Concerted action of human chorionic gonadotropin and norepinephrine on intracellular-free calcium in human granulosa-lutein cells: evidence for the presence of a functional alpha-adrenergic receptor
KJ Fohr, A Mayerhofer, K Sterzik, M Rudolf, B Rosenbusch and M Gratzl
Abteilung Anatomie und Zellbiologie, Universitat Ulm, Germany.
Luteal cells are known to possess receptors for LH/hCG and receptors of the
beta-adrenergic type. Interactions of specific agonists with either
receptor lead to the activation of adenylate cyclase and subsequently to an
increase of cAMP. Since in the human there is also evidence for the
presence of alpha-adrenergic receptors, we have investigated whether
activation of these receptors is linked to calcium as a second messenger
and performed measurement of intracellular free calcium (Ca2+) with Fura-2
in single human granulosa-lutein cells. Addition of either hCG (100, 1,000,
25,000 IU/L) or norepinephrine (NE; known to interact with both alpha- and
beta-adrenergic receptors), beta- adrenergic receptor agonist isoproterenol
(ISO), or alpha-adrenergic receptor agonist phenylephrine (PHE; all at 10
and 100 mumol/L) did not increase free intracellular Ca2+. However, the
addition of combinations of NE/hCG, PHE/hCG, but not the combination
ISO/hCG, induced a transient increase in cytosolic free Ca2+. The
NE/hCG-evoked calcium signal was not abolished in the presence of the
beta-adrenergic receptor antagonist propranolol and was not affected by
removal of extracellular Ca2+. Furthermore, we tested whether
catecholamines affected the release of progesterone in the presence or
absence of hCG. As expected, hCG (10,000 IU/L) stimulated progesterone
release by cultured granulosa-lutein cells. When these cells were incubated
with NE, PHE, or ISO (at 10 mumol/L), production of progesterone by these
cells was not affected. However, the combinations of NE and PHE with hCG
abolished the hCG-induced progesterone accumulation, but ISO coincubated
with hCG did not. Taken together, our results indicate: 1) the presence of
functional alpha-adrenergic receptors on human granulosa-lutein cells; 2)
simultaneous activation of two different receptors (for hCG and
alpha-agonists) are able to evoke intracellular Ca2+ elevation, implicating
postreceptor interactions in human granulosa lutein cells; 3) this process
occurs even in the absence of extracellular Ca2+, indicating the
involvement of intracellular Ca2+ stores, most likely due to activation of
phosphoinositide pathway; 4) catecholamines most likely acting via
alpha-adrenergic receptors, inhibit the LH/hCG-induced release of
progesterone.
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