Secretion of LH, Testosterone, Estradiol-17ß and Prolactin as response to simulation and compensation of stress of breeding bulls.
SPANDERN, B., 1997


Ten German Black and White bulls in groups of four elderly and six young aging either 3-5 or2 years, respectively were conducted to standardized procedures inducing or compensating short-term and long-term stress at different stages of the endocrine feedback loop. The secretion profiles of luteinizing hormone (LH), testosterone, estradiol-17ß and prolactin were determined to monitor individual reactions.
Short-term stress was pharmacologically simulated by intramuscular administration of 330 or 250 I.U. of Adrenocorticotrophic hormone (ACTH) and 400 or 250 mg Thyrotropin-releasing hormone (TRH). Stress compensation at the hypothalamic-pituitary level was tested after i.m. injection of 600 or 400 mg of the opioid antagonist Naloxone. The interaction of adrenal and hypothalamic feedback loops was tested by a combined challenge of ACTH and Naloxone. A seven days lasting food restriction was applied as long-term metabolic stresschallenge.
Seven series of blood samples were collected every day in intervals of 30-60 minutes for 5 hours. LH, testosterone and estradiol-17ß were analysed by enzyme immunoassays. Prolactin was analysed by radio-immunoassay.
Basal concentrations of LH were similar after blood collection out of permanent canulae vs. jugularvein puncture, whereas basal testosterone and estradiol-17ß were generally lower and basal prolactin higher after vein puncture. There was a pronounced age difference between older vs. younger bulls concerning basal LH, testosterone and estradiol- 17á but not prolactin. In most bulls the administration of ACTH caused a clear reduction of LH, testosterone, estradiol-17ß and prolactin within 30 minutes lasting 5 hours, while LH, testosterone and estradiol-17ß showed an identical reduction-factor after both blood collecting methods.
The combined injection of ACTH and Naloxone induced an initial stimulation witin 30 minutes and a subsequent suppression of LH, testosterone and estradiol-17ß, which was more pronounced in younger bulls. Prolactin release was increased particularly in younger bulls. TRH-injection led to an initial individual but not age related increase of LH, testosterone, estradiol- 17á and prolactin. Food restriction had no effect on LH, but suppressed testosterone, estradiol-17ß and prolactin. Levels of LH, testosterone and estradiol-17ß in bulls are subject to age depending changes. Estradiol-17ß and prolactin are influenced by the blood sampling method. The suppression of LH, testosterone and estradiol-17ß after ACTH may be due to a direct action at the pituitary and gonadat level rather than an indirect one via corticosteroid inhibition.
Endogenous opioid peptides participate in the pathophysiological regulation of LH, testosterone, estradiol-17ß and prolactin with an age related sensitivity of tbeir receptors. TRH mediates stress regulation of LH, testosterone, estradiol-17ß and prolactin. The decrease of LH and prolactin due to induction of metabolic stress appears to prove an adjustment at the hypothalamic and pituitary level.

Full print version:
LH-, Testosteron-, Estradiol-17ß- und Prolaktin -Sekretion nach Simulation und Kompensation von Streß bei Zuchtbullen. Berlin 1997 
Cuvillier Verlag Göttingen, ISBN 3-89588-933-4