Effects of a gonadotropin-releasing hormone agonist on serum luteinizing hormone concentrations in female white-tailed deer

Abstract

As part of a study to develop contraceptive technologies for white-tailed deer ( Odocoileus virginianus), the potential for a gonadotropin-releasing hormone (GnRH) agonist, Histrelin (HIS), to inhibit luteinizing hormone (LH) secretion in does was investigated. Three experiments were conducted during the breeding season to determine the effects of dose, route, and pattern of administration of HIS on serum LH concentrations. The first experiment included six treatments, each given as an i.v. injection: 0.1, 1, 10, and 100 μg HIS, 10 μg GnRH, and saline (control); the second experiment included four treatments, as s.c. injection: 10, 50, and 100 μg HIS, and saline. Maximum LH concentrations 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 μg i.v. HIS and the 50 and 100 μg s.c. HIS groups ( P < 0.05) as compared with controls. In a third experiment 8.3 μg HIS h −1 (200 μg HIS per day) were administered s.c. continuously for 14 days 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 higher 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 duration of infusion. On Day 10 both groups received a s.c. injection of 100 μg 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 LH secretagogue in white-tailed deer, as evidenced by the increase in serum LH concentrations following a single injection of HIS. Furthermore, continuous s.c. administration of HIS during the breeding season inhibits LH secretion in does, and could be a useful tool for preventing ovulation, thereby preventing pregnancy of deer.