Derivation of a three compartment model describing disappearance of plasma insulin-131-I in man

Insulin Clearance in Obesity and Type 2 Diabetes

Plasma insulin clearance is an important determinant of plasma insulin concentration. In this review, we provide an overview of the factors that regulate insulin removal from plasma and discuss the interrelationships among plasma insulin clearance, excess adiposity, insulin sensitivity, and type 2 diabetes (T2D). We conclude with the perspective that the commonly observed lower insulin clearance rate in people with obesity, compared with lean people, is not a compensatory response to insulin resistance but occurs because insulin sensitivity and insulin clearance are mechanistically, directly linked. Furthermore, insulin clearance decreases postprandially because of the marked increase in insulin delivery to tissues that clear insulin. The commonly observed high postprandial insulin clearance in people with obesity and T2D likely results from the relatively low insulin secretion rate, not an impaired adaptation of tissues that clear insulin.

Characterisation of preproendothelin-1 derived peptides identifies Endothelin-Like Domain Peptide as a modulator of Endothelin-1

Endothelin-1 (ET-1) is involved in the pathogenesis of cardiac and renal diseases, and in the progression of tumour growth in cancer, but current diagnosis and treatment remain inadequate. Peptides derived from the 212 amino acid precursor preproendothelin-1 (ppET-1) may have utility as biomarkers, or cause biological effects that are unaffected by endothelin receptor antagonists. Here, we used specific immunoassays and LC-MS/MS to identify NT-proET-1 (ppET-1_[18–50]), Endothelin-Like Domain Peptide (ELDP, ppET-1_[93–166]) and CT-proET-1 (ppET-1_[169–212]) in conditioned media from cultured endothelial cells. Synthesis of these peptides correlated with ET-1, and plasma ELDP and CT-proET-1 were elevated in patients with chronic heart failure. Clearance rates of NT-proET-1, ELDP and CT-proET-1 were determined after i.v. injection in anaesthetised rats. CT-proET-1 had the slowest systemic clearance, hence providing a biological basis for it being a better biomarker of ET-1 synthesis. ELDP contains the evolutionary conserved endothelin-like domain sequence, which potentially confers biological activity. On isolated arteries ELDP lacked direct vasoconstrictor effects. However, it enhanced ET-1 vasoconstriction and prolonged the increase in blood pressure in anaesthetised rats. ELDP may therefore contribute to disease pathogenesis by augmenting ET-1 responses.

Pharmacokinetic predictions for patients with renal impairment: focus on peptides and protein drugs

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

• Renal impairment may affect the pharmacokinetics of peptide and protein drugs. • Molecular size is a predictor. Small molecules are eliminated by the kidneys, whereas large molecules (>67 kDa) are not. • Urinary recovery of peptide and protein drugs in healthy volunteers is not predictive for pharmacokinetic changes in patients with renal impairment.

WHAT THIS STUDY ADDS

• An apparently continuous non-linear relationship between molecular weight and pharmacokinetic alterations as observed in patients with severe renal impairment or end-stage renal disease is described. • Potentially relevant pharmacokinetic changes were found for drugs with a molecular weight below 50 kDa. • Analysis of observed pharmacokinetics in patients with severe renal impairment may be a useful approach, especially when urinary recovery in healthy volunteers is not predictive.

AIM

Drug dosage adjustments in renal impairment are usually based on estimated individual pharmacokinetics. The extent of pharmacokinetic changes in patients with renal impairment must be known for this estimation. If measured data are not available, an estimate based on drug elimination in urine of healthy subjects or patients with normal renal function is commonly made. This is not reliable, however, if renal drug metabolism is involved, as is presumably the case for many peptide and protein drugs. In the present study a new method to predict pharmacokinetic changes for such drugs based on molecular weight was derived.

METHODS

Articles reporting measured pharmacokinetics of peptide and protein drugs in patients with severe renal impairment or end-stage renal disease were identified from the scientific literature, the pharmacokinetic parameter values were extracted and a statistical data synthesis was performed. A sigmoid E(max) model was applied and fitted to the data and the prediction error was analyzed.

RESULTS

Overall, 98 peptide and protein drugs were identified. Relevant pharmacokinetic data in patients with renal impairment were found for 21 of these drugs. The average drug clearance was 30% and the average prolongation in half-life was 3.1-fold for low molecular weight peptides or proteins. The median root squared percentage of the prediction error was 18% (drug clearance) and 12% (half-life).

