Hyperproinsulinemia is not a characteristic feature in the offspring of patients with different phenotypes of type II diabetes

OBJECTIVE: The purpose of this work was to study whether there are differences in plasma proinsulin levels and proinsulin-to-specific insulin ratio in the offspring of patients with different phenotypes of type II diabetes. DESIGN: Eleven glucose-tolerant offspring of type II diabetic patients with deficient insulin secretion phenotype (IS group), nine glucose-tolerant offspring of patients with insulin-resistant phenotype (IR group), and fourteen healthy control subjects without a family history of diabetes were studied. METHODS: Plasma specific insulin, plasma proinsulin, and plasma C-peptide levels were measured during a 2-h oral glucose tolerance test and during hyperglycemic clamp. RESULTS: Plasma proinsulin levels during the oral glucose tolerance test and the hyperglycemic clamp did not differ among the study groups. The IR group had a lower fasting plasma proinsulin-to-specific insulin ratio (10.3+/-1.7%) than the control group (15.4+/-1.4%; P<0.05) and the IS group (18.6+/-2.7%; P<0.05). Furthermore, the IR group had lower plasma proinsulin-to-specific insulin ratio at 30, 60 and 90 min after the oral glucose load than the IS group. However, there were no significant differences in proinsulin-to-C-peptide ratio during the oral glucose tolerance test among the study groups. In stepwise multiple regression analysis, hepatic specific insulin extraction in the fasting state (beta =0.65; P<0.001) and fasting blood glucose (beta =0.32; P<0.05) together explained 52% of the variation in fasting plasma proinsulin-to-specific insulin ratio. CONCLUSIONS: Hyperproinsulinemia is not a characteristic finding in glucose-tolerant offspring of type II diabetic probands with deficient insulin secretion or insulin-resistant phenotype. The differences in proinsulin-to-specific insulin ratios were most likely explained by different hepatic extraction among the study groups.     

The metabolic state of diabetic monkeys is regulated by fibroblast growth factor-21

Fibroblast growth factor (FGF)-21 has been recently characterized as a potent metabolic regulator. Systemic administration of FGF-21 reduced plasma glucose and triglycerides to near normal levels in genetically compromised diabetic rodents. Importantly, these effects were durable and did not come at the expense of weight gain, hypoglycemia, or mitogenicity. To explore the therapeutic properties of FGF-21 in a nongenetically modified primate species, and thus demonstrate the potential for efficacy in humans, we evaluated its bioactivity in diabetic nonhuman primates. When administered daily for 6 wk to diabetic rhesus monkeys, FGF-21 caused a dramatic decline in fasting plasma glucose, fructosamine, triglycerides, insulin, and glucagon. Of significant importance in regard to safety, hypoglycemia was not observed at any point during the study. FGF-21 administration also led to significant improvements in lipoprotein profiles, including lowering of low-density lipoprotein cholesterol and raising of high-density lipoprotein cholesterol, beneficial changes in the circulating levels of several cardiovascular risk markers/factors, and the induction of a small but significant weight loss. These data support the development of FGF-21 for the treatment of diabetes and other metabolic diseases.     

Metabolic effects of isradipine versus hydrochlorothiazide in diabetes mellitus

Most antihypertensive drugs have negative effects on metabolic control in diabetic patients. Calcium antagonists have been widely used in antihypertensive treatment of diabetics, although a possible influence on glucose tolerance, insulin secretion, and insulin action is unknown. Therefore, the effect of the calcium antagonist isradipine on glucose tolerance and insulin secretion (75 g oral glucose tolerance test) and on peripheral and hepatic insulin action (euglycemic clamp) was evaluated in 11 type II diabetic patients. All patients were treated with placebo or isradipine for 8 weeks (double-blind, crossover design). A second group of six diabetic patients received a thiazide diuretic, hydrochlorothiazide, according to the same protocol. Systolic blood pressure was significantly lowered after isradipine and hydrochlorothiazide compared with placebo (127 +/- 3 versus 139 +/- 6 mm Hg and 129 +/- 4 versus 142 +/- 4, respectively; p less than 0.05). Fasting blood glucose (190 +/- 21 versus 152 +/- 15 mg/dl; p less than 0.01), glucose levels, basal and glucose-stimulated insulin levels were significantly higher after hydrochlorothiazide compared with placebo but remained unchanged after calcium antagonist treatment. Basal hepatic glucose production and peripheral insulin resistance were significantly elevated after hydrochlorothiazide compared with placebo or calcium antagonist therapy. These data indicate that the calcium antagonist isradipine has no effect on glucose tolerance, insulin secretion, and insulin action in type II diabetic patients and might therefore be a useful drug for antihypertensive treatment in diabetes mellitus. However, diuretic treatment can lead to impairment of metabolic control and reduction of insulin action in type II diabetes mellitus.     

