Decreased insulin binding to pancreatic islets of genetically obese (fa/fa) rats

Binding of insulin and insulin secretion were studied in isolated pancreatic islets of homozygous obese fa/fa rats, their lean littermates (Fa/?) and Wistar rats. Despite normoglycemia fa/fa rats exhibit hyperinsulinemia. Glucose-induced insulin secretion from pancreatic islets in vitro was increased by more than 50% in fa/fa rats compared with islets of lean littermates and normal Wistar rats when calculated per microgram islet protein. Exogenous insulin inhibited glucose (16.7 mM)-induced insulin secretion in islets of either of these rats, and maximum inhibition was rather the same (secretion was reduced by 62.3-65.6%). However, the EC50 (half-maximal effective concentration) for inhibition was increased in fa/fa rats being 1.4 +/- 0.1 nM compared with 0.6 +/- 0.2 and 0.5 +/- 0.2 nM in lean littermates and Wistar rats, respectively (P less than 0.05 vs. fa/fa rats). Islets of fa/fa rats found 24% less [125I]insulin (P less than 0.01) than islets of lean littermates and of Wistar rats. Scatchard analysis of data of displacement of [125I]insulin binding by native insulin showed 2 binding sites; a decrease in the number of high affinity insulin binding sites (Bmax) from 4.2 +/- 1.3 and 4.7 +/- 1.6 fmol/mg protein to 2.6 +/- 0.7 fmol/mg protein was calculated when islets of lean littermates and normal Wistar rats were compared to islets of fa/fa rats. The Kd of the high affinity binding site was not changed (0.77 +/- 0.06, 0.78 +/- 0.11 and 0.61 +/- 0.14 nM, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased insulin binding of erythrocytes and insulin sensitivity in adrenal insufficiency

We have studied 125I-insulin binding to erythrocytes (RBC) in five patients with hypoadrenocortisolism, and compared to 17 normal subjects and in nine patients with Cushing's syndrome. In another study insulin sensitivity index (ISI) was measured by the IV insulin tolerance test in four patients with hypoadrenocortisolism (1.82 +/- 0.15 mg/dL/min), and compared to 19 normal subjects and 23 patients with Cushing's syndrome (1.56 +/- 0.1 mg/min/dL). Mean insulin binding in hypocortisolism was 17.9 +/- 0.7%, and was significantly higher (P less than .01) than in normal subjects (12.0 +/- 1.4%) and was significantly (P less than .001) decreased toward normal (11.8 +/- 1.47) during replacement therapy. Increased binding in untreated hypoadrenocortisolism was due to elevated high affinity site receptor concentration as compared to the treated patients (0.10 +/- 0.015 v 0.053 +/- 0.003 nmol/L,P less than .01). These results suggest that increased insulin binding in chronic hypoadrenocortisolism may be attributed to increased insulin binding to the receptor, which can revert to normal by replacement therapy. The role of increased insulin binding to increased insulin sensitivity in hypoadrenocortisolism is discussed.     

The influence of caloric deprivation and food composition on TSH, thyroid hormones and nuclear binding of T3 in mononuclear blood cells in obese women

In vivo changes in thyroid-stimulating hormone (TSH), thyroxin (T4), triiodothyronine (T3) and nuclear binding of T3 (NBT3) in mononuclear blood cells were studied in obese women during seven days of caloric deprivation (maximum 1,100 kcal/d). In seven women given a high protein diet (80% protein, 7% carbohydrates, 7% fat) and in two women who fasted (group 1), total T3 (TT3) decreased from 1.66 +/- 0.43 nmol/L to 1.11 +/- 0.32 nmol/L (P less than .01), free T3 (FT3) decreased from 5.7 +/- 1.1 pmol/L to 4.3 +/- 1.6 pmol/L (P less than .01), and free T4 (FT4) increased from 17.8 +/- 2.3 pmol/L to 21.1 +/- 2.0 pmol/L (P less than .01). In five women given a carbohydrate diet (Dextrin-maltose 100%) (group 2), thyroid hormones were unchanged, TT3 was at start 1.66 +/- 0.24 nmol/L and after seven days 1.43 +/- 0.26 nmol/L (NS), FT3 changed from 6.4 +/- 1.8 pmol/L to 6.0 +/- 2.1 pmol/L (NS) and FT4 changed from 20.4 +/- 5.1 pmol/L to 20.6 +/- 3.1 pmol/L (NS). The caloric intake and the weight reduction was the same in the two groups. Basal TSH and TSH after thyrotropin-releasing hormone (TRH) (TSH+30min) declined in both groups. In group 1, basal TSH declined from 1.88 +/- 1.07 microU/mL (P less than .03), and TSH+30min declined from 12.44 +/- 7.49 microU/mL to 9.38 +/- 5.97 microU/mL (P less than .03). In group 2, basal TSH declined from 2.09 +/- 0.87 microU/mL to 1.66 +/- 0.92 microU/mL (P less than .03), and TSH+30min declined from 15.63 +/- 7.90 microU/mL to 11.93 +/- 7.20 microU/mL (NS).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of low-protein diet and testosterone on sex hormone-binding globulin capacity in male rabbits

