Biomedical subjects

D R Matthews

Publications and source records attributed to D R Matthews.

At least 127 records · Page 7Linked to original sources

PubMed1990

The effect of islet amyloid polypeptide (amylin) and calcitonin gene-related peptide on glucose removal in the anaesthetized rat and on insulin secretion from rat pancreatic islets in vitro.

The effect of intravenous infusion of islet amyloid polypeptide (IAPP/amylin) and calcitonin gene-related peptide (CGRP) on blood glucose and plasma insulin in the basal and glucose-stimulated state was investigated in the anaesthetized rat. Both peptides had no effect on basal blood glucose or plasma insulin but following an intravenous bolus of glucose, CGRP-treated rats were hyperglycaemic and hyperinsulinaemic compared with control animals which were similar to IAPP-treated rats. IAPP had no effect on glucose-stimulated islet insulin secretion. These results suggest that CGRP, but not IAPP, alters glucose removal in vivo.

Amyloid↗

PubMed1990

The application of deconvolution analysis to elucidate the pulsatile nature of growth hormone secretion using a variable half-life of growth hormone.

A deconvolution analysis model to calculate pituitary growth hormone (GH) secretion rate from measured serum GH concentration has been developed. This uses an iterative method of 'curve-stripping' based on an estimate of the half-life. The model has been applied to serum GH profiles and demonstrates that GH secretion occurs in discrete bursts with quiescent periods between secretory episodes, an 'on-off' phenomenon. The model can clearly dissect complicated concentration profiles such as the serum GH concentration response to growth hormone releasing hormone. The estimate was derived from calculating the half-life of serum GH in 10 subjects following an intravenous bolus injection of 50 mU of biosynthetic human growth hormone (b-hGH) and following infusions of the exogenous hormone (3 mU/kg/h) for 15, 30, 60 and 180 min. Endogenous GH secretion was suppressed by a continuous infusion of somatostatin (1-14). An asymptotic relationship between the duration of GH infusion and the GH half-life was established. A half-life of 15.3 min was achieved after exposure to GH for 60 min and a maximum half-life of 15.7 min after 180 min exposure.

Adolescent↗

PubMed1990

The dawn phenomenon is related to overnight growth hormone release in adolescent diabetics.

We have investigated the relation between nocturnal insulin requirements and nocturnal growth hormone (GH) release in 26 diabetic adolescents at various puberty stages and have examined the effect of nocturnal GH suppression on pre-breakfast insulin requirement. In all the studies, euglycaemia was maintained overnight using a computer-calculated variable-rate insulin infusion, and 15-min blood samples were collected for GH assay. During initial clamp studies, insulin infusion rates were greater from 0500-0800 h (15.22 +/- 0.95 mU/kg/h, mean +/- SEM) than from 0100-0400 h (12.42 +/- 0.84 mU/kg/h, P less than 0.001). The increase in insulin infusion rate correlated with mean overnight GH concentration (r = 0.68, P less than 0.001), and was maximal at puberty stage 3 in both sexes. In seven of the subjects, a second identical clamp was performed following administration of 100 mg oral pirenzepine. During these studies, mean overnight GH levels were reduced by 11-85%, from 17.6 +/- 1.6 to 7.5 +/- 2.2 mU/l; P less than 0.01. Insulin requirements were not significantly different between the periods 0100-0400 and 0500-0800 h during these studies, and the reduction in pre-breakfast (0500-0800 h) insulin requirement when compared with the baseline studies correlated with the fall in GH secretion (rs = 0.82, P less than 0.01). The dawn increase in insulin requirement in adolescents with IDDM is related to the overnight GH secretion during puberty, and pre-breakfast insulin requirement can be reduced by suppressing nocturnal GH release.

Adolescent↗

PubMed1990

Increased overnight growth hormone concentrations in diabetic compared with normal adolescents.

To determine the extent to which spontaneous plasma GH concentrations are abnormal in adolescents with insulin-dependent diabetes mellitus we performed 12-h overnight plasma GH profiles in 21 diabetic adolescents (11 males and 10 females; aged 9.8-16.5 yr; median, 13.6 yr) and 34 healthy adolescent controls (17 males and 17 females; aged 9.1-20.9 yr; median, 13.1 yr). Data were analyzed using the pulse detection program Pulsar and time series analysis, and are presented with respect to age and puberty stage. Mean and maximum GH concentrations, sum of the peak amplitudes, and mean calculated baseline concentrations in the normal children were higher during puberty; highest levels were seen in girls at puberty stages 2-3, and in boys at stages 4-5. A similar pattern was observed in the diabetic adolescents, but all measures of pulse height and mean calculated baseline concentrations were significantly greater than those in the normal subjects (multivariate analysis, P less than 0.001). Pulse frequency did not change during puberty in the normal or diabetic subjects, and the dominant pulse periodicity in both groups was about 180 min. We conclude that the predominant change in GH release during puberty is in pulse amplitude, and that this is increased in diabetes, whereas pulse frequency remains constant in both normal and diabetic adolescents.

