A Prospective Study of Renal Transplant Recipients: A Fall in Insulin Secretion Underpins Dysglycemia After Renal Transplantation.

BACKGROUND: Dysglycemia (encompassing impaired glucose tolerance and diabetes mellitus) arising after renal transplantation is common and confers a significant cardiovascular mortality risk. Nonetheless, the pathophysiology of posttransplant dysglycemia is not well described. The aim of this study was to prospectively and comprehensively assess glucose handling in renal transplant recipients from before to 12 months after transplantation to determine the underpinning pathophysiology. MATERIALS AND METHODS: Intravenous and oral glucose tolerance testing was conducted before and at 3 and 12 months posttransplantation. An intravenous glucose tolerance test was also performed on day 7 posttransplantation. We followed up 16 transplant recipients for 3 months and 14 recipients for 12 months. Insulin secretion, resistance and a disposition index (DI (IV)), a measure of ß cell responsiveness in the context of prevailing insulin resistance, were also determined. RESULTS: At 12 months, 50% of renal transplant recipients had dysglycemia. Dysglycemia was associated with a dramatic fall in DI (IV) and this loss in ß cell function was evident as early as 3 months posttransplantation (23.5 pretransplant; 6.4 at 3 months and 12.2 at 12 months posttransplant). Differences in the ß cell response to oral glucose challenge were evident pretransplant in those destined to develop dysglycemia posttransplant (2-hour blood glucose level 5.6 mmol/L versus 6.8 mmol/L; P < 0.01). CONCLUSIONS: Dysglycemia after renal transplantation is common, and the loss of insulin secretion is a major contributor. Subclinical differences in glucose handling are evident pretransplant in those destined to develop dysglycemia potentially heralding a susceptible ß cell which under the stressors associated with transplantation fails.

Endogenous incretin hormone augmentation of acute insulin secretion in normoglycemic relatives of type 2 diabetic subjects: a 10-year retrospective pathophysiological study.

AIMS/HYPOTHESIS: The pathophysiological role of gut incretin hormone argumentation on acute insulin release in the genesis of type 2 diabetes (TDM2) is uncertain. We examined retrospectively at 0 year and 10 years the endogenous incretin hormone action (IHA) on acute insulin release and glucose tolerance in normoglycemic relatives (REL) of TDM2 and control (CON) subjects. METHODS: At 0 year and 10 years, glucose tolerance, paired oral glucose tolerance test (OGTT)- and i.v. glucose tolerance test (IVGTT)-induced acute (0-30 min) insulin release (insulinogenic index IGIOGTT and IGIIVGTT), and IHA were calculated in 19 REL and 18 CON subjects by cross-correlation linear regression slope analyses of the OGTT (0-30 min) matched insulin/glucose profiles vs the early (0-5 min) and delayed (10-30 min) IVGTT profiles. RESULTS: At 0 year, REL and CON IGIOGTT and IGIIVGTT were similar, but the REL 2- to 5-min IVGTT-induced insulin responses were reduced (P < .03). By 10 years, glucose tolerance deteriorated in nine dysglycemic REL (RELDGT), with raised fasting glucose and 2-hour OGTT glucose. Retrospective analyses of RELDGT at 0 year demonstrated raised proinsulin/insulin molar ratios and fasting glucose and a reduced IVGTT insulin/glucose slope, but the RELDGT IHA was similar to normoglycemic REL (RELNGT) and CON. By 10 years, RELDGT OGTT insulin/glucose slopes were reduced (P = .03-.01), but more so for the early (P < .01-.003) and delayed (P < .005-.002) IVGTT slopes, compared to the normoglycaemic REL and CON subjects. CONCLUSIONS: IHA on acute insulin release is maintained in normoglycemic REL and CON subjects over 10 years. The apparent deterioration in IHA in RELDGT is consistent with a progressive failure of acute ß-cell function over 10 years.

The metabolic responses induced by acute dexamethasone predict glucose tolerance and insulin secretion over 10 years in relatives of type 2 diabetic subjects.

