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Biomedical subjects

G Reach

Publications and source records attributed to G Reach.

At least 109 records · Page 6Linked to original sources
PubMed1989

Strategies for calibrating a subcutaneous glucose sensor.

The calibration of the glucose sensor is a critical issue for the subcutaneous implantation of such devices, since it allows from the sensor output the estimation of the prevailing subcutaneous glucose concentration. This study has compared estimations of subcutaneous glucose concentration in rats, calculated from the sensor's signal by using calibration parameters (sensitivity coefficient and background current) determined either under in vitro or in vivo conditions. The in vitro calibration was performed in phosphate buffer at 37 degrees C. The in vivo parameters were calculated by comparing changes in the sensor output current to concomitant changes in blood glucose concentration, induced by intravenous insulin injection and glucose infusion. The apparent subcutaneous glucose concentration, calculated with in vitro parameters, remained much lower than the concomitant blood glucose levels throughout the experiments. By contrast, when it was calculated with the calibration parameters determined in vivo, either in the hypoglycemia or hyperglycemia range, the apparent subcutaneous glucose concentration well reflected blood glucose levels with a five min time lag. We conclude that it is the two-point in vivo calibration procedure which allows the calculation of an apparent subcutaneous glucose concentration best reflecting blood glucose levels.

Biosensing Techniques↗
PubMed1989

Monitoring the kinetics of glucose transfer across a bioreactor membrane with a glucose sensor.

Bioreactors for cell culture, in which hollow fibers are sealed into a protective jacket, cells are seeded in the fibers' outer surface and a culture medium circulates through the fibers, have been proposed as a bioartificial pancreas. We used a needle-type glucose sensor to study the kinetics of glucose transfer across the membrane of one such device. The glucose transfer was found to be dependent on the flow rate of the circulating medium, which suggests the involvement of an ultrafiltration flux across the membrane. The glucose concentration was heterogeneous within the cell compartment. This heterogeneity, and the delay in transmission of changes in glucose concentration from the circulating medium to the cell compartment, can be ascribed to the large volume of the compartment. The design of these bioreactors should therefore be modified, in order to meet the requirements of glucose transfer kinetics of a bioartificial pancreas.

Equipment Design↗
PubMed1988

In vitro kinetics of insulin release by microencapsulated rat islets: effect of the size of the microcapsules.

Microencapsulation has been proposed to protect islets of Langerhans against immune rejection in xenogenic transplantation. However, to achieve glucose homeostasis in human diabetic patients, insulin release by microencapsulated islets must increase in response to a glucose load. We microencapsulated isolated rat islets using the alginate-polylysine procedure. Capsule size was found to range from 300 to 800 micron, and microencapsulated islets were separated according to their size. Groups of 10 microencapsulated islets, either small (350 micron) or large (650 micron) were placed in plastic microwells, in minimal Eagle's culture medium containing either 5.5 mol/l glucose (basal) or 16.5 mol/l glucose and 5.5 mol/l theophylline (stimulatory medium). The increase in insulin concentration in the surrounding medium was then serially determined over 30 min: (1) With the small capsules, insulin concentration rose from 199 +/- 20 to 297 +/- 58 microU/ml in basal medium, and from 236 +/- 23 to 510 +/- 121 microU/ml in stimulatory medium (n = 10 preparations), the difference between the data obtained with the basal or the stimulatory medium being significant (p less than 0.01) from the 5th min onwards. (2) With large capsules, insulin concentration increased from 182 +/- 9 to 266 +/- 44 microU/ml, and from 216 +/- 19 to 297 +/- 34 microU/ml in basal and stimulatory medium, respectively, with no apparent significant difference. The magnitude of insulin secretion in response to glucose by unencapsulated islets was, under similar conditions, seven-fold greater. We conclude therefore that the size of the microcapsules is an essential parameter which has to be considered for the optimisation of the microencapsulation procedure.

Animals↗
PubMed1988

Absence of effect of heparin on insulin secretion.