Fibroblast Growth Factor 21 as an emerging metabolic regulator: clinical perspectives

Fibroblast growth factor 21 (FGF21), a metabolic hormone predominantly produced by the liver, is also expressed in adipocytes and the pancreas. It regulates glucose and lipid metabolism through pleiotropic actions in these tissues and the brain. In mice, fasting leads to increased PPAR‐α mediated expression of FGF21 in the liver where it stimulates gluconeogenesis, fatty acid oxidation, and ketogenesis, as an adaptive response to fasting and starvation. In the fed state, FGF21 acts as an autocrine factor in adipocytes, regulating the activity of PPAR‐γ through a feed‐forward loop mechanism. Administration of recombinant FGF21 has been shown to confer multiple metabolic benefits on insulin sensitivity, blood glucose, lipid profile and body weight in obese mice and diabetic monkeys, without mitogenic or other side effects. Such findings highlight the potential role of FGF21 as a therapeutic agent for obesity‐related medical conditions. However, in human studies, high circulating FGF21 levels are found in obesity and its related cardiometabolic disorders including the metabolic syndrome, type 2 diabetes, non‐alcoholic fatty liver disease and coronary artery disease. These findings may indicate the presence of FGF21 resistance or compensatory responses to the underlying metabolic stress, and imply the need for supraphysiological doses of FGF21 to achieve therapeutic efficacy. On the other hand, serum FGF21 has been implicated as a potential biomarker for the early detection of these cardiometabolic disorders. This review summarizes recent developments in the understanding of FGF21, from physiological and clinical perspectives.     

Lack of overt FGF21 resistance in two mouse models of obesity and insulin resistance

Circulating levels of fibroblast growth factor 21 (FGF21), a metabolic regulator of glucose, lipid, and energy homeostasis, are elevated in obese diabetic subjects, raising questions about potential FGF21 resistance. Here we report tissue expression changes in FGF21 and its receptor components, and we describe the target-organ and whole-body responses to FGF21 in ob/ob and diet-induced obese (DIO) mice. Plasma FGF21 concentrations were elevated 8- and 16-fold in DIO and ob/ob mice, respectively, paralleling a dramatic increase in hepatic FGF21 mRNA expression. Concurrently, expression levels of βKlotho, FGF receptor (FGFR)-1c, and FGFR2c were markedly down-regulated in the white adipose tissues (WAT) of ob/ob and DIO mice. However, dose-response curves of recombinant human FGF21 (rhFGF21) stimulation of ERK phosphorylation in the liver and WAT were not right shifted in disease models, although the magnitude of induction in ERK phosphorylation was partially attenuated in DIO mice. Whole-body metabolic responses were preserved in ob/ob and DIO mice, with disease models being more sensitive and responsive than lean mice to the glucose-lowering and weight-loss effects of rhFGF21. Endogenous FGF21 levels, although elevated in diseased mice, were below the half-maximal effective concentrations of rhFGF21, suggesting a state of relative deficiency. Hepatic and WAT FGF21 mRNA expression levels declined after rhFGF21 treatment in the absence of the increased expression levels of βKlotho and FGFR. We conclude that overt FGF21 resistance was not evident in the disease models, and increased hepatic FGF21 expression as a result of local metabolic changes is likely a major cause of elevated circulating FGF21 levels.     