The effects of a low-protein high-carbohydrate (LPHC) diet (8% protein 65% to 72% carbohydrate) were compared to those of regular rabbit chow (14% to 16% protein 57% to 64% carbohydrate) on sex hormone-binding globulin (SHBG) capacity in 12 male rabbits. The six rabbits who were fed the LPHC diet for 8 weeks showed a significant increase in their mean SHBG capacity (mean +/- SE: from 70 +/- 16 nmol/L to 332 +/- 45 nmol/L, P less than .01) whereas the six rabbits fed the standard diet showed a slight decrease (from 106 +/- 22 nmol/L to 76 +/- 20 nmol/L, NS). These changes in SHBG capacity were mirrored by a decrease in percent-free T (from 2.64 +/- 0.26% to 1.64 +/- 0.16%, P less than .01) in the LPHC diet group and no change in percent-free T in the regular diet group (from 2.36 +/- 0.21% to 2.19 +/- 0.10%). The changes in SHBG capacity and percent-free T were not associated with significant changes in testosterone (T), free T, estradiol (E2), thyroxine, triiodothyronine, thyroxine-binding globulin, or cortisol binding globulin levels. In a subsequent experiment, testosterone cyclopentyl propionate (TCP) was administered to six male rabbits while on regular rabbit chow and again after 6 weeks of the LPHC diet. TCP administration did not cause any significant change in the SHBG capacity, but the LPHC resulted again in a significant (P less than .05) increase in SHBG capacity from 80 +/- 18 nmol/L. to 198 +/- 22 nmol/L.(ABSTRACT TRUNCATED AT 250 WORDS)     

Insulin inhibits glucagon-induced glycogenolysis normally in perivenous hepatocytes of Wistar fatty rats

Wistar fatty (WF) rats are obese, hyperinsulinemic and hyperglycemic, and thus a model of type 2 diabetes mellitus. Since we have found that insulin specifically inhibits glucagon-induced glycogenolysis in perivenous hepatocytes (PVH) from normal rats, we examined the inhibitory effect of insulin on glucagon-induced glycogenolysis in PVH of hyperinsulinemic WF rats. Basal glucose release was 64.0+/-4.1 nmol/mgprotein/30 min from PVH of lean littermates (WL rats) and 137.0+/-19.3 nmol/mgprotein/30 min from that of WF rats (p<0.01). These were proportional to the glycogen content in PVH of WL and WF rats (56.7+/-7.2 and 131.0+/-20.3 microg/mgprotein, p<0.01), and increased to 109.0+/-8.8 and 225.8+/-17.9nmol/mgprotein/30min, respectively, with 0.1 nmol/l glucagon. When 10 nmol/l insulin was coincubated, 0.1 nmol/l glucagon-induced increase in glucose release decreased to 93.3+/-10.9 nmol/mgprotein/30 min in PVH of WL rats (p<0.01) and to 181+/-20.7 nmol/mgprotein/30 min in PVH of WF rats (p<0.01). Thus, insulin antagonized glucagon-induced glycogenolysis in PVH similarly between WL and WF rats, to 56.7+/-13.3% and to 46.1+/-7.5%, respectively. Thus, the antagonizing effect of insulin on glucagon-induced increase in glycogenolysis was preserved in PVH of hyperinsulinemic and hyperglycemic WF rats.     

Effects of chromium picolinate supplementation on insulin sensitivity, serum lipids, and body weight in dexamethasone-treated rats

