The pharmacokinetics of porcine glucose-dependent insulinotropic polypeptide (GIP) in man

Abstract. The pharmacokinetics of porcine glucose-dependent insulinotropic polypeptide were investigated in six healthy volunteers. At the maximum infusion dose (0·5 pmol kg^-1 min^-1) a plateau concentration of 115 ± 5·0 pmol/l plasma was obtained. On discontinuation of the infusion, the half-time of disappearance was calculated to be 20·3 ± 1·2 min. The metabolic clearance rate was 2·6 ± 0·1 ml kg^-1 min^-1 and the apparent space of distribution was 75·8 ± 5·7 ml kg^-1. Blood glucose, pancreatic and gastrointestinal hormones remained at basal concentrations throughout. No side effects were noted by any of the subjects studied.     

Postprandial stimulation of insulin release by glucose-dependent insulinotropic polypeptide (GIP). Effect of a specific glucose-dependent insulinotropic polypeptide receptor antagonist in the rat.

Glucose-dependent insulinotropic polypeptide (GIP) is a 42-amino acid peptide produced by K cells of the mammalian proximal small intestine and is a potent stimulant of insulin release in the presence of hyperglycemia. However, its relative physiological importance as a postprandial insulinotropic agent is unknown. Using LGIPR2 cells stably transfected with rat GIP receptor cDNA, GIP (1-42) stimulation of cyclic adenosine monophosphate (cAMP) production was inhibited in a concentration-dependent manner by GIP (7-30)-NH2. Competition binding assays using stably transfected L293 cells demonstrated an IC50 for GIP receptor binding of 7 nmol/liter for GIP (1-42) and 200 nmol/liter for GIP (7-30)-NH2, whereas glucagonlike peptide-1 (GLP-1) binding to its receptor on ++betaTC3 cells was minimally displaced by GIP (7-30)-NH2. In fasted anesthetized rats, GIP (1-42) stimulated insulin release in a concentration-dependent manner, an effect abolished by the concomitant intraperitoneal administration of GIP (7-30)-NH2 (100 nmol/ kg). In contrast, glucose-, GLP-1-, and arginine-stimulated insulin release were not affected by GIP (7-30)-NH2. In separate experiments, GIP (7-30)-NH2 (100 nmol/kg) reduced postprandial insulin release in conscious rats by 72%. It is concluded that GIP (7-30)-NH2 is a GIP-specific receptor antagonist and that GIP plays a dominant role in mediating postprandial insulin release.     

Comparison of the effect of GIP and GLP-1 (7–36amide) on insulin release from rat pancreatic islets

After ingestion of glucose both GIP (gastric inhibitory polypeptide, glucose-dependent insulinotropic polypeptide) and GLP-1(7-36amide) (glucagon-like polypeptide-1, 7-36amide) may play a physiological role in augmenting insulin release. Their insulinotropic effect was compared in isolated rat islets after 24-h maintenance in tissue culture (11 mmol l-1 glucose). Ten islets per vial were then incubated in Krebs-Ringer-Hepes buffer for 30 min; insulin was measured radioimmunologically. Both hormones were always compared in the same experiment. At 16.7 mmol l-1 glucose both GIP and GLP-1(7-36amide) 2 x 10(-10) mol l-1 significantly increased insulin release; 10(-10) mol l-1 of either hormone had no significant effect. The response at 10(-9) and 10(-8) mol l-1 was similar for both; at 4 x 10(-10) mol l-1 GLP-1(7-36amide), however, was clearly more effective than GIP. At low glucose (2.8 or 5.0 mol l-1) no significant differences were found. A concentration of 10(-8) mol l-1 of both hormones was slightly stimulatory. At 8.3 mmol l-1 glucose, 10(-9) mol l-1 GLP-1(7-36amide) was 60% more effective than GIP (4.8 +/- 0.4 vs. 3.0 +/- 0.4, n = 13, P less than 0.005), the response to 10(-8) mol l-1 was similar. These data show comparable effects of high concentrations of GIP and GLP-1(7-36amide) on glucose-induced insulin release; at presumably physiological concentrations, however, GLP-1(7-36amide) was clearly more effective. The combination of the two peptides was not more than additive, suggesting that they act via the same final mechanism.     

