Effect of the GnRH antagonist, acyline, on canine testicular characteristics

The primary objective was to assess the effects and clinical safety of a single high-dose of the third generation GnRH antagonist, acyline, on testicular characteristics in male dogs. Seven dogs were followed up weekly for six, 2-week periods (-2, -1, 1, 2, 3 and 4). At the end of the second period, they were given acyline (330 microg/kg sc). Responses to treatment varied among individual animals. Testicular consistency and scrotal diameter were slightly diminished (P>0.05) in Periods 1, 2, and 3. Libido and erection decreased during Periods 1 and 2 (P<0.05). Second and third fractions of the ejaculate volume, sperm count and motility varied throughout periods (P<0.01); there was a clear impairment of these parameters (< or =0.2 mL, < or =0.6 mL, < or =0.5 million/mL and < or =30%, respectively) around the second week of Period 1, followed by slow improvement (to the end of the study). Semen volumes and motility diminished during Period 1 (P<0.05). Sperm count decreased during Periods 1, 2, and 3, relative to Periods -2 and -1 (22.7+/-11.7, 62.8+/-19.9, and 51.0+/-25.4 versus 235.7+/-63.3 and 315.5+/-27.3, respectively; P<0.05; (L.S.M.+/-S.E.M.). Morphologically abnormal sperm increased during Periods 2 and 3 (up to 64.9+/-2.6%; P<0.05). Throughout the study, no dog had hematological, biochemical, local, or systemic side effects. In conclusion, a single high-dose acyline treatment severely decreased semen quality with no adverse effects.