CONCLUSION

An apparently continuous non-linear relationship between molecular weight and pharmacokinetic alterations in patients with severe renal impairment was found. The derived equations could be used as a rough guide for decisions on drug dosage adjustments in such patients.

Increased hypoglycemia associated with renal failure during continuous intravenous insulin infusion and specialized nutritional support

OBJECTIVE

To evaluate glycemic control for critically ill, hyperglycemic trauma patients with renal failure who received concurrent intensive insulin therapy and continuous enteral nutrition (EN) or parenteral nutrition (PN).

METHODS

Adult trauma patients with renal failure who were given EN or PN concurrently with continuous graduated intravenous regular human insulin (RHI) infusion for at least 3 d were evaluated. Our conventional RHI algorithm was modified for those with renal failure by allowing greater changes in blood glucose (BG) concentrations before the infusion rate was escalated. BG concentration was determined every 1 to 2 h while receiving the insulin infusion. BG control was evaluated on the day before RHI infusion and for a maximum of 7 d while receiving RHI. Target BG during the RHI infusion was 70 to 149 mg/dL (3.9 to 8.3 mmol/L). Glycemic control and incidence of hypoglycemia for those with renal failure were compared with a historical cohort of critically ill, hyperglycemic trauma patients without renal failure given our conventional RHI algorithm.

RESULTS

Twenty-one patients with renal failure who received the modified RHI algorithm were evaluated and compared with 40 patients without renal failure given our conventional RHI algorithm. Average BG concentration was significantly greater for those with renal failure (133±14 mg/dL or 7.3±0.7 mmol/L) compared with those without renal failure (122±15 mg/dL or 6.8±0.8 mmol/L), respectively (P<0.01). Patients with renal failure showed worsened glycemic variability, with 16.1±3.3 h/d within the target BG range, 6.9±3.2 h/d above the target BG range, and 1.4±1.1 h/d below the target BG range compared with 19.6±4.7 h/d (P<0.001), 3.4±3.0 h/d (P<0.001), and 0.7±0.8 h/d (P<0.01) for those without renal failure, respectively. Moderate hypoglycemia (<60 mg/dL or<3.3 mmol/L) occurred in 76% of patients with renal failure compared with 35% without renal failure (P<0.005). Severe hypoglycemia (BG<40 mg/dL or<2.2 mmol/L) occurred in 29% of patients with renal failure compared with none of those without renal failure (P<0.001).

CONCLUSION

Despite receiving a modified RHI infusion, critically ill trauma patients with renal failure are at greater risk for developing hypoglycemia and have more glycemic variability than patients without renal failure.

Glycemic Control during Critical Illness: Tight or Not?

Nutrition Support Pharmacist features issues pertinent to the practice of clinical pharmacy in the area of metabolic support. In this review, a critical analysis of six current major intensive insulin therapy trials (Leuven I, Leuven II, Leuven III, NICE-SUGAR, VISEP, and Glucontrol) for critically ill surgical and medical patients is provided. Practical suggestions for managing hyperglycemia, defining an effective target blood glucose concentration range, avoiding hypoglycemia, and designing a safe and effective insulin infusion algorithm are given.

The effect of renal transplantation on basal serum gastrin concentration

Basal serum gastrin concentration was measured before and every week during the initial 5 weeks after renal transplantation in 9 of 20 patients with chronic renal failure who obtained a well functioning renal transplant. Furthermore, calcium and phosphorus metabolism in relation to serum gastrin was investigated in all 20 patients 5 weeks after transplantation. Before renal transplantation, serum gastrin was markedly elevated as compared with the levels in normal controls. During the first 3-5 weeks after renal transplantation, serum gastrin decreased towards normal values. A slight but significant increase in serum gastrin persisted 5 weeks after transplantation. No significant relation between changes in serum gastrin concentration and in calcium and phosphorus metabolism was observed.

Relation between insulin kinetics and insulin sensitivity in pregnancy

BACKGROUND

Different time-concentration profiles of plasma insulin following insulin modification of a frequently sampled intravenous glucose-tolerance-test (FSIVGTT) were observed in a study investigating maternal metabolism and fetal macrosomia. We aimed to investigate whether these differences were related to the volume of distribution of insulin, insulin clearance, or both.