Impaired feedback control of fat induced gastric inhibitory polypeptide (GIP) secretion by insulin in obesity and glucose intolerance

Abstract. To investigate the role of endogenous insulin on the secretion of immunoreactive gastric inhibitory polypeptide (IR-GIP) the response of IR-GIP and immunoreactive insulin (IRI) to an oral fat load (100 g triglyceride) alone and during an intravenous glucose infusion (0.7 g/kg/h) was examined in normal weight and obese subjects. In normal weight subjects the fat induced integrated rise of IR-GIP was 112.7 ± 9.4 ng/ml/120 min. When glucose and fat were given together this IR-GIP response was lowered to 46.2 ± 2.9 ng/ml/120 min while the serum IRI response to i.v. glucose and the glucose tolerance were enhanced by fat ingestion. In obese subjects with normal glucose tolerance the GIP suppressing effect of i.v. glucose infusion was less marked than in controls. The integrated IR-GIP response to fat ingestion was 225.6 ± 20.3 ng/ml/120 min and to fat plus glucose 152.6 ± 14.8 ng/ml/120 min. In obese subjects with glucose intolerance i.v. glucose completely failed to lower the exaggerated secretion of IR-GIP following oral fat. Thus, a graded abnormality of the GIP response to glucose induced insulin release occurs in obesity with normal and pathological glucose tolerance. After reducing the ideal body weight of six obese subjects with glucose intolerance by hypocaloric diet for 3 weeks the exaggerated rise of IR-GIP after oral fat was reversed and the lowering effect of i.v. glucose on the IR-GIP response re-established.     

Effects of four orally administered analogues of prostaglandin E1 and E2 on glucose tolerance and on the secretion of pancreatic and gastrointestinal hormones in man

Oral glucose tolerance tests (75 g, 300 ml) were performed in 12 healthy volunteers, with prior administration of placebo, misoprostol (400 micrograms), rioprostil (300 micrograms), enprostil (70 micrograms), or nocloprost (200 micrograms), in a double-blind, randomized manner. None of the drugs significantly affected glucose tolerance, although with misoprostal some volunteers displayed an impaired glucose tolerance. Nocloprost was without effect on gastric inhibitory polypeptide (GIP) and did not influence insulin or C-peptide concentrations. Misoprostol and rioprostil reduced integrated incremental responses of GIP by 57% (P less than or equal to 0.001) and 45% (P less than or equal to 0.01), respectively, and both gave rise to an initial (approximately 10 min) delay of insulin and C-peptide responses, without a significant overall reduction in integrated incremental responses. Enprostil almost totally inhibited the GIP response (by 94%; P less than or equal to 0.001), delayed initial insulin and C-peptide responses, but reduced the integrated incremental C-peptide response (which corresponds to the overall release of insulin) by only 14% (P less than or equal to 0.05). Enprostil more substantially reduced the integrated incremental response of insulin by 36% (P less than or equal to 0.01), and also reduced the ratio of insulin and C-peptide incremental responses (P less than or equal to 0.001). In conclusion, prostaglandin E analogues which caused a reduction in GIP responses, and thereby disrupting the enteroinsular axis to varying degrees, delayed the time-course of insulin secretion without a significant impact on glucose tolerance.(ABSTRACT TRUNCATED AT 250 WORDS)     

携带可调控人胰岛素基因的腺病毒载体的构建和鉴定

目的:构建携带葡萄糖依赖性促胰岛素多肽(GIP)启动子控制下的人胰岛素基因的腺病毒载体。方法:将GIP- hIns基因自pCDNA3-GIP-hIns质粒中酶切下来,克隆至切除CMV启动子的pCA13-△CMV质粒中,形成转移质粒 pCA13-GIP-hIns,然后与质粒pBHGE3共转染至293细胞株,在其中同源重组形成腺病毒颗粒。采用PCR方法对重组体进行鉴定,同时测定病毒滴度。体外转染STC-1细胞,并采用RT-PCR检测感染腺病毒的细胞内有无hIns mRNA 的转录。结果:由pCA13-GIP-hIns和pBHGD共转染至293细胞后,可得到阳性重组体Ad.GIP-hIns,经PCR检测表明已含有GIP-hIns基因。纯化所得腺病毒滴度约为1×1011 pfu／ml。RT—PCR证实在感染重组体腺病毒Ad．GIP— hIns的细胞中有相应mRNA的转录。结论:成功构建了携带GIP启动子控制下的人胰岛素基因的腺病毒载体,为进一步胰岛素基因治疗糖尿病的实验研究奠定了基础。     

