The presence of methionine-enkephalin in plasma and urine in normal human subjects and various patients.

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Abstract
The present study was performed to investigate whether or not there were enkephalins in plasma and urine in normal subjects and in patients with various diseases. Two kinds of antisera were developed to detect M-enk and L-enk. One has specific affinity with the C-terminus of methionine-enkephalin sulfoxide (M-O-enk), the oxidized form of M-enk, and the other with the N-terminus of L-enk. M-enk-like substance (MELS) was present in blood and urine in normal subjects, but not L-enk-like substance (LELS). Plasma MELS and its urinary output averaged 38±14pg/ml (N=19) and 605±235mg/day (N=15, M.±S. D.), respectively. There was a significant increase in plasma MELS and its urinary output in patients with pheochromocytoma. Plasma MELS did not show any significant increase or decrease in Cushing's disease, Addison's disease, panhypopituitarism or chronic glomerulonephritis. The urinary output of MELS was significantly increased in patients with essential hypertension, renovascular hypertension and primary aldosteronism, but was decreased in central diabetes insipidus.