Adolescent↗

PubMed1990

Failure of current insulin regimes to meet the overnight requirements of adolescents with insulin-dependent diabetes.

The study was undertaken to determine whether overnight insulin requirements were being met during conventional insulin therapy in adolescents with IDDM. Overnight glucose and insulin profiles were compared when the subjects were on their usual insulin regime (baseline) and when the blood glucose was clamped using a variable rate insulin infusion (clamp). Thirteen adolescents (5 boys and 8 girls, median age 12.2 yr; range 10.5-15.4 yr; Median HBA1 11.4%; range 8.4-15.6) took part in the study. Three were on twice daily, two on multiple injection therapy and two on once daily insulin therapy. During the baseline studies, blood glucose concentrations fell to a nadir at 0200-0400 hr and then rose during the early hours of the morning. The clamp studies confirmed that the insulin requirement for euglycaemia was higher between 0500 and 0800 hr (15.4 +/- 0.9 mU/kg/hr) than between 0100 and 0400 (12.1 +/- 1.1 mU/kg/hr; p = 0.002). Comparison of the free insulin concentrations between the baseline and clamp nights, indicated that during the baseline study subjects were relatively over-insulinized during the early part of the night and under-insulinized during the latter part of the night irrespective of what insulin regime they were receiving. We conclude that current insulin regimes do not provide appropriate insulin delivery for the control of blood glucose during puberty.

Adolescent↗

PubMed1990

Diabetes associated with Guillain-Barre syndrome.

Transient diabetes is not recognized as one of the known metabolic complications of acute inflammatory polyradiculopathy or Guillain-Barré syndrome (GBS). Four patients are described who developed this disorder during the paralytic phase of their illness and one who was hyperinsulinaemic but not hyperglycaemic. The mean age of the patients was 34.4 yr. No patient received steroids and three were ventilated. The mean cerebrospinal fluid protein concentration was 1.6 g/l. Two patients required short term insulin therapy. Four had intravenous glucose tolerance tests performed acutely (AP) and after one month (1 M). Three had a repeat study after long term follow-up. One subject had increased his Body Mass Index from 23.8-26.8 and therefore his IVGTT reflected insulin resistance. The other three patients had elevated basal glucose during GBS and similar first phase glucose response to IVGTT. The mean fasting glucose was 6.9 mmol/l (AP), 3.9 mmol/l (1 M) and 4.4 mmol/l at 6 yr. The mean fasting insulin was 114.9 pM/l (AP), 114.9 pM/l (1 M) and 25.9 pM/l (6 yr). The mean fasting C-peptide was 1.3 nmol/l (AP), 1.0 nmol/l (1 M) and 0.5 nmol/l (6 yr). Homeostatic modelling of the paired insulin and C-peptide data show a trend consistent with the hypothesis that insulin resistance is the dominant feature of impaired glucose tolerance in Guillain-Barre syndrome.

Adolescent↗

PubMed1990

Application of structural model of glucose-insulin relations to assess beta-cell function and insulin sensitivity.

A structural mathematical model of glucose-insulin relationships based on known quantitative responses of the major organs involved with glucose metabolism has been computed. Different degrees of beta-cell function and insulin sensitivity can be included, and the effect of their interaction assessed (i) in a steady state, basal homeostasis after an overnight fast and (ii) in response to a glucose infusion. By comparing a patient's basal plasma glucose and insulin (or C-peptide) concentrations with the predictions of a basal homeostatic model, the degree of impairment of beta-cell function and insulin sensitivity can be assessed. Similarly, the plasma glucose and insulin (or C-peptide) concentrations after a continuous glucose infusion can also be compared with predictions from the model to estimate beta-cell function and insulin sensitivity. These assessments of pathophysiology can be applied to data from individual patients or to patient populations.

