production (Ra) and total glucose clearance (including urinary glucose loss) were 459 +/- 24 mg/dl, 1.7 +/- 0.5 mmol/liter, 7.8 +/- 0.9 mg/kg-min and 1.6 +/- 0.1 ml/kg-min, respectively. When corrected for urinary glucose excretion, basal glucose metabolic clearance rate (MCR) was 0.7 +/- 0.1 mg/kg-min and rose twofold (P less than 0.0001) during exercise. Despite lower lactate (3.3 +/- 0.6 vs. 6.6 +/- 1.3 mmol/liter; P less than 0.005) and FFA levels (1.1 +/- 0.2 vs. 2.2 +/- 0.2 mmol/liter; P less than 0.0001) with PI, PI failed to influence MCR during exercise. Ra rose by 3.7 +/- 1.7 mg/kg-min during exercise (P less than 0.02) while with PI the increase was only 1.9 +/- 0.7 mg/kg-min (P less than 0.002). Glucose levels remained unchanged during exercise alone but fell slightly with PI (P less than 0.0001). Therefore, in total insulin deficiency, MCR increases marginally with exercise (13% of normal); the beta adrenergic effects of catecholamines that stimulate both FFA mobilization and muscle glycogenolysis do not regulate muscle glucose uptake. The exercise-induced rise in hepatic glucose production does not require an increase in glucagon levels, but is mediated partially by catecholamines. Present and previous data in normal and alloxan-diabetic dogs, suggest that (a) in total insulin deficiency, control of hepatic glucose production during exercise is shifted from glucagon to catecholamines and that this may involve catecholamine-induced mobilization of peripheral substrates for gluconeogenesis and/or hepatic insensitivity to glucagon, and (b) insulin is not essential for a small exercise-induced increase in muscle glucose uptake, but normal insulin levels are required for the full response. Furthermore, the catecholamines appear to regulate muscle glucose uptake during exercise only when sufficient insulin is available to prevent markedly elevated FFA levels. We speculate that the main role of insulin is not to regulate glucose uptake by the contracting muscle directly, but to restrain lipolysis and thereby also FFA oxidation in the muscle.

3-Hydroxybutyric Acid↗
PubMed1988

Mild type II diabetes markedly increases glucose cycling in the postabsorptive state and during glucose infusion irrespective of obesity.

Glucose cycling (GC; G in equilibrium G6P) equals 14% of glucose production in postabsorptive man. Our aim was to determine glucose cycling in six lean and six overweight mild type II diabetics (fasting glycemia: 139 +/- 10 and 152 +/- 7 mg/dl), in postabsorptive state (PA) and during glucose infusion (2 mg/kg per min). 14 control subjects were weight and age matched. GC is a function of the enzyme that catalyzes the reaction opposite the net flux and is the difference between hepatic total glucose output (HTGO) (2-[3H]glucose) and hepatic glucose production (HGP) (6-[3H]-glucose). Postabsorptively, GC is a function of glucokinase. With glucose infusion the flux is reversed (net glucose uptake), and GC is a function of glucose 6-phosphatase. In PA, GC was increased by 100% in lean (from 0.25 +/- 0.07 to 0.43 +/- .08 mg/kg per min) and obese (from 0.22 +/- 0.05 to 0.50 +/- 0.07) diabetics. HGP and HTGO increased in lean and obese diabetics by 41 and 33%. Glucose infusion suppressed apparent phosphatase activity and gluconeogenesis much less in diabetics than controls, resulting in marked enhancement (400%) in HTGO and HGP, GC remained increased by 100%. Although the absolute responses of C-peptide and insulin were comparable to those of control subjects, they were inappropriate for hyperglycemia. Peripheral insulin resistance relates to decreased metabolic glucose clearance (MCR) and inadequate increase of uptake during glucose infusion. We conclude that increases in HGP and HTGO and a decrease of MCR are characteristic features of mild type II diabetes and are more pronounced during glucose infusion. There is also an increase in hepatic GC, a stopgap that controls changes from glucose production to uptake. Postabsorptively, this limits the increase of HGP and glycemia. In contrast, during glucose infusion, increased GC decreases hepatic glucose uptake and thus contributes to hyperglycemia. Obesity per se did not affect GC. An increase in glucose cycling and turnover indicate hepatic insulin resistance that is observed in addition to peripheral resistance. It is hypothesized that in pathogenesis of type II diabetes, augmented activity of glucose-6-phosphatase and kinase may be of importance.

