ACTH stimulation in four Asian bull elephants (Elephas maximus): an investigation of androgen sources in bull elephants.

The phenomenon of musth is a very stressful event, both behaviorally and physiologically. An ACTH stimulation test was conducted in four adult Asian bull elephants to investigate the possibility that the classical hypothalamic-pituitary-adrenal (HPA) axis is active during musth, resulting in an increase in adrenally produced steroids. Serum cortisol, testosterone (T), androstenedione (A4), androstenediol (A5), and dehydroepiandrosterone (DHEA) were measured. Cortisol increased 3-10 times above baseline in response to ACTH stimulation, and DHEA doubled. A4 and A5 were erratic, while testosterone decreased significantly in all bulls. The pattern of results suggests that the adrenal steroid increase which occurs during musth results from some mechanism other than the classical HPA axis.