Blood Glucose↗

PubMed1989

Similar reduction of first- and second-phase B-cell responses at three different glucose levels in type II diabetes and the effect of gliclazide therapy.

To characterize the abnormal B-cell response to glucose in type II diabetes, five diet-treated diabetic and six weight-matched non-diabetic subjects were studied using the hyperglycemic clamp technique on three separate days at glycemic levels of 7.5, 10 and 15 mmol/L for 150 minutes with assessment of plasma insulin and C-peptide responses. To reduce possible secondary effects of hyperglycemia, diabetic subjects on a weight-maintaining diet were chosen who had only a slight elevation of the fasting plasma glucose, mean 6.0 mmol/L. They had a normal time-course of both first- and second-phase responses, but both were impaired at each glucose clamp concentration. The first-phase and second-phase C-peptide responses of the diabetic subjects were similarly reduced to mean 49% and 59% of normal, respectively, and the first- and second-phase insulin responses were also reduced to mean 39% and 44% of normal, respectively. The ratio of second- to first-phase plasma C-peptide responses were similar in the diabetic and normal subjects, median 1.6 and 1.5, respectively, as were the same ratios for the insulin responses, 1.4 and 1.1, respectively. The previously described selective reduction of the first-phase response in type II diabetes may be partly a function of the bolus intravenous glucose tests used, in which impaired glucose tolerance in the diabetics gave a greater glycemic stimulus to the second phase than in normal subjects, and partly secondary to long-term hyperglycemia. The diabetic subjects were re-studied after treatment with a sulphonylurea, gliclazide, with a normal fasting plasma glucose, mean 5.1 mmol/L.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Spontaneous growth hormone (GH) pulsatility is the major determinant of GH release after thyrotrophin-releasing hormone in adolescent diabetics.

GH release is abnormally regulated in insulin-dependent diabetes (IDDM), and paradoxical stimulation of GH release after TRH has been reported. However, overnight GH pulsatility is increased in IDDM, and it may be difficult to distinguish TRH-stimulated release from spontaneous secretory episodes. To resolve this question, we carried out two overnight GH profiles followed by either TRH or saline control tests in six adolescents with IDDM; ages 11.4-14.7 years, duration IDDM 2.4-6.7 years. A rise in GH was seen in four of six following TRH, but with no consistent pattern. A rise was also seen in four of six following saline. Peak GH levels were similar after TRH and saline (19.3 +/- 4.4 vs 25.8 +/- 5.5 mU/l; mean +/- SEM). Mean blood glucose was no different during TRH and saline tests (9.5 +/- 1.6 vs 7.5 +/- 0.6 mmol/l). The two subjects who had an early GH peak after TRH were those in whom GH levels had already begun to rise, suggesting the coincident occurrence of a spontaneous GH pulse. The timing of the next GH pulse could be predicted equally well after TRH and saline from the overnight secretory profile using autocorrelation. Paradoxical GH stimulation after TRH is not seen in adolescents with IDDM, but apparent responses may be due to timing coincident with the increased spontaneous pulsatility.

Adolescent↗

PubMed1989

The half-life of exogenous growth hormone after suppression of endogenous growth hormone secretion with somatostatin.

We have estimated the half-life of serum growth hormone (GH) in six subjects on 14 occasions following an intravenous bolus injection of either 50 or 500 mU of biosynthetic human growth hormone (B-hGH) while endogenous GH secretion was suppressed by a continuous infusion of somatostatin. The disappearance curve of serum GH was mono-exponential and the mean half-life was 8.9 min (SD 1.5). This is less than previously reported and has important implications for the performance of GH profiles, which should be performed with 10-15 min sampling intervals, and the calculation of pituitary GH secretion rates.

Adolescent↗

PubMed1989

Hepatic glucose output in humans measured with labeled glucose to reduce negative errors.

Steele and others have suggested that minimizing changes in glucose specific activity when estimating hepatic glucose output (HGO) during glucose infusions could reduce non-steady-state errors. This approach was assessed in nondiabetic and type II diabetic subjects during constant low dose [27 mumol.kg ideal body wt (IBW)-1.min-1] glucose infusion followed by a 12 mmol/l hyperglycemic clamp. Eight subjects had paired tests with and without labeled infusions. Labeled infusion was used to compare HGO in 11 nondiabetic and 15 diabetic subjects. Whereas unlabeled infusions produced negative values for endogenous glucose output, labeled infusions largely eliminated this error and reduced the dependence of the Steele model on the pool fraction in the paired tests. By use of labeled infusions, 11 nondiabetic subjects suppressed HGO from 10.2 +/- 0.6 (SE) fasting to 0.8 +/- 0.9 mumol.kg IBW-1.min-1 after 90 min of glucose infusion and to -1.9 +/- 0.5 mumol.kg IBW-1.min-1 after 90 min of a 12 mmol/l glucose clamp, but 15 diabetic subjects suppressed only partially from 13.0 +/- 0.9 fasting to 5.7 +/- 1.2 at the end of the glucose infusion and 5.6 +/- 1.0 mumol.kg IBW-1.min-1 in the clamp (P = 0.02, 0.002, and less than 0.001, respectively).

