Early response of plasma insulin to small doses of intravenous glucose: effect of obesity

Glucose intolerance in patients with chronic inflammatory diseases is normalized by glucocorticoids

Nine of 16 patients with inflammatory connective tissue diseases (rheumatoid arthritis, polymyalgia rheumatica, scleroderma and mixed connective tissue disease) had glucose intolerance defined a a K-rate less than one but a normal early insulin response to intravenous glucose loading. The degree of the impaired glucose handling was related to the degree of inflammatory activity as defined by acute phase reactants. Glucocorticoid therapy induced within three days an improved and normalized glucose tolerance and an augmented early insulin response (p less than 0.001). The glucocorticoid effect was still present up to six months of ongoing therapy. It is suggested that glucose intolerance in chronic inflammation is a consequence of a peripheral insulin antagonism and an inhibition of insulin secretion. This inhibition may be mediated directly or indirectly by inflammatory cell products and may be sensitive to glucocorticoids.

Simple empirical assessment of beta-cell function by a constant infusion of glucose test in normal and type 2 (non-insulin-dependent) diabetic subjects

The plasma insulin or C-peptide response to a 90-min constant glucose infusion 5 mg.kg ideal body weight-1.min-1 provides Beta-cell assessment comparable to more intensive methods. In 14 diet-treated Type 2 (non-insulin-dependent) diabetic subjects and 12 non-diabetic subjects, plasma insulin and C-peptide concentrations gave near linear plots against simultaneous glucose values. The 'glucose-insulin and glucose-C-peptide vectors' (G-I and G-C vectors), could be extrapolated to predict insulin and C-peptide levels during a 12 mmol/l hyperglycaemic clamp. Predicted concentrations correlated with clamp concentrations, r = 0.94 and r = 0.98 respectively, p less than 0.001, validating the vectors as empirical glucose dose-response curves. The vector slopes correlated highly with %Beta, a mathematical model-derived measure of Beta-cell function using constant infusion of glucose model assessment, Spearman r = 0.95 and 0.93 for insulin and C-peptide, respectively. G-I vector slopes in 21 diet-treated Type 2 diabetic subjects with fasting glucose (mean + 1 SD) 7.5 +/- 2.3 mmol/l, were lower than in 28 non-diabetic subjects, (geometric mean, 1 SD range, 8.4 pmol/mmol (3.3-21.0) and 25.1 pmol/mmol (14.3-44.1), p less than 0.001, respectively), indicating an impaired Beta-cell response. The G-I vector slopes correlated with obesity in both groups (r = 0.54 p less than 0.02 and 0.72, p less than 0.001 respectively), and, in 15 non-diabetic subjects, correlated inversely with insulin sensitivity as measured by a euglycaemic clamp (r = -0.66, p less than 0.01). Thus, Beta-cell function needs to be interpreted in relation to obesity/insulin resistance and, taking obesity into account, only 4 of 21 diabetic patients had Beta-cell function (G-I vector slope) in the non-diabetic range. The fasting plasma glucose in the diabetic subjects correlated inversely with the obesity-corrected G-I and G-C vector slopes (partial r = -0.57, p less than 0.01 and -0.86, p less than 0.001, respectively). The insulin or C-peptide response to the glucose infusion provides a direct empirical measure of the Beta-cell function, which can be interpreted in relation to obesity or to insulin resistance to assess underlying pancreatic responsiveness.

Enhanced synthesis, storage, and secretion of insulin in pancreatic islets derived from obese subjects

Insulin biosynthesis, content, and secretion were investigated in islets derived from pancreas specimens of normal weight (100.4 +/- 1.1% of ideal body weight) and obese (137.2 +/- 5.9% of ideal weight) patients. The pancreatic islets from the obese subjects were characterized by a significantly enhanced glucose-induced insulin secretion and biosynthesis and by an insulin content that was nearly double when compared with islets from the nonobese subjects. The results support the hypothesis that an enhanced beta-cell reactivity significantly contributes to the insulin hyperresponse observed in the obese state.

Glycemic response to lipid infusion in the premature neonate

The effect of lipid infusion on glucose homeostasis in the preterm newborn infant was evaluated. Seven infants were given a test dose of 0.25 gm/kg/hour of lipid emulsion. Their response was characterized by :(1) a two fold increase in serum free fatty acid concentrations, (2) a small, transient rise in insulin values, and (3) a sustained increase in serum glucose concentration (mean increment in serum glucose was 24% over baseline). Nine infants received a test dose of 0.5 gm/kg/hr of lipid. Their response was similar to that in the lower infusion group, but of a greater magnitude: an eightfold increase in free fatty acids, sustained increase in serum insulin concentration, and a mean increment in serum glucose values of 65% over baseline. Increased lipid availability in the low-birth-weight newborn infant plays a significant role in promoting an increase in serum glucose concentrations.

Exploration of the early insulin response by two small successive loads of I.V. glucose in normal and obese subjects

Two 5 g glucose loads at 1-h interval were given to healthy controls and obese subjects with slightly altered or normal OGTT in order to explore the capacity of restoration of the "rapid insulin response" to i.v. glucose. In the normal subjects, the two successive loads gave rise to identical responses as far as maximum increase (delta max), average increase at 2-5 min (delta 2-5 min), area of increase 0-15 min (delta 0-15 min) for both glucose and IRI, were concerned. Obese subjects could be divided on the basis of their insulin response to the first load into normal responders (group I) and high-responders (group II). In group I obese subjects, the responses to the second load were identical to those to the first. In group II obese subjects delta max, delta 2-5 min and delta 0-15 min of the insulin response to the second load were reduced as compared to the first.

Arterial concentration and forearm extraction of glucose and insulin during the early phase of a glucose infusion

The concentrations of glucose and insulin were determined with high precision at half minute intervals in arterial and deep forearm vein blood after a bolus injection of glucose (4 g), followed by a constant i. v. infusion (200 mg/min), in four healthy subjects. The values for the deep vein were corrected for the transit time, which was determined by injection of Cardio-green. Arterial glucose peaked at the end of the bolus injection, venous glucose 1 1/2 min later. Arterial insulin reached its maximum later than glucose, after 2 1/2-4 min. The venous insulin reached its maximum later and was much lower than the arterial level, in two cases only around 50% of the arterial concentration. It is concluded that early after glucose administration there is a considerable extraction of both glucose and insulin by the forearm. Since the insulin extraction was quite variable venous insulin concentrations cannot be used for the assessment of early insulin response to glucose.

Beta-cell function improved by supplementing basal insulin secretion in mild diabetes

Insulin supplements, predominantly as a constant basal fish insulin infusion, were given to patients with mild diabetes to reduce the overnight fasting glucose level to normal. The basal plasma human insulin levels were reduced to subnormal levels by the infusion, and the insulin response to intravenous glucose was enhanced. The beta-cell in diabetes seems to be in a vicious circle in which an impaired insulin response to glucose produces hyperglycaemia, which stresses beta-cell function, making it more inefficient. A constant basal insulin supplement to induce basal normoglycaemia may benefit beta-cell function in diabetes.