Cyproterone acetate reduced antler growth in surgically castrated fallow deer

We studied the role of androgens in antler growth. In particular, we invest igated whether the onset of antler regrowth is triggered by a short-term pu lse of testosterone and ii low levels of androgens are required for antler growth. The study was conducted on 12 surgically castrated fallow deer buck s (Dama dama) aged approximately 27 months. Six animals (CA group) were giv en the antiandrogen, cyproterone acetate (CA, 1000 mg/treatment); the other s were given vehicle solution only (control). Before each CA treatment, blo od was sampled and analysed for testosterone, androstenedione, IGF-1, corti sol, FSH, and LH. CA treatment and blood sampling were performed 2 days bef ore castration, on the day of castration and afterwards 2-day intervals unt il day 22. Subsequently, CA treatment and blood sampling continued at weekl y intervals until day 270. All animals cast their antlers, followed by antl er regrowth in all control bucks, but in only four of the six CA-treated ca strates. Plasma testosterone concentrations were low in all animals (betwee n 0.01 and 0.20 ng/ml), but were significantly (P<0001) greater in the cont rols. In both groups, a temporary increase in testosterone values was recor ded around the time of antler regrowth, the peak bring significantly (P<0.0 1) higher in the controls. Androstenedione showed a similar pattern as test osterone. Plasma IGF-1 concentrations increased sharply during the antler g rowth spurt and did not differ significantly between the two groups through out the study period. Cortisol concentrations were greater in controls than in the CA group. However, no link with the antler cycle was apparent. FSH and LH concentrations were higher in the controls for most of the study. An tlers produced by the control bucks were significantly larger than those in the CA group (P<0.03). For antler length, testosterone, androstenedione an d IGF-1, areas under the curve (AUC) were calculated over the period of ant ler growth. For the pooled deer (n=12) significant correlations existed bet ween AUCs of antler length and testosterone, but not for antler length and IGF-1. Also, a trend for a positive correlation between AUCs of antler leng th and androstenedione was noted. It is concluded that a plasma androgen co ncentration at least above a minimal threshold level is a necessary prerequ isite for normal antler regrowth in fallow deer, and that this androgen eff ect is not mediated via circulating IGF-1. The biological role of low level s of androgens may be to sensitize antler cells to the stimulating effect o f IGF.