Abstract: | Bull seminal plasma administered to male rats at the time of castration inhibited the rise in the levels of FSH and LH otherwise seen in the serum 24 h later. That the gonadotrophin-inhibiting activity was also present in the seminal plasma from vasectomized bulls suggests that it was not of testicular origin. Although the substance with gonadotrophin-inhibiting activity was a protein, it may be chemically distinct from inhibin. |