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 progesteron e 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 prec astration 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 consiste d of the i.v. administration of 0.5 mg of ACTH on day 20 post-castration, i mmediately after the first sample had been taken. During the second treatme nt, subcutaneous progesterone implants were given to group T for 5 days. Co ntrol samplings were performed one week before each treatment. Prior to cas tration, the testosterone levels were low, while after castration they were below the detection limit of the assay. Cortisol and progesterone concentr ations were basal before castration in all of the animals and after castrat ion in group U and also in the control samplings for group T. ACTH treatmen t caused a significant increase in both cortisol and progesterone levels fo r 3 h (P < 0.001). Progesterone implants raised progesterone levels in grou p T, but cortisol levels remained basal. Before castration, all animals had low LH levels and hardly any pulse activity was seen. After castration, bo th the number of LH pulses and the mean LH production increased significant ly in all of the animals (P < 0.01). During the ACTH trial, LH pulse freque ncy was significantly reduced for the first 4 h following ACTH administrati on (P=0.013), however, no such differences occurred in the prior control pe riod. 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). (C) 1999 Elsevier Science B.V. All rights reserved.