Prednisolone enhances beta-cell function independently of ambient glycemic levels in type II diabetes.

This study examined the changes in beta-cell response and insulin sensitivity induced by a single overnight dose of 15 mg prednisolone in eight type II diabetic subjects, seven nondiabetic normal controls, and eight subjects with a first-degree type II diabetic relative who were therefore at risk of developing diabetes. beta-Cell secretion was assessed by use of the hyperglycemic clamp technique, and insulin sensitivity was assessed with the clamp and the Continuous Infusion of Glucose with Model Assessment (CIGMA) technique. Subjects were studied in random order on two occasions, after placebo and after prednisolone administration. Normal subjects showed an increase of median fasting glucose level from 4.7 to 5.2 mmol.L-1 after prednisolone (P < .02) and at-risk subjects showed an increase from 4.8 to 5.5 mmol.L-1 (P < .005), whereas diabetic subjects showed no significant increase in median fasting plasma glucose level (7.0 mmol.L-1 after placebo and 6.3 mmol.L-1 after prednisolone). Six of these eight diabetic subjects showed a paradoxical decrease of fasting plasma glucose level after prednisolone therapy. All three groups showed a significant elevation of clamp steady-state plasma insulin levels following prednisolone, with a median percentage elevation of 46%, 66%, and 31% for normal, at-risk, and diabetic subjects, respectively. All three groups showed significant reduction in insulin sensitivity measured by CIGMA following prednisolone of 51%, 41%, and 25% of pre-prednisolone levels in normal, at-risk, and diabetic subjects, respectively, with a significantly greater reduction in normal subjects than in diabetics (P < .02).(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Suppression of insulin secretion by falling plasma glucose levels is impaired in type 2 diabetes.

The ability of Type 2 diabetic patients to suppress islet B-cell secretion in response to falling plasma glucose levels has been studied with two different protocols. (1) Five diet-treated diabetic patients and 6 normal subjects were studied after the termination of a hyperglycaemic clamp at 15 mmol l-1 for 150 min, with the plasma glucose levels then being allowed to fall and the glucose clamp re-established at 10 mmol l-1. The plasma insulin levels fell in normal subjects from 178 +/- 141 (+/- SD) mU l-1 at the end of the 15 mmol l-1 clamp to 147 +/- 97 mU l-1 (p less than 0.02) 20 min later, whereas in diabetic patients there was no significant change from 61 +/- 41 to 56 +/- 35 mU l-1, respectively (NS). (2) The second study was performed to assess the turn-off of islet B-cell secretion with diabetic patients and normal subjects starting at comparable plasma insulin levels. Twelve diet-treated diabetic patients and 11 normal subjects were given a continuous low-dose glucose infusion for 60 min at a rate of 5 mg kg-1 ideal body weight min-1, after which the infusion was turned off and the plasma glucose level allowed to fall.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

Haemolysis affects insulin but not C-peptide immunoassay.

Venous blood was taken at the end of a glucose infusion test in 19 individuals and divided into four aliquots, 3 of which were variably haemolysed by repeated passage through a 23-gauge needle to simulate traumatic venepuncture. Plasma insulin (measured by both a charcoal separation and a double-antibody method), C-peptide, and haemoglobin were measured in each aliquot, and haemolysis was also assessed visibly. A significant loss of immuno-assayable plasma insulin was found in samples with only a trace of visible haemolysis, with up to 90% lost in severely haemolysed samples. Plasma C-peptide was unaffected by haemolysis. This represents an additional advantage for the use of plasma C-peptide in assessing insulin secretion.

Normal calcium-activated potassium channel in red cells in type 2 diabetes.

The diminished insulin secretion of type 2 diabetes might result from abnormal regulation of the potassium permeability which leads to beta-cell depolarization. The possibility of a generalized defect has been investigated in vitro by the stimulation of 86Rb efflux from red cells of type 2 diabetic patients by calcium ionophore and its inhibition by quinine. Diabetic subjects and control subjects had identical 86Rb efflux stimulated by 0.2-0.6 microM calcium ionophore A23187 and identical inhibition by quinine with mean Ki 6 microM and 4 microM quinine respectively for 0.2 microM ionophore and mean Ki 38 microM and 37 microM quinine respectively for 0.6 microM ionophore.

Beta-cell dysfunction, rather than insulin insensitivity, is the primary defect in familial type 2 diabetes.

Continuous infusion of glucose with model assessment was used to measure glucose tolerance, beta-cell function, and insulin sensitivity in 154 first-degree relatives of 55 patients with type-2 diabetes. The plasma glucose achieved at 1 h was normally distributed in normal control subjects, but 31 (20%) of relatives of type-2 diabetics had values above the normal distribution mean +2 SD. Insulin secretion, assessed from the first or second phase plasma-C-peptide responses, was significantly lower in the glucose-intolerant relatives than in normoglycaemic relatives of similar sex, age, and obesity. beta-cell function, estimated by means of model analysis, was severely impaired in the glucose-intolerant relatives but was not impaired in the normoglycaemic relatives (geometric mean 41% and 109% of normal beta-cell response, respectively). Reduced beta-cell function was found with all degrees of glucose intolerance, whereas only the more severely hyperglycaemic relatives had impaired insulin sensitivity. This suggests that the primary defect in familial type-2 diabetes is beta-cell dysfunction.

Sulphonylurea therapy doubles B-cell response to glucose in type 2 diabetic patients.

