Evidence for the LH-releasing pathway of seminal plasma NGF in male camelids.

In the female camelid, systemic administration of NGF induces a preovulatory LH surge that results in ovulation, but the effects of seminal NGF in the male are unknown. In the present study, we tested the hypothesis that the LH-releasing pathway of NGF is present in male camelids. In Experiment 1, male llamas and alpacas were treated with NGF or GnRH (n = 2 llamas and 3 alpacas) and blood samples were collected from 1 h before to 3 h after treatment. Plasma LH concentrations increased after treatment in a surge-like fashion in both GnRH- and NGF-treated groups, but concentrations reached a maximum 2.5 times higher and remained elevated for at least 2 h longer in the NGF-treated group (treatment-by-time interaction, P = 0.01). In Experiment 2, we evaluated the LH and testosterone response to NGF vs saline treatment (n = 3 llamas and 3 alpacas). The LH response to NGF was similar to that in Experiment 1, and plasma testosterone concentrations were higher in the NGF group than in the saline group at 2, 4 and 6 h after treatment (P < 0.05). Results support the hypothesis that the LH-releasing pathway for NGF exists in male South American camelids. The LH response to NGF sustained circulating testosterone concentrations in llamas, suggesting a moderate role of NGF in testosterone secretion.