The effect of gastrin on basal and aminoacid-stimulated insulin and glucagon secretion in man

Abstract. The effect of gastrin on basal and aminoacid-stimulated glucagon and insulin secretion was studied in eleven normal young subjects. The concentrations of glucagon, insulin and gastrin in plasma or serum were measured radioimmunochemically. The results of amino-acid-stimulation were compared to those obtained during a protein-rich meal.
Intravenous injection of synthetic human gastrin-17 in doses from 15.6 ng to 1 μg/kg increased the concentration of glucagon and insulin in peripheral venous blood to a maximum within 5 min. In spite of the enhanced concentrations of insulin induced by gastrin, corresponding concentrations of glucose were either unchanged or increased. Infusion of a mixture of fifteen aminoacids increased the concentrations of glucose, glucagon and insulin. While the increases in glucose and insulin concentrations were similar to those obtained after a protein-rich meal, the glucagon response was much larger after the infusion. Injection of gastrin-17 after 30 min of infusion of aminoacids did not potentiate either the glucagon or the insulin response.
The results indicate that gastrin, besides stimulating insulin secretion, can also stimulate glucagon secretion in a dose-dependent manner. The concentrations of gastrin necessary to stimulate glucagon secretion significantly correspond to the concentrations found in diseases with endogenous hypergastrinaemia (achlorhydria and Zollinger-Ellison syndrome). While gastrin potentiates the glucose-induced insulin secretion, it does not potentiate neither the aminoacid-induced insulin nor glucagon secretion.     

The glucose-induced gastrointestinal stimulation of insulin secretion in man: relation to age and to gastrin release.

An oral 50 g glucose tolerance test and a simple intravenous glucose infusion test were performed in 20 young (20 - 32 years), 20 middle-aged (42 -55 years), and 20 old (65 - 81 years) normal subjects. Blood glucose, serum insulin, and serum gastrin concentrations were measured during all tests. The intravenous glucose infusion duplicated the oral blood glucose curve in young, middle-aged, and half of the old subjects. In the remaining old subjects the intravenous blood glucose curve was below the oral blood glucose curve. Glucose and insulin concentrations were of similar magnitude in all groups, but maximum concentrations were reached later in the old subjects. Glucose per os induced a rapid rise in serum gastrin concentrations of the order of 10 pmol/1 and a subsequent decrease of about 20 pmol/1 in all groups. The intravenous glucose infusion induced no significant changes in serum gastrin concentrations. The non-glycaemic (i.e. enteral) stimulation of insulin secretion was expressed as the difference between the integrated incremental areas of the oral and intravenous insulin curves in subjects with identical glucose curves during the two tests. This stimulation was of similar magnitude in all age groups, and it was not correlated to variations in gastrin concentrations. However, in the young subjects the enteral stimulation was greater during the first 30 minutes and smaller during the two last hours when compared to the old subjects. The results suggest that: 1. A simple intravenous glucose infusion test can be used to copy the oral blood glucose curve. 2. The size of the enteral stimulation of insulin secretion during the whole test is independetn of age. 3. The action of the glucose-induced enteral stimulation is delayed with age, and closely linked to the dynamics of the glycaemic stimulus. 4. The glucose-induced gastrin release is probably too small to affect insulin secretion significantly.     