BACKGROUND: This study aimed to compare the metabolic and insulin secretory responses to dexamethasone with the metabolic responses observed at 10 years in normoglycaemic relatives of type 2 diabetic and healthy control subjects. METHODS: Twenty relatives and 20 matched control subjects were studied twice at 0 year (pre- and post-dexamethasone) and at 10 years, employing a 75-g oral glucose tolerance test (OGTT), with serial measurements of glucose and insulin, for determination of glucose tolerance and calculations of acute insulin release (ΔI30 /ΔG30 ; insulinogenic index) and insulin sensitivity (SIHOMA ). RESULTS: Following dexamethasone, the relatives group developed varying degrees of glucose intolerance, associated with reduced insulin sensitivity and insulinogenic index. By 10 years, fasting glucose and 2-h OGTT glucose were raised in the relatives group, especially in the relatives most metabolically affected by dexamethasone, including a reduced insulinogenic index. Multiple regression analysis of the data in relatives demonstrated that the 2-h OGTT glucose and fasting glucose values at 10 years depended on the 0-year post-dexamethasone 2-h OGTT glucose, post-dexamethasone fasting glucose and post-dexamethasone insulin sensitivity, r(2) adj = 56% (p < 0.001) and r(2) adj = 60% (p < 0.0001), respectively. No pre-dexamethasone metabolic or insulin secretory responses entered these models. CONCLUSIONS: In relatives, fasting and 2-h OGTT glucose concentrations and ß-cell responses to acute dexamethasone-induced insulin resistance are similar to those observed at 10 years, especially in relatives who develop the most disturbed dexamethasone-induced glucose intolerance and impaired acute insulin secretion. The combined 0-year, post-dexamethasone fasting and 2-h OGTT glucose concentrations and insulin resistance, measured as SIHOMA , are the best predictors in relatives of future dysglycaemia.

Glucose effectiveness and insulin sensitivity measurements derived from the non-insulin-assisted minimal model and the clamp techniques are concordant.

BACKGROUND: We investigated the concordance between glucose effectiveness (SG) and insulin sensitivity (SI), derived from the unmodified dynamic non-insulin-assisted intravenous glucose tolerance test (IVGTT) implemented by SG(MM) and SI(MM); simulation analysis and modelling/conversational interaction (SAAM/CONSAM) versus the eu/hyperglycaemic basal insulinaemic and the euglycaemic hyperinsulinaemic clamp (SG(CLAMP) and SI(CLAMP)). METHODS: Twenty-seven of 30 normoglycaemic subjects completed a (1) euglycaemic hyperinsulinaemic clamp, (2) 6-h eu/hyperglycaemic near-normoinsulinaemic pancreatic clamp with hyperglycaemia present over the final 2 h of the clamp (Day 2 study), (3) identical clamp to (2) but with euglycaemia maintained over the entire 6 h (Day 3 study) and (4) IVGTT. SG(CLAMP) was calculated in two ways based on data from study (2) alone (Day 2 SG(CLAMP210-240')) or from data from study day (2) and (3) (Day 2-3 SG(CLAMP330-360')). RESULTS: SG(MM) was unrelated to the magnitude of endogenous insulin release (AIR). The single-day (Day 2) and two-day (Day 2 and 3) SG(CLAMP) protocols correlated (r = 0.72, p = 0.003), but SG(CLAMP210-240') was significantly (p = 0.001) higher than SG(CLAMP330-360'). Employing the Day 2 and 3 SG(CLAMP) protocol, the whole body SG(CLAMP330-360') was similar to SG(MM) (1.80 ± 0.82 versus 1.73 ± 0.58 dL/min) and correlated (r = 0.45, p < 0.02). SG(CLAMP210-240') did not correlate with SG(MM) (r = 0.24). SI(MM) and SI(CLAMP) were similar (0.093 ± 0.060 versus 0.087 ± 0.029 dL/min per mU/L) and correlated (r = 0.76, p < 0.001). CONCLUSIONS: The time-dependent increase in glucose disposal observed during a prolonged 6-h clamp significantly influences the estimation of SG(CLAMP), and significant concordance coefficients are observed between SG(MM), and SG(CLAMP330-360'), and SI(MM) and SI(CLAMP).

The 4-mg intravenous dexamethasone suppression test in the diagnosis of Cushing's syndrome.

