The separation of total plasma insulin from binding proteins using gel filtration: its application to the measurement of rate of insulin disappearance

Intentional overdose with insulin: prognostic factors and toxicokinetic/toxicodynamic profiles

Introduction

Prognostic factors in intentional insulin self-poisoning and the significance of plasma insulin levels are unclear. We therefore conducted this study to investigate prognostic factors in insulin poisoning, in relation to the value of plasma insulin concentration.

Methods

We conducted a prospective study, and used logistic regression to explore prognostic factors and modelling to investigate toxicokinetic/toxicodynamic relationships.

Results

Twenty-five patients (14 female and 11 male; median [25th to 75th percentiles] age 46 [36 to 58] years) were included. On presentation, the Glasgow Coma Scale score was 9 (4 to 14) and the capillary glucose concentration was 1.4 (1.1 to 2.3) mmol/l. The plasma insulin concentration was 197 (161 to 1,566) mIU/l and the cumulative amount of glucose infused was 301 (184 to 1,056) g. Four patients developed sequelae resulting in two deaths. Delay to therapy in excess of 6 hours (odds ratio 60.0, 95% confidence interval 2.9 to 1,236.7) and ventilation for longer than 48 hours (odds ratio 28.5, 95% confidence interval 1.9 to 420.6) were identified as independent prognostic factors. Toxicokinetic/toxicodynamic relationships between glucose infusion rates and insulin concentrations fit the maximum measured glucose infusion rate (E_max) model (E_max 29.5 [17.5 to 41.1] g/hour, concentration associated with the half-maximum glucose infusion rate [EC₅₀] 46 [35 to 161] mIU/l, and R² range 0.70 to 0.98; n = 6).

Conclusion

Intentional insulin overdose is rare. Assessment of prognosis relies on clinical findings. The observed plasma insulin EC₅₀ is 46 mIU/l.

The relationship of acute insulin sensitivity to the progression of vascular disease in long-term type 1 (insulin-dependent) diabetes mellitus

In 51 individuals with Type 1 (insulin-dependent) diabetes mellitus initially of more than 15 years' duration, the acute hypoglycaemic effect of intravenous insulin (0.11 IU/kg) was related to outcome over 18 years. This acute insulin sensitivity, or glucose assimilation index, was reproducible over the period of study. At 18-year follow-up, initial low glucose assimilation index (less than 0.082 mmol X l-1 X min-1 was significantly (p less than 0.01) associated with death from vascular disease. Low glucose assimilation index was similarly significantly (p less than 0.01) associated with progression of atherosclerotic disease, but not with microangiopathy alone. Hypertension (systolic blood pressure greater than 150 mmHg and/or diastolic blood pressure greater than 95 mmHg) was the only other parameter significantly (p less than 0.01) related to outcome, but this relationship was no longer significant once glucose assimilation index had been taken into account. A linear logistic analysis confirmed that acute insulin sensitivity was independently associated with outcome. Neither initial clinical control of diabetes nor glycosylated haemoglobin level in the 26 survivors was related to vascular prognosis.

Attempted suicide by insulin overdose in insulin-requiring diabetics

Four cases of suicidal insulin overdose in insulin-requiring diabetics presented to one hospital in three years. In three cases there was a history of depression; but despite huge doses of insulin (3,000 and 1,500 units) in two, no patient died and only one had residual signs of clinical brain damage. The estimated plasma insulin level was not well correlated with the severity of the hypoglycaemia. It is probable that suicidal insulin overdose is more common than reports in the literature suggest, and may often be unrecognized. The dissociation between huge doses of insulin and the severity of the subsequent hypoglycaemia in diabetics is unexplained.