Integrated regulation of hepatic metabolism by fibroblast growth factor 21 (FGF21) in vivo

Fibroblast growth factor (FGF21) plays an important role in regulating hepatic oxidation of fatty acids and gluconeogenesis in response to fasting and during consumption of a ketogenic diet. However, the metabolic pathways through which FGF21 regulates hepatic function are not well defined. To identify the effects of FGF21 on the liver in vivo, we administered FGF21 to mice and analyzed acute effects on signaling and gene expression. We found that FGF21 acts directly on the liver to stimulate phosphorylation of fibroblast growth factor receptor substrate 2 and ERK1/2. Acute FGF21 treatment induced hepatic expression of key regulators of gluconeogenesis, lipid metabolism, and ketogenesis including glucose-6-phosphatase, phosphoenol pyruvate carboxykinase, 3-hydroxybutyrate dehydrogenase type 1, and carnitine palmitoyltransferase 1α. In addition, injection of FGF21 was associated with decreased circulating insulin and free fatty acid levels. FGF21 treatment induced mRNA and protein expression of peroxisome proliferator-activated receptor-γ coactivator (PGC-1α), suggesting that PGC-1α may play a role in regulating FGF21 action. However, studies using mice with liver-specific ablation of PGC-1α revealed the same regulation of gluconeogenic gene expression by FGF21 as seen in wild-type mice, indicating that PGC-1α is not necessary for the effect of FGF21 on glucose metabolism. These data demonstrate that FGF21 acts directly on the liver to modulate hepatic metabolism. The direct effects we examined are not dependent on PGC-1α. In addition, FGF21 treatment is associated with decreased serum insulin levels that my affect hepatic function.     

FGF23 contributes to insulin sensitivity in obese adolescents - preliminary results

Fibroblast growth factor‐23 (FGF23) is a hormonal regulator of circulating phosphate and vitamin D levels. Recent investigations revealed that besides a key role in the pathogenesis of calcium–phosphorus disorders, in some patients FGF23 may be an indicator of cardiovascular complications. As a ‘hormone‐like’ factor, it may also be involved in some metabolic processes, especially in the metabolism of glucose and fat. Its potential contribution to metabolic syndrome (MS) development has not been confirmed yet. Objective The study was to examine the possible correlations between FGF23 serum levels and body composition, blood pressure and selected parameters of glucose, insulin and fat metabolism in adolescents with simple obesity. Patients and design In 68 (35 female) adolescents (mean age 13·9 years) with simple obesity [mean BMI SDS 4·9 (95% CI 4·4–5·4)], the levels of FGF23, total cholesterol, low‐density lipoprotein cholesterol, high‐density lipoprotein cholesterol and triglycerides were measured. Standard oral glucose tolerance tests were performed with the assessment of fasting and after 120′ postload glucose and insulin levels; the insulin resistance index HOMA‐IR was calculated. Results Regardless of gender, there was a significant inverse correlation between FGF23 and fasting insulin level (r = ?0·3), as well as HOMA‐IR (r = ?0·29). Multiple regression model showed the independent association between FGF23 and HOMA‐IR. Conclusion FGF23 seems to be a novel factor contributing to insulin sensitivity. Further investigations are needed to define its role in the development of MS.     

Nonalcoholic steatohepatitis, insulin resistance, and metabolic syndrome: further evidence for an etiologic association

This study aims to determine the presence of the components of the metabolic syndrome in primary nonalcoholic steatohepatitis (NASH) and to assess the role of liver disease in the genesis of peripheral hyperinsulinemia. Nineteen patients (18 men and 1 woman; mean age, +/- SD, 38 +/- 10 years; body mass index [BMI], 26 +/- 2 kg/m(2)) with histologic evidence of NASH were enrolled; 19 age- and sex-matched normal subjects were investigated as controls. Plasma glucose, insulin, and C-peptide levels were measured during an oral glucose tolerance test, and a frequently sampled intravenous glucose tolerance test (FSIGT), analyzed by minimal modeling technique, was performed. Compared with controls, the NASH group had lower insulin sensitivity (3.84 +/- 2.44 vs. 7.48 +/- 3.01 10(-4) x min(-1)/microU/mL; P =.0003) and higher total insulin secretion (21 +/- 13 vs. 10 +/- 3 nmol/L in 240 minutes; P =.001). Hepatic insulin extraction was similar in both groups (69.8% +/- 16.1% vs. 70.2% +/- 18.3%; P =.854). According to the results of the oral glucose tolerance test, no patient was classified as diabetic, 5 were classified as glucose intolerant, and 1 was classified as having impaired fasting glycemia. Nine patients (47%) had at least the 2 minimum criteria required to define the metabolic syndrome according to the European Group for the Study of Insulin Resistance (EGIR). In conclusion, hyperinsulinemia and insulin resistance occur frequently in patients with NASH; these conditions do not stem from a reduced hepatic insulin extraction but from an enhanced pancreatic insulin secretion compensatory to reduced insulin sensitivity. The derangement of insulin regulation, often associated with the metabolic syndrome, may play a causal role in the pathogenesis of NASH.     

