CANINE PLASMA CORTISOL (HYDROCORTISONE) MEASURED BY RADIOIMMUNOASSAY - CLINICAL ABSENCE OF DIURNAL-VARIATION AND RESULTS OF ACTH STIMULATION AND DEXAMETHASONE SUPPRESSION TESTS

  • 1 January 1978
    • journal article
    • research article
    • Vol. 39  (11) , 1766-1770
Abstract
A radioimmunoassay for plasma cortisol (hydrocortisone) was developed and validated for sensitivity, specificity, accuracy, precision and parallelism. Steroids were extracted with ethyl ether, and cortisol was purified by gel column chromatography prior to assay. [1,2-3H] cortisol and a commercially available sheep antibody to cortisol-21-hemisuccinate were used. Free steroids were separated from bound steroids by centrifugation after adsorption to dextran-coated charcoal. Plasma cortisol was measured by this technique in 6 normal dogs. Circadian rhythm of cortisol secretion was not detected in samples obtained by venipuncture at 8 different h on 3 separate days, suggesting that adrenal function tests may be started in clinical patients at any time of day. Resting plasma cortisol concentrations averaged 19.4 .+-. 3.0 (SD) ng/ml and ranged from nondetectable (less than 3 ng/ml) to 77.5 ng/ml. Of 144 canine plasma samples, 95% contained less than 50 ng of cortisol/ml. Injection i.m. of 2.2 units of ACTH/kg of body wt caused detectable increase in plasma cortisol concentrations; maximum response (68.3-111.6 ng/ml) occurred 1-2 h after injection. Oral administration of dexamethasone suppressed plasma cortisol to nondetectable concentrations for 32 h in all 6 dogs.

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