Correlation between insulin receptor binding in isolated fat cells and insulin sensitivity in obese human subjects

This study examined the relationship between receptor binding of insulin in a metabolically significant target tissue in vitro and sensitivity to insulin in vivo in obese human subjects. Specific insulin binding was measured at 24 degrees C in isolated enlarged fat cells obtained from 16 patients, by observing the effect of increasing concentrations of unlabeled insulin on the binding of [125I]insulin. Scratchard plots of the binding data were curvilinear with an upward concavity, similarity shaped, and essentially parallel. Kinetic studies on the dissociation of [125I]insulin from fat cells indicated that these curvilinear Scratchard plots could be explained by the presence of site:site interactions of the negative cooperative type. Differences in binding between individual patients were predominantly due to differences in the numbers of receptor sites whether expressed in relation to cell number, cell volume, or cell surface area. These findings were not accounted for by differences in [125I]insulin degradation. Acute exposure of adipose tissue to insulin in vitro had no significant effect on [125I]insulin binding to isolated cells. The number of receptor sites was directly correlated with insulin sensitivity in vivo, measured as the rate constant (Kitt) for the fall in blood glucose after intravenous insulin, and was inversely correlated with the level of fasting plasma insulin. These findings corroborate those from other studies using human mononuclear leukocytes and various tissues from the obese mouse, which indicate that decreased insulin binding is a characteristic feature of insulin resistance in obesity.

Insulin sensitivity of adipose tissue in vitro and the response to exogenous insulin in obese human subjects

The effect of varying concentrations of insulin on 1-14C-glucose conversion to 14CO2 was measured in subcutaneous adipose tissue samples obtained from 16 obese human subjects (10 nondiabetic, 6 diabetic). An index of insulin sensitivity in vitro, Kins, was calculated as the concentration of insulin stimulating one-half maximal 14CO2 production. An index of insulin sensitivity in vivo, Kitt, was calculated as the rate constant for decrease in blood glucose after rapid intravenous administration of 0.05 U/kg insulin. There was, over-all, a significant correlation between Kins and Kitt, indicating that insulin sensitivity of 1-14C-glucose oxidation by adipose tissue in vitro reflects the general state of sensitivity of glucose metabolism to insulin in vivo in obese human subjects. The mean values for both Kins and Kitt in the nondiabetic subjects were significantly different from those in the diabetic subjects, indicating greater sensitivity to insulin in the former group. The nondiabetic group was also distinguished by a significantly greater plasma insulin:blood glucose ratio in the oral glucose tolerance test. These results support the view that tissue insulin sensitivity as well as pancreatic beta cell response play an important role in determining glucose tolerance in obesity.

Neontal hypoglycaemia in infants of insulin-dependent diabetic mothers

Neonatal hypoglycaemia (blood glucose smaller than 20 mg/100 ml) occurred in the first 6 hours of life in 25 of 34 infants born to diabetic mothers receiving insulin. Despite severe hypoglycaemia (blood glucose smaller than 10 mg/100 ml) in 17, clinical features of hypoglycaemia were absent in all but 2. Hypoglycaemia was not related either to the level of plasma insulin in cord blood, determined as nonextracted immunoreactive insulin, or to the degree of control of maternal blood glucose during pregnancy. The frequent occurrence of severe neonatal hypoglycaemia in the infants born to diabetic mothers receiving insulin appears to be due rather to failure to maintain basal glucose homoeostasis after birth than to hyperinsulinism.

Factors influencing the prognosis of vascular disease in insulin-deficient diabetes of long duration: a seven-year follow-up

Fifty-one insulin-dependent nonobese diabetics with duration of disease from 15 to 40 yr were reassessed after 7 yr. Those presenting with clinical vascular disease, hypertension, or elevated fasting triglycerides initially were found to have a bad prognosis. Serum cholesterol fasting blood sugar, age, or duration of diabetes were not related to outcome, Acute insensitivity to intravenous insulin was correlated with presence of initial vascular disease and was significantly related to both death and clinical deterioration in either large or small vessels over the period of follow-up. Insulin sensitivity was reproducible and may be of value in predicting the progression of long-term vascular changes in the insulin-requiring diabetic.