Effects of noradrenaline on GnRH-secreting immortalized hypothalamic (GT1-7) neurons.
Noradrenaline (NA) is one of the most important neurotransmitters involved in the regulation of gonadotropin-releasing hormone (GnRH) secretion. In this study, the effects of NA on GnRH secretion, intracellular Ca2+ concentrations ([Ca2+]i), and membrane potentials were investigated in immortalized hypothalamic neurons (GT1-7) to determine the direct effects of NA on GnRH cells. Cells were perfused in a plastic minicolumn, and GnRH concentrations of the effluents were measured. NA increased the release of GnRH in a dose-dependent manner. Cells were loaded with a 4 microM Fura 2-AM, and the ratio of the intensities of fluorescent emission at 510 nm with excitation at 340 and 380 nm was calculated at 100-ms intervals. NA increased the [Ca2+]i responses of single GnRH cells dose-dependently. The NA-induced [Ca2+]i increase was attenuated in the absence of extracellular calcium and was blocked by the beta-adrenergic antagonist propranolol, but not by the alpha-adrenergic antagonist phentolamine. The cell membrane potential was recorded with a whole-cell patch clamp amplifier with glass-electrodes. NA induced membrane depolarization under current-clamp conditions. The depolarization was also inhibited by propranolol, but not by phentolamine. The results show that NA directly affects the membrane potential of GT1-7 cells via beta-adrenergic receptors and induces Ca2+ mobilization; these effects stimulate GnRH secretion.
Uemura
T
T
Department of Obstetrics and Gynecology, Yokohama City University School of Medicine, Japan.
Nishimura
J
J
Yamaguchi
H
H
Hiruma
H
H
Kimura
F
F
Minaguchi
H
H
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002461:Cell Line, Transformed; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D007987:Gonadotropin-Releasing Hormone / Q000187:drug effects / Q000378:metabolism*; D007031:Hypothalamus / Q000378:metabolism / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology*; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D007987:Gonadotropin-Releasing Hormone; D011433:Propranolol; D002118:Calcium; D009638:Norepinephrine; D010646:Phentolamine