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The euglycaemic clamp, insulin sensitivity test with somatostatin, and insulin sensitivity test without somatostatin, were compared as in vivo methods of assessing insulin sensitivity. Fifteen subjects with varying degrees of glucose tolerance were studied. Somatostatin was not found to influence the assessment of insulin sensitivity by the insulin sensitivity test. When glucose disposal was expressed as metabolic clearance rate significant strong correlations were found between the euglycaemic clamp technique and the insulin sensitivity test with (r = 0.90) and without (r = 0.83) somatostatin. The effects of the tests on intermediary metabolism were also similar, and all 3 tests showed a similar impairment of insulin sensitivity in subjects with abnormal glucose tolerance. The insulin sensitivity test without somatostatin thus provides a simple and economical tool for studying insulin sensitivity.

Experiments were carried out in human volunteers to investigate the mechanism by which guar gum improves glucose tolerance. Guar reduced both plasma glucose and insulin responses to an oral glucose load, and delayed gastric emptying. However, there was no correlation between changes in individual blood glucose responses and changes in gastric emptying rates induced by guar. With a steady-state perfusion technique, glucose absorption was found to be significantly reduced during perfusion of the jejunum with solutions containing guar, but returned to control values during subsequent guar-free perfusions. Preperfusing the intestine with guar did not affect electrical measurements of unstirred layer thickness in the human jejunum in vivo. Experiments in vitro established that glucose diffusion out of a guar/glucose mixture was delayed under conditions of constant stirring. We conclude that guar improves glucose tolerance predominantly by reducing glucose absorption in the small intestine. It probably does this by inhibiting the effects of intestinal motility on fluid convection.

Using the glucose clamp technique, human insulin (Novo) and natural porcine insulin were found to have identical potency in terms of glucose delivery in the second hour of i.v. infusion at low (0.02 U/kg/h; 265 +/- 25 versus 232 +/- 35 mg/min, respectively) and high (0.05 U/kg/h; 467 +/- 47 versus 452 +/- 41 mg/min, respectively) doses in normal man. Insulin metabolic clearance rates, serum in vivo half-life, and rate of onset of action were also similar. In insulin-dependent diabetic subjects, whose blood glucose levels were also held constant by feedback glucose infusion, the free insulin profiles after s.c. injection of neutral soluble human insulin and porcine insulin (0.2 U/kg) were identical, and similar to those after conventional and highly purified bovine insulin preparations. Glucose requirement to maintain normoglycemia for the first 5 h after injection was 49.6 +/- 8.2 g for conventional bovine insulin, 50.4 +/- 10.0 g for highly purified bovine, 40.5 +/- 6.9 g for human insulin, and 50.6 +/- 12.4 g for porcine insulin (NS by analysis of variance). No difference in insulin activity was detected when glucose requirement was expressed in terms of the prevailing free insulin concentration. Responses of blood intermediary metabolite levels were indistinguishable between all insulins in both studies.

Two main methods are available for assessing insulin sensitivity with the hyperinsulinaemic euglycaemic clamp technique: one employs a glucose-controlled insulin infusion system (the Biostator) with automatic feedback control; the second depends on frequent glucose measurement and the use of an algorithm and a pocket calculator ('manual') to determine the glucose infusion rate. The amount of glucose infused is a measure of insulin sensitivity. The efficiency of the two methods was compared in nine normal subjects (seven lean, two obese). After an overnight fast subjects were infused with insulin at 50 mU X kg-1 X h-1 for 2 h; this rate was doubled during the first 10 min for the manual technique. Blood glucose averaged 4.7 +/- 0.1 and 4.8 +/- 0.1 mmol/l from 0 to 120 min for Biostator and manual techniques and did not deviate significantly from the desired level. Variability of the clamp was also similar over the same period (coefficient of variation 5.1 +/- 0.6% and 6.4 +/- 0.7%, Biostator and manual). Glucose infused to maintain steady state from 60 to 120 min was higher, however, with the manual than the Biostator method (5.7 +/- 0.6 versus 4.4 +/- 0.6 mg X kg-1 X min-1, p less than 0.01) even when the loading dose was omitted, although the two methods correlated closely (p less than 0.05). Glucose infusion rate varied more from minute to minute with the Biostator (coefficient of variation 28.8 +/- 3% versus 12.2 +/- 2.1%). Steady-state serum insulin levels (30-120 min) were the same during both methods.(ABSTRACT TRUNCATED AT 250 WORDS)