Adult↗
PubMed1988

Modeling error and apparent isotope discrimination confound estimation of endogenous glucose production during euglycemic glucose clamps.

We previously demonstrated that conventional tracer methods applied to euglycemic-hyperinsulinemic glucose clamps result in substantially negative estimates for the rate of endogenous glucose production, particularly during the first half of 180-min clamps. We also showed that addition of tracer to the exogenous glucose infusate resulted in nonnegative endogenous glucose production (Ra) estimates. In this study, we investigated the underlying cause of negative estimates of Ra from conventional clamp/tracer methods and the reason for the difference in estimates when tracer is added to the exogenous glucose infusate. We performed euglycemic-hyperinsulinemic (300-microU/ml) clamps in normal dogs without (cold GINF protocol, n = 6) or with (hot GINF protocol, n = 6) tracer (D-[3-3H]glucose) added to the exogenous glucose infusate. In the hot GINF protocol, sufficient tracer was added to the exogenous glucose infusate such that arterial plasma specific activity (SAa) did not change from basal through the clamp period (P greater than .05). In the cold GINF studies, plasma SAa fell 81 +/- 2% from the basal level by the 3rd h of clamping. We observed a significant, transient, positive venous-arterial difference in specific activity (SAv-SAa difference) during the cold GINF studies. The SAv-SAa difference reached a peak of 27 +/- 6% at 30 min and diminished to a plateau of 7 +/- 1% between 70 and 180 min. We also observed a positive but constant SAv-SAa difference (4.6 +/- 0.2% between 10 and 180 min) during the hot GINF studies. The observations of a difference between hot and cold GINF endogenous Ra estimates and a positive but transient SAv-SAa difference during the cold GINF studies are consistent with the interpretation that a portion of the underestimation of Ra is due to insufficient mixing of endogenous and exogenous glucose for the one-compartment, fixed-pool volume model to be applicable. Alternatively, our results suggest that the one-compartment, fixed-pool volume model of glucose kinetics is insufficient to account for the complex dynamics of labeled and unlabeled glucose during euglycemic-hyperinsulinemic clamps. Improved mixing through addition of tracer to the exogenous glucose infusate or improved modeling by allowing for a variable-pool volume appears to improve the accuracy of the tracer methods; however, these approaches remain to be validated. The constant positive SAv-SAa difference observed during the hot GINF studies is consistent with the interpretation that an additional contributor to underestimation of endogenous Ra is apparent isotope discrimination.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Importance of glucagon in the control of futile cycling as studied in alloxan-diabetic dogs.

In order to determine the role of glucagon in futile or substrate cycling in diabetes, we measured tracer determined glucose kinetics during a combined infusion of 2-3H-glucose (total glucose production) and 6-3H-glucose (glucose production) in six alloxan-diabetic dogs. The animals received either a 420 min infusion of (1) somatostatin alone (0.3 microgram X kg-1 X min-1), (2) somatostatin with insulin replacement (100 microU X kg-1 X min-1) or (3) glucagon (6 ng X kg-1 X min-1) together with somatostatin and transient insulin replacement. When somatostatin was given alone, plasma glucagon (p less than 0.004) and insulin (p less than 0.0001) were suppressed. Glucose production and disappearance and plasma glucose concentrations fell (p less than 0.0001), but the metabolic clearance of glucose did not change significantly. In the basal state, futile cycling comprised 29 +/- 4%, 33 +/- 4% and 33 +/- 3% of total glucose production in the three groups of studies, which is high compared to normal dogs. The absolute rate of futile cycling fell slightly but significantly from 10.0 +/- 1.7 to 8.3 +/- 1.7 mumol X kg X -1 min-1 (p less than 0.0008). When insulin replacement was given during somatostatin infusion to correct for the small somatostatin-induced insulin suppression, there were similar changes in plasma glucagon, glucose concentrations and glucose kinetics as seen during the infusion of somatostatin alone. Futile cycling decreased to a slightly greater extent from 12.8 +/- 2.8 to 9.5 +/- 1.7 mumol X kg-1 X min.-1 (p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Beta endorphin modulation of the glucoregulatory effects of repeated epinephrine infusion in alloxan-diabetic and normal dogs.

