Sp. Brinsko et al., GONADAL AND PITUITARY-RESPONSIVENESS OF STALLIONS IS NOT DOWN-REGULATED BY PROLONGED PULSATILE ADMINISTRATION OF GNRH, Journal of andrology, 19(1), 1998, pp. 100-109
The objective of this study was to determine if prolonged pulsatile ad
ministration of homologous gonadotropin-releasing hormone (GnRH) at th
erapeutic or 5x therapeutic doses would cause down-regulation of the s
tallion's hypothalamic-pituitary-testicular axis. Fifteen stallions we
re randomly assigned to three treatment groups (n = 5(group) and recei
ved a 0.5 ml subcutaneous dose of saline (group 1), 50 mu g GnRH (grou
p 2), or 250 mu g GnRH (group 3) every 2 hours for 75 days. Weekly eva
luations of follicle stimulating hormone, luteinizing hormone, and tes
tosterone and monthly evaluations of daily sperm output and spermatozo
al motility failed to demonstrate any decreased pituitary or gonadal r
esponsiveness within or among treatment groups (P > 0.1) as a result o
f treatment with GnRH. Results of th is study demon strate that the hy
pothalamic-pituitary-testicular axis of the stallion, unlike that of o
ther domestic species, is remarkably refractory to GnRH-induced down-r
egulation.