Effect of glibenclamide on insulin release at moderate and high blood glucose levels in normal man

Insulin release occurs in two phases; sulphonylurea derivatives may have different potencies in stimulating first- and second-phase insulin release. We studied the effect of glibenclamide on insulin secretion at submaximally and maximally stimulating blood glucose levels with a primed hyperglycaemic glucose clamp. Twelve healthy male subjects, age (mean ± SEM) 22.5 ± 0.5 years, body mass index (BMI) 21.7 ± 0.6 kg m^?2, were studied in a randomized, double-blind study design. Glibenclamide 10 mg or placebo was taken before a 4-h hyperglycaemic clamp (blood glucose 8 mmol L^?1 during the first 2 h and 32 mmol L^?1 during the next 2 h). During hyperglycaemic clamp at 8 mmol L^?1, the areas under the Δinsulin curve (AUC_Δinsulin , mean ± SEM) from 0 to 10 min (first phase) were not different: 1007 ± 235 vs. 1059 ± 261 pmol L^?1 × 10 min (with and without glibenclamide, P = 0.81). However, glibenclamide led to a significantly larger increase in AUC_Δinsulin from 30 to 120 min (second phase): 16 087 ± 4489 vs. 7107 ± 1533 pmol L^?1 × 90 min (with and without glibenclamide respectively, P < 0.03). The same was true for AUC_ΔC-peptide: no difference from 0 to 10 min but a significantly higher AUC_ΔC-peptide from 30 to 120 min on the glibenclamide day (P < 0.01). The M/I ratio (mean glucose infusion rate divided by mean plasma insulin concentration) from 60 to 120 min, a measure of insulin sensitivity, did not change: 0.26 ± 0.05 vs. 0.22 ± 0.03 μmol kg^?1 min^?1 pmol L^?1 (with and without glibenclamide, P = 0.64). During hyperglycaemic clamp at 32 mmol L^?1, the AUC_Δinsulin from 120 to 130 min (first phase) was not different on both study days: 2411 ± 640 vs. 3193 ± 866 pmol L^?1 × 10 min (with and without glibenclamide, P = 0.29). AUC_Δinsulin from 150 to 240 min (second phase) also showed no difference: 59 623 ± 8735 vs. 77389 ± 15161 pmol L^?1 × 90 min (with and without glibenclamide, P = 0.24). AUC_ΔC-peptide from 120 to 130 min and from 150 to 240 min were slightly lower on the glibenclamide study day (both P < 0.04). The M/I ratio from 180 to 240 min did not change: 0.24 ± 0.04 vs. 0.30 ± 0.07 μmol kg^?1 min^?1 pmol L^?1 (with and without glibenclamide, P = 0.25). In conclusion, glibenclamide increases second-phase insulin secretion only at a submaximally stimulating blood glucose level without enhancement of first-phase insulin release and has no additive effect on insulin secretion at maximally stimulating blood glucose levels. Glibenclamide did not change insulin sensitivity in this acute experiment.     

胰岛素对大鼠动脉条分泌肾上腺髓质素的刺激作用

目的观察葡萄糖、胰岛素对大鼠动脉条合成与分泌肾上腺髓质素 (ADM )的作用。方法在孵育液中分别加入不同浓度的葡萄糖、胰岛素及葡萄糖 胰岛素 ,用放免分析方法测定组织和孵育液中ADM的含量。结果与对照组比较 ,各组组织中ADM含量均无明显改变 (P >0 .0 5 ) ,孵育液中 ,葡萄糖各组和低浓度胰岛素组ADM的含量无显著性差异 (P >0 .0 5 ) ,高浓度胰岛素组和葡萄糖 胰岛素组大鼠动脉条合成和分泌ADM明显增加 ,并呈剂量依赖性。结论高浓度胰岛素可刺激大鼠动脉条合成、分泌ADM增加。     

Effect of insulin on motilin release in man

The effect of insulin on motilin release was investigated by use of the euglycemic glucose clamp technique. By use of this technique plasma glucose concentration was maintained constant at 80-90 mg/100 ml, and plasma insulin immunoreactivity (IRI) was increased from 15 +/- 6 microU/ml to 171 +/- 22 microU/ml in 10 min, and remained at this level for 2 hr. Plasma motilin like immunoreactivity (MLI) concentration decreased within 10 min from 199 +/- 36 pg/ml to 120 +/- 28 pg/ml and remained low during the course of study. A significant negative correlation between MLI and IRI concentrations (r = -0.72, p less than 0.01) was observed. The present results indicate that the suppressive effect of insulin on motilin release is a direct action of insulin and is not mediated by glucose.     

