Substantial Rise of Plasma β-Endorphin Levels after Insulin-Induced Hypoglycemia in Human Subjects*

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Abstract
To elucidate whether insulin-induced hypogly-cemia enhances the release of β-endorphin in man, plasma extracts obtained from healthy subjects and patients with Graves' disease before and 45 min after insulin injection were subjected to gel chromatography, and the fractions obtained were measured by RIA for β-endorphin. In four healthy subjects, basal plasma β-endorphin levels were <3 to 3.1 pg/ml, and the levels rose substantially to 47.5 ± 12.4 pg/ml (mean ± SE) 45 min after insulin injection. Basal plasma β-endorphin levels in three hyperthyroid patients (< to 3.8 pg/ml) did not seem to be different from those in healthy subjects; however, the rise after insulin injection tended to be higher in cases of hyperthy-roidism, with a peak value of 68.5 ± 9.7 pg/ml. Plasma β-lipotropin and ACTH levels also rose in parallel with β-endor-phin in response to insulin-induced hypoglycemia in both healthy subjects and hyperthyroid patients. It would thus appear that β-endorphin, like ACTH or βlipotropin, is released in human subjects by hypoglycemic stress.