When repeated epinephrine infusions are given to normal dogs as a partial stress model, there is exaggerated hyperglycaemia, associated with reduced plasma insulin levels and markedly decreased glucose clearance. In the present study, we have examined the hormonal and metabolic responses to two successive 60-min epinephrine (0.1 microgram . kg-1 . min-1) infusions with or without concomitant infusion of beta endorphin (0.3 microgram . kg-1 . min-1) in 6 alloxan-diabetic dogs. These studies have been compared to similar studies in 5 normal dogs. In the diabetic dogs, plasma glucose rose from 12.3 +/- 2.2 to 16.2 +/- 2.4 mmol/l (p less than 0.001) in response to the first epinephrine infusion and rose further to 18.1 +/- 2.5 mmol/l (p less than 0.001) during the second epinephrine infusion. The increases in plasma glucagon and glucose production were comparable with both infusions, but considerably greater than previously observed in normal dogs. In normal dogs, beta endorphin diminished the insulin response to the first epinephrine infusion (p less than 0.02), and abolished this response to the second (p less than 0.05). In addition beta endorphin also diminished the glucagon response to the second epinephrine infusion (p less than 0.01) and greatly potentiated epinephrine-induced suppression of glucose metabolic clearance during both infusions (p less than 0.001). However, beta endorphin did not appreciably alter the hyperglycaemic response to epinephrine due to a concomitant attenuation of the epinephrine-induced increase in hepatic glucose production. In contrast to normal dogs, beta endorphin did not modulate the effects of either the first or second epinephrine infusion on glucose kinetics in diabetic dogs. Also, beta endorphin failed to inhibit glucagon or insulin secretion in response to epinephrine in the diabetic animals. Since the alloxan-diabetic and normal dogs respond differently to the combined infusion of beta endorphin and epinephrine we conclude that the effects of beta endorphin observed in the normal dogs are dependent upon intact pancreatic endocrine function.

Animals↗
PubMed1987

Lack of effect of beta-endorphin on basal or glucagon-stimulated hepatic glucose production in vitro.

beta-Endorphin appears to have effects on hepatic glucose production in vivo. In order to determine whether beta-endorphin modulates glucose production directly, the effects of beta-endorphin on isolated rat hepatocytes were investigated. This permitted isolation of the effects of beta-endorphin from hormonal and/or neuronal influences. A significant dose-related stimulatory effect of glucagon (10(-10) to 10(-6) mol/L) on both hepatic glucose production and glycogen phosphorylase a activity was demonstrated. No effect of either physiologic (10(-11) to 10(-9) mol/L) or supraphysiologic (10(-6) mol/L) concentrations of beta-endorphin on these parameters, under basal or glucagon-stimulated conditions, could be detected. These results suggest that reported in vivo effects of beta-endorphin to inhibit hepatic glucose production were either indirect or centrally mediated.

Animals↗
PubMed1987

Glucagon-like immunoreactive peptides in a rat ileal epithelial cell line (IEC-18).

