Evidence for episodic but not circadian activity in plasma concentrations of adrenocorticotrophin, cortisol and thyroxine in dogs

Abstract

Concentrations of immunoreactive (i) ACTH, cortisol and thyroxine were determined in plasma samples obtained at 20-min intervals for 25 h in nine normal and two adrenalectomized dogs. The dogs were exposed to a 12 h light: 12 h darkness photoperiod for 30 days before the sampling period. Episodic secretion of iACTH and cortisol was evident in each normal dog, with an average of 9.0 iACTH peaks and 10.1 cortisol peaks in a 24-h period. Levels of iACTH and cortisol were significantly correlated in each normal dog, but periods of dissociation between levels of the two hormones were apparent. A sex difference in 24-h mean iACTH and cortisol levels, numbers of cortisol peaks, and amplitude of iACTH peaks was observed, with females showing higher mean levels and greater peak frequency and amplitude in each instance. Adrenalectomy resulted in a 50- to 150-fold increase in mean iACTH concentrations with an apparent increase in iACTH peak amplitude. Cortisol levels were unchanging in the adrenalectomized dogs. Thyroxine concentrations showed episodic variation in each of the normal dogs, but the mean number of peaks (3.3/24-h period) was considerably less than for iACTH or cortisol. Female dogs a had significantly higher 24-h mean levels of thyroxine than did males. No circadian rhythmicity was obvious for the plasma levels of any of the three hormones measured.

Accuracy of an Adrenocorticotropic Hormone (ACTH) Immunoluminometric Assay for Differentiating ACTH‐Dependent from ACTH‐Independent Hyperadrenocorticism in Dogs

“…During the last 30 years, a number of imaging techniques and endocrine tests, including plasma ACTH measurement, have been developed for this purpose. [5][6][7][8][9][10][11][12][13][14] Over this period, techniques used for ACTH measure have changed from radioimmunoassay (RIA) [15][16][17] to immunoradiometric (IRMA) 18 and immunoluminometric assays (ILMA), 19 with concomitant improvements in the analytical sensitivity and specificity. Despite its widespread use, few surveys have evaluated the diagnostic accuracy of ACTH determination for investigations of the cause of Cushing's syndrome.…”

Validation of Nonradioactive Chemiluminescent Immunoassay Methods for the Analysis of Thyroxine and Cortisol in Blood Samples Obtained from Dogs, Cats, and Horses

“…An RIA b that has been validated for the analysis of hormones in human and in animal samples 3,5,14,15 was used as the reference method. The performances of the nonradioactive methods were compared with the RIA for samples obtained from different animal species.…”

The Effect of Temperature and Aprotinin on the preanalytical stability of adrenocorticotrophic hormone

“…The delayed decline according to our study (19 h vs 4 h) may arise using different assay methods. The ACTH assay we used in our study employs two monoclonal antibodies specific for ACTH [9][10][11][12] and for the C-terminal region (ACTH 36-39). Due to common antigenic structure, the antibodies recognize intact biologically active ACTH 1-39 and the ACTH precursors POMC and pro-ACTH [1].…”

“…A proteinase inhibitor, aprotinin, has been used in samples collected for ACTH measurement [8][9][10][11], but no studies have been examined effects of this enzyme inhibitor on preservation of chemiluminescence immunoassay study in plasma stored at different temperatures for a long term period. Our study examined the effect of using aprotinin, with human blood at the time of collection for subsequent measurement of ACTH concentration in plasma stored at various temperatures over 4 days.…”