Increased insulin binding of erythrocytes and insulin sensitivity in adrenal insufficiency

Influence of glucocorticoids and growth hormone on insulin sensitivity in humans

The seminal concept proposed by Sir Harold Himsworth more than 75 years ago that a large number of patients with diabetes were 'insulin insensitive', now termed insulin resistance, has now expanded to include several endocrine syndromes, namely those of glucocorticoid excess, and growth hormone excess and deficiency. Synthetic glucocorticoids are increasingly used to treat a wide variety of chronic diseases, whereas the beneficial effects of recombinant growth hormone replacement therapy in children and adults with growth hormone deficiency have now been well-recognized for over 25 years. However, clinical and experimental studies have established that increased circulating levels of glucocorticoids and growth hormone can also lead to worsening of insulin resistance, glucose intolerance, overt diabetes mellitus and cardiovascular disease. Improved understanding of the physiological 24-h rhythmicity of glucocorticoid and growth hormone secretion and its influence on the dawn phenomenon and the Staub-Trauggot effect has therefore led to renewed interest in studies on the mechanisms of insulin resistance induced by exogenous administration of glucocorticoids and growth hormone in humans. In this review, we describe the physiological events that result from the presence of resistance to insulin action at the level of skeletal muscle, adipose tissue, and liver, describe the known mechanisms of glucocorticoid- and growth hormone-mediated insulin resistance, and provide an update of the contributions of glucocorticoids and growth hormone to understanding the pathophysiology of insulin resistance and its effects on several endocrine syndromes.

Body fatness and fat distribution as predictors of metabolic abnormalities and early carotid atherosclerosis

OBJECTIVE

To test the hypothesis that intra-abdominal fat plays a primary role over general adiposity for metabolic abnormalities and atherosclerosis.

RESEARCH DESIGN AND METHODS

We cross-sectionally studied 849 Japanese men aged 50.3 +/- 8.5 years (range 20-78) with BMI 23.5 +/- 2.9 kg/m(2). Intimal-medial thickness (IMT) of the carotid artery was measured by ultrasound. General adiposity was assessed by BMI. Waist circumference and waist-to-hip ratio (WHR) were used as a surrogate measure for abdominal fat. Abdominal subcutaneous fat area (ASF) and intra-abdominal fat area (IAF) were measured by computed tomography. Correlations between these measures and carotid IMT were analyzed. The interaction of generalized adiposity (BMI) and IAF in relation to metabolic variables, such as glucose tolerance, insulin resistance, and serum lipids, was also evaluated.

RESULTS

BMI, waist circumference, WHR, ASF, and IAF were all correlated with carotid IMT. Adjustment for BMI eliminated the associations between IMT and waist circumference, ASF, and IAF. In contrast, WHR retained a significant correlation with IMT. BMI and IAF were associated with insulin resistance, glucose tolerance, HDL cholesterol, and blood pressure independently of each other. IAF was an independent correlate for serum triglyceride, but BMI was not.

CONCLUSIONS

The primary importance of IAF over general adiposity for carotid atherosclerosis was not confirmed. Caution is recommended when using WHR as a measure of abdominal fat. The roles of IAF for metabolic abnormalities may be more limited than conventionally thought. BMI and WHR are simple and better clinical predictors for carotid atherosclerosis versus IAF.

Increased insulin sensitivity in patients with aldosterone producing adenoma

OBJECTIVE

Primary aldosteronism is a recognized endocrine cause of glucose intolerance. A blunted insulin response to glucose in patients with primary aldosteronism is well known, but insulin sensitivity has not been thoroughly determined. We investigated insulin sensitivity and insulin secretion in patients with aldosterone producing adenoma.

DESIGN

Glucose tolerance and insulin responses to glucose were evaluated using a standard 75 g oral glucose tolerance test in patients with aldosterone producing adenoma before and after surgery, and in control subjects. Parameters for insulin resistance (HOMA-R) and pancreatic beta-cell function (HOMA-beta F) were derived from a homeostasis model assessment.

PATIENTS

Fifteen patients with aldosterone producing adenoma and 41 control subjects with normal glucose tolerance matched for age and body mass index, were studied. Eight patients were re-evaluated after surgical removal of the adenoma. In 5 patients 125I-insulin binding to erythrocytes was also measured.