Chromium (Cr) is essential for the regulation of insulin action, and Cr supplementation has been studied as a potential therapy of insulin resistance and lipid abnormalities. Corticosteroid treatment is well known to cause the abnormality of carbohydrate metabolism. Recently, it has been reported that corticosteroid increases urinary loss of Cr, and Cr supplementation recovers steroid-induced diabetes mellitus. In this experiment, rats were treated daily with dexamethasone (DEX) (0.2 mg/kg, intraperitoneal [IP]) for the first 7 days and were further treated with DEX plus either chromium picolinate (CrP, 30 mg/kg/d) orally or a placebo for a period of 14 days. At the end of experiment (D21), the control rats, which were treated only with DEX weighed 320 g (80% of initial weight) on average, but CrP-treated rats weighed 364 g (91% of initial weight. P <.05). Glucose tolerance tests (GTTs) and insulin sensitivity tests were conducted. During insulin sensitivity tests, the area under the curve (AUC(0-->120)) of the time-glucose concentrations curves in CrP-treated group were decreased compared with those in the control group (271.4 +/- 74.9 v 1,097.4 +/- 722.2 mmol/L/min, P <.01). Fasting serum insulin levels in CrP-treated rats were clearly decreased by 46.9% compared with those in the control group (0.52 +/- 0.19 v 0.98 +/- 0.36 nmol/L, P <.05). During the GTTs, the AUC(0-->120) for time-glucose concentrations curves in CrP-treated group was not significantly different from the control group, but the AUC(0-->120) of serum insulin concentrations in the CrP-treated group were 55.8% lower than those in the control group (123.1 +/- 42.5 v 278.2 +/- 59.1 nmol/L/min, P <.01). The mean AUC(0-->120) of time-cholesterol concentration curves during GTTs did not significantly differ between the 2 groups (867.6 +/- 155.2 v 827.7 +/- 94.3 mmol/L/h, P = not significant [NS]). In contrast, 1-hour and 2-hour plasma triglycerides were significantly lower in the CrP-treated group, and the mean AUC of the time-triglyceride curve was significantly lower in CrP-treated group than in the control group (3.4 +/- 0.5 v 5.9 +/- 1.3 mmol/L/h, P <.05). We suggest that Cr supplementation in DEX-treated rats can relatively reverse a catabolic state and increase insulin sensitivity. Our results support the hypothesis that Cr supplementation can be considered to improve carbohydrate and lipid metabolism in patients receiving corticosteroid treatment.     

Postnatal growth and fatty acid synthesis in overgrown rat pups induced by fetal hyperinsulinemia

Fetal hyperinsulinemia in the rat results in increased body weight, lipid content, and enhanced lipogenesis in liver and carcass. The purpose of our study was to determine whether the macrosomia and enhancement of fatty acid (FA) synthesis and/or content persisted postnatally in this animal model. Fetal hyperinsulinemia was produced in Sprague-Dawley rats by injecting fetuses with 2 units of insulin at 20.5 days of gestation. Alternate pups in the same litter were injected with saline. Pups were delivered surgically at 22.5 days of gestation, were weighed daily and sacrificed on day 15. FA content and synthesis rates of liver and skeletal muscle were measured. We found: (1) At birth, insulin-treated pups were 12% heavier than saline littermates, (5.88 +/- 0.14 g v 5.26 +/- 0.14 g, P less than .01); and (2) The enhanced growth associated with prenatal insulin treatment persisted during the suckling period, ie, compared with saline-treated controls, insulin pups were 15.7% heavier at 15 days of age (P less than .01); growth velocity of insulin pups, beginning on day 3, significantly exceeded that of control pups (P less than .05). FA contents of liver and muscle in insulin pups, (62.6 +/- 5.7 mumol/g and 62.7 +/- 13.2 mumol/g) were significantly greater (P less than .05) than in saline littermates (45.1 +/- 5.6 mumol/g and 30.2 +/- 4.7 mumol/g, respectively). We conclude that.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chronic undernutrition may accentuate the beta cell dysfunction of type 2 diabetes

Seven undernourished and seven obese, insulin-requiring type 2 diabetic subjects, who were matched for age, sex, and duration of diabetes, were subjected to oral glucose tolerance tests. Although fasting glucose and free insulin levels were similar in both groups, glucose tolerance was markedly worse in the undernourished subjects, with a mean incremental glucose area (+/- SE) of 22.8 +/- 2.3 mmol/l.h vs. 12.4 +/- 1.3 in the obese diabetic subjects (P less than 0.001). The incremental insulin response (area under the curve) to oral glucose in the undernourished group (39.3 +/- 7.9 mU/l.h) was 50% lower than the response in both the obese group (89.2 +/- 19.9, P less than 0.001) and a group of non-diabetic, normal weight-for-height subjects (77.1 +/- 5.7, P less than 0.01). Peak insulin levels were similarly reduced to approximately half the levels seen in the obese and control groups (P less than 0.01). Undernutrition is known to impair both glucose tolerance and insulin secretory reserve by reducing the beta cell number, size, and granulation. It is concluded that chronic undernutrition accentuates beta cell dysfunction in undernourished diabetics, leading to increased glucose intolerance.     