DESIGN

Forty-four women were studied between 33 and 35 weeks' gestation using an insulin-modified FSIVGTT. Specific insulin was assayed with an enzyme-linked immunosorbent assay. Insulin sensitivity was calculated using the minimal model and the homeostasis model assessment (HOMA). The volume of distribution and clearance of insulin were calculated from measurements between 2 and 155 min after insulin modification using a one-compartment model.

RESULTS

In accordance with the method for deriving the volume of distribution, there was a significant negative correlation between the increment in insulin concentration and the volume of distribution (rho=-0.92, P<0.0001). The insulin increment was also related negatively to the clearance of insulin (rho=-0.88, P<0.0001). There was a significant correlation between the volume of distribution and both the insulin sensitivity index (rho=0.56, P<0.0001) and HOMA-%S (rho=0.30, P=0.048), and between the clearance of insulin and both the insulin sensitivity index (rho=0.83, P<0.0001)) and HOMA-%S (rho=0.34, P=0.025).

CONCLUSION

The different time-concentration profiles of plasma insulin resulted from differences in the volume of distribution and clearance of insulin. There was a correlation between insulin kinetics and the insulin sensitivity index. Further research is required to investigate possible mechanisms by which insulin kinetics may be related to insulin sensitivity.

The insulin status of sheep with genetic differences in glucose clearance

Lines of sheep have been selected for Slow or Fast glucose clearance after a glucose tolerance test. The aim of this work was to establish what characteristics of the insulin status were altered by the breeding program. Six animals from each line with consistently Slow (T-half > 70 min) or Fast (T-half < 60 min) decreases in plasma glucose concentration were studied in three different experiments. After the injection of [125I]insulin, blood was sampled for 300 min. The change in radioactivity with time was used in a three-compartment series model to estimate theoretical insulin pool sizes and flow rates between pools. All three pools were significantly (P < 0.05) larger in the Slow (61, 115, and 191 mU) than in the Fast glucose clearance animals (45, 82, and 112 mU). Flow rates between the pools were not significantly different. A euglycemic clamp experiment was performed at two insulin infusion rates, each for 4 hr. A significantly higher glucose infusion rate was required to maintain blood glucose at basal levels in the Slow (3 and 9 mg of glucose/kg liveweight [lwt]0.75 per min) than in the Fast glucose clearance animals (1 and 5 mg/kg lwt0.75 per min). The increase in glucose infusion rate when the insulin infusion rate was increased from 0.63 to 3.46 mU/kg lwt0.75 per min (insulin sensitivity index) was significantly greater in Slow than in Fast glucose clearance animals (0.68 vs. 0.35 mU of insulin/kg lwt0.75 per min). There was no difference between the lines in insulin binding to membranes isolated from muscle or adipose tissue. It is concluded that selection for Slow or Fast glucose clearance has altered several aspects of insulin status, but further work is required to identify the primary difference between the lines.

A probabilistic approach to glucose prediction and insulin dose adjustment: description of metabolic model and pilot evaluation study

A model of carbohydrate metabolism has been implemented as a causal probabilistic network, allowing explicit representation of the uncertainties involved in the prediction of 24-h blood glucose profiles in insulin-dependent diabetic subjects. The parameters of the model were based on experimental data from the literature describing insulin and carbohydrate absorption, renal loss of glucose, insulin-independent glucose utilisation and insulin-dependent glucose utilisation and production. The model can be adapted to the observed glucose metabolism in the individual patient and can be used to generate predicted 24-h blood glucose profiles. A penalty is assigned to each level of blood glucose, to indicate that high and low blood glucose levels are undesirable. The system can be asked to find the insulin doses that result in the most desirable 24-h blood glucose profile. In a series of 12 patients, the system predicted blood glucose with a mean error of 3.3 mmol/l. The insulin doses suggested by the system seemed reasonable and in several cases seemed more appropriate than the doses actually administered to the patients.