Diabetes Mellitus↗

PubMed1989

Unbiased and flexible iterative computer program to achieve glucose clamping.

Glucose clamping has become a widely used test for assessing insulin sensitivity and beta-cell function. We present a new method of achieving a reliable and unbiased clamp using an iterative computer program. After initial parameter estimation, the program uses no fixed algorithm or physiological preconceptions but makes predictions according to previous glycemic responses to infusion rates. The program can be used for human or animal studies and for euglycemic or hyperglycemic clamps. The program has flexible data entry, graphic display, running statistics of mean infusion data, and mean glucose levels and their standard deviations. These form part of the criteria for the assessment of glucose clamping, which includes the sampling interval, the duration of the clamp, the achieved glucose concentration (together with its coefficient of variation), and the percent change of glucose infused at the end of the clamp. Data for 151 consecutive clamp studies were analyzed. Median coefficient of variation of glucose values at the end of the clamp was 2%.

Algorithms↗

PubMed1988

Impaired pulsatile secretion of insulin in relatives of patients with non-insulin-dependent diabetes.

In fasting nondiabetic subjects, insulin is secreted in regular pulses every 12 to 15 minutes, but patients with non-insulin-dependent diabetes lack regular oscillatory insulin secretion. To investigate whether abnormal insulin oscillations are an early feature of diabetes, we studied 10 minimally glucose-intolerant first-degree relatives of patients with non-insulin-dependent diabetes and 10 controls matched for age and obesity. We performed a time-series analysis of fasting plasma insulin levels in blood samples obtained at 1-minute intervals for 150 minutes. Fasting plasma glucose levels were higher in the relatives than in the controls (mean +/- SD, 5.4 +/- 0.7 vs. 4.4 +/- 0.3 mmol per liter). Autocorrelation of pooled data showed no regular oscillatory activity in the relatives but a 13-minute cycle in the controls (r = 0.23, P less than 0.001). Similarly, Fourier transform analysis showed no significant peak in the relatives but the expected significant peak at 13 to 14 minutes in the controls (P less than 0.05). First-phase (0 to 10 minutes) insulin secretory responses to glucose administered intravenously were not significantly impaired in the relatives (geometric mean, 188 pmol per liter [26.2 mU per liter]; range of SD, +103 to -67 pmol per liter [+14.4 to -9.3 mU per liter]), as compared with the controls (geometric mean, 231 pmol per liter [32.2 mU per liter]; range of SD, +131 to -83 pmol per liter [+18.2 to -11.6 mU per liter]). We conclude that abnormal oscillatory insulin secretion may be an early phenomenon in the development of non-insulin-dependent diabetes.

Adult↗

PubMed1988

The glucose stimulus-response curve of the beta-cell in physically trained humans, assessed by hyperglycemic clamps.

In order to examine the effect of habitual exercise on beta-cell responses over a wide range of plasma glucose levels, plasma insulin and C-peptide responses to 2 1/2-hour hyperglycemic clamps at 7.5, 10, and 15 mmol/L glucose were assessed in six trained athletes and six age- and weight-matched sedentary controls. Athletes were significantly fitter than controls (estimated maximal oxygen uptake [VO2 max] mean 44 v 30 mL.kg-1.min-1, P less than .05) and were more sensitive to insulin as assessed by dividing the mean glucose infusion rate over the last 20 minutes of the clamp by the steady-state plasma insulin (mean 0.44 v 0.19 mg.min-1.kg-1.nmol-1. L, respectively, P less than .01). Plasma C-peptide responses were lower in the athletes, both fasting (geometric mean 0.28 v 0.62 nmol/L, P less than .05), and at the end of all clamps (at 7.5, 10, and 15 mmol/L plasma glucose, respectively, 0.65 v 1.43, 1.25 v 2.85, and 2.40 v 4.46 nmol/L each, P less than .05). First-phase plasma C-peptide responses were lower in the athletes at the 10 and 15 mmol clamp levels. The slope of the glucose-C-peptide stimulus-response curve was approximately linear over the range examined, the slope being significantly shallower in athletes than controls for both first phase (P less than .01) and second phase (P less than .01). Plasma insulin responses were similar to C-peptide responses. The attenuation of beta-cell responsiveness over a wide glucose range may be an adaptation to the enhanced peripheral insulin sensitivity seen in athletes.

