Growth hormone-releasing hormone stimulates GH release while inhibiting ghrelin- and sGnRH-induced LH release from goldfish pituitary cells

- gGHRH induces GH release but did not potentiate GH responses to gGRLN19 or sGnRH.
- gGHRH inhibits basal and gGRLN19- or sGnRH-stimulated LH release.
- gGHRH-induced GH release is greater at gonadal regression than early recrudescence.
- 1st study of GHRH and stimulators of both LH and GH secretion in teleost.
- Novel effects of GHRH as a negative regulator of LH release in vertebrates.

Goldfish GH-releasing hormone (gGHRH) has been recently identified and shown to stimulate GH release in goldfish. In goldfish, neuroendocrine regulation of GH release is multifactorial and known stimulators include goldfish ghrelin (gGRLN19) and salmon gonadotropin-releasing hormone (sGnRH), factors that also enhance LH secretion. To further understand the complex regulation of pituitary hormone release in goldfish, we examined the interactions between gGHRH, gGRLN19, and sGnRH on GH and LH release from primary cultures of goldfish pituitary cells in perifusion. Treatment with 100 nM gGHRH for 55 min stimulated GH release. A 5-min pulse of either 1 nM gGRLN19 or 100 nM sGnRH induced GH release in naïve cells, and these were just as effective in cells receiving gGHRH. Interestingly, gGHRH abolished both gGRLN19- and sGnRH-induced LH release and reduced basal LH secretion levels. These results suggest that gGHRH does not interfere with sGnRH or gGRLN19 actions in the goldfish somatotropes and further reveal, for the first time, that GHRH may act as an inhibitor of stimulated and basal LH release by actions at the level of pituitary cells.