The evaluation of glucagon infusion algorithms for a counterregulatory system in artificial endocrine pancreas

As counterregulatory system of artificial endocrine pancreas, glucagon infusion algorithm has been developed and its usefulness has been examined in pancreatectomized dogs and a pancreatectomized diabetic patient. Glucagon infusion rate (G1nIR(t)) was determined depending on proportional plus derivative action to blood glucose concentration (BG(t] with the time delay (tau) to start infusion as follows. G1nIR(t) = Gp(BGp- BG(t-tau)) + Gd(-dBG(t-tau)) + Gc where BGp is the projected value of blood glucose concentration, Gp, and Gd are the coefficients and Gc is the constant for basal glucagon supplement. Glucagon infusions based only on proportional action (Gp/Gd/Gc/tau) = (0.2/0/0.4/10 or 0.4/0/0.4/10) failed in simulating the pattern of blood glucose or glucagon response seen in normal dogs. Glucagon infusion based on proportional plus derivative action (Gp/Gd/Gc/tau = 0.2/0.4/0.4/10) successfully mimicked the pattern of blood glucose concentration and plasma glucagon profile seen in normal dogs. This glucagon infusion algorithm has been applied to control insulin-induced hypoglycemia in a pancreatectomized patient with the same infusion parameters. Hypoglycemia was recovered to normoglycemia in 80 min and the plasma glucagon patterns showed no significant difference from those in healthy volunteers. These data indicate that glucagon infusion algorithm thus developed is effective to render hypoglycemia to normoglycemia and mimic plasma glucagon response seen in normal subjects.     

清醒大鼠胰岛素钳夹术及其糖代谢变化

为准确地评价在体组织对胰岛素 (Ins)的敏感性及探讨在胰岛素抵抗 (IR)状态下机体糖代谢变化。采用 6 ,6 D2 葡萄糖作为示踪剂 ,建立了自由状态下大鼠正常血糖 -高胰岛素钳夹术 ,并动态观察了其体内糖代谢的动态改变及血浆游离脂肪酸 (FFA)和Ins浓度随时间变化的过程。大鼠在 4 8mU (kg·min)速率Ins输注下 ,血糖稳定在正常水平而肝糖输出被抑制 ,胰岛素介导的机体葡萄糖利用率较基础状态显著增加 ,游离脂肪酸 (FFA)浓度显著下降。本钳夹术平均血糖变异系数为 5 76 %。平均GIR变异系数为 6 2 5 % ,GRd为 9 17%。重复试验GIR与GRd误差范围为 1 2 %和 1 7%。以 6 ,6 D2 葡萄糖作为示踪剂建立的自由状态下的大鼠正常血糖钳夹技术具有准确、可靠 ,无放射污染等优点 ,在外源性胰岛素 -葡萄糖代谢稳定状态下 ,机体对葡萄糖利用显著增加 ,脂肪分解显著减少。     

脂质灌注对大鼠血浆抵抗素和ghrelin的影响*

目的：探讨脂质灌注对大鼠血浆抵抗素和ghrelin的影响。 方法： 采用正糖钳夹技术，在钳夹前后分别测定生理盐水对照组和脂质灌注组血浆抵抗素和ghrelin浓度，并用［3H］-葡萄糖作为示踪剂测定外周组织和肝糖的代谢。 结果： 脂质灌注组大鼠血浆游离脂肪酸（FFA）明显增加（P<0.01），葡萄糖输注率（GIR）明显降低（P<0.01）。对照组肝糖产率（HGP）明显被抑制（88%）。脂质输注组胰岛素对HGP的抑制作用明显减弱。在钳夹期间，脂质组与对照组比葡萄糖清除率（GRd）轻度降低。在正糖钳夹术结束时，对照组血浆ghrelin水平与钳夹前相比明显降低(P<0.05)。4 h的脂质灌注也引起了血浆ghrelin浓度的明显下降(P<0.05)，但是在钳夹结束时和对照组比没有明显差异。相关性分析表明空腹血浆ghrelin水平与空腹胰岛素和血糖呈明显负相关（r=-0.52和r=-0.61, P<0.05）。脂质灌注后大鼠血浆抵抗素水平较灌注前和对照组明显升高（P<0.01），空腹血浆抵抗素浓度与空腹FFA（r=0.68, P<0.01）、血糖（r=0.66, P<0.01）呈明显正相关。 结论： 脂质灌注诱导了肝脏和外周的胰岛素抵抗，抵抗素在胰岛素抵抗的形成中可能具有重要作用。高胰岛素血症，而不是游离脂肪酸，降低了大鼠循环ghrelin水平。     