OBJECTIVE: Optimal diagnostic criteria for the 4-mg intravenous dexamethasone suppression test (IVDST) in patients with Cushing's syndrome (CS), compared with normal subjects, have not been established. We evaluated the performance of the 4-mg IVDST for differentiating CS from normal subjects and to define the responses in CS of various aetiologies. DESIGN, SUBJECTS, MEASUREMENTS: Thirty-two control subjects [normal and overweight/obese participants with or without type 2 diabetes) were prospectively studied, and data from 66 patients with Cushing's disease (CD), three with ectopic ACTH syndrome (EAS), 14 with adrenal Cushing's (AC)] and 15 with low probability of CS (LPC) from three tertiary hospitals were retrospectively evaluated. Dexamethasone was infused at 1 mg/h for 4 h. Plasma cortisol and ACTH were measured at -60 min (baseline), -5 min, +3 h, +4 h, +5 h and at +23 and +23.5 h on Day 2. RESULTS: Control subjects (including those with type 2 diabetes) exhibited a marked suppression of cortisol which was maintained until Day 2. Two of 15 patients with LPC had Day 2 cortisol results that overlapped with CS. Patients with CD demonstrated partial suppression, with rebound hypercortisolism on Day 2. Patients with AC and EAS did not suppress cortisol levels. Day 2 cortisol level of >130 nmol/l (or >20% of the baseline) diagnosed CS with 100% sensitivity and 96% specificity. CONCLUSION: While the IVDST allowed complete discrimination between control subjects and CS, 13% of LPC overlapped with CS. Given the small number of EAS, no conclusion can be drawn regarding the utility of this test in the differential diagnosis of CS.

Dexamethasone administration inhibits skeletal muscle expression of the androgen receptor and IGF-1--implications for steroid-induced myopathy.

CONTEXT: Glucocorticoids are a well-recognized cause of muscle weakness. The early effects of glucocorticoids on skeletal muscle (SkM) androgen and IGF-1 pathways have not been previously investigated in human subjects. OBJECTIVE: To determine if administration of the potent glucocorticoid dexamethasone down-regulates SkM androgen receptor and the IGF-1 signalling pathway. METHODS AND SUBJECTS: Twenty-four subjects (12 men and 12 women), including 12 with type 2 diabetes and 12 nondiabetics were enrolled. Venous blood sampling and biopsy of vastus lateralis were performed before and after administration of oral dexamethasone 4 mg/day for 4 days. MAIN OUTCOME MEASURES: Changes in plasma testosterone and IGF-1, SkM androgen receptor mRNA, SkM IGF-1mRNA and SkM IGF-1 receptor mRNA by quantitative RT-PCR after dexamethasone. RESULTS: Relative expression of SkM androgen receptor was similar in male (1.63 +/- 0.37) vs. female (1.57 +/- 0.30) subjects, despite the significant difference in plasma testosterone levels. Plasma IGF-1 and SkM expression of IGF-1 and IGF-1 receptor were also similar between males and females. Following dexamethasone, there was a significant down-regulation of SkM androgen receptor (1.60 +/- 0.23 vs. 1.11 +/- 0.16, P < 0.05) and IGF-1 (1.72 +/- 0.29 vs. 1.06 +/- 0.14, P < 0.05) mRNA, but no change in expression of the IGF-1 receptor. Plasma testosterone fell significantly in both sexes (male: 15.0 +/- 1.3 vs. 11.3 +/- 1.2 nmol/l, P < 0.01, female: 1.8 +/- 0.5 vs. 0.5 +/- 0.1 nmol/l, P < 0.05). CONCLUSIONS: Exogenous steroid excess results in relative androgen deficiency at two levels, reduced circulating testosterone and SkM androgen receptor mRNA, along with reduced SkM IGF-1 mRNA. These defects may contribute to the development of steroid-induced myopathy.

Skeletal muscle 11beta hydroxysteroid dehydrogenase type 1 activity is upregulated following elective abdominal surgery.