The presence of cells containing glucagon-like immunoreactive (GLI) peptides was demonstrated in a rat ileal epithelial cell line (IEC-18) by both immunofluorescence and radioimmunoassay. When cell extracts were subjected to gel filtration chromatography, the cells were found to contain 3.5 Kd glucagon in addition to significant quantities of large molecular weight GLI peptides (apparent molecular weights of 4, 6, 8 and 10 Kd) and a 9 Kd peptide with apparent glucagon immunoreactivity. This was in contrast to extracts of adult rat ileum, which contained only large molecular weight GLI peptides (apparent molecular weights of 6 and 12 Kd). Production of GLI peptides by the IEC-18 cells was stimulated by glucose (p less than 0.02) and inhibited by insulin (p less than 0.01). In conclusion, these results demonstrate that the IEC-18 cells produce both GLI peptides and glucagon, and thus support the notion that proglucagon processing is cell-specific. IEC-18 cells may therefore provide a tool for investigations of some aspects of GLI peptide and glucagon synthesis.

Animals↗
PubMed1987

Elevated somatostatin in pancreatic islets of adrenalectomized dogs.

We have observed both hyperglucagonemia and hypoinsulinemia in adrenalectomized (Adx) dogs. To determine whether these hormonal alterations are related to changes in distribution of islet hormones in the pancreas, we examined the concentration and total mass of insulin, glucagon, and somatostatin in the head, body, and tail of the pancreas by immunoassay and immunocytochemistry. We studied 6 normal dogs, 5 Adx dogs deprived of cortisol for 24 h (Adx I) and 5 for 48-72 h (Adx II). In normal dogs, single and double immunocytochemical staining showed that, in contrast to some other species, B (insulin) cells are mostly in the central region of islet, whereas A (glucagon) and D (somatostatin) cells are distributed randomly. This topographic distribution was not altered by adrenalectomy. In normal dogs, insulin concentration (micrograms per g) and total mass (micrograms) were higher in the tail (174 +/- 22, 2001 +/- 396) and body (165 +/- 22, 2850 +/- 600) than in the head (91 +/- 17, 668 +/- 156) of pancreas. Glucagon concentration (micrograms per g) and total mass (micrograms) were 17 +/- 2, 178 +/- 17 in the tail; 9.5 +/- 2, 158 +/- 32 in the body, and negligible (0.78 +/- 0.32, 7 +/- 3) in the head, whereas somatostatin concentration (micrograms per g) and total mass (micrograms) were 0.58 +/- 0.26, 4.20 +/- 1.5 in the T, 0.23 +/- 0.10, 3.9 +/- 1.6 in the B, and 0.22 +/- 0.05, 1.8 +/- 0.6 in the H. The striking finding was that adrenalectomy caused large increases in somatostatin in all three regions of pancreas in both Adx I and Adx II. The total mass of somatostatin in Adx I and Adx II increased 4-fold in the tail (P less than 0.02-0.005), 5-fold in the body (P less than 0.01-0.001), and 7-9-fold in the head (P less than 0.05-0.005) and concentration increased 6-fold in the body (P less than 0.005) and 7- to 8-fold in the head (P less than 0.01-0.001). There were no significant changes in the content of insulin and glucagon after adrenalectomy. Plasma concentration of glucagon increased by 50% in Adx I (P less than 0.005) and 70% in Adx II (P less than 0.02), insulin decreased by 39% (P less than 0.005), 23% (NS), respectively, and somatostatin increased by 258% (P less than 0.001) in Adx II. Thus the adrenal glands appear to play an important role in regulation of the content of somatostatin in pancreatic islets.

Adrenalectomy↗
PubMed1987

Fetal rat intestinal cells in monolayer culture: a new in vitro system to study the glucagon-like immunoreactive peptides.