A mathematical model for the glucose induced insulin release in man

Abstract. The dynamics of the insulin response to intravenously administered glucose were studied in man. It was shown that (a) insulin response to prolonged stimulation is biphasic; (b) if the glucose stimulus is repeated with short intervals, inhibition of the second response occurs; (c) if longer time-intervals are used, enhancement of the response is noted at the second stimulation. These findings suggest that when the pancreatic islets are exposed to hyperglycaemia, three kinetically distinct phenomena are initiated. Glucose induces almost instantaneous initiation of insulin release. Shortly thereafter, the pancreas enters a refractory phase. Thirdly, and at a later stage, a state of potentiation is built up in the islets. The effect of glucose on insulin synthesis is not considered here.—Against this background, and based on an earlier model, a mathematical model for the analysis of the glucose-insulin interplay during glucose infusions was constructed. The model describes the eventual occurrence of glucosuria, changes in the concentration of glucose in its pool, and mimics the effects of regulatory hormones when hypo-glycaemia appears. Insulin secretion is assumed to be controlled, in a multiplicative manner, by an immediate glucose function, a hypothetical potentiator that is slowly generated by glucose, and a negative factor with a shorter time-course which corresponds to the refractory phase of the pancreas. A three compartment model is used in the simulation of the metabolism and distribution of insulin after its release. Finally, glucose utilization is described as a multiplicative function, related to the prevailing concentrations of glucose in blood and insulin in the extracellular space.—This model is able to simulate all the experimental situations described in this report, both in normal man and in the diabetic syndrome, in which insulin secretion shows varying degrees of impairment. The results of the simulation of individual experiments are given either as a set of theoretical parameter values, or described as the insulin response of the model to a standard, hypothetical glucose stimulus. The latter alternative is an attractive method for objectively evaluating the insulin response to a standard glucose load in clinical materials.     

门冬胰岛素与生物合成人胰岛素治疗新诊断Ⅱ型糖尿病的对照研究

目的比较门冬胰岛素与生物合成人胰岛素治疗新诊断Ⅱ型糖尿病的临床疗效。方法将新诊断的96例Ⅱ型糖尿病患者随机均分为2组,分别为门冬胰岛素(治疗)组和生物合成人胰岛素(对照)组。患者分别在每日餐前给予皮下注射门冬胰岛素和生物合成人胰岛素,且均每晚定时皮下注射一次甘精胰岛素。比较2组患者血糖、低血糖事件、胰岛素用量的差异。结果用药后2组餐前及餐后的血糖含量均明显降低,且门冬胰岛素组餐前、餐后血糖均低于生物合成人胰岛素组;门冬胰岛素组患者低血糖发生次数低于生物合成人胰岛素组,差异有统计学意义;但2组胰岛素用量无显著差异。结论门冬胰岛素能够更好地控制Ⅱ型糖尿病的血糖,对Ⅱ型糖尿病的治疗更加有效。     

Effect of insulin treatment on serum lipoprotein(a) in non-insulin-dependent diabetes

Abstract. In order to evaluate whether Lp(a), a lipoprotein that is potentially thrombogenic and atherogenic, is a potential risk factor for CAD in non-insulin-dependent diabetes (NIDDM), we compared the Lp(a) and its distribution in 145 NIDDM patients with that in 94 healthy control subjects. Furthermore, we studied the effect of insulin treatment on serum Lp(a) in 108 patients with NIDDM. Male and female NIDDM patients had similar Lp(a) concentrations to healthy controls (median value 167 mg L^-1, range 15–1550 mg L^-1 vs. 157 mg L^-1, range 15–919 mg L^-1, NS and 92, range 15–1190 mg L^-1 vs. 103 mg L^-1, range 15–842 mg L^-1, NS). Also, the cumulative distribution of Lp(a) did not differ between the NIDDM patients and healthy subjects. Insulin treatment increased Lp(a) in diabetics with a Lp(a) concentration of less than 300 mg ^-1L, but this effect was not related to the concomitant improvement in metabolic control (mean change (±SEM) of HbA_1c from 9.80±0.15 to 8.00±0.12; P < 0.001). In subjects with elevated Lp(a) concentrations (>300 mg L^-1) the Lp(a) concentration was unaffected by insulin, despite a similar improvement in glycaemic control. These results suggest that insulin may modulate the concentration of Lp(a).     