Five-compartment model of insulin kinetics and its use to investigate action of chloroquine in NIDDM

We have constructed a five-compartment model of insulin kinetics. The model structure was chosen to reflect insulin distribution in systemic plasma, hepatic plasma, and interstitial fluid and insulin binding to the liver and peripheral receptors, and it included receptor-mediated and non-receptor-mediated insulin degradation. Model parameters were estimated from plasma insulin concentrations measured during hyperinsulinemic euglycemic clamp studies. In the fasting condition, the model-derived mean residence time of endogenously secreted insulin was 71 min, of which 62 min were spent bound to the liver receptor, 6 min bound to the peripheral receptor, 2 min circulating in hepatic or systemic plasma, and 1 min in the interstitial fluid. More than 80% of total insulin was bound to the liver receptor, indicating that the liver is by far the largest insulin reservoir. The model was employed to assess the effect of chloroquine on insulin kinetics in patients with non-insulin-dependent diabetes mellitus (NIDDM). Chloroquine significantly altered parameter vector. However, the mean residence times of insulin in the system and in the periphery were not affected, indicating that the beneficial effect of chloroquine in patients with NIDDM under conditions of euglycemia could not be attributed to changes in insulin kinetics.

Comparison of the continuously calculated fractional splanchnic extraction of insulin with its fractional disappearance using a new double-tracer technique

These studies were designed to calculate the fractional disappearance rate (FDR) and splanchnic extraction of insulin in response to an exogenous (intraperitoneal) input of insulin. A double-tracer technique using insulin tritiated on both the A1 and B1 positions was introduced for the measurement of hepatic extraction. The A1 tracer, not previously characterized in vivo, was compared in terms of its kinetics with H3-B1-insulin and unlabeled insulin. The metabolic clearance rates (MCR) of the three insulins were identical, as were the decay curves of the two tracers. To measure splanchnic insulin extraction, one tracer was infused systemically to evaluate the FDR of insulin, and the second was infused into the splanchnic circulation (superior mesenteric artery) and its peripheral appearance was calculated. Splanchnic extraction was determined from the difference between this rate of appearance and the rate of infusion of the mesenteric tracer. After intraperitoneal insulin injection, insulin levels increased to peaks of 549 +/- 93 microU/mL (portal vein) and 473 +/- 99 microU/mL (inferior vena cava) and decreased to basal levels over 3 hours. The FDR decreased from 0.295 +/- 0.051 min-1 to 0.125 +/- 0.026 min-1, and splanchnic extraction decreased from 0.534 +/- 0.06 to 0.232 +/- 0.088. The latter returned to near-basal values more rapidly than did the FDR. In conclusion, the kinetics of insulin both in and out of the steady state have been shown to be nonlinear through physiological insulin concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Massive insulin overdose: detailed studies of free insulin levels and glucose requirements

The course of a diabetic patient who self-administered 2500 U of NPH insulin subcutaneously was examined in detail. Despite resumption of oral intake on day 3, she required iv glucose for 6 days, during which time serum free insulin levels remained elevated. Glucose requirements closely matched those calculated from published euglycemic clamp data on maximal glucose disposal rates during insulin infusion. We postulate that her prolonged course was due to delayed absorption of the subcutaneous insulin. This is the first case of massive insulin overdose studied in such detail, and the results may facilitate management of future cases.

The beta cell glucose stimulus-response curve in normal humans assessed by insulin and C-peptide secretion rates

Insulin and C-peptide secretion rates have been measured and compared in 12 nondiabetic subjects to characterize the glucose stimulus-response of B cell secretion in man. On three different days, glucose concentrations were clamped for 150 minutes at 7.5, 10, and 15 mmol/L, respectively. Plasma samples taken during the clamps were assayed for C-peptide and insulin. C-peptide secretion rates were estimated by the technique of deconvolution. Model-based estimation of insulin secretion rates from insulin concentrations yielded concordant results. In response to glucose, C-peptide concentrations rose less quickly than did insulin concentrations, but the estimated first- and second-phase secretion rates were similar when assessed from either the C-peptide or insulin concentrations. First-phase secretion peaks were larger than inspection of the plasma concentration data might suggest, with median values of 1.3, 2.0, and 2.9 nmol/min for C-peptide in response to 7.5, 10, and 15 mmol/L glucose clamp levels, respectively. The second-phase reached steady state by 90 to 120 minutes, with median C-peptide secretion rates of 0.31, 0.56, and 0.85 nmol/min after 120 minutes at 7.5, 10, and 15 mmol/L, respectively. The slopes of the curves of steady-state insulin and C-peptide secretion rates v the four glucose levels (basal plus the three clamp levels) were maximally steep between 7.5 and 10 mmol/L in the majority of subjects, consistent with in vitro sigmoidal responses. A characterization of the secretory response of the B cell of normal humans at different glucose concentrations has been obtained. With appropriate models, insulin secretion rates may be estimated from either plasma insulin or C-peptide concentration data.