Bioartificial pancreatic devices containing isolated islets of Langerhans have been designed, in which the blood of the recipient circulates in contact with an artificial membrane, protecting the islets against immune rejection. This system assumes that heparin, required to prevent blood clotting, does not alter insulin secretion. However, heparin has been reported to inhibit in vitro insulin secretion by rat islets and to suppress in vivo insulin secretion in dogs. Therefore, the following evaluation was made on the effect of different heparin preparations on insulin secretion. (a) Isolated rat islets of Langerhans were perfused or incubated in the absence or presence of 20 micrograms/ml heparin; insulin secretion in response to a stimulation by glucose 20 mM was not altered by the presence of heparin. (b) Insulin secretion by an insulin-secreting cell line (RINm5F) in response to leucine and theophylline was not suppressed by heparin up to 100 micrograms/ml concentration. However, an inhibitory effect was observed at 200 micrograms/ml, which is 100 times higher than the heparin concentration commonly used for therapeutic use. (c) Neither in normal rats nor in dogs did heparin alter portal plasma insulin levels and the increase in plasma insulin following an intravenous injection of glucose. In conclusion, these data do not confirm the formerly observed inhibitory effect of heparin, which can therefore be used for the in vivo evaluation of a bioartificial pancreas.

Animals↗
PubMed1988

Analysis of ultrafiltration and mass transfer in a bioartificial pancreas.

A bioartificial pancreas is an implantable device which contains insulin secreting cells (Langerhans islets), separated from the circulating blood by a semi-permeable membrane to avoid rejection. This paper describes the operation of such a device and evaluates the respective contributions of diffusion and ultrafiltration to the glucose and insulin mass transfer. It is shown that the pressure drop along the blood channel produces across the first half of the channel an ultrafiltration flux toward the islet compartment followed in the second half by an equal flux in reverse direction from islets to blood. The mass transfer analysis is carried out for an optimal geometry in which a U-shaped blood channel surrounds closely a very thin islet compartment formed by a folded flat membrane. A complete model of insulin release by this device is developed and is compared with in vitro data obtained with rats islets. Satisfactory kinetics is achieved with a polyacrylonitrile membrane used in hemodialysis. But the model shows that the membrane hydraulic permeability should be increased by a factor of 10 to significantly improve the performance.

Acrylic Resins↗
PubMed1988

Evaluation of implantable glucose enzyme-based sensors with extracorporal blood shunt.

This paper presents several methods and instruments developed for the characterization of enzymatic membranes and enzyme electrodes: 1. amplitude and response time of steady-state and transient responses to glucose, automatically determined with an Apple II based workstation, 2. enzyme electrode response to in vitro simulated I.V.G.T.T. and to in vivo I.V.G.T.T. when connected to an extracorporal blood shunt of conscious rats.

Animals↗
PubMed1987

Dietary and hormonal regulation of L-type pyruvate kinase gene expression in rat small intestine.

L-type pyruvate kinase is an enzyme of the glycolytic pathway whose activity and mRNA levels fluctuate in the small intestine according to dietary status. Both the enzyme activity and mRNA concentration decline during fasting and increase upon refeeding either a glucose-rich or a fructose-rich diet. Using a single-strand M 13 phage complementary to L-type pyruvate kinase mRNA as probe, we determined the level of the mRNA in the small intestine of normal, adrenalectomized, thyroidectomized, diabetic and glucagon-treated or cAMP-treated animals refed either a glucose-rich or a fructose-rich diet. The specific mRNA is present in the small intestine of normal fasted rats and increases twofold and threefold on refeeding glucose and fructose respectively. However, the hormonal control of the gene expression differs according to the dietary carbohydrate. The L-type pyruvate kinase mRNA increase, induced by glucose feeding, is hormone-dependent and requires the presence of thyroid hormones and insulin. In fructose-fed rats a certain level of mRNA increase occurs regardless of the hormonal status of the animals, but the full induction of the mRNA by fructose requires the presence of glucocorticoids, thyroid hormones and insulin. Thus, the hormonal regulation of L-type pyruvate kinase gene expression in the small intestine is largely similar to that described in normal rat liver but the basal mRNA level and the stimulation of the mRNA increase by fructose are higher in the small intestine.

Adrenalectomy↗
PubMed1987

Reversible morphological and functional abnormalities of RINm5F cells cultured on polystyrene sulfonate beads.

RINm5F cells (an insulin-secreting cell line) were cultured on PSSO3Na microbeads under static conditions. The cell growth rate was either identical to that of cells grown on plastic wells or slower, depending on the initial cell concentration. With both supports, it was similarly influenced by the fetal calf serum concentration in the culture medium, and protein content per cell was identical. However, no spreading was observed when cells were cultured on microbeads. RINm5F cells cultured on plastic wells responded to arginine + theophylline and to leucine + theophylline by a significant increase in insulin secretion. By contrast, in cells cultured on PSSO3Na microbeads, the increase in this secretion was only slight or nil. All these abnormalities were reversible. Thus, when cells cultured on microbeads were detached and seeded on plastic wells, normal spreading and insulin secretion were observed. Lastly, PSSO3Na beads had an acute suppressive effect on insulin secretion by cells cultured on plastic wells. This study provides an example of cell-biomaterial interaction in which cell growth is possible, but with altered cell function.

