Isolated Adrenal Cells: Adrenocorticotropic Hormone, Calcium, Steroidogenesis, and Cyclic Adenosine Monophosphate

Sayers, George; Beall, Robert J.; Seelig, Steven

doi:10.1126/science.175.4026.1131

Cited by 125 publications

(37 citation statements)

References 15 publications

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“…Ca 2+ enhances cyclic AMP responses in nonskeletal tissues [29][30][31][32][33][34][35], and does so by modifying cyclic AMP synthesis but not agonist binding [31,36,37]. In these nonskeletal systems, the Ca 2+ effect appears rapidly, persists, and is evident at low as well as at high agonist concentrations.…”

Section: Discussionmentioning

confidence: 99%

Calcium-mediated enhancement of the cyclic AMP response in cultured bone cells

1981

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We have examined the influence of extracellular Ca2+ on cyclic AMP metabolism in an osteoblast-enriched population of bone cells isolated from the calvaria of rat fetuses. The cyclic AMP response to stimulators of cyclic AMP formation (PTH and PGE2), but not basal cyclic AMP levels, increased progressively as the extracellular Ca2+ concentration was raised from 0.2 to 4.0 mM. The response to changes in extracellular Ca2+ were rapid (within 3.5 min), and the level of responsivity that characterized each Ca2+ concentration persisted for at least 6 h when the Ca2+ concentration was kept constant. The effect of Ca2+ spanned the entire time course of PTH action, was not accompanied by altered excretion of cyclic AMP from the cells, and was evident at low as well as at high hormone concentrations. Ca2+ augmented the action of PTH in the presence as well as in the absence of cyclic AMP phosphodiesterase inhibitors, and failed to decrease cyclic AMP phosphodiesterase activity in the short term. Mn2+ and, to a smaller degree, Ba2+ substituted for Ca2+ in promoting the cyclic AMP response to PTH. Verapamil, an inhibitor of Ca2+ penetration, blunted the Ca2+-mediated increments in the cyclic AMP response, and the divalent cation ionophore A23187 enhanced these increments. These results indicate that Ca2+ and other cations are positive effectors of the stimulated cyclic AMP response in isolated bone cells. Accumulation into an as yet unknown cellular compartment may be required for the cation effect. The data are most consistent with enhancement of adenylate cyclase reactivity as the mode of cation action.

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Section: Discussionmentioning

confidence: 99%

Calcium-mediated enhancement of the cyclic AMP response in cultured bone cells

1981

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“…Thus agents such as calcium ions, which alter the conformational state of the mitochondria, dramatically alter the rate of cholesterol side-chain cleavage. Consequently it is tempting to propose that calcium could play a role in the trophic stimulus a t the mitochondrial level as well as the a t level of the plasma membrane [3,5] in view of the ability of mitochondria to bind calcium [30]. Possibly the "labile protein factor" of Garren and his colleagues [32] could be involved in this process.…”

Section: Effect Of Calcium Ions On Cholesterol Side-chain Cleavagementioning

confidence: 99%

Effect of Calcium Ions on Steroid‐Binding Spectra and Pregnenolone Formation in Rat–Adrenal Mitochondria

