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 elephants (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 per 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 concentrations of serum LH and testosterone on day 2 compared with day 0, with no effect of dose. Similarly LH and testosterone release induced by GnRH were also reduced (P < 0.05) in the Detirelix-treated bulls (50-70% reduction in peak concentrations). In Study 2, elephants were given 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-mannitol carrier (n = 4) i.m. on day 0. All bulls were recaptured and given GnRH on day 2 (103-201-40 treatment) or on days 2 and 20 (Lupron Depot treatment) after the initial injection. In contrast to Detirelix, 103-201-40 did not inhibit basal or GnRH-induced LH or testosterone secretion. 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 returned to baseline values and the response to GnRH was markedly reduced (P < 0.05), indicating that the pituitary was at least partially desensitized. Basal testosterone concentrations had also returned to baseline values by day 20 after Lupron Depot treatment. However, despite the attenuated LH response to GnRH, subsequent testosterone secretion was increased (P < 0.05) compared with controls, suggesting the testes of agonist-treated bulls had instead, become hyper-responsive to small increases in LH secretion. These results suggest that GnRH analogues can 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.