EFFECTS OF GNRH ANALOGS ON PITUITARY-TESTICULAR FUNCTION IN FREE-RANGING AFRICAN ELEPHANTS (LOXODONTA-AFRICANA)

We tested the ability of several GnRH analogues to suppress pituitary- testicular activity and potentially musth in free-ranging African elep hants (Loxodonta africana). In Study I, adult bulls were given 4 or 12 mg GnRH antagonist (Detirelix) or saline i.m. on day 0 (n = 3 bulls p er treatment). Animals were then recaptured on day 2 (about 48 h later ) and given 300 mu g GnRH i.v. to assess the ability of the antagonist to block pituitary activity. Detirelix reduced (P < 0.05) basal conce ntrations of serum LH and testosterone on day 2 compared with day 0, w ith no effect of dose. Similarly LH and testosterone release induced b y GnRH were also reduced (P < 0.05) in the Detirelix-treated bulls (50 -70% reduction in peak concentrations). In Study 2, elephants were giv en 30 mg of a structurally similar GnRH antagonist (103-201-40; n = 6) , 22.5 mg of a long-acting GnRH agonist (Lupron Depot; n = 4) or D-man nitol carrier (n = 4) i.m. on day 0. All bulls were recaptured and giv en GnRH on day 2 (103-201-40 treatment) or on days 2 and 20 (Lupron De pot treatment) after the initial injection. In contrast to Detirelix, 103-201-40 did not inhibit basal or GnRH-induced LH or testosterone se cretion. Pituitary-testicular responses to Lupron Depot were initially stimulatory, as evidenced by increased (P < 0.05) LH and testosterone secretion on days 0 and 2. By day 20, basal LH concentrations had ret urned to baseline values and the response to GnRH was markedly reduced (P < 0.05), indicating that the pituitary was at least partially dese nsitized. Basal testosterone concentrations had also returned to basel ine values by day 20 after Lupron Depot treatment. However, despite th e attenuated LH response to GnRH, subsequent testosterone secretion wa s increased (P < 0.05) compared with controls, suggesting the testes o f agonist-treated bulls had instead, become hyper-responsive to small increases in LH secretion. These results suggest that GnRH analogues c an suppress the pituitary-gonadal axis in African elephants; however, longer treatment periods, more frequent injection intervals or higher doses are probably needed to inhibit testosterone secretion completely and, thus, musth.