Fat distribution, endocrine and metabolic profile in obese women with and without hirsutism

The relationship between adipose tissue distribution, androgen levels, and metabolic complications of obesity was studied in 20 hirsute and 20 nonhirsute obese premenopausal women. The group of hirsute women showed preferentially an upper body type of obesity as assessed by the waist-to-hip ratio (0.902 + 0.017 v 0.778 +/- 0.015, P less than .01). They had higher serum concentrations of total testosterone (100.4 + 11.7 v 48.8 +/- 4.5 ng/dL, P less than .01) and lower levels of serum sex-hormone-binding globulin (28.1 +/- 3.6 v 44.0 + 4.2 nmol/L, P less than .05) exhibiting an increased androgenic activity as compared to the nonhirsute women. Serum glucose and insulin levels after an oral glucose load were significantly higher in the hirsute women. In addition, the group of hirsute females has significantly higher fasting concentrations of total cholesterol (5.82 +/- 0.28 v 4.75 +/- 0.14 mmol/L, P less than .05) and triglycerides (2.51 +/- 0.38 v 1.14 +/- 0.10 mmol/L, P less than .01). The hirsute group also showed higher systolic (166.7 +/- 5.1 v 142.1 +/- 4.5 mm Hg, P less than .01) and diastolic (100.9 +/- 3.6 v 85.2 +/- 2.5 mm Hg, P less than .01) blood pressure values than the nonhirsute women. Analysis of correlation revealed that an increasing waist-to-hip ratio was accompanied by increasing testosterone levels (r = .39, P less than .05) and by decreasing sex-hormone-binding globulin levels (r = .37, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of aging on glucose metabolism in adipocytes from Fischer rats

We have studied glucose metabolism in adipocytes from younger (6 months) and older (24 months) Fischer rats. Insulin binding was similar in both groups, expressed per cell number (2.67 +/- 0.41% vs. 2.96 +/- 0.38%) or per cell surface area (4.59 +/- 0.70% vs. 4.15 +/- 0.53%) in the 6- and 24-month-old animals, respectively. Maximal insulin-stimulated 3-O-methylglucose transport was decreased by 40% in the older group (0.234 +/- 0.032) compared with that in the younger group (0.411 +/- 0.031 pmol/2 X 10(9) micron 2 X sec (P less than 0.01), with no change in basal rates of transport. The decrease in glucose transport was due to a 36% reduction in the maximum velocity (91 pmol/sec in the younger vs. 59 pmol/sec in the older group), with no change in the Km. Postglucose transport steps of glucose metabolism, including CO2 oxidation, triglyceride synthesis, and lactate production, were measured at a higher glucose concentration (2 mM), where glucose transport is not rate limiting. Overall maximal insulin-stimulated glucose metabolism was decreased by 45% in the older group (15.6 nmol) compared with that in the younger group (28.6 nmol/10(5) cells X h; P less than 0.05). Glucose oxidation was decreased by 42% (2.9 vs. 5.0 nmol/10(5) cells X h; P less than 0.05), triglyceride synthesis by 40% (5.9 vs. 9.8 nmol/10(5) cells X h; P less than 0.05), and lactate production by 47% (6.3 vs. 11.8 nmol/10(5) cells X h; P less than 0.05). We conclude that in adipocytes from aged Fischer rats, cellular insulin resistance is due to multiple post-binding defects involving the glucose transport system and more distal intracellular processes.     

Effects of caloric restriction and exercise on insulin receptors in obesity: association with changes in membrane lipids

We have studied the effects of supervised caloric restriction and exercise on mononuclear leukocyte lipid composition, membrane fluidity, and insulin receptors in ten nondiabetic obese adults, (175 +/- 9.3% of ideal body weight) and ten normal adult subjects. In a second study, we examined the effects of caloric restriction alone using a very low calorie liquid diet in the treatment of another ten obese adults. In both groups of obese adults, fasting insulin levels were elevated and fell to normal levels following treatment. Insulin binding to monocytes, which was reduced in obese subjects, increased toward normal after short-term treatment; this was due to the restoration of total insulin binding capacity to levels one half of that seen in the normal adult group. Obese subjects undergoing either treatment had elevated membrane cholesterol/phospholipid ratios prior to treatment (0.499 +/- 0.050 and 0.446 +/- 0.011 v 0.400 +/- 0.025 mol/mol in normal adults P less than 0.005 by ANOVA). Prior to treatment, for all subjects there was a significant inverse correlation between insulin tracer binding and membrane cholesterol/phospholipid ratios (r = .484, n = 34, P less than 0.005). This relationship did not change significantly in obese subjects in either treatment group. Cell membrane microviscosity was determined by fluorescence polarization (FP) using DPH (2 X 10(-6) mol/L). Prior to weight loss, obese subjects had significantly higher FP values than controls (0.304 +/- 0.006 and 0.319 v 0.259 +/- 0.009, P less than 0.005, by ANOVA) indicating greater microviscosity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antidiabetic agent englitazone enhances insulin action in nondiabetic rats without producing hypoglycemia

