Effect of gonadotrophin releasing hormone variants on reproductive organs and plasma testosterone in the male lizard, Podarcis s. sicula

The effects of various gonadotrophin-releasing hormone (GnRH) forms (mammalian GnRH (mGnRH), chicken I GnRH (cGnRH-I), chicken II GnRH (cGnRH-II) and salmon GnRH (sGnRH)) on the genital apparatus and plasma testosterone level in the male lizard, Podarcis s. sicula, have been investigated. In short duration experiments (20 min to 76 h) GnRH forms did not affect testicular and epididymal morphology. A single dose (0.05 μg) of mGnRH, cGnRH-II and sGnRH, however, induced a rise in plasma testosterone after 20 to 40 min. Variable results were obtained in the animals given GnRH variants every 12 h for 3 days since mGnRH and cGnRH-I caused a decrease of circulating hormone; cGnRH-II and sGnRH a slight increase. Daily peptide administration, for 15 to 30 days, caused severe inhibition of both testicular and epididymal activity and a significant drop of circulating testosterone. In Podarcis s. sicula, species specificity of pituitary sensitivity to GnRH variants appeared to be low. On the other hand, this gland seemed to show some desensitization after chronic peptide administration.