Derivative weighted active insulin control modelling and clinical trials for ICU patients

Close control of blood glucose levels significantly reduces vascular complications in Type 1 and Type 2 diabetic individuals. Heavy derivative controllers using the data density available from emerging biosensors are developed to provide tight, optimal control of elevated blood glucose levels, while robustly handling variation in patient response. A two-compartment glucose regulatory system model is developed for intravenous infusion from physiologically verified subcutaneous infusion models enabling a proof-of-concept clinical trial at the Christchurch Hospital Department of Intensive Care Medicine. This clinical trial is the first of its kind to test a high sample rate feedback control algorithm for tight glucose regulation. The clinical trial results show tight control with reductions of 79–89% in blood glucose excursions for an oral glucose tolerance test. Experimental performance is very similar to modelled behaviour. Results include a clear need for an additional accumulator dynamic for insulin behaviour in transport to the blood and strong correlation of 10% or less between modelled insulin infused and the amounts used in clinical trials. Finally, the heavy derivative PD control approach is seen to be able to bring blood glucose levels below the (elevated) basal level, showing the potential for truly tight control.     

Effects of two different levels of computerized decision support on blood glucose regulation in critically ill patients

Introduction

Although the use of computerized decision support systems (CDSS) in glucose control in the ICU has been reported, little is known about the effect of the systems’ operating modes on the quality of glucose control. The objective of this study was to evaluate the effect of providing patient-specific and patient non-specific computerized advice on timing of blood glucose level (BGL) measurements. Our hypothesis was that both levels of support would be effective for improving the quality of glucose regulation and safety, with patient specific advice being the most effective strategy.

Patients and methods

A prospective study was performed in a 30-bed mixed medical-surgical intensive care unit (ICU) of a university hospital. In phase 1 the CDSS provided non-specific advice and thereafter, in phase 2, the system provided specific advice on timing of BGL measurements. The primary outcome measure was delay in BGL measurements before and after the two levels of support. Secondary endpoints were sampling frequency, mean BGL, BGL within pre-defined targets, time to capture target, incidences of severe hypoglycemia and hyperglycemia. These indicators were analyzed over the course of time using Statistical Control Charts. The analysis was restricted to patients with at least two blood glucose measurements.

Results

Data of 3934 patient admissions were evaluated, which corresponded to 119,116 BGL measurements. The BGL sampling interval, delays in BG sampling, and percentage of hypoglycemia all decreased after introducing either of the two levels of decision support. The effect was however larger for the patient specific CDSS. Mean BGL, time to capture target, hyperglycemia index, percentage of hyperglycemia events and “in range” measurements remained unchanged and stable after introducing both patient non-specific and patient specific decision support.

Conclusion

Adherence to protocol sampling rules increased by using decision support with a larger effect at the patient specific level. This led to a decrease in the percentage of hypoglycemia events and improved safety. The use of the CDSS at both levels, however, did not improve the quality of glucose control as measured by our indicators. More research is needed to investigate whether other socio-technical factors are in play.     

Development of a transcutaneous blood-constituent monitoring method using a suction effusion fluid collection technique and an ion-sensitive field-effect transistor glucose sensor

The paper describes a method for the transcutaneous monitoring of blood constituents. It combines the use of a suction effusion fluid (SEF) collecting technique with a silicon on sapphire/ion-sensitive field-effect transistor (SOS/ISFET) biosensor. SEF is directly collected by a weak evacuation through skin from which the stratum corneum has been removed. An SEF collecting cell with a stainless-steel mesh at the bottom is kept in a weak vacuum condition, and SEF is sucked up through the mesh and deposited in a reservoir above. An ISFET glucose sensor is able to detect glucose concentrations in very small SEF samples through the use of two small ISFETs and an immobilised enzyme membrane. The reliability of transcutaneously obtained SEF was first confirmed in an experiment using rabbits. A clinical analyser was used to determine levels of glucose, urea nitrogen and creatinine in SEF obtained transcutaneously; these results are compared with results obtained by the same analyser directly from sera. The ISFET glucose sensor was successfully tested on human subjects for the monitoring of blood glucose levels. During these tests, glucose level changes in the SEF followed acutal blood glucose level changes with a slight time delay. Results suggest the feasibility of non-invasive, transcutaneous monitoring of low molecular weight substances in the blood without the use of ordinary blood sampling.     