OBJECTIVE: Cortisol has been traditionally implicated in the causation of peri-operative skeletal muscle (SkM) insulin resistance, but cortisol levels return to normal within 72 h of surgery. Tissue cortisol bioactivity may be prolonged by local upregulation of the enzyme 11betaHSD1. We aimed to investigate the changes of SkM 11betaHSD1 enzyme activity and mRNA expression, relative to plasma cortisol, insulin and glucose levels following elective abdominal surgery. PATIENTS AND DESIGN: Eight non-diabetic subjects (two male, six female) underwent serial plasma hormone sampling and muscle biopsy of vastus lateralis at baseline and on day 5 following elective laparoscopic cholecystectomy. METHODS: SkM 11betaHSD1 and H6PDH mRNA levels were measured by quantitative RT-PCR and enzyme activity by % conversion of (3)H cortisone to cortisol. Plasma glucose, insulin, free fatty acids (FFA), tumour necrosis factor-alpha and cortisol by standardised assays. RESULTS: Compared with baseline, SkM 11betaHSD1 activity was significantly increased on day 5 after surgery (14.7+/-2.1 vs 20.4+/-3.2%, P=0.005). Neither 11betaHSD1 nor H6PDH mRNA levels were altered after surgery. Plasma cortisol (P=0.027), FFA (P=0.01) and glucose (P=0.004) rose rapidly following surgery and had returned to baseline values by 24 h post-surgery. There was no significant change in plasma insulin. CONCLUSIONS: This is the first study to demonstrate an upregulation of SkM 11betaHSD1 activity in response to a physiological stressor. Sustained activation of this enzyme may increase tissue cortisol bioactivity.

Adiponectin, skeletal muscle adiponectin receptor expression and insulin resistance following dexamethasone.

OBJECTIVE: Skeletal muscle is a major site of adiponectin action and of glucocorticoid-induced insulin resistance. Little human data exist however, regarding the impact of exogenous glucocorticoids on adiponectin receptors in skeletal muscle. DESIGN AND PATIENTS: Twelve subjects with type 2 diabetes and 12 controls underwent blood sampling and muscle biopsy of vastus lateralis before and after 4 days of 4 mg dexamethasone. MEASUREMENTS: (i) Total and high molecular weight (HMW) plasma adiponectin, glucose and insulin; (ii) Skeletal muscle adiponectin receptor AdipoR1 and AdipoR2 mRNA levels by quantitative real time RT-PCR. RESULTS: Baseline total adiponectin (8.0 +/- 0.89 vs. 12.5 +/- 1.46 microg/ml, P = 0.013), HMW adiponectin (2.8 +/- 0.44 vs. 5.9 +/- 1.04 microg/ml, P = 0.014) and AdipoR2 mRNA levels (mean DeltaC(T )14.71 +/- 0.35 vs. 13.37 +/- 0.28, P = 0.017) were significantly lower in diabetic subjects. After dexamethasone, AdipoR2 mRNA fell in the controls but there was no change in the diabetic group, while there was a significant increase in total (P = 0.002) and HMW adiponectin (P < 0.001) across both groups. Total and HMW plasma adiponectin correlated with clinical and biochemical measures of insulin sensitivity. However following dexamethasone which increased insulin resistance, the relationship between adiponectin and the biochemical measures was lost. CONCLUSIONS: Plasma adiponectin and skeletal muscle AdipoR2 mRNA expression are reduced in subjects with diabetes; both are likely to contribute to the observed insulin resistance. Dexamethasone inhibits AdipoR2 mRNA expression in nondiabetic subjects, while there is a small rise in plasma adiponectin levels. The close relationship between plasma adiponectin and biochemical measures of insulin sensitivity is lost in the setting of glucocorticoid-induced insulin resistance.

Altered activity of 11beta-hydroxysteroid dehydrogenase types 1 and 2 in skeletal muscle confers metabolic protection in subjects with type 2 diabetes.