The effect of sulphonylurea therapy for 3 weeks on glucose-stimulated insulin secretion and insulin resistance was studied in Type 2 diabetic patients. The fasting plasma insulin and C-peptide concentrations on diet alone were compared with each subject's fasting concentrations on sulphonylurea treatment at a lower fasting plasma glucose and at the original diet-alone glycaemic level obtained by the hyperglycaemic clamp technique. At this isoglycaemic level (mean 11 mmol/l), plasma insulin levels increased from 6.9 mU/l on diet alone to 12.1 mU/l on sulphonylurea treatment (p less than 0.01). The subjects were also studied by the hyperglycaemic clamp technique at mean glycaemic levels of 13 mmol/l before and after sulphonylurea treatment; the incremental insulin response was similarly enhanced from 7.6 +/- 3.5 to 13.7 +/- 6.9 mU/l (p less than 0.02) respectively. Sulphonylureas appear to reduce glycaemia by enhancing B-cell function two-fold. In the patients studied this was from approximately 21% to 37% of a normal response. Insulin resistance assessed by the same hyperglycaemic clamps as endogenous plasma insulin concentrations divided by glucose infusion rates was unchanged by sulphonylurea therapy (mean 4.37 compared to 4.40 mU X 1(-1) X mg-1 X kg X min on diet alone).

Continuous infusion of glucose with model assessment: measurement of insulin resistance and beta-cell function in man.

Continuous infusion of glucose with model assessment (CIGMA) is a new method of assessing glucose tolerance, insulin resistance and beta-cell function. It consists of a continuous glucose infusion 5 mg glucose/kg ideal body weight per min for 60 min, with measurement of plasma glucose and insulin concentrations. These are similar to postprandial levels, change slowly, and depend on the dynamic interaction between the insulin produced and its effect on glucose turnover. The concentrations can be interpreted using a mathematical model of glucose and insulin homeostasis to assess insulin resistance and beta-cell function. In 23 subjects (12 normal and 11 with Type 2 (non-insulin-dependent diabetes) the insulin resistance measured by CIGMA correlated with that measured independently by euglycaemic clamp (Rs = 0.87, p less than 0.0001). With normal insulin resistance defined as 1, the median resistance in normal subjects was 1.35 by CIGMA and 1.39 by clamp, and in diabetic patients 4.0 by CIGMA and 3.96 by clamp. In 21 subjects (10 normal and 11 Type 2 diabetic) the beta-cell function measured by CIGMA correlated with steady-state plasma insulin levels during hyperglycaemic clamp at 10 mmol/l (Rs = 0.64, p less than 0.002). The CIGMA coefficient of variability was 21% for resistance and 19% for beta-cell function. CIGMA is a simple, non-labour-intensive method for assessing insulin resistance and beta-cell function in normal and Type 2 diabetic subjects who do not have glycosuria during the test.

The half-life of endogenous insulin and C-peptide in man assessed by somatostatin suppression.

The in-vivo half-lives of insulin and C-peptide have been assessed in normal man by a method which examines the decline of endogenously produced insulin and C-peptide after somatostatin suppression of secretion. Venous blood samples were taken each minute from seven normal subjects: i.v. glucose (0.1 g/kg ideal body weight) was given over 1 min to stimulate secretion, followed by a bolus of 250 micrograms of somatostatin-14 and an infusion of a further 250 micrograms somatostatin-14 over the subsequent 30 min. Plasma samples were analysed for C-peptide, glucose and insulin. The initial mono-exponential half-lives over 8 min were 3.9 +/- 0.3 and 10.2 +/- 0.7 min respectively (mean +/- SEM), with subsequent slower declines. Log transformed insulin and C-peptide yielded biphasic declinations which were assessed by a two-pool model. The rate constant of clearance of insulin implied avid uptake, while the kinetics of C-peptide clearance were slower, and irreversible loss might be explained by glomerular filtration alone. The somatostatin suppression method of measuring hormone kinetics could be used for newly described hormones which are not available for in-vivo studies.

Control of pulsatile insulin secretion in man.

Plasma insulin and glucose concentrations were examined in man in a basal state from central venous samples taken at 1-min intervals for up to 2.5 h. Normal subjects have insulin oscillations of mean period 14 min (significant autocorrelation, p less than 0.0001) with changes in concentration of 40% over 7 min. The pulsation frequency was stable through cholinergic, endorphin, alpha-adrenergic or beta-adrenergic blockade, or small perturbations with glucose or insulin. Stimulation of insulin secretion by intravenous glucose, tolbutamide or sodium salicylate increased the amplitude of the insulin oscillations while the frequency remained stable. Patients with a truncal vagotomy or after Whipple's operation had longer-term oscillations of 33 and 37 min periodicity (autocorrelation: p less than 0.0001), with insulin-associated glucose swings four times larger than those of normal subjects. Type 2 (non-insulin-dependent) diabetic patients had a similarly increased insulin-associated glucose swing of six times that seen in normal subjects. The hypothesis is proposed that the 14-min cycle of insulin production is controlled by a 'pacemaker' which assists glucose homeostasis. The longer 33-37-min oscillations, seen in those with denervation, may arise from a limit-cycle of the feedback loop between insulin from the B cells and glucose from the liver. The vagus may provide hierarchical control of insulin release.

Serum total hydroxyproline assay: effects of age, sex and Paget's bone disease.

An assay was developed for total hydroxyproline (protein, peptide and free) in 12 h fasted human serum. Values obtained from 80 adults judged normal by laboratory and physical examinations showed age and sex effects; values increased with age and were higher for men. Assay of serum samples from 22 patients with Paget's bone disease revealed values significantly above normal taking age and sex into consideration (p = 0.001). Serum alkaline phosphatase and serum hydroxyproline values for these patients were correlated (r = 0.91). Serum total hydroxyproline may be a useful assay for evaluating metabolic bone diseases but age and sex must be taken into consideration in the interpretation.