To establish an in vitro model to investigate the glucagon-related peptides, fetal rat intestinal cells were enzymatically dispersed and placed into culture for up to 7 days. After 1 day in culture, the presence of epithelial-like cells containing glucagon-like immunoreactivity (GLI) was demonstrated using immunocytochemical techniques. The cell peptides were extracted by passage through a cartridge of octadecylsilyl silica and characterized by gel filtration and RIA. Two GLI moieties were detected with apparent mol wts of 11,000-12,000 and 5,000-6,000. The immunoreactive profile obtained for the cells in culture was identical to that of both whole fetal rat intestine and adult rat ileum. The presence of glucagon could not be demonstrated in any of the extracts. The basal levels of GLI and apparent immunoreactive glucagon (IRGa) were 1,457 +/- 381 and 198 +/- 57 pg/dish, respectively, on day 1 of culture. The GLI content of the cells, but not the IRGa, declined with time in culture for up to 5-7 days (P less than 0.03). Addition of insulin to the culture medium (10 or 100 mU/ml) did not influence the decrease in GLI content of the cells, but did inhibit the production of IRGa (P less than 0.05). Addition of 500 mg/dl glucose to the cells in the presence of 20 microU/ml insulin increased the secretion of GLI by 42 +/- 7% over 2 h (P less than 0.05). The stimulation by glucose was not seen in the absence of insulin or with higher insulin concentrations (100 microU/ml), nor did insulin alone (100 microU/ml) have any effect on the release of GLI. Thus, fetal rat intestinal cells in culture produce the GLI peptides, and secrete them in response to glucose. This system may provide a means by which the synthesis and control of secretion of the glucagon-related peptides can be investigated.

Animals↗
PubMed1987

Estimation of endogenous glucose production during hyperinsulinemic-euglycemic glucose clamps. Comparison of unlabeled and labeled exogenous glucose infusates.

Tracer methodology has been applied extensively to the estimation of endogenous glucose production (Ra) during euglycemic glucose clamps. The accuracy of this approach has been questioned due to the observation of significantly negative estimates for Ra when insulin levels are high. We performed hyperinsulinemic (300 microU/ml)-euglycemic glucose clamps for 180 min in normal dogs and compared the standard approach, an unlabeled exogenous glucose infusate (cold GINF protocol, n = 12), to a new approach in which a tracer (D-[3-3H]glucose) was added to the exogenous glucose used for clamping (hot GINF protocol, n = 10). Plasma glucose, insulin and glucagon concentrations, and glucose infusion rates were similar for the two protocols. Plasma glucose specific activity was 20 +/- 1% of basal (at 120-180 min) in the cold GINF studies, and 44 +/- 3 to 187 +/- 5% of basal in the hot GINF studies. With the one-compartment, fixed pool volume model of Steele, Ra for the cold GINF studies was -2.4 +/- 0.7 mg X min-1 X kg-1 at 25 min and remained significantly negative until 110 min (P less than .05). For the hot GINF studies, Ra was never significantly less than zero (P greater than .05) and was greater than in the cold GINF studies at 20-90 min (P less than .05). There was substantially less between-(78%) and within- (40%) experiment variation for the hot GINF studies compared with the cold GINF studies. An alternate approach (regression method) to the application of the one-compartment model, which allows for a variable and estimable effective distribution volume, yielded Ra estimates that were suppressed 60-100% from basal. In conclusion, the one-compartment, fixed pool volume model of glucose kinetics is inadequate for the estimation of Ra during euglycemic glucose clamps. Two new strategies for estimating Ra from the one-compartment model, the hot GINF protocol and the regression method calculation, yielded more accurate and physiologically plausible estimates of Ra than currently used methodology.

Animals↗
PubMed1986

Interaction between insulin and counterregulatory hormones in control of substrate utilization in health and diabetes during exercise.

In summary, the appropriate balance of glucagon and insulin at the liver and the catecholamines and insulin in the periphery provide the most optimal balance of substrate fluxes to the working muscle. When the hormonal balance is perturbed such as is seen in diabetes or with glucagon suppression, or when the effect of a hormone is impaired such as with beta blockade, optimal substrate balance is lost. The effects of these hormones can be overridden by metabolic factors in muscle, as evidenced by the uncoupling of the normal catecholamine antagonism of glucose uptake from the actual glucose uptake observed during exercise under conditions of tissue hypoxia.

Animals↗