One month's insulin treatment of type II diabetes: the early and medium-term effects following insulin withdrawal

In order to see if subcutaneous insulin treatment of type II diabetes might produce lasting physiologic changes, ten patients received one month's insulin treatment under strict dietary supervision. When compared to the pretreatment period, 48 hours after discontinuing insulin treatment fasting plasma glucose had fallen (P = 0.005), fasting serum insulin had risen (P = 0.005), and fasting hepatic glucose production measured by 3H-3-glucose turnover had fallen (P = 0.008). The metabolic clearance rate of glucose measured with the glucose clamp rose significantly after treatment at insulin infusion rates of 40 mU m-2 min-1 (P = 0.015) and 400 mU m-2 min-1 (P = 0.012). The serum insulin and C-peptide responses to oral glucose improved after the treatment in association with the improvement in glucose tolerance, but the plasma glucose response was unchanged. Six other type II diabetic patients who received only dietary supervision did not show significant changes in these variables. Six weeks after discontinuing insulin, the patients' fasting hepatic glucose production was still reduced compared to pretreatment (P = 0.028) and insulin action was still improved at both the lower (P = 0.028) and the higher (P = 0.028) insulin infusion rates, but the fasting plasma glucose and insulin and C-peptide responses to oral glucose had returned to pretreatment values. The improvement in glucose tolerance and beta-cell function induced by insulin treatment seems to be of more limited duration than the improvements in basal hepatic glucose production and in insulin action.     

Short-term low-dose growth hormone administration in subjects with impaired glucose tolerance and the metabolic syndrome: effects on beta-cell function and post-load glucose tolerance

OBJECTIVE: Modest elevations in circulating IGF-I levels have been suggested to protect against the development of glucose intolerance in insulin-resistant subjects. To further understand the interactions of GH and IGF-I on beta-cell function and post-load glucose tolerance in glucose-intolerant subjects predisposed to diabetes, we performed a pilot study in 12 subjects with impaired glucose tolerance and the metabolic syndrome using a low GH dose (1.7 microg/kg per day) known to increase endogenous IGF-I production. DESIGN: Fourteen daily GH or placebo injections in a double-blind cross-over study. METHODS: Baseline and post-treatment oral glucose tolerance tests were performed. The homeostasis model assessment and the insulinogenic index was used to estimate fasting insulin sensitivity (S(I)) and beta-cell function respectively, whereas changes in the incremental area under the curve were used to estimate post-load glucose tolerance (DeltaAUC(glu)) and post-load insulin levels (DeltaAUC(ins)). RESULTS: GH increased total IGF-I (P<0.02), free IGF-I (P<0.04) and fasting insulin (P<0.04) levels, but did not modify plasma IGF-binding proteins (IGFBPs)-1 and -3, fasting glucose, non-esterified fatty acid and C-peptide levels, and fasting S(I). After oral glucose intake, glucose tolerance improved (P<0.03), but post-load insulin levels and beta-cell function remained unchanged. CONCLUSION: Short-term low-dose GH administration induced fasting hyperinsulinaemia possibly by reducing insulin clearance but improved post-load glucose tolerance, suggesting that increased bioavailable IGF-I enhanced post-load S(I) without altering beta-cell function. Longer-term studies are required to ascertain whether these positive effects on post-load glucose tolerance and the preservation of beta-cell function can be sustained by this GH dose in these high-risk subjects.     

Decreased hepatic insulin extraction in subjects with mild glucose intolerance

The fact that hyperinsulinemia occurs in simple obesity and mild glucose intolerance has been well established. Altered hepatic insulin extraction may influence the levels of circulating hormone. The simultaneous measurement of insulin and C-peptide concentrations in peripheral blood enables an in vivo estimation of hepatic insulin removal. To evaluate hepatic insulin extraction, insulin and C-peptide responses to oral glucose were studied in 176 obese and nonobese subjects with normal, impaired, or diabetic glucose tolerance. Insulin levels as well as insulin incremental areas in glucose intolerant subjects were significantly higher than in weight-matched controls. The levels of C-peptide as well as C-peptide incremental areas were only slightly enhanced in subjects with impaired glucose tolerance, whereas they were reduced in subjects with diabetic tolerance. The molar ratios of C-peptide to insulin, both in the fasting state and after ingestion of glucose, as well as the relationship between the incremental areas of the two peptides were used as measures of hepatic insulin extraction. They were significantly reduced in glucose intolerant subjects and, to a lesser extent, in nondiabetic obese subjects. These results indicate that peripheral hyperinsulinemia in subjects with simple obesity or impaired glucose tolerance is a result of both pancreatic hypersecretion and diminished hepatic insulin extraction. In subjects with a more severe degree of glucose intolerance, decreased hepatic insulin removal is the primary cause of hyperinsulinemia.     

