PARENT SESSION
PLATFORM SESSION 19. PITUITARY HORMONES AND GROWTH FACTORS

Tuesday, August 3, 2004
4:30 PM–6:30 PM
Buchanan A102
Chair: Christine Quirk Co-Chair: James Dias

(582) EFFECTS OF GnRH-PAP ON GONADOTROPH SECRETION AND TESTICULAR WEIGHT IN RAMS.

Ashley, Ryan¹, Allen, Matthew¹, Staley, Airica¹, Nett, Terry¹, ¹ Animal Reproduction & Biotechnology Laboratory, Fort Collins, CO

ABSTRACT- The purpose of this study was to evaluate the effects of a GnRH analogue conjugated to a cytotoxin, pokeweed antiviral protein (PAP), on reproductive function in adult rams. Rams were divided into 3 groups and received 0.267 mg GnRH-PAP kg^-1 either intravenously (IV, n = 4), subcutaneously (SubQ, n = 6), or 0.02 mg GnRH (control, n = 5). Blood samples were collected at 30-min intervals for 4 h after treatment. At 2, 4, 10 and 24 weeks post treatment, all rams were administered a GnRH challenge (0.02 mg IV) after which blood samples were taken at 30-min intervals for 4 h. Serum concentrations of testosterone and LH were determined by radioimmunoassay. Testes were collected at the conclusion of the study, weighed, and examined histologically. GnRH-PAP treatment suppressed testicular weight in 4 (3 SubQ, 1 IV) of the 10 treated rams. In rams that responded to GnRH-PAP treatment, testicular weights were reduced (p < 0.05) with an average of 40.0 ± 2.8g compared to 162.0 ± 9.2 and 190.2 ± 14.1g in rams that did not respond and controls, respectively. Testosterone and LH release were assessed by measuring area under the response curve after challenge with GnRH. In rams that responded to GnRH-PAP with reduced testicular weight, serum concentrations of testosterone were decreased (p < 0.05) between weeks 2-24 post treatment compared to controls. Likewise, serum concentrations of LH were suppressed (p < 0.05) between weeks 4-24 post treatment compared to controls. Serum concentrations of testosterone and LH in rams that did not respond to GnRH-PAP treatment were similar to controls throughout the study. In conclusion, in rams that responded, administration of GnRH-PAP either IV or SubQ was able to suppress secretion of testosterone and LH and inhibited testicular functions for at least 24 weeks post treatment. Supported by USDA-531433.

KEY WORDS: LH, Rams, GnRH-PAP, Testosterone