In vitro release of gonadotropin-releasing hormone from the brain preoptic-anterior hypothalamic region and pituitary of female goldfish

In vitro release of gonadotropin releasing hormone (GnRH) from slices of the preoptic-anterior hypothalamic (P-AH) region and fragments of the pituitary of goldfish was studied using a static incubation system. Release of GnRH from both tissue preparations was stimulated by depolarizing concentrations of extracellular potassium ions (K +). Other putative secretagogues, calcium ionophore A21387 (1 μ M), forskolin (100 μ M), and prostaglandin E 2 1 μ M) also stimulated release of GnRH from both tissue preparations. Omission of Ca 2+, or chelating the remaining remaining Ca 2+ by EGTA (0.1 m M), abolished the release of GnRH stimulated by high K + concentrations (60 m M), but did not reduce spontaneous release. Verapamil (1 μ M), a voltage-sensitive calcium channel blocker, abolished the release of GnRH stimulated by high K + or A21387 from both tissue preparations. The GnRH released in vitro from both the P-AH region and pituitary was concentrated by Sep-Pak and then separated by high-performance liquid chromatography. The major peak of the GnRH immunoreactivity was found to coelute with synthetic salmon GnRH ([Trp 7, Leu 8]-GnRH) and the minor peak with chicken GnRH-II ([Gln 8]-GnRH). Dopamine (10 and 100 μ M) inhibited GnRH release from both P-AH slices and pituitary fragments, while serotonin (1–100 μ M) stimulated release from both. Norepinephrine (10–100 μ M) stimulated GnRH release from P-AH slices but not from pituitary fragments. The results demonstrate that the release of GnRH from goldfish P-AH slices and pituitary fragments in vitro in response to various secretagogues and monoamines can be studied using a static incubation system.