RELATIONSHIP BETWEEN CORTISOL AND TESTOST ERONE UNDER RESTING CONDITIONS, AFTER ACUTE STRESS AND HORMONAL-STIMULATION IN THE BULL

In this study the relationship between peripheral concentrations of co rtisol and testosterone was investigated in 7 adult bulls under restin g conditions as well as after sexual and hormonal stimulation. The ani mals were kept under natural photoperiods of 16L:8D and for hormone de terminations blood was withdrawn from an indwelling jugular vein cathe ter every 30 minutes for 24 and 48 h, respectively. Evaluation of the hormonal profiles revealed that both steroids are secreted episodicall y characterized by irregular, short term fluctuations with high indivi dual variability. A clear circadian rhythm with high levels in the mor ning and during the day and low concentrations in the evening and duri ng night was observed for cortisol only. Concentrations of both steroi dal hormones were not significantly correlated with each other. Intens e sexual stimulation (mounting several times with ejaculation) during 30 minutes caused a rapid increase of cortisol without affecting testo sterone secretion. After intravenous application of 1500 IU hCG and 0. 5 mg GnRH a sharp rise of testosterone concentrations occurred with hi gh values remaining for several hours but leaving the circadian cortis ol pattern unchanged. The intravenous injection of 5 mg PGF2 alpha sti mulated both the cortisol and testosterone secretion. Results from thi s investigation show that cortisol and testosterone are secreted episo dically without any interrelationship under resting conditions. Sexual stress induced an increase of cortisol which did not inhibit testoste rone secretion and high testosterone levels did neither influence the cortisol pattern. The concomitant increase of cortisol and testosteron e after PGF2 alpha suggests a central (hypothalamus/hypophysis) action for prostaglandin.