Kinetic models for insulin disappearance from plasma in type I diabetic patients

We have tested whether our previous finding in normal subjects that the disappearance of insulin from plasma obeys saturation kinetics alone also applies to type I diabetic patients. In six long-term diabetic patients steady state plasma insulin concentrations resulting from constant insulin infusion at different rates were compared with the predictions of three models for the kinetics of insulin in plasma. The models allowed the existence of non-saturable (first order equation) or saturable (Michaëlis-Menten equation) mechanisms, or both. The minimal acceptable model included saturation kinetics alone in four subjects and first order kinetics alone in two subjects. The clearance of insulin in diabetic patients, calculated from the best fitting model, was 18.0 (median, range 10.0-23.7) ml X kg-1 X min.-1 versus 25.0 (18.6-47.1) ml X kg-1 X min.-1 in six normal subjects (2p = 0.008). Insulin thus disappears from plasma at a lower rate in diabetic patients than in normal subjects at physiological plasma concentrations.

Pharmacokinetics of insulin following intravenous and subcutaneous administration in canines

Studies were conducted to examine the absorption and disposition kinetics of insulin in dogs following intravenous (IV) and subcutaneous (SC) administration of commercial preparations. After IV and SC dosing, the plasma levels were described by models which considered basal insulin level contributions. Intersubject variation in the disposition kinetics was small with half-lives of 0.52 +/- 0.05 h and total body clearances of 16.21 +/- 2.08 ml min-1 kg-1. Calculated insulin plasma secretion rates in the canines were 14.4 +/- 3.3 mUh-1 kg-1. Following SC injection of regular insulin, the rate and extent of absorption were noted to be quite variable. The absorption process appeared first-order with half-life values of 2.3 +/- 1.3 h and extents of absorption of 78 +/- 15 per cent with a range of 55-101 per cent. Insulin absorption from SC NPH preparations was evaluated as being composed of two zero-order release phases, a rapid and a slow release phase. With a dose of 1.65 U kg-1, the rapid release phase had an average duration of 1.5 h and a rate of 580 +/- 269 mUh-1 (4.2 per cent of dose) while the slow phase had a zero-order rate of 237 +/- 92 mU h-1 which continued beyond 12 h. The extent of absorption from the NPH preparation was 23.6 +/- 5.1 per cent and was significantly lower than that for the regular injection.

In vivo kinetics of insulin action on peripheral glucose disposal and hepatic glucose output in normal and obese subjects

To determine whether abnormal kinetics of insulin's biologic actions contribute to the overall insulin resistance in obesity, we compared the rate of activation and deactivation of insulin's effects to stimulate glucose disposal rate (Rd) and inhibit hepatic glucose output (HGO) in 12 nonobese and 10 obese subjects using the euglycemic clamp technique at insulin infusion rates of 15, 40, 120, and 1,200 mU/M2 per min. In both groups, stimulation of Rd was faster the higher the insulin infusion rate and the time to reach half maximal stimulation (A50 value) in normals was 52 +/- 4, 44 +/- 2, 29 +/- 3, and 21 +/- 2 min at infusion rates of 15, 40, 120, and 1,200 mU/M2 per min, respectively. In the obese subjects, the rate of activation was slower (higher A50 values) with A50 values of 74 +/- 6, P less than 0.001 (compared to normal), 64 +/- 8 min, P less than 0.001, and 28 +/- 3 min, P less than 0.01, at the 40, 120, and 1,200 mU/M2 per min insulin infusions. Deactivation of the insulin effect to stimulate glucose disposal rate (Rd) was faster in the obese group compared with normal individuals after all comparable insulin infusions. In summary: for both groups, the higher the insulin infusion rate, the higher the steady state Rd value, the faster the rate of activation and the slower the subsequent rate of deactivation. In insulin-resistant obese subjects, the rate of activation of insulin action was slower and the rate of deactivation faster at comparable insulin infusion rates. The rate of suppression of HGO was comparable in normal and obese subjects, but the rate of recovery of HGO back to basal values was faster in the obese group. And in view of the phasic manner in which insulin is normally secreted following meals, steady state insulin action is not normally achieved. Therefore, the abnormal kinetics of insulin action in insulin-resistant obese individuals may represent functionally important manifestations of the insulin resistance in this condition.

