[Relationship between cortisol and testosterone during resting conditions, after acute stress and hormone stimulation...

In this study the relationship between peripheral concentrations of cortisol and testosterone was investigated in 7 adult bulls under resting conditions as well as after sexual and hormonal stimulation. The animals were kept under natural photoperiods of 16L:8D and for hormone determinations blood was withdrawn from an indwelling jugular vein catheter every 30 minutes for 24 and 48 h, respectively. Evaluation of the hormonal profiles revealed that both steroids are secreted episodically characterized by irregular, short term fluctuations with high individual variability. A clear circadian rhythm with high levels in the morning and during the day and low concentrations in the evening and during night was observed for cortisol only. Concentrations of both steroidal hormones were not significantly correlated with each other. Intense sexual stimulation (mounting several times with ejaculation) during 30 minutes caused a rapid increase of cortisol without affecting testosterone secretion. After intravenous application of 1500 IU hCG and 0.5 mg GnRH a sharp rise of testosterone concentrations occurred with high values remaining for several hours but leaving the circadian cortisol pattern unchanged. The intravenous injection of 5 mg PGF2 alpha stimulated both the cortisol and testosterone secretion. Results from this investigation show that cortisol and testosterone are secreted episodically without any interrelationship under resting conditions. Sexual stress induced an increase of cortisol which did not inhibit testosterone secretion and high testosterone levels did neither influence the cortisol pattern. The concomitant increase of cortisol and testosterone after PGF2 alpha suggests a central (hypothalamus/hypophysis) action for prostaglandin.