Insulin-resistant patients with type 2 diabetes mellitus have higher serum leptin levels independently of body fat mass

In obese people, an increase of plasma leptin levels is well-known and is seen as a consequence of the increased body fat mass. Moreover, a relationship between fasting concentrations of leptin and insulin has been described. Hyperinsulinemia is considered to be indicative of insulin resistance. We aimed at elucidating the interrelations between leptin, insulin and insulin resistance in type 2 diabetic patients. Under metabolic ward conditions, we investigated 21 moderately overweight men with type 2 diabetes. The patients had a mean age of 49.1 years, a mean body mass index (BMI) of 26.8 kg/m², and a mean diabetes duration of 82.5 months. All patients were treated with diet alone. We measured fasting leptin and insulin levels, body composition by determination of total body water, and insulin resistance by euglycemic hyperinsulinemic clamp technique. At univariate analysis, fasting leptin level significantly and positively correlated with BMI (r=0.49, p=0.02) and with fasting insulin (r=0.69, p=0.001), while it negatively correlated with the glucose disposal rate (r=−0.62, p=0.002). Furthermore, leptin was inversely correlated with HDL-cholesterol (r=−0.45, p=0.04). When excluding the influence of body fat mass or of BMI in partial correlation analysis, the correlations between leptin and insulin or insulin sensitivity remained significant. The relationship between insulin resistance (as measured directly in the clamp experiments) and leptin concentrations was also shown by subdividing the diabetic patients according to tertiles of insulin sensitivity. The highest fasting leptin levels were observed in those patients with the most expressed insulin resistance. Our data point to a functional relationship between insulin resistance and leptin concentrations in insulin-resistant type 2 diabetic men, independently of body composition. This relationship is believed to be mediated by insulin. Received: 2 August 2000 / Accepted in revised form: 20 February 2002     

Association of serum fibroblast growth factor 21 and urinary glucose excretion in hospitalized patients with type 2 diabetes

AimUrinary glucose excretion (UGE) is mainly regulated by the sodium glucose cotransporter (SGLT)-2 in the proximal tubule of kidney. Lower UGE was associated with higher extent of insulin resistance in patients with type 2 diabetes. Animal studies suggested the relation of Fibroblast growth factor 21 (FGF21) and UGE. However, little was known about the association of FGF21 and UGE in human. We conducted a study to investigate the association of serum FGF21 and low UGE in patients with type 2 diabetes.MethodA cohort of 2066 hospitalized patients with type 2 diabetes was screened for the fasting urinary glucose concentration and fasting blood glucose in the medical records. 70 patients with high UGE and 61 patients with Low UGE were analyzed. Frozen serum samples were used for the test of FGF21 levels.ResultsThe body mass index (BMI) and serum FGF21 levels were higher in low UGE group. Multivariable logistic regression indicated the association of FGF21 and low UGE after adjusting for age, sex, renal function, fasting plasma glucose, the treatment of insulin, and Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) index.ConclusionHigher serum FGF21 levels were independently associated with low UGE in patients with type 2 diabetes.     

成纤维细胞生长因子21与糖尿病性大血管病变

成纤维细胞生长因子21(FGF21)是近几年新发现的代谢调节因子,它与糖尿病性大血管病变之间的关系已成为近些年的研究热点。内源性FGF21水平在糖耐量受损时升高,随着2型糖尿病大血管病变的出现,其水平进一步升高,推测其可能机制是FGF21抵抗。血管内皮细胞有FGF21基因表达,且FGF21在动脉粥样硬化早期可能起保护作用,这暗示着FGF21有望成为预防和治疗糖尿病性大血管病变的靶点。     

Antidiabetic effect of diasulin, a herbal drug, on blood glucose, plasma insulin and hepatic enzymes of glucose metabolism in hyperglycaemic rats

