Ghrelin stimulation of gonadotropin (LH) release from goldfish pituitary cells: Presence of the growth hormone secretagogue receptor (GHS-R1a) and involvement of voltage-sensitive Ca2+ channels

Ghrelin (GRLN) stimulates maturational gonadotropin (LH) secretion in goldfish. This study identified GRLN receptors (GHS-Rs) in goldfish tissues and examined the involvement of voltage-sensitive Ca2+ channels (VSCCs) in ghrelin action. A partial goldfish GHS-R1a sequence was obtained and expression observed in brain, pituitary, spleen, kidney, heart, gill, ovary, testis, and intestine. Synthetic goldfish GRLN (gGRLN19) stimulated LH secretion from dispersed goldfish pituitary cells in column perifusion and increased intracellular Ca2+ ([Ca2+]i) in identified goldfish gonadotropes. gGRLN19 did not stimulate LH secretion either in the presence of Ca2+-free media, or the L-type VSCC inhibitors nifedipine and verapamil. Similarly, gGRLN19-elicited increases in [Ca2+]i were attenuated by Ca2+-free media and nifedipine. Furthermore, when LH release and [Ca2+]i were elevated by Bay K8644, gGRLN19 had no further effect. These results indicate that GHS-R1a is present in goldfish pituitary and Ca2+ entry through VSCC mediates direct gGRLN19 action on LH release in goldfish pituitary cells.