Requirement of extracellular calcium in fish pituitary gonadotropin release by gonadotropin hormone-releasing hormone.
Influence of extracellular calcium on gonadotropin hormone-releasing hormone (GnRH)-stimulated gonadotropin hormone (GtH) release from a teleostean fish (Channa punctatus) pituitary was examined in vitro by preparing enzymatically dispersed pituitary cell incubation. Effect of Ca2+ on GnRH-augmented GtH release was evaluated with partially purified C. punctatus GnRH (cGnRH) and synthetic mammalian GnRH (mGnRH). Cells were dispersed by 0.3% collagenase plus 0.05% trypsin in culture medium and a high yield of viable cells were obtained. Addition of cGnRH (10 micrograms/ml) to pituitary cells in Ca2+-free medium resulted in a significant increase in GtH release, but the addition of Ca2+ (2 mM) enhanced it to about four- and threefold over cGnRH and mGnRH, respectively. Increasing concentrations of Ca2+ (0.1-2.0 mM/well) with fixed concentrations of GnRH (10 micrograms/ml) or increasing doses of GnRH (2.5 to 20 micrograms/ml) with fixed amount of Ca2+ (2 mM/well) resulted in a dose dependent increase in GtH release. EDTA or EGTA (2 mM/well) completely suppressed the Ca2+-augmenting effect of GnRH-stimulated GtH release. Addition of lanthanum (La3+, 4 mM/well), a competitive inhibitor of Ca2+, reduced 60% of the Ca2+ (2 mM/well) stimulation. Verapamil, a specific Ca2+ channel blocker, when added in increasing concentrations (1-100 microM/well) to pituitary cell incubations containing GnRH-stimulated GtH release in Ca2+-free medium could be waived by EGTA (2 mM/well), indicating availability of extracellular calcium from tissue sources. The uptake of radioactive Ca2+ by pituitary cells was greatly enhanced by GnRH while the addition of verapamil (10 microM/well) not only inhibited the GnRH-stimulated uptake, but also reduced it below the control level.(ABSTRACT TRUNCATED AT 250 WORDS)
Jamaluddin
M
M
Department of Zoology, School of Life Sciences, Visva-Bharati University, Santiniketan, West Bengal, India.
Banerjee
P P
PP
Manna
P R
PR
Bhattacharya
S
S
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005399:Fishes / Q000378:metabolism*; D006065:Gonadotropins, Pituitary / Q000378:metabolism*; D007811:Lanthanum / Q000378:metabolism; D010902:Pituitary Gland / Q000166:cytology; D010906:Pituitary Hormone-Releasing Hormones / Q000378:metabolism*; D014700:Verapamil / Q000378:metabolism
D006065:Gonadotropins, Pituitary; D010906:Pituitary Hormone-Releasing Hormones; D007811:Lanthanum; D014700:Verapamil; D002118:Calcium