AIM: The present study was designed to investigate the effect of diasulin, a polyherbal drug, on blood glucose, plasma insulin and the activities of hepatic glucose metabolic enzymes in alloxan-induced diabetic rats. METHODS: Male Wistar rats, body weight of 180-200 g (12 normal and 30 diabetic rats), were used in this study. The rats were divided into seven groups after the induction of alloxan diabetes. In the experiment, six rats were used in each group. Group 1: normal rats given 2 ml of saline; group 2: normal rats given aqueous solution of diasulin (0.20 g/kg of body weight); group 3: diabetic control rats given 2 ml of saline; group 4: diabetic rats given aqueous solution of diasulin (0.05 g/kg of body weight); group 5: diabetic rats given aqueous solution of diasulin (0.10 g/kg of body weight); group 6: diabetic rats given aqueous solution of diasulin (0.20 g/kg of body weight) and group 7: diabetic rats given aqueous solution of glibenclamide (600 micro g/kg of body weight). The treatment was given for 30 days. After the treatment, fasting blood glucose, plasma insulin, urine sugar and the activities of hepatic glucose metabolic enzymes were determined in normal and experimental animals. RESULTS: Treatment with diasulin resulted in a significant reduction in blood glucose, glycosylated haemoglobin and an increase in plasma insulin and total haemoglobin and a significant improvement in glucose tolerance. Diasulin also resulted in a significant reduction in the activities of glucose-6-phosphatase and fructose-1,6-bisphosphatase in the liver, whereas the level of plasma insulin and hepatic hexokinase activity was significantly increased in alloxan diabetic rats. CONCLUSIONS: The present investigation suggests that diasulin, a polyherbal drug, controls the blood glucose level by increasing glycolysis and decreasing gluconeogenesis with a lower demand of pancreatic insulin than in untreated rats. This is possible, because it regulates the activities of hepatic glucose metabolic enzymes.     

Hepatic insulin expression improves glycemic control in type 1 diabetic rats

Low levels of hepatic insulin production have been shown to prevent lethal ketoacidosis associated with type 1 diabetes. To assess the beneficial effects of sustained hepatic production of insulin on glycemic control in type 1 diabetes, we have employed the adenovirus-mediated gene delivery system to transfer an engineered rat preproinsulin gene to the livers of streptozotocin-induced diabetic nude rats. Hepatic insulin production resulted in the reduction of blood glucose in treated diabetic rats, the degree of blood glucose reduction correlated with both the vector dose and the level of hepatic insulin expression. At moderate vector doses, 0.3-0.7 ng/ml of plasma insulin was produced in treated diabetic animals, resulting in significant reduction of nonfasting hyperglycemia and improvement in glucose tolerance. Furthermore, these animals maintained euglycemia after 12-h fast. At higher vector doses, greater than 1 ng/ml of plasma insulin was produced, completely reversing nonfasting hyperglycemia in treated rats. However, all of the treated animals developed severe hypoglycemia upon fasting. This study has defined the maximal tolerable level of hepatic insulin production that is sufficient to reduce the degree and ameliorate the adverse effects of nonfasting hyperglycemia without risk of fasting hypoglycemia in type 1 diabetic rats.     

胰岛素生成,胰岛素分泌及2型糖尿病:问题的核心在于β细胞

近年来,有人将2型糖尿病(T2DM)定义为由胰岛素抵抗引起的一种疾病,作为代谢综合征的一部分。胰岛素抵抗确实存在于T2DM,但同时也以同样程度存在于许多并无糖尿病的人群中,这些人可有或无代谢综合征。因而单独胰岛素抵抗不可能是T2DM的决定性致病因素。T2DM从其最早的阶段包括糖耐量受损(IGT)及空腹血糖受损(IFG),甚或在可测出的这些血糖变化之前的“糖尿病前期”就出现胰岛素释放动力学的障碍;其主要特征是对葡萄糖反应的胰岛素释放第一相丧失,随之而来的是逐渐加重的第二相胰岛素和总胰岛素分泌的受损。第一相胰岛素反应丧失的后果为肝脏未能迅速胰岛素化,延迟了对肝葡萄糖输出的抑制,从而引起餐后高血糖。在某些研究中,确已发现T2DM时β细胞量总体的减少,但并非所有研究中都有此同样结果,故对此尚须进一步证实。现已明确,糖尿病易发人群的β细胞的分泌适应能力是有限的,在胰岛素抵抗或热量负荷对胰岛素释放要求增加时,就难以胜任。此外,即使轻度的高血糖也会严重影响胰岛素的分泌并减少胰岛素原的合成,从而使代谢所需的胰岛素进一步减少。转录因子PDX-1在此损伤过程中起关键作用。因而,及早并有效地将T2DM血糖控制于接近正常水平至关重要,尤其是对胰岛素一相分泌的恢复更是如此。     