CONTEXT: There is little information regarding the regulation of 11beta-hydroxysteroid dehydrogenase (11beta-HSD) enzymes in skeletal muscle in the setting of type 2 diabetes. OBJECTIVE: Our objective was to investigate whether there is differential mRNA expression and enzyme activity of 11beta-HSD1 and 11beta-HSD2 in the skeletal muscle of diabetic subjects compared with controls at baseline and in response to dexamethasone. DESIGN: Participants underwent muscle biopsy of vastus lateralis at baseline and after dexamethasone. SETTING: The study took place at a university teaching hospital. PARTICIPANTS: Twelve subjects with type 2 diabetes and 12 age- and sex-matched controls participated. INTERVENTION: Subjects were given oral dexamethasone, 4 mg/d for 4 d. MAIN OUTCOME MEASURES: We assessed 11beta-HSD1, 11beta-HSD2, and H6PDH mRNA levels by quantitative RT-PCR and enzyme activity by percent conversion of [(3)H]cortisone and [(3)H]cortisol, respectively. RESULTS: At baseline, mRNA levels were similar in diabetic and control subjects for 11beta-HSD1, 11beta-HSD2, and H6PDH. 11beta-HSD1 activity was reduced in diabetic subjects (percent conversion of [(3)H]cortisone to [(3)H]cortisol was 11.4 +/- 2.5% vs. 18.5 +/- 2.2%; P = 0.041), and 11beta-HSD2 enzyme activity was higher in diabetic subjects (percent conversion of [(3)H]cortisone to [(3)H]cortisol was 17.2 +/- 2.6% vs. 9.2 +/- 1.3%; P = 0.012). After dexamethasone, 11beta-HSD1 mRNA increased in both groups (P < 0.001), whereas 11beta-HSD2 mRNA decreased (P = 0.002). 11beta-HSD1 activity increased in diabetic subjects (P = 0.021) but not in controls, whereas 11beta-HSD2 activity did not change in either group. At baseline, there was a significant negative correlation between 11beta-HSD1 and 11beta-HSD2 enzyme activity (r = -0.463; P = 0.026). CONCLUSIONS: The activities of skeletal muscle 11beta-HSD1 and 11beta-HSD2 are altered in diabetes, which together may reduce intracellular cortisol generation, potentially conferring metabolic protection.

11Beta hydroxysteroid dehydrogenase type 1 is expressed and is biologically active in human skeletal muscle.

OBJECTIVE: No data exist regarding the distribution and oxoreductase enzyme activity of 11beta hydroxysteroid dehydrogenase type 1 (11beta HSD-1) in fresh human skeletal muscle. We aimed to investigate the mRNA and protein expression of 11beta HSD-1 in fresh skeletal muscle, confirm its biological activity and determine its relationship with hexose-6-phosphate dehydrogenase (H6PDH). We also examined the muscle fibre localization of 11beta HSD-1. DESIGN: Eleven non-diabetic community volunteers underwent muscle biopsy of vastus lateralis. MEASUREMENTS: (i) 11beta HSD-1 and H6PDH mRNA expression by quantitative reverse transcription polymerase chain reaction (RT-PCR); (ii) protein localization and fibre type specificity by immunohistochemistry; and (iii) enzyme oxoreductase activity by percentage conversion of 3H cortisone to cortisol. RESULTS: 11beta HSD-1 mRNA was expressed at low levels compared to human liver. Mean DeltaCT of skeletal muscle in 11 subjects was 19.57 (range 18.40-20.79) compared to DeltaCT of 12.75 in human liver, which equates to an approximate 100-fold higher level of expression. H6PDH mRNA was also detected with a mean DeltaCT of 14.46 (range 13.13-16.60), approximately 35-fold more abundant than 11beta HSD-1 in skeletal muscle. There was a significant correlation between 11beta HSD-1 and H6PDH (r = 0.67, P = 0.03). 11beta HSD-1 immunostaining was present in all muscle specimens, with similar distribution among fast and slow twitch fibres. 11beta HSD-1 oxoreductase activity was demonstrated, with mean conversion of cortisone to cortisol of 17.7% per 200 mg of muscle per 24 h (range 7.1-29.5%). CONCLUSIONS: 11beta HSD-1 mRNA and protein is expressed in fresh human skeletal muscle along with readily demonstrable oxoreductase activity. 11beta HSD-1 localization is not muscle fibre type specific. High levels of skeletal muscle H6PDH should ensure that oxoreductase activity predominates in vivo.

Impact of in vivo fatty acid oxidation blockade on glucose turnover and muscle glucose metabolism during low-dose AICAR infusion.

