Gonadotrophin-inhibiting activity in seminal plasma from intact and vasectomized bulls

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.