KiSS-1 and GPR54 Genes are Co-Expressed in Rat Gonadotrophs and Differentially Regulated In Vivo by Oestradiol and Gonadotrophin-Releasing Hormone

Kisspeptin, the product derived from KiSS‐1, and its cognate receptor, GPR54, both exert a role in the neuroendocrine control of reproduction by regulating gonadotrophin‐releasing hormone (GnRH) secretion. In the present study, we demonstrate, using dual immunofluorescence with specific antibodies, that the KiSS‐1 and GPR54 genes are both expressed in rat gonadotrophs. All luteinising hormone β‐immunoreactive (LHβ‐ir) cells were stained by the KiSS‐1 antibody but some kisspeptin‐ir cells were not LHβ positive; thus, we cannot exclude the possibility that kisspeptins are expressed in other pituitary cells. All GPR54‐ir are co‐localised with LHβ cells, but only a subset of LHβ cells are stained with the GPR54 antibody. Using the real‐time reverse transcription‐polymerase chain reaction (RT‐PCR), we found that the expression of KiSS‐1 and GPR54 is differentially regulated by steroids. In the female, KiSS‐1 mRNA levels dramatically decreased following ovariectomy (OVX), and this decrease was prevented by administration of 17β‐oestradiol (E2), but not by administration of GnRH antagonist or agonist. Administration of E2 in OVX rats receiving either GnRH antagonist or agonist clearly shows that E2 acts directly on the pituitary to positively control KiSS‐1 expression. In OVX rats, administration of the selective oestrogen receptor (ER)α ligand propylpyrazoletriol, but not the selective ERβ ligand diarylpropionitrile, mimics this effect. By contrast, our study shows that GPR54 expression is positively regulated by GnRH and negatively controlled by chronic exposure to E2. In summary, our data document for the first time that, in the female rat pituitary, KiSS‐1 expression is up‐regulated by oestradiol, similarly to that seen in the anteroventral periventricular nucleus of the hypothalamus. Conversely, GPR54 is up‐regulated by GnRH, which exclusively targets gonadotrophs.