A New Approach to Radioimmunoassay of Plasma ACTH and its Clinical Application
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概要
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A new technique for ACTH radioimmunoassay has been developed, on the basis of the discovery of an increase in binding of ACTH to antibody upon addition of small increments of ACTH to relatively high concentrations of antisera. A progressive increase in B/F ratio occurs instead of the conventional decrease. This paradoxical binding has been utilized to develop an accurate and convenient method for measuring ACTH levels in unextracted plasma. The method shows satisfactory recovery, sensitivity, reproducibility and specificity.<BR>Diurnal variations in plasma ACTH levels were measured in 6 normal subjects. The mean peak ACTH level occurred at 6 a. m. and the nadir at midnight. Plasma ACTH values fluctuated widely during the day in individual subjects. With 5 g of metyrapone intravenously infused from 8 a. m. over 4 hours, plasma corf. sol fell almost completely 2 hours after the start of infusion and began to rise gradually towards the base-line after the infusion ended. Plasma ACTH began to rise significantly 4 hours after the start of infusion and reached the maximum a few hours after the end of infusion, after which it decreased towards the base line levels in 12 hours. Plasma 11-deoxycortisol levels rose in a similar fashion to plasma ACTH. When metyrapone was given orally to 7 normal subjects in 6 doses of 750 mg at 4 hours' intervals started at 8 a. m., plasma ACTH level began to rise after the first or second dose of metyrapone but tended to fall between late afternoon and midnight. Again, a highly elevated plasma ACTH level was observed in the following morning in accordance with the diurnal variation of plasma ACTH. Plasma 11- deoxycortisol responded in a quite similar way to plasma ACTH. The diurnal variation of plasma ACTH response to metyrapone, which was evidenced by the high and sustained plasma ACTH and 11-deoxycortisol levels on the day following -133- the oral metyrapone administration, can actount for the well known observation of a higher urinary steroid response also on that day. Following intravenous administration of Piromin, 0.5μg/kg, to 5 normal subjects, plasma ACTH levels began to rise 1/2 to 1 hour after the injection preceding or in parallel with elevation of plasma cortisol levels and reached the maximum in 1 and 1/2 to 3 hours, after which they decreased towards the base line levels though they remained still elevated in 2 subjects who developed severe constitutional symptoms including nausea and vomiting. In these 2 cases, plasma cortisol levels continued to rise in spite of a slight decrease in plasma ACTH concentrations. It appears likely that pituitaryadrenal response to bacterial pyrogen depends on not only the rise in body temperature but also severity of the accompanying side-effect symptoms. In normal subjects, 8 a. m. values ranged from 22 to 175pg/ml with the mean of 70.8 a. m. ACTH levels were subnormal in patients with hypopituitarism and undetectable in 3 patients with Cushing's syndrome caused by an adrenal tumor. ACTH was very high in 5 patients who had had a bilateral adrenalectomy for Cushing's syndrome due to adrenal hyperplasia, and in 3 patients with untreated Addison's disease.
- Japan Society of Clinical Chemistryの論文