GNRH1 and Infertility: Thus, although there is ample evidence that prolactin can act in the pituitary gland to suppress LH secretion (Smith 1978, 1982, Cheung 1983, Morel et al. 1994, Tortonese et al. 1998), in animal models, as in clinical studies, the primary cause of infertility appears to be the suppression of the activity of GnRH neurons.