Effects of training on blood glucose kinetics during glucose challenge in rats

We hypothesized that endurance training would alter blood glucose kinetics in rats given an exogenous glucose challenge. Primed-continuous infusion of H¹⁴CO₃-and [3-³H]glucose were given to fasted rats during an intravenous glucose load of approximately 150% of the normal endogenous appearance rate for 3 h. In all rats blood glucose concentrations increased with loading, but in trained animals glucose stabilized at significantly lower levels. Trained animals had lower blood glucose turnover rates than the controls (75±2.3 vs. 120±6.3 moles/kg×min, respectively). Glucose metabolic clearance rates in trained rats (11.5±1.7) were not different from those in controls (11.6±1.2 ml/kg×min). Gluconeogenic rates estimated from incorporation of¹⁴C into blood glucose did not differ between trained and untrained groups. However, the rate of hepatic glucose release estimated from the difference between tracer measured and exogenous appearance rate was lower in the trained group. These findings support the concept that when resting trained animals are challenged with an exogenous load, more glucose is diverted to anabolic processes as opposed to increased turnover.     

Interference of the nutritional condition of the rat with peripheral glucose regulation determined by CNS mechanisms

Glucose and insulin levels of the cerebrospinal fluid (CSF) were changed by an infusion of either glucose, insulin or a mixture of glucose and insulin in the third ventricle of freely moving undisturbed rats. Before, during and after infusions venous blood samples were withdrawn to determine insulin- and glucose concentrations. In rats on carbohydrate rich food neither plasma insulin nor blood glucose changed during infusion of either glucose, insulin or a mixture of both. However, in rats on carbohydrate free food an immediate decline in blood glucose of about 7 mg/dl occurred 15 min after the start of the infusion. During infusion of a mixture of glucose and insulin, blood glucose rose slightly and reached a value which was in between those attained when glucose and insulin were infused separately. Plasma insulin did not change following central infusions. It is argued that the central nervous system (CNS) is sensitive to changes in CSF levels of glucose and insulin and affects peripheral glucose homeostasis mainly by changing glucose output from the liver. This action of the CNS, however, is dependent on the nutritional condition of the animal.     

Glucose clamp technique: a method for quantifying insulin secretion and resistance.

Methods for the quantification of beta-cell sensitivity to glucose (hyperglycemic clamp technique) and of tissue sensitivity to insulin (euglycemic insulin clamp technique) are described. Hyperglycemic clamp technique. The plasma glucose concentration is acutely raised to 125 mg/dl above basal levels by a priming infusion of glucose. The desired hyperglycemic plateau is subsequently maintained by adjustment of a variable glucose infusion, based on the negative feedback principle. Because the plasma glucose concentration is held constant, the glucose infusion rate is an index of glucose metabolism. Under these conditions of constant hyperglycemia, the plasma insulin response is biphasic with an early burst of insulin release during the first 6 min followed by a gradually progressive increase in plasma insulin concentration. Euglycemic insulin clamp technique. The plasma insulin concentration is acutely raised and maintained at approximately 100 muU/ml by a prime-continuous infusion of insulin. The plasma glucose concentration is held constant at basal levels by a variable glucose infusion using the negative feedback principle. Under these steady-state conditions of euglycemia, the glucose infusion rate equals glucose uptake by all the tissues in the body and is therefore a measure of tissue sensitivity to exogenous insulin.     

Glucose predictability,blood capillary permeability,and glucose utilization rate in subcutaneous,skeletal muscle,and visceral fat tissues

