Biomedical subjects
R C Turner
Publications and source records attributed to R C Turner.
Lipid abnormalities in untreated maturity-onset diabetics and the effect of treatment.
Plasma cholesterol and serum triglyceride levels and frequency of lipoprotein abnormalities were investigated in 126 untreated maturity-onset diabetics and 126 age- and sex-matched control subjects. Serum triglyceride levels were higher (mean: 1.67 mmol/l) and type IV hyperlipoproteinaemia occurred more frequently (16.7%) in the diabetic group as compared with the controls (1.29 mmol/l and 4.8% respectively). These findings were not explained by an excessive frequency of renal disease, hypertension or drug treatment amongst the diabetics. Normal men showed higher serum triglyceride (mean: 1.36 mmol/l) and lower plasma cholesterol (mean: 5.6 mmol/l) levels than normal women (1.21 mmol/l and 6.4 mmol/l respectively). No sex difference was seen amongst the diabetics. Triglyceride levels fell after one month of dietary treatment but only remained lowered in diabetics who required sulphonylureas for glycaemic control. After treatment for one year the correlation between serum triglycerides and blood glucose rose from r = 0.15 (NS) before treatment to r = 0.43 (p less than 0.001). Similarly the correlation between serum triglycerides and ponderal index rose from r = 0.19 (NS) to r = 0.28 (p less than 0.02).
Insulin deficiency and insulin resistance interaction in diabetes: estimation of their relative contribution by feedback analysis from basal plasma insulin and glucose concentrations.
The liver and beta cells function in a negative feedback loop, which appears to have a predominant role in regulating both the basal plasma glucose and insulin concentrations. The degree of basal hyperglycemia in diabetes probably provides a bioassay of both the effect of a reduction in insulin secretory capacity and the degree of insulin resistance. A mathematic model of the interaction of insulin deficiency and insulin resistance has been constructed, based on the known response characteristics of the beta cells to glucose, and of plasma glucose and insulin control of hepatic and peripherpal glucose flux. The degree to which beta cell deficiency increases basal plasma glucose reflects the hyperbolic shape of the normal insulin secretory response to different glucose concentrations. The height of basal plasma insulin is a function of the degree of insulin resistance. From the basal plasma insulin and glucose concentrations, the model provides an estimate of the degree to which both beta cell deficiency and insulin resistance contribute to diabetes. The predictions arising from the model are in accord with experimental data in man and in animals. In normal-weight diabetics who do not have increased insulin resistance, the model predicts that more than 85% of beta cell function has to be lost for the basal plasma glucose to rise to 6 mmol/liter, but a further 5%--10% loss increases the basal plasma glucose to over 10 mmol/liter. In a third of a consecutive series of 65 newly presenting, uncomplicated diabetics, both normal weight and obese, the analysis from the model suggested that insulin resistance, rather than beta cell deficit, was the predominant feature.
Physiological responses to insulin hypoglycaemia in spinal man.
The physiologically responses to hypoglycaemia induced by fish insulin were studied in nine tetraplegic subjects with physiological complete cervical spinal cord transection between C4 and C8. During hypoglycaemia there was a reduction in both systolic and diastolic blood pressure unlike in normal subjects. This was accompanied by a rise in heart rate. The normal rise in plasma adrenaline levels did not occur. Plasma human insulin levels were suppressed. The usual neuroglycopenic symptoms accompanying hypoglycaemia did not occur in the tetraplegics.
Increased plasma activities of N-acetyl-beta-D-glucosaminidase isoenzymes in human diabetes mellitus.
Plasma N-acetyl-beta-D-glucosaminidase activities are raised in maturity-onset insulin-dependent diabetic patients. Continuous gradient DEAE-cellulose column chromatography and assay of heat-stable enzyme activity both show that the activities of all isoenzymes are equally increased rather than a previously described increase of specific isoenzymes. Plasma enzyme activities are similarly increased in patients with and without diabetic retinopathy, and correlate with simultaneous plasma glucose concentrations.
High-density lipoprotein, lipid, and carbohydrate metabolism during increasing fitness.
Eleven unfit bank executives in sedentary employment exercised daily for 10 weeks according to the Canadian Air-Force 5BX Exercise Programme. Over this period no changes were observed in the glucose or insulin responses to a standard breakfast or to intravenous glucose, or in the glucose response to intravenous insulin. There was a significant reduction in high-density-lipoprotein cholesterol, but total plasma triglyceride and cholesterol levels were unaffected by exercise.
