Endocrine response to exogenous GnRH in male dogs treated with a GnRH antagonist

GARCÍA ROMERO G., RISSO A., VALIENTE C., CORRADA Y., RODRÍGUEZ R., GOBELLO C.

Jornada; II Jornadas Internacionales del Instituto de Investigación y Tecnología en Reproducción Animal; 2010

Introduction: Acyline is a potent and safe, third generation GnRH antagonist which has a promising place in future canine reproduction control. The objective of this study was to describe testosterone (T) response to GnRH challenge in GnRH antagonist-treated dogs over a 30-day period. Materials and Methods: Eight reproductively normal mixed-bred dogs were randomly assigned to acyline (NIH, USA) 330 g/kg sc (ACY; n=4) or a placebo group (PLA; n=4; day 0), and challenged with the agonist busereline (Receptal®, Intervet) 0.2 µg/kg sc on days -7, 1, 3, 7, 14, 21 y 30. Blood samples were collected before (-30 minutes) and 60, 120 and 180 minutes after the injection for T determinations. Testosterone was measured by electrochemiluminiscense (Elecsys®, Cobas, England) and data analyzed by ANOVA for repeated measures (SPSS®). Results: Before treatments (day -1) there were no differences in T concentrations between groups (P > 0.1). After treatments, there was an interaction between treatment and day (P 0.05). Testosterone varied in the ACY (P < 0.01) but not in the PLA group (P > 0.1). In the ACY group, day 30 differ from days 1, 3, 7 and 10 (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. Conclusion: The GnRH antagonist treated canine gonadal axis seemed to be unable to physiologically respond to agonistic challenge during 14 days.