This study suggests an approach for the comparison and evaluation of particular compartments with modest experimental setup costs. A glucose level prediction model was used to evaluate the compartment's glucose transport rate across the blood capillary membrane and the glucose utilization rate by the cells. The glucose levels of the blood, subcutaneous tissue, skeletal muscle tissue, and visceral fat were obtained in experiments conducted on hereditary hypertriglyceridemic rats. After the blood glucose level had undergone a rapid change, the experimenter attempted to reach a steady blood glucose level by manually correcting the glucose infusion rate and maintaining a constant insulin infusion rate. The interstitial fluid glucose levels of subcutaneous tissue, skeletal muscle tissue, and visceral fat were evaluated to determine the reaction delay compared with the change in the blood glucose level, the interstitial fluid glucose level predictability, the blood capillary permeability, the effect of the concentration gradient, and the glucose utilization rate. Based on these data, the glucose transport rate across the capillary membrane and the utilization rate in a particular tissue were determined. The rates obtained were successfully verified against positron emission tomography experiments. The subcutaneous tissue exhibits the lowest and the most predictable glucose utilization rate, whereas the skeletal muscle tissue has the greatest glucose utilization rate. In contrast, the visceral fat is the least predictable and has the shortest reaction delay compared with the change in the blood glucose level. The reaction delays obtained for the subcutaneous tissue and skeletal muscle tissue were found to be approximately equal using a metric based on the time required to reach half of the increase in the interstitial fluid glucose level.     

A new glucose clamp algorithm: clinical validation

A new glucose clamp technique for in vivo studies of insulin sensitivity was validated clinically. Eighteen patients (10 males, 8 females, age 35-80 years, body mass index 34.6-17.04) were connected to a computer-assisted artificial pancreas "Betalike R", using a new algorithm based on a "minimal model", to carry out the glucose clamp technique automatically and especially to overcome the well-known problems of its priming phase. We performed the euglycemic hyperinsulinemic clamp in four patients and the hyperglycemic hyperinsulinemic clamp in 14. In one patient both clamps were done. The mean priming time to reach steady-state glycemia was 20 min. Plasma insulin concentrations were measured every 20 min. This new automatic glucose clamp technique enables the priming phase to be run without any significant overshoot, and accidental variations of glycemia in steady state were reduced to a minimum. The system showed satisfactory safety and stability in controlling the patient's glycemia and assured high speed of the priming phase.     

Simulation of Oral Glucose Tolerance Tests and the Corresponding Isoglycemic Intravenous Glucose Infusion Studies for Calculation of the Incretin Effect

The incretin effect, which is a unique stimulus of insulin secretion in response to oral ingestion of nutrients, is calculated by the difference in insulin secretory responses from an oral glucose tolerance test (OGTT) and a corresponding isoglycemic intravenous glucose infusion (IIGI) study. The OGTT model of this study, which is individualized by fitting the glucose profiles during an OGTT, was developed to predict the glucose profile during an IIGI study in the same subject. Also, the model predicts the insulin and incretin profiles during both studies. The incretin effect, estimated by simulation, was compared with that measured by physiologic studies from eight human subjects with normal glucose tolerance, and the result exhibited a good correlation (r > 0.8); the incretin effect from the simulation was 56.5% ± 10.6% while the one from the measured data was 52.5% ± 19.6%. In conclusion, the parameters of the OGTT model have been successfully estimated to predict the profiles of both OGTTs and IIGI studies. Therefore, with glucose data from the OGTT alone, this model could control and predict the physiologic responses, including insulin secretion during OGTTs and IIGI studies, which could eventually eliminate the need for complex and cumbersome IIGI studies in incretin research.

Graphical Abstract

相似文献   

Marked suppression of ghrelin concentration by insulin in Prader-willi syndrome

The plasma ghrelin has been reported to be elevated in Prader-Willi syndrome (PWS) and modulated by insulin. It was hypothesized that insulin might have a more pronounced effect on reducing plasma ghrelin in PWS patients, which would influence appetite. This study investigated the degree of ghrelin suppression using an euglycemic hyperinsulinemic clamp in children with PWS (n=6) and normal children (n=6). After a 90-min infusion of insulin, the plasma ghrelin level decreased from a basal value of 0.86+/-0.15 to 0.58+/-0.12 ng/mL in the controls, and from 2.38+/-0.76 to 1.12+/-0.29 ng/mL in children with PWS (p=0.011). The area under the curve below the baseline level over the 90 min insulin infusion was larger in children with PWS than in controls (-92.82+/-44.4 vs. -10.41+/-2.87 ng/mL/90 min) (p=0.011). The insulin sensitivity measured as the glucose infusion rate at steady state was similar in the two groups (p=0.088). The decrease in the ghrelin levels in response to insulin was more pronounced in the children with PWS than in the controls. However, the level of ghrelin was always higher in the children with PWS during the clamp study. This suggests that even though insulin sensitivity to ghrelin is well maintained, an increase in the baseline ghrelin levels is characteristic of PWS.     