Measurement using tracers of steady-state turnover and metabolic clearance of insulin in dogs

In nine conscious dogs, the steady-state metabolic clearance rate (MCR) and the systemic appearance rate (Ra) of insulin were determined by the tracer dilution method. [3H-PheB1]insulin ([3H]insulin) was infused as a tracer from time 0 at a constant rate. After tracer equilibration was attained, unlabeled porcine insulin was infused at variable constant rates (10.6-279 mU/min) with somatostatin (0.3 microgram . kg-1 . min-1) to suppress endogenous insulin secretion. Glucose was infused to prevent hypoglycemia. Tritiated and immunoreactive insulin (IRI) concentrations were determined in plasma samples after extraction on a C-18 reverse-phase column. Tracer-determined basal Ra of insulin was 2.39 +/- (SE) 0.61 mU/min. The calculated steady-state Ra of insulin for plasma IRI from 20 to 2,300 microU/ml showed good agreement with insulin infusion rates. The mean ratio of these rates was 0.973 +/- 0.018. The MCR of insulin under basal conditions was 29.9 +/- 3.4 ml . kg-1 . min-1, and it decreased with increasing insulin concentrations. It is concluded that 1) insulin turnover rates can be measured accurately using [3H]insulin as a tracer and 2) insulin kinetics are nonlinear.

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.

A numerical method for biphasic curve fitting with a programmable calculator

Elimination kinetics of bromsulphalein (BSP) after a single injection into the circulation of rats were examined by means of a four-compartment model. BSP plasma concentrations were measured colorimetrically. A program written for the Texas Instruments TI-59 programmable calculator is presented, which will calculate the fractional blood clearance of BSP using an iteration procedure. A simple method of fitting biphasic decay curves to experimental data is also proposed.

Kinetic analysis of plasma insulin disappearance in nonketotic diabetic patients and in normal subjects. A tracer study with 125I-insulin

The studies so far reported on the metabolic clearance rate of insulin in human diabetes mellitus have given conflicting results, probably because they have been conducted on few patients and have used a variety of experimental techniques and data treatments. We investigated the kinetics of insulin distribution and degradation in 35 normal subjects and in 42 nonketotic, nonobese, overtly diabetic patients, of whom 26 were above 40 yr old and 16 were 40 yr old or less at diagnosis. The design of the study combined (a) the use of a tracer to perturb minimally the steady state and to avoid glucose infusion; (b) the preparation of purified [(125)I]-monoiodoinsulin, which has a metabolic behavior similar to that of native insulin; and (c) noncompartmental analysis of the plasma immunoprecipitable (125)I-insulin disappearance curves, which were recorded for 2 h after pulse i.v. injection of the tracer.Metabolic clearance rate was found to be similar in diabetics (404+/-18 ml/min.m(2), mean+/-SEM) and in normals (420+/-14), although the latter-onset patients had slightly, if not significantly, lower metabolic clearance rate values than the earlier-onset diabetics (385+/-19 and 443+/-36, respectively). The initial distribution volume of the hormone also did not significantly differ in diabetics and normals and was similar to plasma volume. The reentry rate into the initial distribution volume of the hormone and the total, plasma-equivalent distribution volume of insulin were both significantly raised in diabetics (251+/-12 ml/min.m(2) and 10.3+/-0.5 liters/m(2)) in comparison with normals (195+/-8 and 7.5+/-0.3). The posthepatic delivery rate of insulin was found to be slightly raised in later-onset diabetics (194+/-20 mU/h.m(2)), but somewhat reduced in earlier-onset diabetics (133+/-15) in comparison with normals (172+/-14); these differences reflected the different basal plasma insulin concentrations in these three groups. Chronic treatment with oral hypoglycemic drugs, age, duration of the disease, and degree of metabolic control appeared to have only little effect on the kinetics of insulin.On the basis of these results, we conclude that insulin-independent adult diabetics show, already in the fasting state, a combination of insulin resistance and insulin deficiency and a derangement in insulin distribution, the precise significance of which is uncertain.

