24-Hour Profiles of Plasma Cortisol and Testosterone in the Male Dog: Absence of Circadian Rhythmicity, Seasonal Influence and Hormonal Interrelationships |
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| Authors: | R Thun E Eggenberger K Zerobin |
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| Institution: | Clinic of Andrology and Gynecology Department of Reproduction;Faculty of Veterinary Medicine, University of Zürich, 8057 Zürich, Switzerland |
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| Abstract: | Contents: Temporal changes of plasma cortisol and testosterone concentrations were measured in intact adult male beagle dogs during the spring and autumn with natural photoperiods of 16L:BD and 10L:14D, respectively. Each animal was fitted with an indwelling cephalic vein catheter and blood was withdrawn every 30 min for 24 h. Examination of the hormonal profiles revealed that both steroids are secreted episodically characterized by irregular short term fluctuations which were variable among different dogs. In several instances sustained elevations of cortisol and testosterone secretion occurred but were unrelated to photoperiod. Despite individual variability in the secretion patterns the daily means of each hormone were similar and not statistically different between spring and autumn .
When the 24 h were divided into three 8-h periods, namely 8.00–16.00 h (I), 16.00–24.00 h (II) and 24.00–8.00 h (III) overall and baseline mean cortisol and testosterone levels were not significantly different between the individual time periods. It appears that the dog differs from other species in that cortisol secretion was not related to the light-dark cycle. Concentrations of both hormones were not significantly correlated with each other throughout the sampling periods. Results from this study indicate that in intact male dogs cortisol and testosterone are secreted episodically without any evidence of circadian rhythmicity and seasonal variation and that an endocrine interrelationship between the adrenal cortex and the testis is not prominent under normal physiological conditions . |
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| Keywords: | 24-h profiles — cortisol — estosterone — circadian rhythm — seasonality — male dog |
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