Mechanism of sympathetic activation during prolonged physical exercise in dogs

It seems likely that depletion of body carbohydrates may account for the rise in the sympathetic activity during prolonged exercise, since glucose given during or before exercise reduces the increase in plasma catecholamines. The aim of the present study was to find out whether the increase in plasma noradrenaline (NA) in response to exercise can be reduced by 1. increasing of the amount of carbohydrate available for metabolism without producing hyperinsulinemia and 2. by inhibition of afferent activity from hepatic glucoreceptors. The study was performed on dogs which exercised whilst receiving either the intravenous fructose infusion (2.2 mmol/min) or a slow glucose infusion (0.25 mmol/min) which was given either via the portal or a peripheral vein. Fructose infusion reduced the muscle glycogen depletion during exercise and reduced the increase in plasma NA and glycerol concentrations without altering the blood glucose or insulin levels. The exercise-induced increases in plasma NA and gycerol concentrations were significantly smaller with intraportal than with peripheral glucose infusion but there were no differences between these two cases in the concentration of glucose in the systemic circulation. These findings indicate that the reduction of the plasma NA response to physical effort under conditions of increased carbohydrate availability cannot be attributed to the inhibitory effect of insulin on sympathetic activity and provide evidence for the participation of hepatic glucoreceptors in the control of the sympathetic activity during exercise.This work was supported by the Polish Academy of Sciences within the project 10.4.03.1.1     

玉泉丸防治糖尿病慢性并发症的作用机理研究

目的：探讨玉泉丸对2型糖尿病的防治作用及可能的作用机理。方法：新生大鼠自出生第二天起颈部皮下住射L谷氨酸钠（MSG）5g·kg^-1隔天一次,共三次,诱导肥胖大鼠胰岛素抵抗模型,8w后将其分为空白对照组,模型组,玉泉丸3．O、6．0、12．0g·kg^-1组及阳性对照（罗格列酮）组,运用正糖钳技术测定胰岛素敏感性,ELISA法测定大鼠的胰岛素水平,考察玉泉丸对胰岛素抵抗的影响;运用高脂膳食加腹腔注射链脲佐茵素（Streptozotocin,STZ）20mg·kg^-1复制Ⅱ型糖尿病大鼠模型,分为空白对照组,模型组,玉泉丸3．O、6．0、12．0g·kg^-1组及阳性对照（罗格列酮）组,考察玉泉丸对血液脂质等指标的影响。结果：（1）与对照组相比,MSG模型大鼠血糖水平明显升高,Lee’s指数及胰岛素水平明显升高,葡萄糖输注速率（Glucose infusion rate,GIR）显著降低;与MSG模型大鼠相比,玉泉丸3．0g·kg^-1可显著降低MSG模型大鼠血糖水平,玉泉丸各剂量组均可显著增加MSG模型大鼠GIR。（2）与对照组相比,STZ诱导的2型糖尿病大鼠血清TG、TC、HDL显著升高,经玉泉丸3．0g·kg-1治疗可显著降低血清TC以及LDL水平,而玉泉丸6．Og·kg^-1可显著降低Ⅱ型糖尿病大鼠血清TC、HDL以及LDL水平。结论：玉泉丸一方面可通过改善胰岛素敏感性发挥其防治糖尿病慢性并发症的作用,另一方面也可通过调节血脂代谢改善糖尿病患者大血管病变以及微血管病变,为临床应用该药以改善糖尿病慢性并发症提供了一定的实验依据,其详细作用机理有待进一步研究。     

Stimulation of insulin release and suppression of feeding by hepatic portal glucagon infusion in rats

Plasma insulin and glucose concentrations were measured in rats by remote blood sampling techniques 5 and 25 min after the start of a continuous intraportal glucagon infusion (0.33, 1.0, 3.3, 10 and 33 micrograms/kg/min). Plasma insulin levels were elevated in a dose-related fashion by glucagon, with the highest dose producing a 23-fold increase above control levels. In contrast, the glycemic effect of glucagon was not dose-related. Glucagon-induced hyperglycemia was similar for all glucagon doses, despite the fact that a glucagon dose range spanning two orders of magnitude was used. In a second experiment, plasma glucose and insulin were measured as described above at two glucagon infusion rates (1 and 10 micrograms/kg/min), but the animals were allowed to eat during the infusion. Results showed that the effects of glucagon infusions on plasma insulin and glucose were additive with the normal prandial changes in these substances. Finally, food intake was inversely related to insulin level and dissociated from the hyperglycemia during glucagon infusion. These results show that exogenous glucagon provides a potent stimulus for insulin release in the rat both in the presence and in the absence of food. Furthermore, these results in combination with other data suggest that glucagon-induced hyperinsulinemia merits further investigation as one possible determinant of glucagon satiety in the rat.     