The new antihyperglycemic agent englitazone (CP-68,722) was examined in nondiabetic rats. Administration of englitazone at 50 mg/kg/d for 8 days did not produce overt hypoglycemia but it lowered basal plasma insulin by 59% and 41% in rats fed ad libitum and fasted overnight on the last day, respectively. Drug treatment also lowered (P less than .05) plasma nonesterified fatty acids (1.09 +/- 0.05 to 0.36 +/- 0.05 mmol/L) and cholesterol (2.41 +/- 0.08 to 2.06 +/- 0.07 mmol/L) in fasted rats, and glycerol (0.25 +/- 0.02 to 0.14 +/- 0.02 mmol/L) in fed rats but had no effect on 3-hydroxybutyrate or lactate levels despite the hypoinsulinemia. Disposition of an oral glucose load (1 g/kg) in drug-treated fed rats was identical to that in control rats despite a 40% reduction in the area under the plasma insulin curve. Insulin-stimulated 2-deoxy-D-3H-glucose uptake was significantly (P less than .05) enhanced in adipocytes prepared from both fasted and fed drug-treated rats (0.56 +/- 0.07 to 0.84 +/- 0.03 and 0.79 +/- 0.02 to 1.00 +/- 0.02 nmol/5 min, respectively, at insulin concentration of 2,500 microU/mL). There was also a significant increase in the basal rate of 2-deoxyglucose uptake (0.07 +/- 0.01 to 0.24 +/- 0.07 nmol/5 min) in adipocytes from fasted rats only. Insulin-stimulated lipogenesis from 3H-2-glucose was enhanced in adipocytes from drug-treated fed rats (7.72 +/- 0.09 to 10.19 +/- 0.10 nmol glucose/45 min at insulin concentration of 2,500 microU/mL) but no effect was observed in adipocytes from fasted rats (2.57 +/- 0.30 to 2.33 +/- 0.16 nmol glucose/45 min).(ABSTRACT TRUNCATED AT 250 WORDS)     

Adrenodemedullation does not impair the beneficial effect of physical training in streptozotocin-diabetic rats.

This study was designed to ascertain if the improvement in glucose homeostasis found in diabetic animals submitted to physical training is due to an increased secretion of epinephrine by the adrenal medullae. Male Wistar rats were surgically adrenodemedullated (ADM group) or sham-operated (SHAM group). After a 3-week recovery period, a bolus of streptozotocin (40 mg/kg) was injected intravenously (IV), and the animals presenting 1 week later with a blood glucose value between 14 and 22 mmol/L were retained in the protocol and randomly assigned to a sedentary (SHAM-DS and ADM-DS) or trained (SHAM-DT and ADM-DT) group. Physical training was done on a treadmill according to a 10-week progressive program. An IV glucose tolerance test (0.5 g/kg) was performed in previously cannulated rats, 64 hours after the last bout of exercise. Pancreatic insulin and glucagon content was also determined. In sedentary diabetic rats, adrenodemedullation had no effect on plasma glucose, insulin, or glucagon levels, neither in the basal state nor following the glucose load. Basal glucose levels were diminished by training in both SHAM (16.1 +/- 1.5 v 21.8 +/- 0.4 mmol/L; P less than .01) and ADM (12.4 +/- 1.7 v 21.1 +/- 1.2 mmol/L; P less than .01) groups, with values lower in ADM-DT than in SHAM-DT rats (P less than .05). After glucose loading, the glucose levels were significantly lower (P less than .01) throughout the test in both SHAM-DT and ADM-DT rats than in their sedentary counterparts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reduced action of insulin glargine on protein and lipid metabolism: possible relationship to cellular hormone metabolism

Insulin analogues are used in the treatment of diabetes to mimic physiological insulin secretion. Glargine is used to provide basal insulin levels. Previous work has shown no differences in glucose uptake when glargine was compared to native insulin. The action of insulin on protein and lipid metabolism is studied infrequently, but these important actions should be considered with insulin analogues. In HepG2 cells, protein degradation was inhibited significantly less by glargine (15% over 3 hours) than by insulin (approximately 20% over 3 hours) (P < .05). Lipid metabolism was investigated in 3T3-L1 cells. In these cells glucose oxidation to CO2 was effected equally, but glargine was less potent than insulin at inhibiting epinephrine-stimulated lipolysis (EC50 = 1.4 v 0.35 nmol/L, P < .001) and at stimulating lipogenesis (EC50 = 1.27 v 8.06 nmol/L, P < .01). Since the action of insulin on protein and lipid metabolism has been suggested to be due to the metabolism of the hormone, we compared the cellular handling of 125I[A14]-glargine to 125I[A14]-insulin in HepG2 cells. While binding of glargine to the insulin receptor was identical to insulin, degradation of glargine was reduced compared to insulin (16.3% +/- 0.3% v 21.6% +/- 0.4% degraded/h, P < .01). Less degraded glargine than insulin was released from cells previously loaded with radiolabeled material (50.1% +/- 2.4% v 58.3% +/- 1.4%/2 h, P < .02). The amount of intact glargine released was concomitantly increased compared to insulin (44.8% +/- 2.6% v 35.8% +/- 1.4%/2 h, P < .02). These data provide further evidence for a relationship between insulin metabolism and insulin action on protein and lipid metabolism; however, the clinical relevance of these differences is hard to realize, since for the most part glargine, used as a basal insulin, is administered in addition to other shorter-acting insulin or analogues, and their effects will mask or reduce glargine effects on lipolysis and protein degradation. However, these studies do show that properties of insulin other than glucose metabolism and mitogenesis must be considered when studying insulin analogues.     

