Mechanisms by which Calcium Ions Regulate the Steroidogenic Actions of Luteinizing Hormone in Isolated Ovarian Cells in Vitro*

Abstract

Incubation of swine granulosa cells in chemically defined medium selectively deficient in calcium ions markedly impaired progesterone production in response to submaximal and maximally stimulating concentrations of LH. Accumulation of progesterone in response to LH was reduced significantly in both cells and medium, without a discernible shift in the time-course of progestin production. The reduction in progesterone accumulation could not be accounted by increased formation of the catabolite 20 alpha-hydroxypregn-4-en-3-one. In addition, progesterone secretion basally or in response to exogenously supplied pregnenolone was not altered in calcium-deficient incubations. Administration of verapamil or diltiazem, organic inhibitors of net transmembrane calcium uptake, also suppressed LH-stimulated progesterone production. Conversely, micromolar concentrations of the divalent cation ionophore A23187 significantly enhanced the stimulatory effects of LH. The mechanisms of calcium action were examined further in relation to the cAMP effector system. Calcium deprivation significantly suppressed the dose-dependent accumulation of cAMP in granulosa cells treated with LH but had no effect on basal levels. Omission of calcium ions from the extracellular medium also markedly impaired production of progesterone in response to 8-bromo-cAMP, cholera toxin, or 3-isobutyl-l-methylxanthine. The present studies suggest that calcium ions significantly modulate LH-stimulated progesterone biosynthesis in isolated ovarian cells in vitro. Specific regulatory actions of calcium ions in granulosa cells may be exerted at several levels, including LH-stimulated cAMP accumulation and at intracellular loci distal to the actual generation of cAMP.

Regulation of ovarian steroidogenesis in vitro by gonadotropin in common carp Cyprinus carpio: interaction between calcium- and adenylate cyclase-dependent pathways and involvement of ERK signaling cascade

“…Consistent with observations in other vertebrates and in fish (reviewed in Leung & Steele (1992) and Benninghoff & Thomas (2006a)), increased steroid production by co-incubated carp ovarian follicle cells in presence of FK and dbcAMP, the modulators of adenylate cyclase and PKA respectively, and inhibition of HCG-stimulated steroid production in the presence of a specific adenylate cyclase inhibitor, SQ22536, demonstrate the regulatory role of adenylate cyclase and PKA in gonadotropin-induced ovarian steroidogenesis in such fish. Although conflicting reports are available on the requirement of calcium ion in gonadotropin-stimulated cAMP production by rat and bovine granulosa cells (Tsang & Carnegie 1984, Davis et al 1987, reports with other mammals indicate that action of HCG to increase cAMP production requires the presence of calcium (Veldhuis & Klase 1982, Asem & Hertelendy 1986). The possible target for calcium is the adenylate cyclase, and increased intracellular calcium concentrations have both positive and negative effects on adenylate cyclase leading to increased and decreased production of cAMP (Jamaluddin et al 1992, Srivastava & Van Der Kraak 1994.…”

Functional Assessment of the Calcium Messenger System in Cultured Mouse Leydig Tumor Cells: Regulation of Human Chorionic Gonadotropin-Induced Expression of the Steroidogenic Acute Regulatory Protein

“…(Endocrinology 140: 1739 -1751, 1999) T HE ENDOCRINE regulation of Leydig cells occurs predominantly through the LH/hCG receptor after coupling to the adenylate cyclase signal transduction system (1,2). The role of Ca 2ϩ as a second messenger has been extensively studied in the regulation of diverse cellular functions (3)(4)(5). Specific extracellular stimuli increase the intracellular free Ca 2ϩ levels, which, in turn, stimulate various functions of the target cells (6,7).…”

The influence of cadmium on Prussian carp oocyte maturation, development of eggs and hatching

“…We suppose that such an effect could come from the chemical similarity of Cd to calcium. Calcium is a very important regulator of ovarian steroidogenesis (Veldhuis and Klase, 1982;Carnegie, 1983, 1984;Kleiss-San Francisco and Schuetz, 1987). The calcium channel blockers were shown to inhibit the forskolin (a direct adenyl cyclase activator) stimulated testosterone production in goldfish (Van Der Kraak, 1991).…”