To test the hypothesis that frequent episodes of ketoacidosis and severe hyperglycaemia in brittle diabetes result from an exaggerated response to insulin withdrawal, the metabolic response to insulin deprivation in 16 severely brittle female diabetics has been compared with that in 6 C-peptide negative stable female diabetic patients of similar age and body weight. 4 hr after stopping insulin infusion, blood glucose was significantly higher in the brittle diabetics (22.8 vs 17.0 mmol/l, p less than 0.001) but blood 3-hydroxybutyrate was not different (1.8 vs 1.6 mmol/l). Concentrations of free insulin and counter-regulatory hormones were similar, basally and during the deprivation. Insulin antibody levels were significantly elevated in the brittle patients (11.2 vs 5.2 mmol/l, p less than 0.05) and there was no relationship between glucose or ketone body response and antibody level. Blood lactate, pyruvate, alanine and glycerol were significantly elevated basally in the brittle diabetic patients, but did not respond differently to insulin deprivation. Basal lactate and pyruvate concentrations were significantly correlated with overnight insulin requirements (lactate, rs 0.62, p less than 0.05; pyruvate, rs 0.70, p less than 0.05) suggesting that the elevated basal concentrations resulted from the higher peripheral insulin delivery rates required to maintain overnight normoglycaemia in the brittle patients. We conclude that although there are demonstrable abnormalities of intermediary metabolism in brittle diabetics, neither elevated levels of counter-regulatory hormones, nor an exaggerated response to insulin withdrawal explains the frequent episodes of ketoacidosis in these patients.

Six C-peptide deficient diabetics receiving twice daily mixtures of short and intermediate acting insulins were selected for study because of persistently raised blood glucose concentrations before and after breakfast. They were investigated to assess the effect of moving their evening injection of intermediate acting insulin to bedtime. The patients' usual twice daily insulin treatment was optimised and compared with the bedtime regimen during inpatient metabolic studies and an outpatient crossover study. With the conventional injection regimen blood glucose concentration rose sharply from 0500 to reach a fasting mean value of 10 +/- SE 1 . 6 mmol/l (180 +/- 29 mg/100 ml) and 16 . 8 +/- 2 . 2 mmol/l (303 +/- 40 mg/100 ml) after breakfast. By contrast, when the evening dose of intermediate acting insulin was delayed until bedtime the nocturnal rise in blood glucose concentration started later and was significantly lower both fasting (7 . 5 +/- 1 . 1 mmol/l (135 +/- 20 mg/100 ml); p less than 0 . 02) and after breakfast (13 . 2 +/- 1 . 4 mmol/l(238 +/- 25 mg/100 ml); p less than 0 . 02). Fasting blood concentrations of ketone bodies (3-hydroxybutyrate) were also significantly decreased. Plasma free insulin concentrations showed the predicted changes in five of the six patients. Blood glucose profiles collected over four months during the outpatient study confirmed the beneficial effect of giving intermediate acting insulin at bedtime.

The effect of mixing human soluble insulin with two newly developed formulations of human crystalline zinc-suspension insulin was studied in two groups of 8 normal and 6 diabetic subjects. Mixing Human Actrapid with Human Ultratard and Humulin-S with Humulin-Zn, for 60 s before subcutaneous injection, significantly blunted the rise in free insulin levels (p less than 0.05) and the onset of action of the short-acting insulins (p less than 0.01). The loss of solubility that occurs on mixing these insulins, with the consequent loss of the rapid acting component, may diminish their therapeutic usefulness in the control of post-prandial blood glucose.

Sensitivity to porcine insulin has been compared in overnight fasted hyperthyroid and control subjects using a euglycaemic clamp technique. Basal values for blood glucose, lactate, pyruvate, alanine, serum insulin and C-peptide were similar in the two groups, whilst blood glycerol (hyperthyroid 0.11 +/- 0.02 (mean +/- S.E.) vs. control 0.06 +/- 0.01 mmol/l, P less than 0.01) and blood 3-hydroxybutyrate (0.28 [0.03-0.79, range ]vs 0.09 [0.01-0.29 ]mmol/l, P less than 0.05) were increased in hyperthyroidism. During the 2 hour insulin infusion (0.05 U/kg/h), serum insulin plateaued at the same level (44 +/- 4 vs 44 +/- 1 mU/l) and insulin metabolic clearance rates were similar (1.21 +/- 0.10 vs 1.25 +/- 0.03 l/min). Serum C-peptide levels also decreased by similar amounts (40 +/- 8 vs 47 +/- 6%). The amount of glucose infused to maintain euglycaemia was identical during the second hour of insulin infusion (290 +/- 50 vs 330 +/- 30 mg/kg) as were the increments in lactate and pyruvate concentrations. Blood glycerol values decreased in both groups although values in hyperthyroid patients remained significantly higher than in controls. 3-Hydroxybutyrate concentrations fell to similar values in the two groups. These findings suggest that insulin-stimulated glucose metabolism and inhibition of ketogenesis are normal in hyperthyroidism.