EFFECTS OF A GONADOTROPIN-RELEASING-HORMONE AGONIST ON SERUM LUTEINIZING-HORMONE CONCENTRATIONS IN FEMALE WHITE-TAILED DEER

As part of a study to develop contraceptive technologies for white-tai led deer (Odocoileus virginianus), the potential for a gonadotropin-re leasing hormone (GnRH) agonist, Histrelin (HIS), to inhibit luteinizin g hormone (LH) secretion in does was investigated. Three experiments w ere conducted during the breeding season to determine the effects of d ose, route, and pattern of administration of HIS on serum LH concentra tions. The first experiment included six treatments, each given as an i.v. injection: 0.1, 1, 10, and 100 mu g HIS, 10 mu g GnRH, and saline (control); the second experiment included four treatments, as s.c. in jection: 10, 50, and 100 mu g HIS, and saline. Maximum LH concentratio ns occurred by 240 min after injection in both experiments. At 360 min post-injection, serum LH concentrations were still elevated in the 10 and 100 mu g i.v. HIS and the 50 and 100 mu g s.c. HIS groups (P < 0. 05) as compared with controls. In a third experiment 8.3 mu g HIS h(-1 ) (200 mu g HIS per day) were administered s.c. continuously for 14 da ys to four does; controls received continuous saline infusions (n=3). On Day 1 (Day 0 is day of minipump insertion), the HIS group had a hig her mean serum LH concentration than controls (16.0 +/- 5.3 vs. 0.9 +/ - 0.4 ng/ml, respectively; P = 0.06). By Day 2 mean LH concentrations did not differ between the groups and remained at base line for the du ration of infusion. On Day 10 both groups received a s.c. injection of 100 mu g HIS. At 240 min the mean serum LH concentration for controls was 17.8 +/- 3.3 ng/ml and was still elevated at 600 min. In contrast , serum LH concentrations in the HIS group remained at base line (0.5 +/- 0 ng/ml). The data indicate that HIS, a GnRH agonist, acts as an L H secretagogue in white-tailed deer, as evidenced by the increase in s erum LH concentrations following a single injection of HIS. Furthermor e, continuous s.c. administration of HIS during the breeding season in hibits LH secretion in does, and could be a useful tool for preventing ovulation, thereby preventing pregnancy of deer.