MEASUREMENTS

Plasma glucose was measured by a glucose oxidase method. Plasma insulin, aldosterone and renin activity were measured by radioimmunoassay.

RESULTS

Both fasting plasma glucose and insulin were lower in the patients than in the controls. Although the areas under the curve for plasma glucose during the oral glucose tolerance test did not differ, that for plasma insulin was less in the patients with hyperaldosteronism. Insulin sensitivity was increased in the patients, as evidenced by decreased HOMA-R compared with controls, while HOMA-beta F was comparable between the groups. 125I-insulin binding to erythrocytes was higher in 5 patients than in 19 normal controls. After surgical removal of adenoma, neither fasting plasma glucose nor the glucose area under the curve during the oral glucose tolerance test changed. However, fasting plasma insulin and the insulin area under the curve increased significantly. HOMA-R increased and HOMA-beta F remained unaltered.

CONCLUSION

Insulin sensitivity was increased in untreated patients with aldosterone producing adenoma. Enhanced insulin receptor binding may contribute to this increased insulin sensitivity.

Increased insulin receptor binding in erythrocytes from growth hormone-deficient children

Erythrocytes from growth hormone-deficient children (GHd-children) (n = 10) showed a statistically significant increase in insulin binding at low unlabeled insulin concentrations, together with a threefold decrease in apparent receptor affinity, as compared to control children (C) (n = 11). Scatchard analysis of the binding data using the two-site model revealed that both the receptor concentration R1 [GHd-children 0.10 +/- 0.01 ng/ml and C 0.03 +/- 0.002 ng/ml] and the dissociation constant KD1 [GHd-children (0.48 +/- 0.05) x 10(-9) M and C (0.19 +/- 0.01) x 10(-9) M] for high affinity-low capacity sites were significantly increased in erythrocytes from GHd-children, while neither receptor concentrations (R2) nor the dissociation constant (KD2) for low affinity-high capacity sites proved to be altered. These events were accompanied by a normal sensitivity to insulin as well as glucose tolerance in the GHd-group. The meaning of the increased insulin binding with normal insulin sensitivity in GH-deficiency is discussed.

Red blood cell insulin receptors in health and disease

CONTENTS

Structure and characteristics of erythrocyte insulin receptor. Red blood cell age and insulin receptors. Insulin receptors in human disease states. Obesity. Chronic renal failure. Acanthosis nigricans. Miscellaneous disease states. Insulin receptors in children. Insulin receptors in women during pregnancy. Insulin binding and other hormones. Comparison of biosynthetic insulin, pancreatic human insulin and porcine insulin binding to erythrocytes. Effect of exercise on insulin binding to red blood cells of normal human volunteers. Miscellaneous insulin binding studies. Insulin internalization and degradation. Insulin and erythrocyte metabolism. Summary and conclusion.

Comparative effects of diet or glibenclamide on insulin secretion and action in non-obese NIDDM

We compared the effects of dietary treatment (D) and diet plus glibenclamide (DPG), for 3 weeks, on glycemia, insulin secretion and action in 2 groups of non-obese patients with NIDDM matched for fasting plasma glucose level. Fasting glycemia decreased in both groups with greater reductions after DPG (n = 7, 10.0 +/- 0.6 to 6.3 + 0.3 mmol/l, M +/- SEM, P less than 0.02) than after D (n = 7, 10.1 +/- 0.8 to 8.7 +/- 0.7 mmol/l, M +/- SEM, P less than 0.02). The magnitude of day-time elevation of plasma glucose over the fasting level, however, was reduced only after DPG. DPG but not D improved the plasma insulin response to glucose ingestion and in vivo insulin action measured by insulin tolerance test with unaltered erythrocyte 125I-insulin binding. This might indicate potentiation of insulin action at post-receptor binding steps. Improvements in in vivo insulin action and in insulin secretion after DPG closely correlated with decrease in fasting glycemia and reduction in the day-time elevation of plasma glucose levels, respectively. In conclusion, diet improved glycemic control in non-obese patients with NIDDM mainly by reducing fasting glycemia, although the mechanism remains unknown. Glibenclamide added to the diet further decreased fasting glycemia by improving in vivo insulin action and reduced the magnitude of day-time elevation of plasma glucose by enhancing endogenous insulin secretion.