Seasonal response of the pituitary and testes to gonadotropin-releasing hormone in the black bear (Ursus americanus).
1. The reproductive physiology of the black bear has not been studied extensively. Our objective was to determine if the sensitivity of the pituitary-testes axis to gonadotropin-releasing hormone (GnRH) changes with season. 2. A GnRH dose-response study was conducted using three captive male black bears. Each bear received the same dose of 30, 95 or 300 micrograms GnRH per total body weight in the fall, winter, spring and summer. Blood was sampled at 15-min intervals 1 hr before and 1 hr after GnRH injection and at 30-min intervals during the second hour after injection. Luteinizing hormone (LH) and testosterone were measured in the serum. 3. A heterologous LH radioimmunoassay was established and rigorously validated to measure black bear LH using bovine (b)LH and a monoclonal anti-bLH antibody. 4. Our results suggest: (1) responsiveness of the pituitary to GnRH was highest in the spring and lowest in the winter and (2) pattern of testosterone production is closely correlated with LH released from the pituitary in response to GnRH.
Horan
K T
KT
Department of Animal Sciences, University of Illinois, Urbana 61801.
Nelson
R A
RA
Palmer
S S
SS
Bahr
J M
JM
D000818:Animals; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D010902:Pituitary Gland / Q000502:physiology*; D012621:Seasons; D013737:Testis / Q000502:physiology*; D013739:Testosterone / Q000097:blood; D001503:Ursidae / Q000502:physiology*
D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone