A single administration of a GnRH antagonist inhibited canine gonadal axis functionality during 14 days

G. GARCÍA ROMERO, M. TÓRTORA., J. DIAZ, R. RODRÍGUEZ, M. ABEYÁ, C. GOBELLO

Wisconsin

Congreso; Society for Theriogenology Annual Conference; 2011

GnRH antagonists, which bind to gonadotrope GnRH receptors and compete successfully with endogenous GnRH for specific receptors, have a great potential as contraceptives [1]. In male dogs, a single administration of the potent, third generation GnRH antagonist acyline, reversibly and safely decreased serum gonadotrophins and testosterone (T) concentrations during 10 days [2]. The functionality of the gonadal axis during antagonist treatment has not been described in this species. The objective of this study was to describe T response to GnRH challenge in GnRH antagonist-treated dogs over a 30-day period. Eight reproductively normal mixed-bred dogs were randomly assigned to acyline (NIH, Bethesda, USA) 330 mg/kg sc (ACY; n=4) or a placebo group (PLA; n=4; day 0), and challenged with the GnRH agonist busereline (Receptal®, Intervet, Bs As, Argentina) 0.2 μg/kg sc on days -7, 1, 3, 7, 14, 21 y 30. Blood samples for T determinations were collected before (-30 minutes) and 60, 120 and 180 minutes after the agonist injection. Serum T was measured by electrochemiluminiscense (Elecsys®, Cobas, West Sussex, England) and statiscally analyzed by ANOVA for repeated measures (SPSS® Inc. Chicago, IL, USA). Before treatments (day -1) there were no differences in T serum concentrations between groups (P > 0.1). After the initial treatment, basal (-30 minutes) T differed throughout the days of the experiment between groups (P 0.05), varying in the ACY (P < 0.01) but not in the PLA group (P > 0.1; Fig 1). Furthermore, day 30 differ from 1, 3, 7 and 10 in the in the ACY group (P < 0.01; Fig 1). On day -1, the stimulation tests had only a time effect (P = 0.05), although on days 7 (P < 0.01; Fig 2) and 14 (P < 0.05; Fig 3) the response differed between groups. It is concluded that a single administration of the GnRH antagonist prevented canine gonadal axis to physiologically respond to agonistic challenge during 14 days. These results warrant further work on new GnRH antagonist on male dog reproduction.