Adult↗

PubMed1988

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.

Adult↗

PubMed1988

Pathogenesis of NIDDM--a disease of deficient insulin secretion.

Type 2 diabetes is a familial disease and studies of both Caucasian and Japanese families have raised the possibility that a major susceptibility gene is involved. The majority of patients have both beta cell dysfunction and impaired insulin sensitivity but studies of relatives of Type 2 diabetic patients suggest that beta cell dysfunction is an early feature of the disease. Impaired insulin sensitivity, from acromegaly, Cushing's disease or steroid therapy, induces diabetes only in a small proportion of the population, and they may be those who have an inherited cell defect. We postulate that a single beta cell defect gene, on its own, may be insufficient to cause overt diabetes and would lead to life-long glucose intolerance unless associated with other defects such as impaired insulin sensitivity. The nature of such a postulated beta cell defect is uncertain. Whilst it has been reported to be specific to glucose, and not to non-glucose stimuli, this feature may be secondary to hyperglycaemia. The occurrence of islet amyloid in 70-90% of Type 2 diabetic patients, and rarely in the normal population, raises the possibility that amyloid deposition causing disruption of the islet is a factor which might affect beta cell function. Amyloid formation may be a primary abnormality or could be secondary to beta cell dysfunction induced by hyperglycaemia. A major susceptibility gene might predispose a proportion, perhaps 10-15%, of a Caucasian population towards diabetes. The subsequent development of diabetes in a particular patient is likely to depend on many factors including other genetic factors, a sedentary life style and obesity. In different populations different genetic influences may operate, including abnormalities of insulin receptor genes and glucose transporter genes, which may allow a beta cell abnormality to become expressed clinically.

Diabetes Mellitus, Type 2↗

PubMed1988

Growth hormone secretion in children determined by time series analysis.

Mid childhood growth has been studied in 26 short children (18M;8F) aged between 5.2 and 11.9 years growing with height velocity standard deviation score (SDS) between 0 and -0.8 and 24 short children (17M;7F) growing with height velocity SDS less than 0.8. Twenty-four hour GH profiles were analysed by an iterative method of pulse detection and subjected to time series analysis to determine dominant periodicity within the data arrays. Children aged less than 7 years displayed no dominant periodicity but after this age a periodicity of 200 min emerged. In the whole sample, differences between growth rate could be explained entirely by pulse amplitude. Nevertheless, the normal decline in height velocity over this age period occurred despite a significant shift in periodicity and an increase in GH pulse amplitude. This modulation of childhood growth by GH pulse amplitude persisted into puberty and the pubertal growth spurt of 14 tall girls was shown to be amplitude modulated with the periodicity unchanged. We conclude that mid childhood and pubertal growth is GH pulse amplitude modulated with a periodicity of approximately 200 min.

Age Factors↗

PubMed1988

Continuous subcutaneous growth hormone releasing factor analogue augments growth hormone secretion in normal male subjects with no desensitization of the somatotroph.

The effects of 8 day continuous subcutaneous (s.c.) infusions of growth hormone releasing hormone analogue (NLE27GRF(1-29)NH2 (GHRH.A)) on growth hormone (GH) secretion were studied in 14 normal adult male volunteers. GHRH.A was administered in doses which ranged from 7.5 to 120 ng/kg/min in doubling steps. Baseline GH profiles obtained during a 24 h infusion of normal saline in each subject were compared with profiles performed on days 1 and 8 of the infusion. Doses above 30 ng/kg/min augmented GH pulse amplitude and frequency. Doses of 60 ng/kg/min and 120 ng/kg/min appeared more satisfactory as these represented doses on the upwards slope of the dose response curve. However, at a dose of 120 ng/kg/min the GH secretion did not return to baseline for 12 of the 24 h. There was no evidence of desensitization or of depletion of the releasable GH pool with any dose. The possibility of treatment of short children with depot preparations of GHRH.A appears promising.

Adult↗