Quantitative brain FDG/PET studies using dynamic aortic imaging

Positron emission tomography (PET) measurements of cerebral glucose utilization using 18F-fluorodeoxyglucose (FDG) are a useful tool in the investigation of localized brain function in normal and disease states. A major impediment to the application of FDG/PET in clinical investigation has been the need for arterial blood sampling to quantify cerebral glucose metabolism (CMRGlc). Qualitative studies, though informative in a variety of clinical settings, are of limited value for research applications and do not utilize the inherent quantitative nature of PET. We present a novel PET technique employing a whole-body PET tomograph with abdominal aortic imaging from 0 to 30 min as an alternative to arterial blood sampling to obtain the input function for cerebral metabolic rate calculations. Two or three arterial samples taken during the 10-45 min period were used to scale and extend the blood curve and the brain was imaged from 35-55 min post-injection. We performed 12 studies in which both arterial blood sampling and aortic scans were obtained. We found the correlation of global metabolic rates (GMR) when comparing the two techniques to be extremely high (R2 = 0.99). This suggests that the use of dynamic aortic imaging is less invasive and a viable alternative to arterial blood sampling in quantitative FDG/PET imaging.     

Pancreatic islet blood flow during euglycaemic, hyperinsulinaemic clamp in anaesthetized rats

Aims: Previous studies have demonstrated that pancreatic islet blood flow is crucially dependent on blood glucose concentration. Thus, hyperglycaemia increases and hypoglycaemia decreases islet blood perfusion, by a combination of nervous and metabolic signals. The aim of the present study was to evaluate if hyperinsulinaemia, without associated hypoglycaemia, affects islet blood flow. Methods: Thiobutabarbital‐anaesthetized Wistar–Furth rats were subjected to an euglycaemic, hyperinsulinaemic clamp, that is they were infused for 60 min with either saline, insulin (18 mU kg^?1 min^?1), glucose (27 mg kg^?1 min^?1) or both glucose and insulin. This was followed by islet blood flow measurements with a microsphere technique. Results: Animals receiving only glucose doubled their blood glucose and serum insulin concentrations, whereas rats receiving only insulin had blood glucose concentrations <2 mmol L^?1 and a 10‐fold increase in serum insulin concentrations. Animals given simultaneous glucose and insulin had normal blood glucose concentrations but a 10‐fold increase in serum insulin concentrations. Total pancreatic blood flow was unaffected in all animals. Islet blood flow was increased in hyperglycaemic and decreased in hypoglycaemic rats compared with control rats. Islet blood flow did not differ between clamped and control rats. Conclusions: Serum insulin concentration per se does not affect islet blood flow, whereas the ambient blood glucose concentration is of major importance in this context.     

Extracellular distribution of insulin in muscle of rats exposed to long-term hyperinsulinaemia

The importance of increased capillary density for the regulation of insulin sensitivity by transcapillary delivery of insulin to muscle cells in insulin-exposed rats was investigated by direct microdialysis measurements of interstitial [¹²⁵I]insulin concentrations in the femoral muscle during an euglycaemic hyperinsulinaemic clamp. In insulin-exposed rats plasma insulin was ～25% (P<0.05) higher than that in control animals during the first 100 min and reached their maximal concentrations after 100 min. After a nitroprusside infusion given at 100 min both groups had similar concentrations of insulin in plasma as well as in muscle interstitial fluid. However, mean glucose infusion rate during the first clamp hour was 20.5±2.3 and 12.6±5.2 mg kg^-1 min^-1 (P<0.05) in insulin-exposed and control animals, respectively. During the second clamp hour the corresponding figures were 21.1±2.4 and 13.9±2.6 (P<0.05). It may be concluded that capillarization and/or nitroprusside affected plasma insulin concentrations without altering either the interstitial insulin levels or the insulin effect on glucose consumption. The data suggest that the elevated insulin sensitivity after chronic insulin exposure is dependent on other than transcapillary transport events and demonstrate the different kinetics for insulin distribution in plasma and in the interstitial fluid.