Role of steroids in antler growth of red deer stags

Abstract

A series of six studies were carried out in red deer stags to test hypotheses concerning the importance of steroid control of velvet antler growth and to investigate mechanisms by which these hormones exert their effects. Medroxyprogesterone acetate (MPA) an LH inhibitor administered to stags during hard antler caused premature antler casting, reduced subsequent antler weight and caused a reduction in the LH and testosterone responses to GnRH. In two separate studies blockade of testosterone receptors with cyproterone acetate (CPA) administered to stags, either during early velvet antler growth or during the hard antler stage, significantly reduced LH and testosterone responses to GnRH. In both studies antler length, but not weight, was increased by CPA treatment. In another study testosterone implants were used to prevent the gradual decline in plasma testosterone levels normally observed during winter. Implants were removed 3 weeks before the anticipated date of antler casting. The implants significantly increased plasma testosterone levels and subsequent antler growth (expressed as a proportional increase compared with the previous year) compared with untreated controls. To determine whether the annual cycle of plasma testosterone response following GnRH stimulation was due simply to a lack of LH stimulation, ovine LH was injected on six occasions at defined stages of the antler cycle to red deer stags and the testosterone response measured. The testosterone responses were low at antler casting and during velvet antler growth compared with antler cleaning and peak rut. It appears low testosterone levels are due, in part, to a loss of responsiveness by the testes to LH as well as a low level of secretion of LH during the antler growing season. Finally synthetic ACTH was injected at the same defined stages of antler growth as in the previous study to determine whether cortisol and adrenal androgen production altered with the stage of the antler cycle. No significant differences were found in the dehydroepiandrosterone (DHEA) response, but cortisol responses were higher from late velvet antler growth to peak rut, compared with the times of antler casting and early velvet growth. Overall it was concluded that velvet antler growth can occur without testosterone stimulation during the period of velvet growth, but the data reinforce the concept that the timing of antler growth is linked to the annual cycle of testosterone.

Ultradian, circadian and seasonal rhythms in cortisol secretion and adrenal responsiveness to ACTH and yarding in unrestrained red deer (Cervus elaphus) stags

“…The increase in cortisol pulse height, pulse nadir and pulse amplitude in November indicates that there is a shift in the regulation of the HPA axis during spring. Changes in height and amplitude reflect to some extent the increased responsiveness of the adrenal gland to ACTH seen at this time of year (Suttie et al 1995, Cassidy 1996. However, the threefold increase in cortisol pulse parameter values compared with that seen during the rut would suggest that the adrenal gland changes are also accompanied by changes in endogenous ACTH secretion.…”

“…Evidence for a seasonal rhythm in adrenal activity or responsiveness in deer varies between species and studies, with seasonal changes reported in white-tailed deer (Bubenik et al 1983), reindeer (Rangifer tarandus) (Nilssen et al 1985), axis deer (Axis axis) (Chapple et al 1991) and red deer (Suttie et al 1995, Cassidy 1996 but not in Eld's deer (Monfort et al 1993) or in another study on axis deer (Bubenik & Brown 1989).…”

“…handling, open field test) challenges are commonly used in assessing the normal functioning of the HPA axis in animal stress research. Seasonal changes in adrenal responsiveness to ACTH challenge have recently been demonstrated in red deer stags (Suttie et al 1995, Cassidy 1996 but there have been no studies of seasonal variation in response to stress or basal activity of the HPA axis.…”

Histological structure of antlers in castrated male fallow deer (Dama dama)

“…Castration of male deer carrying hard antlers as well as the administration of substances interfering with testosterone production or inhibiting both testosterone production and its action at the receptor level causes premature antler casting (Wislocki et al, 1947;Lincoln, 1971;Muir et al, 1982;Jaczewski, 1985;Bubenik GA et al, 1987, 2002Goss et al, 1992;Schams et al, 1992;Kierdorf U et al, 1993Suttie et al, 1995). Administration of testosterone or estradiol to males in hard antler postpones antler casting beyond the normal date (Goss, 1968).…”

“…When male deer carrying velvet antlers are castrated (Blauel, 1935;Wislocki et al, 1947;Goss, 1968) or treated with the antiandrogen cyproterone acetate (Bubenik GA et al, 1975;Kolle et al, 1993), the velvet is not shed. So far, it is a matter of debate whether or not antler growth itself requires (direct or indirect) stimulation by low levels of androgens (Bubenik GA, 1983Schams et al, 1992;Kolle et al, 1993;Suttie et al, 1995;Bartoš et al, 2000;Sadighi et al, 2001).…”