The early phase of insulin release in man--a new method for quantitative analysis

A method is presented for the quantitative analysis of early insulin release in man. There were measured arterial insulin levels after glibornuride administered intravenously. The mathematical procedure has been modified: Modification I is based on the assumption that early insulin release represents a wave like insulin delivery, modification II is based on the assumption that this insulin bolus is immediately followed by a slower insulin release which must be distinguished from the second phase of insulin release. For the calculations there was used a "primary insulin space" derived from experiments with exogenous insulin. The results of calculations were varying up to 1.5 units of early insulin release in healthy volunteers receiving glibornuride with dosages varying up to 50 mg. The value of the presented method for examinations of insulin release for theoretical and clinical purposes is discussed.

Urinary insulin levels in health and disease--a concise review

The kidneys are the most important extrahepatic site of insulin breakdown and play a significant role in regulating the systemic insulin level in normal subjects. In man, a renal arteriovenous insulin concentration difference of about 30% has been measured, and since ‘insulin clearance’ values are less than the glomerular filtration rates, insulin is probably removed from blood by a combination of filtration and tubular secretion. In normal subjects a constant fraction of circulating insulin is removed by the kidney. This fraction is independent of the arterial concentration but varies with creatinine clearance. Of the amount filtered, most is completely resorbed and degraded by the cells of the proximal convoluted tubules. These cells have a high insulinase content and recent evidence would point to the possible existence of a renal tubular transport mechanism for insulin. The amount of insulin excreted in the urine is small and does not exceed 2% of the filtered load. In diabetics the insulin requirements often decrease with progressive renal failure. Derangements in carbohydrate metabolism have been noted in patients with renal failure while ‘insulin clearance’ is elevated in uraemia, chronic and acute renal failure. In nephrotic syndrome there is no change in renal insulin excretion. In severe trauma, ‘insulin clearance’ is elevated in patients with normal renal function despite a relative hypoinsulinaemia for the prevailing degree of glycaemia.

Estimation of thyroxine and triiodothyronine distribution and of the conversion rate of thyroxine to triiodothyronine in man

Studies on peripheral metabolism of simultaneously administered 125-I-labeled L-thyroxine ([125-I]T4) and 131-I labeled L-trilodothyronine ([131-I]T3) were performed in five normal subjects, in four patients with untreated hypothyroidism, and in 3 hypothyroid patients made euthyroid by the administration of T4. The fractional turnover rate (lambda 03) of thyroid hormones irreversibly leaving the site of degradation and the volumes of pool 1 (serum V1) of pool (interstitial fluid, V2), and of pool 3 (all tissues, V3)were obtained by using a three-compartment analysis. In addition to the turnover studies, the ratios for the in vivo T4 to T3 conversion were determined by paper chromatographic study in sera obtained 4, 7, and 10 daysafter the injection. The rate (K12) of the extrathyroidal conversion of T4 to T3 was also estimated by the compartment analysis. The T3 distribution volume (V3) of pool 3, in which T3 is utilized and degraded, was about 60% of totaldistribution volume (V=V1+V2+V3) in normal subjects, whereas only about 25% of the extrathyroidal T4 pool was in the intracellular compartment, indicating that T3 is predominantly an intracellular hormone..

A model of the kinetics of insulin in man

The design of the present study of the kinetics of insulin in man combines experimental features which obviate two of the major problems in previous insulin studies. (a) The use of radioiodinated insulin as a tracer has been shown to be inappropriate since its metabolism differs markedly from that of the native hormone. Therefore porcine insulin was administered by procedures which raised insulin levels in arterial plasma into the upper physiologic range. Hypoglycemia was prevented by adjusting the rate of an intravenous infusion of glucose in order to control the blood glucose concentration (the glucose-clamp technique). (b) Estimation of a single biological half-time of insulin after pulse injection of the hormone has been shown to be inappropriate since plasma insulin disappearance curves are multiexponential. Therefore the SAAM 25 computer program was used in order to define the parameters of a three compartment insulin model. The combined insulin mass of the three compartments (expressed as plasma equivalent volume) is equal to inulin space (15.7% body wt). Compartment 1 is apparently the plasma space (4.5%). The other two compartments are extra-vascular; compartment 2 is small (1.7%) and equilibrates rapidly with plasma, and compartment 3 is large (9.5%) and equilibrates slowly with plasma. The SAAM 25 program can simulate the buildup and decay of insulin in compartments 2 and 3 which cannot be assayed directly. Insulin in compartment 3 was found to correlate remarkably with the time-course of the servo-controlled glucose infusion. Under conditions of a steady-state arterial glucose level, glucose infusion is a measure of glucose utilization. We conclude that compartment 3 insulin (rather than plasma insulin) is a more direct determinant of glucose utilization. We suggest that the combined use of glucose-clamp and kinetic-modeling techniques should aid in the delineation of pathophysiologic states affecting glucose and insulin metabolism.