Basal insulin hypersecretion in insulin-resistant Zucker diabetic and Zucker fatty rats: role of enhanced fuel metabolism.

The biochemical mechanisms responsible for basal hyperinsulinemia in insulin-resistant states have not been fully defined. We therefore studied pancreatic beta-cell function in vitro to characterize the relative importance of fuel metabolism or secretion via a constitutive pathway in the maintenance of high basal insulin secretion in Zucker diabetic fatty (ZDF) and Zucker fatty (ZF) rats. Insulin secretion from ZF (10+/-1.8 v 5+/-0.6 pmol/ng DNA/h) and ZDF (30+/-4 v 7+/-0.8 pmol/ng DNA/h) islets at 2.8 mmol/L glucose was two to four times greater than secretion from islets of lean littermate control rats. In response to a decreasing glucose concentration (from 12 to 0 mmol/L), a paradoxical increase in insulin secretion was observed in perfused ZDF rat pancreas. Insulin secretion at 2.8 mmol/L glucose was suppressed approximately 70% to 80% in islets from ZDF and ZF rats following exposure to diazoxide, a K+-adenosine triphosphate (K(ATP)) channel opener that inhibits membrane depolarization, or rotenone and oligomycin, agents that inhibit ATP production, or by incubation at 23 degrees C. Inhibition of glycolysis with mannoheptulose, 2-deoxyglucose, and iodoacetate or fatty acid oxidation with a carnitine palmitoyltransferase I inhibitor also significantly inhibited basal insulin secretion in islets of ZDF and ZF rats but not their lean littermates. Furthermore, the glycolytic flux at 2.8 mmol/L glucose was significantly higher in ZDF islets versus ZDF lean littermate (ZLC) islets (2.2+/-0.1 v 3.7+/-0.3 pmol/ng DNA/2 h, P < .01) and was suppressed by mannoheptulose. In ZDF and ZF islets, high basal insulin secretion was maintained despite a 50% reduction in the rate of proinsulin/insulin biosynthesis at 2.8 mmol/L glucose. The rate of proinsulin to insulin conversion and the ratio of proinsulin to insulin secretion by islets of ZDF rats were similar to the values in the lean littermates. Thus, basal hypersecretion in these two insulin-resistant models appears to be related to enhanced fuel metabolism rather than the contribution of a constitutive pathway of secretion.     

Preservation of the incretin effect after orthotopic pancreas transplantation in inbred rats.

To establish whether the incretin effect is under neural control, insulin, C-peptide, and glucose-dependent insulinotropic peptide (GIP) responses and hepatic insulin clearance were investigated after oral and "isoglycemic" intravenous glucose in 12 inbred rats after denervation of the pancreas by orthotopic transplantation with portal venous drainage (Tx group) and in 12 laparotomized controls (sham group). Effective pancreas denervation was documented by a decreased pancreatic polypeptide (PP) response to insulin-induced hypoglycemia and by decreased levels of norepinephrine and calcitonin gene-related peptide (CGRP) in pancreatic tissue. Basal and incremental arterial plasma glucose integrated over 180 minutes did not differ between oral and intravenous glucose, but the integrated insulin response (mean +/- SEM) was significantly greater with oral versus intravenous glucose (Tx group, 104.9 +/- 22.0 v 31.0 +/- 4.9 nmol x L(-1) x min, P < .01; sham group, 79.5 +/- 10.6 v 36.6 +/- 5.8 nmol x L(-1) x min, P < .01). The integrated response of C-peptide was similar during both tests (Tx group, 105 +/- 14 v 79 +/- 8 pmol x mL(-1) x min; sham group, 112 +/- 10 v 121 +/- 12 pmol x mL(-1) x min). Hepatic insulin clearance was significantly decreased in both groups by oral compared with intravenous glucose administration (Tx group, 1.3 +/- 0.2 v 3.3 +/- 0.6 mmol/mmol, P < .01; sham group, 1.6 +/- 0.1 v 3.9 +/- 0.6 mmol/mmol, P < .02). The incretin effects for insulin (Tx group, 5.6 +/- 2.7; sham group, 3.0 +/- 0.8) and C-peptide (Tx group, 1.4 +/- 0.2; sham group, 1.1 +/- 0.2), calculated as the ratio of the integrated oral response and integrated intravenous response, and GIP responses to oral and intravenous glucose were not significantly different between the two groups. We conclude that there is preservation of the incretin effect in rats with orthotopically transplanted and hence extrinsically denervated pancreas, thus ruling out the possibility that the autonomic nervous system substantially contributes. Hepatic insulin clearance and insulinotropic hormones such as GIP appear to be more important.     

