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

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 measurements 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 granulosalutein 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.