Adenoma, Islet Cell↗
PubMed1987

[Therapeutic and social determinants of the number of blood glucose tests performed at home by the diabetic child].

The aim of this study was to assess the determinants of the use of blood glucose tests by young diabetic children participating in a summer educational program. 425 children and adolescents with insulin dependent diabetes mellitus (IDDM) were studied. The main source of the data was a questionnaire filled by the children and their parents about the use of urine and blood glucose tests during the 8 weeks before the camp and a questionnaire filled in by the Aide aux Jeunes Diabétiques (AJD) doctors about the practical knowledge of the management of the disease. The children were divided into 2 groups according to the level of their practical knowledge, "good" (n = 153) and "less good" (n = 272). In the whole group, the mean number of urine tests per day was 2.8, 75% of the children performing 3 tests per day and 4.3% not doing any urine tests. The number of blood tests is more variable; from 0 to 28 per week, with a mean of 5.6. In the group having "good" practical knowledge, the blood glucose tests were done 6 times per week, in connection with the number of hypoglycemia at home (p less than 0.01), the number of daily insulin injections (p less than 0.01) and the number of insulin supplements (p less than 0.05); there was a partial substitution between blood and urine tests. In the group having "less good" practical knowledge, the number of blood tests was 4 per week; it was not statistically different, but it was performed in the absence of detectable reasons.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Glucose↗
PubMed1986

[Artificial pancreas in diabetic children].

The current artificial pancreases, which are not wearable, are mainly used for physiological research. However, they may also become useful tools for clinical or therapeutic investigations in diabetes mellitus. This is clearly demonstrated by our own experience of the Biostator in 300 young diabetics. The steady state regulation of plasma glucose offers a wide range of possible investigations: clinical, such as measuring insulin activity in states of insulin resistance, urinary excretion of glucose and renal threshold; therapeutic, like evaluating the hypoglycemic activity of commercial insulins, or alternative routes of insulin administration, such as the peritoneum; physiopathological, for better evaluation of metabolic alterations in diabetes by measuring the turnover of various substrates. Experience of the artificial pancreas also appears to be crucial for a better handling of the many problems involved in the design of future wearable or implantable devices.

Adolescent↗
PubMed1986

Characteristics of children and adolescents with insulin-dependent diabetes mellitus participating in a summer camp educational program.

Clinical, biological and social characteristics were assessed in 456 children and adolescents participating in a summer camp for children with diabetes mellitus. In these subjects, aged from 7 to 18 years, the mean duration of the diabetes was five and a half years. They carried out their usual treatment under parental supervision, 31% of them being of rural origin. Mean glycosylated haemoglobin was approximately twice as high as a reference population (12.2% +/- 2.3, vs. 6.6% +/- 0.7) and was similar to that observed in various specialized hospitals. Factors which correlated with glycosylated haemoglobin included gender, school performance, vacation away from home, time spent watching television and practicing sport and eating patterns. This descriptive analysis gives some insight into the health status of the studied population. It represents the initial phase of a study to assess the efficacy of a diabetes educational programme for children and adolescents.

Adolescent↗
PubMed1986

[Glomerular filtration and tubular reabsorption of glucose in insulin-dependent diabetes in children].

Although glycosuria is important in the control of diabetes in children, few studies clearly show its significance as compared to glycemia. The aim of the present study was therefore to determine the two parameters that control glucose presence in urine, i.e. glucose glomerular filtration rate (GFR) and tubular reabsorption (JrG). GFR was measured by using a 110 min polyfructosan perfusion in 96 diabetic children and adolescents. The results are as follows: 1) In this population there is a significant correlation (p less than 0.01) between the quantity of glucose in urine and mean glycemia during the test; 2) polyfructosan clearance that reflects GFR in diabetic children without renal complication is 2.11 +/- 0.04 ml/s 1.73 m2, or 126 +/- 2.4 ml/min 1.73 m2 (mean +/- SEM); it is higher than in the reference values already published; 3) JrG is correlated with glucose filtered load (p less than 0.01), GFR (p less than 0.01) and sodium reabsorption (p less than 0.01). The ratio JrG/GFR could be substituted for the classical concept of "renal threshold", as it can be easily measured and may help in interpreting glycosuria in some diabetic children. To conclude, in IDD children, the parameters controlling glycosuria may be studied by a simple method. The clinical value of such renal exploration has still to be determined.

Absorption↗