Potent action of RFamide-related peptide-3 on pituitary gonadotropes indicative of a hypophysiotropic role in the negative regulation of gonadotropin secretion

We identified a gene in the ovine hypothalamus encoding for RFRP-3 and tested the hypothesis that this system produces an hypophysiotropic hormone which inhibits the function of pituitary gonadotropes. The RFRP-3 gene encodes for a peptide that appears identical to human RFRP-3 homologue. Using an antiserum raised against RFRP-3, cells were localised to the dorsomedial hypothalamic nucleus/paraventricular nucleus of the ovine brain and shown to project to the neurosecretory zone of the ovine median eminence, predicating a role for this peptide in the regulation of anterior pituitary gland function. Ovine RFRP-3 peptide was tested for biological activity in vitro and in vivo and was shown to reduce LH and FSH secretion in a specific manner. RFRP-3 potently inhibited GnRH-stimulated mobilisation of intracellular calcium in gonadotropes. These data indicate that RFRP-3 is a specific and potent mammalian gonadotropin inhibiting hormone and that it acts upon pituitary gonadotropes to reduce GnRH-stimulated gonadotropin secretion.