Effect of immunoglobulin preparations on the aggregation of human erythrocytes

The aggregation of human erythrocytes induced by four kinds of immunoglobulin preparations was examined by a low shear rheoscope. After removing anti-A+ and anti-B+ activities contaminated in all preparations by incubating with erythrocytes of different blood groups, the facilitating effect on the rouleau formation of erythrocytes was compared: (i) The effect of polyethyleneglycol-treated preparation was the same in A+-, B+-, AB+- and O+-erythrocytes. (ii) Sulfonation did not affect the velocity of rouleau formation. (iii) Some of pepsin-treated preparations showed the strongest facilitation for A+-, B+- and AB+-erythrocytes, but the facilitation was much weaker for O+-erythrocytes. The others showed the weak facilitation for all types of erythrocytes (especially O+-erythrocytes). (iv) Plasmin treatment markedly decreased the velocity of rouleau formation of AB+- and O+-erythrocytes, but was not of A+- and B+-erythrocytes.     

Effect of insulin on protein phosphatase 2A expression in muscle in type 2 diabetes

BACKGROUND: Protein phosphatase 2A (PP2A) acts on a number of enzymes involved in the insulin regulation of glucose uptake and glycogen synthesis. This study was carried out to investigate the effect of insulin on PP2A expression in skeletal muscles of type 2 diabetic and control subjects. MATERIAL AND METHODS: Ten type 2 diabetic and 10 matched, control subjects were studied using the euglycaemic-hyperinsulinaemic clamp technique combined with indirect calorimetry. Immunoreactive protein levels of the catalytic alpha subunit of PP2A (PP2A-C alpha) were measured in biopsies from the vastus lateralis muscle obtained in the basal and insulin-stimulated state. RESULTS: In type 2 diabetic subjects insulin-mediated glucose disposal, glucose oxidation and nonoxidative glucose metabolism were reduced, whereas lipid oxidation was increased (all P < 0.05). Insulin down-regulated PP2A-C alpha expression in skeletal muscle of the control subjects (P < 0.05) but not in the type 2 diabetic subjects. In the control subjects, the insulin-mediated decrease in PP2A-C alpha correlated with the insulin-mediated increase in glucose disposal, glucose oxidation, nonoxidative glucose metabolism (all P < 0.05) and decrease in lipid oxidation (P < 0.01). In the type 2 diabetic subjects these relationships were absent. CONCLUSIONS: Down-regulation of PP2A-C alpha expression by insulin in skeletal muscle seems to be associated with a normal insulin action on glucose storage, glucose and lipid oxidation. Impaired down-regulation of PP2A-C alpha expression by insulin may be a marker for insulin resistance and contribute to the pathogenesis of type 2 diabetes.     

Circulating endogenous vasoactive intestinal polypeptide (VIP) in patients with uraemia and liver cirrhosis

The concentration of vasoactive intestinal polypeptide (VIP) in peripheral venous plasma was median 6.0 pmol l-1 (range 0-20) in 112 normal subjects. In fifty-three patients with decreased kidney function plasma VIP was significantly increased (median 15.0 pmol l-1, range 0.5-70, P less than 0.0001) and positively correlated to serum creatinine concentration (r = 0.51, P less than 0.001). In 133 patients with liver cirrhosis peripheral venous VIP was slightly elevated (median 7.0 pmol l-1 range 0-86, P less than 0.01). Samples obtained during a central venous catheterization showed significant renal extraction of circulating VIP in control subjects (median extraction fraction 23%, P less than 0.05, n = 6) and in patients with cirrhosis (median 60%, P less than 0.02, n = 8), but not in uraemic patients (median 0%, NS n = 5). In control subjects and patients with cirrhosis the concentration of VIP in the hepatic vein was significantly below that of systemic plasma (-42%, P less than 0.05, n = 6 and -45%, P less than 0.01, n = 10, respectively). On the contrary, in uraemic patients hepatic venous VIP was almost similar to systemic VIP (-4%, NS, n = 7). The results indicate that in normal subjects and patients with cirrhosis both the liver and kidneys are involved in the biodegradation of VIP. The elevated level of circulating VIP in uraemic patients may in part be due to decreased renal and hepatic biodegradation but increased neuronal release of VIP, especially in the splanchnic system, may also contribute to the increased plasma VIP in this condition.     