AMPK plays a central role in influencing fuel usage and selection. The aim of this study was to analyze the impact of low-dose AMP analog 5-aminoimidazole-4-carboxamide-1-beta-d-ribosyl monophosphate (ZMP) on whole body glucose turnover and skeletal muscle (SkM) glucose metabolism. Dogs were restudied after prior 48-h fatty acid oxidation (FA(OX)) blockade by methylpalmoxirate (MP; 5 x 12 hourly 10 mg/kg doses). During the basal equilibrium period (0-150 min), fasting dogs (n = 8) were infused with [3-(3)H]glucose followed by either 2-h saline or AICAR (1.5-2.0 mg x kg(-1) x min(-1)) infusions. SkM was biopsied at completion of each study. On a separate day, the same protocol was undertaken after 48-h in vivo FA(OX) blockade. The AICAR and AICAR + MP studies were repeated in three chronic alloxan-diabetic dogs. AICAR produced a transient fall in plasma glucose and increase in insulin and a small decline in free fatty acid (FFA). Parallel increases in hepatic glucose production (HGP), glucose disappearance (R(d tissue)), and glycolytic flux (GF) occurred, whereas metabolic clearance rate of glucose (MCR(g)) did not change significantly. Intracellular SkM glucose, glucose 6-phosphate, and glycogen were unchanged. Acetyl-CoA carboxylase (ACC approximately pSer(221)) increased by 50%. In the AICAR + MP studies, the metabolic responses were modified: the glucose was lower over 120 min, only minor changes occurred with insulin and FFA, and HGP and R(d tissue) responses were markedly attenuated, but MCR(g) and GF increased significantly. SkM substrates were unchanged, but ACC approximately pSer(221) rose by 80%. Thus low-dose AICAR leads to increases in HGP and SkM glucose uptake, which are modified by prior FA(ox) blockade.

Do adiponectin, TNFalpha, leptin and CRP relate to insulin resistance in pregnancy? Studies in women with and without gestational diabetes, during and after pregnancy.

BACKGROUND: The role of adiponectin, tumour necrosis factor alpha (TNFalpha), leptin and C-reactive protein in the insulin resistance of pregnancy is not clear. We measured their levels in women with gestational diabetes (GDM) and in controls, during and after pregnancy, and related them to insulin secretion and action. METHODS: Nineteen women with GDM and 19 BMI-matched healthy pregnant women underwent intravenous glucose tolerance tests in the third trimester of pregnancy and 4 months postpartum to determine insulin sensitivity (SI) and insulin secretion. Adiponectin, TNFalpha, leptin and high sensitivity CRP (hsCRP) were measured in fasted blood. RESULTS: Of the circulating factors, only leptin (r = -0.41, p = 0.01) correlated with SI in pregnancy. Leptin and hsCRP levels were elevated in pregnancy compared to postpartum (leptin (mean +/- SEM): 27.8 +/- 2.4 vs 19.3 +/- 2.1 ng/mL, p < 0.001; hsCRP: 5.2 +/- 0.7 vs 3.2 +/- 0.6 mg/L, p < 0.001). Adiponectin levels did not change from pregnancy to postpartum, despite a marked increase in SI. All four factors correlated with SI postpartum (adiponectin: r = 0.38, p = 0.01; TNFalpha: r = -0.48, p = 0.002; Leptin: r = -0.61, p = 0.001; hsCRP: r = -0.48, p = 0.002). TNFalpha correlated inversely with insulin secretion in pregnancy (r = -0.35, p = 0.03) and was significantly higher in the GDM group (2.62 +/- 0.3 vs 1.88 +/- 0.3 pg/mL, p = 0.01) in pregnancy. CONCLUSION: In our study, the influence of adiponectin, TNFalpha and hsCRP upon SI is overwhelmed by other factors in pregnancy. While leptin and SI correlated in pregnancy, it is unclear whether this represents cause or effect. Finally, TNFalpha may exert an inhibitory effect on insulin secretion in GDM, contributing to the associated hyperglycaemia.

Prevailing hyperglycemia is critical in the regulation of glucose metabolism during exercise in poorly controlled alloxan-diabetic dogs.