Effect of nephrectomy on the rate and pattern of the disappearance of exogenous gastrin in dogs

Studies of gastrin metabolism were performed in four dogs before and after nephrectomy. Synthetic human gastrin I was infused for two hours and serum samples were obtained at various times during and after infusion. Serum concentrations of gastrin were measured by radioimmunoassay. A two-compartment model was employed to calculate half-lives under each of four experimental conditions, low and high infusion rates, used both before and after nephrectomy. The model half-life was greatly prolonged after nephrectomy at both infusion rates (from 2.54 min to 5.15 min at the low rate, and from 2.85 min to 7.88 min at the high rate). The metabolic clearance rate, an expression of the rate of catabolism during infusion, decreased significantly after nephrectomy at both infusion rates. These observations indicate that the kidney is an important organ for the catabolism of exogenous gastrin.

Metabolism of proinsulin, insulin, and C-peptide in the rat

The renal extraction and excretion of bovine proinsulin, insulin, and C-peptide and the contribution of the kidney to their total metabolic clearance rate (MCR) were studied in the rat. Metabolic clearance rates were measured by the constant infusion technique and plasma and urine concentrations of each polypeptide were determined by radioimmunoassay. The MCR of insulin (16.4+/-0.4 ml/min) was significantly greater than that of either proinsulin (6.7+/-0.3 ml/min) or C-peptide (4.6+/-0.2 ml/min). Metabolic clearance rates were independent of plasma levels over a range of steady-state plasma concentrations varying from 1 to 15 ng/ml.In contrast to the differences in their metabolic clearance rates, the renal disposition of the three polypeptides was similar, being characterized by high extraction and very low urinary clearance. The renal arteriovenous difference of proinsulin, insulin, and C-peptide averaged 36, 40, and 44%, respectively, and was linearly related to their arterial concentration between 2 and 25 ng/ml. When glomerular filtration was markedly reduced or stopped by ureteral obstruction, the renal extraction of proinsulin, insulin, and C-peptide was invariably greater than the simultaneously measured extraction of inulin, indicating that these polypeptides are removed from the renal circulation by both glomerular filtration and direct uptake from peritubular capillary blood. The fractional urinary clearance of each polypeptide never exceeded 0.6%, indicating that more than 99% of the amount filtered was sequestered in the kidney. The renal removal of proinsulin and C-peptide from the circulation accounts for 55 and 69% of their metabolic clerance rates, while the renal contribution to the peripheral metabolism of insulin was smaller, averaging 33%. This difference is due to the fact that insulin, but not the other two polypeptides, is metabolized to a significant extent by the liver. These results define the renal handling of proinsulin, insulin, and C-peptide in the rat and indicate that in this species the kidney represents a major site for insulin metabolism and is the main organ responsible for the degradation of proinsulin and C-peptide.

Metabolic clearance rate of radioiodinated human calcitonin in man

The characteristics of the disappearance of radioiodinated synthetic human calcitonin from plasma have been studied in man. After single injection the disappearance curve was multiexponential. The number of exponentials of the theoretical curve fitting the best with the experimental data varied individually. Metabolic clearance rate was determined both from single injection and constant infusion studies, and fast initial distribution volume from the former. Metabolic clearance rate values in normal man calculated from constant infusion studies were 82.3 +/-3.4 ml/min per m(2). Values derived from single injection studies were similar, 77.0 +/-4.7 ml/min per m(2). These results were compared to those obtained in end stage, renal failure patients. Metabolic clearance rate was considerably lower and volume of fast initial distribution slightly larger in that group. This fact emphasizes the important role of kidneys in the utilization and/or the degradation of human calcitonin.