γ‐MSH increases intracellular cAMP accumulation and GnRH release in vitro and LH release in vivo

Abstract
The roles of the melanocortin 3 receptor (MC3‐R) and its agonist, γ2‐melanocyte‐stimulating hormone (γ2‐MSH) in the regulation of the hypothalamo‐pituitary‐gonadal (HPG) axis are poorly understood. Here we show γ2‐MSH stimulated intracellular cAMP accumulation and gonadotrophin‐releasing hormone (GnRH) secretion in the immortalised GnRH cell line GT1‐7. The MC3/4‐R antagonist Agrp blocked these actions. Reverse transcriptase polymerase chain reaction demonstrated GT1‐7 cells express MC3‐R mRNA. γ2‐MSH also stimulated GnRH release from hypothalamic explants. In vivo, γ2‐MSH administration into the medial preoptic area significantly increased plasma luteinising hormone. MC3‐R and γ2‐MSH may modulate the HPG axis.