Two abnormalities of glucose-induced insulin secretion: dose-response characteristics and insulin sensitivity.
To characterize the defect of insulin secretion in diabetes, the response to different iv glucose loads has been studied in women who have had gestational diabetes and are, by definition, latent diabetic (LD). Women who have produced a large-for-dates baby, but who were not known to have been diabetic (LFD), have been investigated to determine if they have abnormal metabolism. Both groups were found to have raised fasting plasma glucose concentrations. Only the LD had glucose intolerance, which was associated with a reduced first phase insulin response to all glucose loads with a decreased maximal secretory capacity (low V max). The LFD women appeared to include a distinct abnormality in which the beta cells had decreased sensitivity to glucose (high Km), with diminished secretory response to small but normal response to large loads. Whereas the LD probably have disordered beta cell function, some of the LFD women may represent the upper end of the normal range of the glucose "set" of beta cell function. Neither group had insulin resistance, as measured by the hypoglycaemic response to an iv insulin bolus. A woman who has produced a LFD, but who was not known to be diabetic, does not necessarily have a diabetic tendency.
Maintenance of basal plasma glucose and insulin concentrations in maturity-onset diabetes.
Normal and mildly diabetic subjects each have their own "set" of basal plasma glucose and insulin concentrations. Diabetic patients have raised basal plasma glucose, with low-normal basal plasma C-peptide concentrations. Restoring normal glucose levels in mild diabetes by an insulin infusion further reduces the C-peptide concentration, but both the plasma glucose and the C-peptide return to their "set" level when the insulin is withdrawn. These results accord with the action of beta cells and liver in a negative feedback loop that maintains basal plasma glucose and insulin concentrations.
A simple and rational twice daily insulin regime. Distinction between basal and meal insulin requirements.
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Automatic lancet for capillary blood sampling.
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Home blood sampling for plasma glucose assay in control of diabetes.
Estimation of plasma glucose in home blood samples is needed to improve diabetic control. Sufficiently precise measurements on capillary blood were obtained by (a) storing Reflotest glucose-oxidase strips in a desiccant container before reading and (b) collecting blood samples into a simple vacuum bottle containing potassium fluoride (assay of sodium content indicating volume of plasma collected). The precision of the methods (+/- 1 SD) was +/-0.35 mmol/1 (+/-6.3 mg/100 ml). Clinical reliability was assessed by measuring the basal plasma glucose concentration at home on different mornings in patients with maturity-onset diabetes, the day-to-day variation (+/- 1 SD) being +/-0.73 and +/-0.92 mmol/1 (+/-13.2 and +/-16.6 mg/100 ml) respectively. The mean basal plasma glucose concentration in all 84 patients with maturity-onset diabetes from three general practices was 8 mmol/1 (144 mg/100 ml), 44 of the values exceeding 6 mmol/1 (108 mg/100 ml). Improving control by monitoring the basal plasma glucose concentration in maturity-onset diabetes might help to prevent diabetic complications.
Localisation of insulinomas.
Small insulinomas may be undetectable by arteriography or palpation of the pancreas. They can be identified, however, by the point at which high insulin levels are detected in the venous effluent sampled at several sites by catheterisation of the splenic and portal veins at laparotomy or via the percutaneous transhepatic route. Diagnosis by catheterisation techniques made it possible to resect only that part of the pancreas containing the tumour (in one patient the head and in another the body of the pancreas). Improved localisation is essential in planning an operation, and often removes the need for lengthy trials of medical therapy before laparotomy.
Basal normoglycemia attained with chlorpropamide in mild diabetes.
Sixteen adult-onset diabetics, who were thought by current criteria to be well controlled on diet alone, had substantially elevated overnight, basal plasma glucose concentrations. Chlorpropamide had a sufficiently prolonged stimulatory effect on the beta cells such that normal basal plasma glucose levels were obtained in 13 patients. Both basal plasma C-peptide levels and the C-peptide response to meals became normal, with improved postprandial glycemia. Diurnal plasma triglyceride levels were reduced. Plasma growth hormone levels were normal both before and after therapy. When diet alone is insufficient to maintain basal normoglycemia in mild diabetes, chlorporpamide is as effective as basal insulin supplements in producing normal basal plasma glucose levels.
Prospective comparison of modified fat-high-carbohydrate with standard low-carbohydrate dietary advice in the treatment of diabetes: one year follow-up study.
