Melatonin inhibition of gnrh-induced lh release from neonatal rat
gonadotroph: involvement of ca++ not camp.
Vanecek, Jiri, and David C. Klein.
Institute of Physiology, Czech Academy of Sciences, 142 20 Prague
4, Czech Republic, and, Section on Neuroendocrinology, Laboratory of
Developmental Neurobiology, National Institute of Child Health and
Human Development, National Institutes of Health, Bethesda, MD 20892,
USA
APStracts 2:0030E, 1995.
Melatonin inhibits GnRH-induced release of luteinizing hormone (LH)
from the neonatal rat gonadotrophs. The second messenger involved is
not known although several candidates exist, including cAMP and
intracellular free Ca++ ([Ca++]i). The present study addresses
the question of which second messenger mediates melatonin inhibition
of LH release. We found that the effect of melatonin was not
prevented by cAMP protagonists, including 8-Br cAMP, dibutyryl cAMP,
isobutyl methylxanthine and forskolin. However, treatments which
enhanced Ca++ influx masked the effects of melatonin and treatments
which blocked Ca++ influx mimicked the effects of melatonin.
Moreover, melatonin decreased K+-induced LH release, which is
dependent upon Ca++ influx, but did not block release of LH due to
thapsigargin-induced mobilization of Ca++ from intracellular stores.
These findings indicate that melatonin inhibits GnRH-induced LH
-release primarily through an action involving inhibition of Ca++
influx, and that cAMP does not seem to be involved in this effect of
melatonin.
Received 2 November 1994; accepted in final form 14 February
1995.
APS Manuscript Number E450-4.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 25 February 1995.