Relationships among islet cell antibodies, residual beta-cell function, and metabolic control in patients with insulin-dependent diabetes mellitus of long duration: use of a sensitive C-peptide radioimmunoassay

Relationships among islet cell antibodies (ICA), residual beta-cell function, and metabolic control were studied in 60 insulin-dependent diabetics (IDDs) of long duration (6 to 31 years). Sensitive C-peptide immunoreactivity (CPR) and ICA assays with limits of 0.017 nmol/L and 5 Juvenile Diabetes Foundation (JDF) U, respectively, demonstrated that baseline (0.16 +/- 0.02 nmol/L, mean +/- SE, n = 26), as well as maximum CPR values (0.34 +/- 0.05 nmol/L), during 100-g oral glucose tolerance tests (OGTT) in ICA-positive IDDs were significantly higher than corresponding values in ICA-negative ones (baseline values, 0.10 +/- 0.01 nmol/L, P less than .05; maximum values, 0.20 +/- 0.04 nmol/L, P less than .01, n = 34). Negative correlation was observed between increment of serum CPR and metabolic control indices, including fasting blood glucose (FBG) and HbA1c levels (P less than .05). In addition, ICA-positive insulin-dependent diabetes mellitus (IDDM) patients had lower values of FBG (8.2 +/- 0.4 mmol/L, P less than .01 v ICA-negative IDDs) and HbA1c (9.2% +/- 0.2%, P less than .05 v ICA-negative IDDs) than ICA-negative ones (FBG, 9.9 +/- 0.4 mmol/L; HbA1c, 9.8% +/- 0.2%). These results indicate that minute CPR responses to OGTT detected by sensitive methods may represent residual pancreatic beta cells, which may contribute to ICA generation and good metabolic control in IDDs of long duration.     

Vascular insulin/insulin-like growth factor-1 resistance in female obese Zucker rats

Because insulin resistance/diabetes may cause inordinate vascular complications in females, we have investigated the effects of insulin and insulin-like growth factor (IGF-1) on vascular reactivity in 12-week-old female Zucker obese (Ob) rats, a rodent model of insulin resistance and its lean (Ln) age-matched counterpart. Endothelium intact aortic rings from Ob animals and their Ln littermates (12 weeks of age) were subjected to contractile concentration responses to phenylephrine (PE) followed by relaxation to isoproterenol (Iso), with and without preincubation for 2 hours with cholera toxin (CTX; 1 microg/mL) or pertussis toxin (PTX; 2 microg/mL) and before and after incubation with either insulin or IGF-1 (100 nmol/L) for 1 hour. Systolic blood pressure was higher (138 +/- 3 v. 109 +/- 4 mm Hg; P <.0001) in the 12-week-old Ob rats. Contractile responses to PE were similar in both groups; however, both insulin and IGF-1 induced a paradoxical increase (P <.001) in contraction in Ob vasculature (929 +/- 92 v. 679 +/- 25 mg, respectively). CTX alone decreased contraction in the Ob (P <.02) and PTX in the Ln (P <.02), but there were no interactions between either IGF-1 or insulin and the toxins. Marked impairment of relaxation to Iso was seen in aortic rings of these female Ob rats (ED(50) = 2.6 micromol/L v. 418 nmol/L, P =.0002), an effect exacerbated by preincubation with either insulin or IGF-1 (P =.0001). Again, no role for G-proteins could be demonstrated. Insulin-dependent glucose uptake was severely impaired (P <.05) in aortic segments of the Ob insulin-resistant rats. Insulin receptor binding, tyrosine kinase activity (TKA), and abundance of several G-protein alpha subunits (inhibitory and stimulatory) in solubilized arterial membrane preparations (assessed by Western blot) were comparable in the 2 groups. These results indicate that resistance to the vascular actions of insulin/IGF-1 in female Ob rats is a postreceptor event that parallels glucose uptake resistance and is independent of G-proteins.     

