Effects of adrenocorticotrophin (ACTH) and progesterone on luteinising hormone (LH) secretion in recently castrated rams.
The goal of the present study was to determine whether ACTH and progesterone have any effect on LH secretion and pulse frequency in recently castrated rams. Six 2-year-old Corriedale rams were castrated in the winter. The day before castration, blood samples were taken in order to establish the precastration LH levels. The rams were divided into an untreated group (group U: n = 2) and a treated group (group T: n = 4). The first treatment consisted of the i.v. administration of 0.5 mg of ACTH on day 20 post-castration, immediately after the first sample had been taken. During the second treatment, subcutaneous progesterone implants were given to group T for 5 days. Control samplings were performed one week before each treatment. Prior to castration, the testosterone levels were low, while after castration they were below the detection limit of the assay. Cortisol and progesterone concentrations were basal before castration in all of the animals and after castration in group U and also in the control samplings for group T. ACTH treatment caused a significant increase in both cortisol and progesterone levels for 3 h (P < 0.001). Progesterone implants raised progesterone levels in group T, but cortisol levels remained basal. Before castration, all animals had low LH levels and hardly any pulse activity was seen. After castration, both the number of LH pulses and the mean LH production increased significantly in all of the animals (P < 0.01). During the ACTH trial, LH pulse frequency was significantly reduced for the first 4 h following ACTH administration (P = 0.013), however, no such differences occurred in the prior control period. No effect was seen on mean LH concentration during the ACTH treatment. Progesterone treatment did not have any effect on either the number of LH pulses nor on LH concentrations (P > 0.05).
Van Lier
E
E
Animal and Forage Science Department, Faculty of Agriculture, University of the Republic of Uruguay, Montevideo.
Regueiro
M
M
Pérez-Clariget
R
R
Andersson
H
H
Kindahl
H
H
Forsberg
M
M
D000324:Adrenocorticotropic Hormone / Q000494:pharmacology*; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000097:blood; D000911:Antibodies, Monoclonal; D006854:Hydrocortisone / Q000097:blood; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D008297:Male; D009919:Orchiectomy / Q000662:veterinary*; D011374:Progesterone / Q000097:blood / Q000494:pharmacology*; D011863:Radioimmunoassay / Q000662:veterinary; D012756:Sheep / Q000502:physiology*; D013739:Testosterone / Q000097:blood; D014583:Uruguay
D000893:Anti-Inflammatory Agents; D000911:Antibodies, Monoclonal; D013739:Testosterone; D011374:Progesterone; D000324:Adrenocorticotropic Hormone; D007986:Luteinizing Hormone; D006854:Hydrocortisone