Radioimmunoassay of ACTH in plasma

Abstract

A B S T R A C T Techniques are described in detail for a radioimmunoassay of plasma adrenocorticotropin (ACTH) that is capable of detecting hormone in unextracted normal human plasma at 1: 5 dilution under the conditions described. The sensitivity of the assay is at the level of 1 ,qLug/ml (equivalent to 0.014 mU/100 ml).In normal subjects ACTH concentrations averaged 22 ,uug/ml (equivalent to 0.308 mU/100 ml) plasma at 8-10 a.m. In a smaller group the concentrations averaged 9.6 lqqg/ml (equivalent to 0.134 mU/100 ml) at 10-11 p.m. Although a circadian rhythm in normal subjects was not always well marked throughout the daytime hours, plasma ACTH usually fell to its lowest value in the late evening. In hospital patients who were not acutely ill, concentrations were infrequently above 100 /A/Ag/ml in the morning and usually fell to significantly lower levels in the late evening. Severely ill hospital patients occasionally exhibited a.m. concentrations above 200 /Apg/ml.In a group of subjects showing frequent spiking -of plasma 17-OHCS concentrations throughout the day parallel spiking of plasma ACTH as well was generally observed.Metyrapone produced marked increases in plasma ACTH within 24 hr in all cases and generally within 3-6 hr except when started late in the day. Dexamethasone brought about a persistent reduction in plasma ACTH in a patient under continued treatment with metyrapone.Hypoglycemia, electroshock, surgery under general anesthesia, histalog and vasopressin administration were usually followed by significant in-*creases in plasma ACTH concentration. Prior

The effects of oral sumatriptan, a 5‐HT1 receptor agonist, on circulating ACTH and cortisol concentrations in man.

“…A similar pattern of release was discovered for ACTH [16]. A rise in the ACTH concentration was found to be closely followed by a rise in cortisol concentration [17].…”

Adrenal maturation of the sheep fetus during late pregnancy

“…ACTH assay. -Plasma ACTH was determined by radioimmunoassay according to Berson and Yalow (1968) without extraction but with a control of the ACTH degradation during incubation. The ACTH used for standardization and iodination was synthetic ACTH l -24 (Synacthen, Ciba).…”

Acth and MSH Assays and Their Clinical Application

“…Withthesubsequent production of synthetic ACTH analogues it became possible to identify more precisely the site of the antigenic determinant within the ACTH molecule for any particular antiserum. This allowed the development of more specific and satisfactory assay systems Orth et al, 1968;Berson & Yalow, 1968).…”

“…In particular an antiserum containing an antibody directed towards the N-terminal portion of the ACTH molecule is likely to produce assay results which are more closely related to steroidogenic biological activity of ACTH than one directed at the C-terminal and of the molecule (Fig. 1) Adequate sensitivity for the measurement of normal basal circulating levels of ACTH by radioimmunoassay may usually be achieved only by preliminary extraction of the ACTH although the antiserum of Berson & Yalow (1968) can measure 5-10 pg/ml in unextracted plasma. Extraction, however, can be made from relatively small volumes of plasma (5-1 0 ml) and this may also improve specificity by removing cross-reacting substances, as well as increasing the sensitivity.…”