四氯化碳诱导大鼠肝纤维化脂质过氧化相关蛋白表达的动态变化及一贯煎的干预效应

目的 探讨四氯化碳(CCl4)诱导大鼠肝纤维化脂质过氧化相关蛋白表达的动态变化及一贯煎的干预效应.方法 Wistar雄性大鼠57只,其中模型组39只,正常组18只.模型大鼠腹腔注射50％的CCl4橄榄油溶液(1ml/lg),每周2次,共9周.造模3、6周后,随机抽取正常及模型大鼠各6只,处死作动态观察.其余模型大鼠随机分为模型组15只及干预组12只,模型组大鼠在8周时处死4只观察成模情况.第7周开始,继续造模的同时,干预组用一贯煎(2.682 g/kg)蒸馏水稀释灌胃,1次/d,共计3周.用药3周结束后,处死大鼠,检测肝功能、肝组织羟脯氨酸(Hyp)和丙二醛(MDA)含量、超氧化物歧化酶(SOD)与谷胱甘肽(GSH)活性,以及热休克蛋白70 (HSP70)、血红素加氧酶-1(HO-1)、转铁蛋白(Transferrin)、过氧化还原酶(Prxd)6、肝脏型脂肪酸结合蛋白(L-FABP)等的表达.计量资料采用单因素方差分析,计数资料采用Ridit分析. 结果 (1)与对照组比较,模型组大鼠6、9周时肝组织MDA含量显著升高[(4.23±0.45) nmol/mg比(2.22±0.59)nmol/mg; (6.29±1.23) nmol/mg比(2.22±0.59) nmol/mg,F值分别为60.13、66.99,P值均＜ 0.05];SOD活性显著降低[(196.94±39.20) U/mg比(264.50±30.44)U/mg,F=11.12,P＜ 0.05; (152.21±51.65) U/mg比(264.50±30.44) U/mg,F=23.11,P＜0.01];GSH含量显著降低[(48.47±7.27) nmol/mg比(60.74±9.04) nmol/mg,F=6.71,P＜0.05;(37.89±9.01) nmol/mg比(60.74±9.04)nmol/mg,F=24.06,P＜0.01];与9周模型组比较,干预组MDA显著降低[(4.25±0.86) nmol/mg比(6.29±1.23) nmol/mg,F=19.52,P＜ 0.01],SOD显著升高[(198.35±46.48) U/mg比(152.21±51.65) U/mg,F=4.65,P＜0.05],GSH显著升高[(53.73±7.54) nmol/mg比(37.89±9.01) nmol/mg,F=19.23,P＜0.01];(2)与正常组比较,9周时模型组大鼠HSP70蛋白表达量升高(1.21±0.06比0.58±0.07,F=166.87,P＜0.0l),HO-1蛋白表达量也升高(1.11±0.06比0.58±0.06,F=123.96,P＜ 0.01),Prdx6蛋白表达量降低(0.04±0.05比1.49±0.05,F=1215.85,P＜0.01),L-FABP表达量降低(0.24±0.02比1.44±0.14,F=219.05,P＜0.01),Transferrin蛋白表达量降低(0.67±0.03比1.67±0.04,F=301.35,P＜0.01).9周时,干预组HSP70和HO-1蛋白表达量分别为0.82±0.04、0.90±0.04,与9周时模型组比较,F值分别为92.31、26.89,P值均＜0.01,差异有统计学意义;9周时,干预组Prdx6、L-FABP和Transferrin蛋白表达分别为0.88±0.11、1.36±0.13、1.04±0.12,与9周时模型组比较,F值分别为150.17、237.19、27.53,P值均＜0.01,差异有统计学意义. 结论 一贯煎具有促进机体抗氧化物质生成、减轻脂质过氧化损伤的作用.     

Calcium binding capacity of erythrocyte membrane in human hypertension and spontaneous hypertensive rats

Several abnormalities of calcium transport have been reported in human essential hypertension (EHT) and spontaneous hypertensive rat (SHR). 45Ca binding capacity to erythrocyte membrane was measured in this study by filtration technique in the presence of 80 nmol/L Ca concentration. Results showed: (1) It was much lower in EHT (33 cases) than normal control (19 men) group, being 0.22 +/- 0.13 versus 0.35 +/- 0.18 nmol Ca2+/mg membrane protein (P less than 0.01), and correlated positively with blood pressure levels. (2) The average Ca binding capacity in young offsprings (15 adolescents) with both parents hypertensive was lower, but statistically not significant. (3) The average Ca binding capacity was also lower in SHR (9 rats) than control WKY (10 rats) group, being 0.83 +/- 0.27 versus 0.98 +/- 0.24 nmol Ca2+/mg membrane protein, yet statistically not significant. Therefore a decrement of membrane binding capacity might be related to the occurrence and maintenance of hypertension.