Existence of APGWamide in the testis and its induction of spermiation in Haliotis asinina Linnaeus

Immunolocalization by using rabbit polyclonal antibody against APGWamide demonstrated that there was APGWamide immunoreactivity (APGW-ir) in the varicosed nerve fibers in the capsule, connective tissue and trabeculae of the testis whereas there was no APGW-ir in the ovary of sexually mature broodstocks of Haliotis asinina. In vivo bioassay, by injecting APGWamide into foot muscle of mature males and females (age over 24 months), showed that most males (87.50%) injected with 200 μl of 10^− 3 M APGWamide (170 μg APGWamide/animal) could be induced to spermiate whereas fewer males (43.75%) injected with 200 μl of 10^− 6 M APGWamide (0.17 μg APGWamide/animal) could spermiate. Following injection with 10^− 3 M, 53% of males spawned within 3 to 4 h, while the remaining males spawned within 2 to 3 h. The former tended to release more sperm at the range of 1.04 to 2 × 10⁹, and the latter at the range 3.62 × 10⁷ to 2.07 × 10⁸ cells, respectively, and that the sperm of the former group appeared to be more motile. Following the injection of 10^− 6 M, all inducible males spawned within 2–3 h, and 43% of spawned males have sperm around 2 × 10⁹, while 57% have fewer sperm number ranging from 2.75 × 10⁷ to 9.94 × 10⁸ cells. In contrast to males, none of the mature females with ripen ovary could be induced to ovulate. These data suggest that APGWamide is an important signaling molecule that plays a role in the male reproductive process that could be used to induce spermiation.