1. A prospective randomized study of two dietary regimens has been started in newly-diagnosed diabetics to determine their effect on circulating metabolites and on diabetic complications. 2. During the first year of treatment the fasting plasma glucose concentrations on both the low-carbohydrate diet and the high-carbohydrate, modified-fat (MF) diet showed a similar decrease. 3. Plasma cholesterol showed a sustained decrease only in patients recommended a MF diet. Transient changes in plasma triglyceride concentrations occurred in patients on both dietary regimens. 4. Increased plasma cholesterol levels are associated with atheromatous disease which is common in diabetics in Europe and North America. A MF diet may therefore have an advantage in that it lowers the plasma cholesterol as well as being effective in lowering the plasma glucose.
betacell function during insulin or chlorpropamide treatment of maturity-onset diabetes mellitus.
Maturity-onset diabetic patients usually have raised overnight-fasting plasma glucose levels associated with "normal" basal plasma insulin levels. The basal hyperglycemia is proportional to the degree of insulin deficiency. Basal insulin or C-peptide levels become subnormal if normal fasting plasma glucose levels are attained with insulin. Basal hyperglycemia is probably a compensatory response to maintain near-normal basal insulin levels. A logical therapy of maturity-onset diabetes is to produce basal normoglycemia by means of a constant basal insulin supplement, which can be provided by ultralente insulin. The reduced insulin response of diabetics to intravenous glucose is slightly increased when basal normoglycemia is established, suggesting that the high plasma glucose levels compromise beta cell function. The insulin response to meals in a mild diabetic is not affected by mild hyperglycemia but can be depleted if gross hyperglycemia occurs. Maintenance of normoglycemia then allows beta cell "recovery". In mild diabetics (c. less than 9 mmol per liter basal plasma glucose), chlorpropamide sufficiently stimulates beta cell secretion so that basal normoglycemia can be produced. The C-peptide response to meals is improved, whereas comparable reduction of the plasma glucose with insulin does not alter the meal response. Thus basal normoglycemia can be produced by "resting" beta cells with a basal insulin supplement or by stimulating them with sulfonylurea therapy.
Diabetes: The quest for basal normoglycaemia.
Diabetes is an endocrine deficiency disease, a logical treatment of which is hormone replacement therapy. Many patients who are thought to be controlled by diet alone continue to have high plasma-glucose levels. As the rise in the basal plasma glucose concentration is the predominant glucose abnormality of diabetes, treatment should be aimed primarily at producing basal normoglycaemia. 18 mild, maturity onset diabetics have been treated with a basal insulin supplement provided by single daily injections of insulin zinc suspension (crystalline) 'Ultralente'. Overnight basal normoglycaemia has been obtained with markedly reduced plasma-glucose levels during the day. Plama-triglyceride levels have become normal in most patients. The required insulin dose need not be determined empirically, but can be calculated from the basal plasma-glucose level and the degree of obesity. There is minimum risk of hypoglycaemia, and rigid dietary restriction is unnecessary. As mild diabetics are prone to complications, treatment with basal insulin supplements may be beneficial when diet alone fails to produce basal normoglycaemia.
Glucose control of basal insulin secretion in diabetes.
The plasma insulin response to both a small increase and decrease in the plasma glucose has been studied in normal and diabetic, non-obese subjects. In a second investigation the plasma insulin concentrations were measured during a gradual reduction of the raised fasting plasma glucose of diabetes to normal levels. In both studies, diabetic patients were found to have a markedly impaired response of the fasting plasma insulin to small changes in plasma glucose. These results do not support the suggestion that stimulated and not basal insulin secretion is impaired in diabetes. Both modes of secretion are probably via the same B-cell release mechanism, which is deficient in diabetes. There was a gradation of response between maturity onset and juvenile onset diabetics.
Suppression of basal insulin secretion by adrenalin in normal man and in patients with insulinomas.
Basal insulin secretion has been thought to be via a different mechanism from stimulated insulin secretion, partly because it is not similarly suppressed by adrenalin. However, adrenalin normally causes hyperglycaemia, but if it is infused while the plasma glucose is kept constant there is marked suppression of insulin secretion. Sympathetic stimulation modulates basal insulin secretion, and alpha adrenergic blockade impaired the suppression of insulin secretion in response to hypoglycaemia. Four of five benign insulinomas had marked suppression of insulin secretion by adrenalin, but one malignant and one benign insulionoma had little suppression. Both had a raised proportion of their basal plasma insulin as proinsulin, and the impaired suppression of secretion by adrenalin probably signified an undifferentiated tumour.