C-peptide immunoreactivity and insulin content in the diabetic human pancreas and the relation to the stability of diabetic serum glucose level

The content of insulin and C-peptide-like immunoreactivity (CPR) were determined in the tail of pancreas from 35 autopsied diabetic and 21 non-diabetic subjects. In the 28 diabetics who had been followed for more than 6 months, the relation between the amount of insulin or CPR in the pancreas and the stability of fasting serum glucose during diabetic life before death was analyzed together with the relation between the serum CPR response to the breakfast tolerance test before death and insulin content at autopsy. As an index of the instability of the blood sugar level, the standard deviation of the mean of 15 successive determinations of fasting serum glucose was used. Both insulin and CPR content in the pancreas were significantly decreased in diabetics as compared with non-diabetics. SD of the mean fasting serum glucose and insulin or CPR content in the tail of pancreas showed a significant inverse correlation on a logarithmic scale (P less than 0.01, r = -0.704 and P less than 0.01, gamma = -0.757, respectively). Serum CPR value during the breakfast tolerance test correlated significantly with the insulin content in the pancreas of diabetic subjects. These findings suggest that one of the causes of the instability of fasting serum glucose levels is the devastation of pancreatic beta-cells and that the pancreatic insulin content is logarithmically and inversely related to fluctuations in fasting serum glucose.     

The effect of portacaval anastomosis on oral carbohydrate tolerance and on plasma insulin levels

In patients with portal hypertension, plasma insulin levels were raised both fasting and after oral glucose or intravenous tolbutamide. This supports previous suggestions that resistance to endogenous insulin plays a major role in producing the impaired glucose tolerance found in chronic hepatic dysfunction.The operation of portacaval anastomosis was followed by impaired oral fructose tolerance, but did not significantly change oral glucose tolerance. Plasma insulin levels were unchanged by the operation, either fasting or following the stimulus of an oral glucose load or intravenous tolbutamide. The insulin response after operation was only higher after intensive pancreatic beta cell stimulation by a combination of glucose, tolbutamide, and glucagon. These results indicate that, in patients with hepatic dysfunction, little insulin is being removed by the liver from the portal blood except when the insulin secretory rate is unusually high.     

Metabolic evolution of type 2 diabetes: a 10-year follow-up from the time of diagnosis

Abstract. Objectives. To investigate fasting and post-load plasma glucose, insulin and C-peptide levels during oral glucose tolerance tests in patients with type 2 diabetes and in control subjects, and the metabolic evolution of the diabetes. Design, setting and subjects. A 10-year prospective study consisting of a representative group of 133 (70 men, 63 women) newly diagnosed type 2 diabetic patients diagnosed at health centres between 1979 and 1981 and 144 (62 men, 82 women) nondiabetic control subjects recruited from the population register. At baseline, diabetic subjects were treated with diet only. The subjects were studied at baseline and after 5 and 10 years. Main outcome measures. The changes in plasma glucose, insulin and C-peptide levels in diabetic and control subjects at baseline and after 5 and 10 years follow-up. Factors associated with the decline in insulin and C-peptide levels in diabetic patients (e.g. metabolic control, islet cell antibodies). Results. A slight increase in glucose levels was seen during the follow-up in both diabetic with diet and/or oral drug treated patients, but post-glucose insulin (and C-peptide and 5- and 10-year examination) levels declined in diabetic patients; this was opposite to the controls, in whom the levels tended to increase. The decline in insulin levels (area under the curve) during the follow-up was greatest in those diabetic patients with poor metabolic control during the follow-up. The cumulative incidence of requirement for insulin based on various cut-off levels for post-glucagon C-peptide nearly doubled between the 5- and 10-year examinations. Islet cell antibodies were predictive of insulin deficiency. Conclusions. Type 2 diabetes was characterized by progressive impairment of insulin response to glucose and this decline was associated with poor metabolic control of diabetes.