Effect of polymorphism in the insulin gene region on IDDM susceptibility and insulin secretion**

Abstract. In addition to the major genetic determinants of insulin-dependent diabetes mellitus (IDDM) in the major histocompatibility complex (MHC) on chromosome 6, there are also minor genetic risk markers, e.g. in the insulin gene region on chromosome 11p15.5 (IDDM2). We studied the significance of the -23 HphI polymorphism in the insulin gene region (-23 HphI INS) in the Finnish population in combination with HLA genotyping data. The frequency of the -23 HphI INS +/+ genotype was higher in diabetic subjects with a low risk HLA DQBI genotype than in control subjects (P= 0.05). Diabetic children in multiple-case families also had a higher frequency of the INS risk genotype than the controls (P<0.05), and this difference was independent of the HLA genotype. Furthermore, we studied siblings positive for islet cell antibodies (ICAs) and/or insulin autoantibodies (IAAs) to evaluate the impact of the -23 HphI INS +/+ genotype on their beta-cell function assessed by sequential intravenous glucose tolerance tests and on their progression to IDDM. When analysing siblings with a low-risk HLA DQBI genotype, those with the -23 HphI INS +/+ genotype had lower first phase insulin responses (P <0.02) on several occasions than the remaining sibling. Six siblings (26.1%) in the former group progressed to clinical disease during the observation period, whereas none in the latter group presented with IDDM (P= 0.01). These observations suggest that the -23 HphI INS +/+ polymorphism is associated with an increased risk of IDDM in subjects without predisposing genes in the MHC region. The enhanced susceptibility may be related to a reduced insulin secretory capacity.     

The effect of a synthetic polypeptide on the renal handling of protein in man

Haemaccel is a synthetic polymer of partially degraded gelatin and a widely used plasma volume expander. The effect of a 17.5 g infusion of Haemaccel on protein excretion was investigated in four normal subjects. The urinary excretion of two low molecular weight proteins, retinol-binding protein and beta 2-microglobulin, increased 1000- and 500-fold respectively above the values found after administration of saline as a control. The urinary excretion of albumin did not change significantly (P greater than 0.5). In the hour after Haemaccel administration the excretion of the two low molecular weight proteins approached at least 50% of a predicted filtered load. This effect of Haemaccel may be due to inhibition of proximal tubular uptake or transport of the two proteins. Absence of any effect on albumin excretion suggests alternative mechanisms for its tubular reabsorption. Haemaccel may be a valuable new agent for the study of renal tubular protein metabolism.     

Protein synthesis in human skeletal muscle tissue: influence of insulin and amino acids

Abstract. The effects of a mild stimulation of endogenous insulin secretion on the rate of incorporation in vitro of amino acids into human skeletal muscle protein were compared with the effects on this rate of adding insulin and amino acids in vitro . An intravenous infusion of 0.83 mmol glucose per kg body weight increased both plasma glucose and insulin levels significantly. The rate of incorporation of leucine into protein in isolated muscle fibres was significantly higher if the subjects had received the glucose infusion. Both insulin and a high concentration of amino acids in the incubation medium stimulated this rate. Amino acids stimulated the rate more than insulin and insulin did not further stimulate the amino acid-stimulated rate. On the other hand, the stimulation of the rate of incorporation by amino acids was the same whether the subjects had received saline and were thus in a basal state or whether they had been infused with glucose (which itself stimulated the rate). The rate of incorporation of leucine was correlated with the tissue concentration of RNA but the correlation was weaker when the rate was stimulated by amino acids than under other experimental conditions. Leucine stimulated the rate of incorporation of phenylalanine but phenylalanine did not stimulate the rate of incorporation of leucine.
It is concluded that the rate of incorporation rate of amino acids into protein in isolated human skeletal muscle fibres is subjected to hormonal and amino acid control.