The separate impacts of the chronic diabetic state and the prevailing hyperglycemia on plasma substrates and hormones, in vivo glucose turnover, and ex vivo skeletal muscle (SkM) during exercise were examined in the same six dogs before alloxan-induced diabetes (prealloxan) and after 4-5 wk of poorly controlled hyperglycemic diabetes (HGD) in the absence and presence of approximately 300-min phlorizin-induced (glycosuria mediated) normoglycemia (NGD). For each treatment state, the approximately 15-h-fasted dog underwent a primed continuous 150-min infusion of [3-(3)H]glucose, followed by a 30-min treadmill exercise test (approximately 65% maximal oxygen capacity), with SkM biopsies taken from the thigh (vastus lateralis) before and after exercise. In the HGD and NGD states, preexercise hepatic glucose production rose by 130 and 160%, and the metabolic clearance rate of glucose (MCRg) fell by 70 and 37%, respectively, compared with the corresponding prealloxan state, but the rates of glucose uptake into peripheral tissues (Rd(tissue)) and total glycolysis (GF) were unchanged, despite an increased availability of plasma free fatty acid in the NGD state. Exercise-induced increments in hepatic glucose production, Rd(tissue), and plasma-derived GF were severely blunted by approximately 30-50% in the NGD state, but increments in MCRg remained markedly reduced by approximately 70-75% in both diabetic states. SkM intracellular glucose concentrations were significantly elevated only in the HGD state. Although Rd(tissue) during exercise in the diabetic states correlated positively with preexercise plasma glucose and insulin and GF and negatively with preexercise plasma free fatty acid, stepwise regression analysis revealed that an individual's preexercise glucose and GF accounted for 88% of Rd(tissue) during exercise. In conclusion, the prevailing hyperglycemia in poorly controlled diabetes is critical in maintaining a sufficient supply of plasma glucose for SkM glucose uptake during exercise. During phlorizin-induced NGD, increments in both Rd(tissue) and GF are impaired due to a diminished fuel supply from plasma glucose and a sustained reduction in increments of MCRg.

Skeletal muscle basal AMP-activated protein kinase activity is chronically elevated in alloxan-diabetic dogs: impact of exercise.

The effect of diabetes and exercise on skeletal muscle (SkM) AMP-activated protein kinase (AMPK)alpha1 and -alpha2 activities and site-specific phosphorylation of acetyl-CoA carboxylase was examined in the same six dogs before alloxan (35 mg/kg)-induced diabetes (C) and after 4-5 wk of suboptimally controlled hyperglycemic and hypoinsulinemic diabetes (DHG) in the presence and absence of 300-min phlorizin (50 microg.kg-1.min-1)-induced "normoglycemia" (DNG). In each study, the dog underwent a 150-min [3-3H]glucose infusion period, followed by a 30-min treadmill exercise test (60-70% maximal oxygen capacity) to measure the rate of glucose disposal into peripheral tissues (Rdtissue). SkM biopsies were taken from the thigh (vastus lateralis) before and immediately after exercise. In the C and DHG states, the rise in plasma free fatty acids (FFA) with exercise ( approximately 40%) was similar. In the DNG group, preexercise FFA were significantly higher, but the absolute rise in FFA with exercise was similar. However, the exercise-induced increment in Rdtissue was significantly blunted (by approximately 40-50%) in the DNG group compared with the other states. In SkM, preexercise AMPKalpha1 and -alpha2 activities were significantly elevated (by approximately 60-125%) in both diabetic states, but unlike the C group these activities did not rise further with exercise. Additionally, preexercise acetyl-CoA carboxylase phosphorylation in both diabetic states was elevated by approximately 70-80%, but the increases with exercise were similar to the C group. Preexercise AMPKalpha1 and -alpha2 activities were negatively correlated with Rdtissue during exercise for the combined groups (both P < 0.02). In conclusion, the elevated preexercise SkM AMPKalpha1 and -alpha2 activities contribute to the ongoing basal supply of glucose and fatty acid metabolism in suboptimally controlled hypoinsulinemic diabetic dogs; but whether they also play a permissive role in the metabolic stress response to exercise remains uncertain.