The Collaborative International Dictionary of English v.0.48:

gonadotropin \gonadotropin\ n. (Physiology)
   A hormone secreted by the pituitary gland and placenta, which
   stimulates the gonads and controls reproductive activity.

   Syn: gonadotropic hormone.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

gonadotropin
    n 1: hormone secreted by the anterior pituitary gland and
         placenta; stimulates the gonads and controls reproductive
         activity [syn: gonadotropin, gonadotrophin,
         gonadotropic hormone, gonadotrophic hormone]