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We describe a direct radioimmunoassay for cortisol in 10-microliter volumes of parotid saliva or whole saliva. Binding proteins are absent from these fluids, as demonstrated by the excellent correlation between results for samples assayed directly and by a comparison procedure involving extraction with 1,2-dichloroethane. The direct assay is specific, precise, and had a lower limit of sensitivity of 4 pg per assay tube. Comparison of cortisol concentrations in plasma, parotid saliva, and whole saliva in persons undergoing investigations for assessing adrenal function, including stimulation with cosyntropin (Synacthen) and suppression with dexamethasone, indicated that changes in plasma cortisol concentration were accurately and immediately reflected in saliva from either the parotidgland or whole saliva. A marked circadian rhythm has also been demonstrated for cortisol in parotid-gland saliva and whole saliva. We had to modify the 1,2-dichloroethane extraction procedure for accurate determination of cortisol in parotid saliva and whole saliva of patients undergoing treatment with metyrapone.
Walker et al. (Fri,) studied this question.