Simpson

Jefcoate

McCarthy

et al. 1974

European Journal of Biochemistry

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The effect of calcium ions on steroid-induced difference spectra of cytochrome P-450, and on pregnenolone formation, has been studied in rat adrenal mitochondria. I n the presence of phosphate, addition of calcium chloride to suspensions of these mitochondria resulted in an increase in the inverted type-I difference spectrum induced by pregnenolone or methylandrostenediol, and a disappearance of the type I spectrum induced by 25-hydroxycholesterol. The difference in the inverted type I spectrum between mitochondria from ether-stressed animals and those given cycloheximide was abolished. Cholesterol side-chain cleavage was increased, providing an NADPH generator was used as source of reducing equivalents. The difference in side-chain cleavage activity between mitochondria from ether-stressed animals and those given cycloheximide, was maintained.I n the absence of phosphate, addition of calcium chloride again resulted in a loss of the type I difference spectrum induced by 25-hydroxycholesterol, but this time there was almost no change in the inverted type I spectrum induced by pregnenolone in mitochondria from rats subjected to ether anaesthesia, and the change in cycloheximide-treated rats was only about 50°/, of the change in the 25-hydroxycholesterol-induced difference spectrum. These observations are interpreted in terms of interconversions of the various forms of cytochrorne P-450 associated with side-chain cleavage proposed to exist in intact adrenal mitochondria.Factors such as bovine serum albumin and EDTA, which increase respiratory control in these mitochondria, also stimulate cholesterol side-chain cleavage activity, as do magnesium ions, but without altering the magnitude of the steroid-binding spectra.It is wellestablished that calcium ions are required for the stimulating effect of adrenocorticotrophic hormone on steroid output in the adrenal [1-41. Calcium ions are required for the stimulation of adenyl cyclase activity by adrenocorticotrophic hormone in plasma membrane fractions [5]. However, calcium ions can also stimulate steroid hydroxylation reactions of adrenal cortex mitochondria in. vitro [6,7]. This stimulation when NADPH is used as source of reducing equivalents may be partially attributed to calcium-induced permeability of the mitochondria to pyridine nucleotides [8]. It seemed pertinent, however, to examine the effect of calcium ions further to see if other factors were also involved.I n this paper we describe changes in cholesterol side-chain cleavage in isolated rat adrenal mitochondria produced by additions of calcium ions, by addition of EDTA and other factors such as bovine serum albumin and magnesium ions, which are known to regulate the ability of the isolated rat adrenal mitochondria to exhibit respiratory control [9]. These changes are discussed in relation to alterations in the binding of specific steroids to cytochrome P-450, which are believed t o monitor the different spin states of ferric cytochrome P-450 [10,11]. MATERIALS AND METHODSAdrenal mitochondria were prepared from...

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“…Calcium chelators have been shown to inhibit corticotropin stimulation of adenylate cyclase in broken cells [18,19]. However, in intact cells the requirement of calcium for the steroidogenic effect of calcium is relative: Sayers et al [20] and Bowyer and Kitabchi [21 ] have shown that in the absence of calcium high doses of corticotropin were able to induce a very small increase of cyclic AMP formation in isolated rat adrenal cells. Therefore, the data we obtained with both EGTA and EDTA could be explained by an incomplete inhibition of the corticotropin stimulation of cyclic AMP production.…”

Section: Discussionmentioning

confidence: 99%

Mechanism of Corticotropin Action on Adrenal Protein Synthesis

Dazord¹,

Langlois-Gallet²,

Saez³

1981

Horm Res

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We have recently shown that beside a general stimulation of most adrenal proteins, corticotropin induces a marked increase in a specific adrenal cytosolic protein, protein E. in intact and hypophysectomized rats. To further clarify the mechanisms by which corticotropin exerts its trophic action we have investigated the effects of cycloheximide, calcium and calcium chelator administration on intact and hypophysectomized animals. These substances were injected in rats with or without corticotropin, and slices of adrenal glands from control and treated animals were removed 5 h later, incubated with [¹⁴C]- or [³H]-leucine for 2 h, and cytosolic proteins analyzed by polyacrylamide gel electrophoresis using a dual labelling technique. When high doses of cycloheximide (higher than 500 µg) were injected in rats, incorporation of labelled leucine in adrenal slices of control and corticotropin-treated animals was inhibited. With 500 µg cycloheximide per rat, incorporation of labelled leucine in adrenal slices of control animals was normal, but the corticotropin stimulation of both protein E and total protein synthesis was inhibited. Lower doses of cycloheximide (100 µg per rat) completely inhibited the stimulatory effect of corticotropin on total protein synthesis but did not affect protein E synthesis, while after 50 µg per rat both stimulatory effects were preserved. The two higher doses of cycloheximide (500 and 100 µg per rat) could not completely block the steroidogenic effect of the hormone. The effects of calcium and calcium chelators were studied in 1-day hypophysectomized rats. Calcium alone or injected simultaneously with corticotropin has no effect. Calcium chelators injected simultaneously with corticotropin partially inhibited the stimulatory effects of corticotropin on steroidogenesis but totally inhibited stimulation of total protein synthesis, while the stimulation of protein E persisted. Our results show that after corticotropin, stimulation of protein E synthesis correlates better with steroidogenesis than with total protein synthesis.

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Isolated Adrenal Cells: Adrenocorticotropic Hormone, Calcium, Steroidogenesis, and Cyclic Adenosine Monophosphate

Cited by 125 publications

References 15 publications

Calcium-mediated enhancement of the cyclic AMP response in cultured bone cells

Calcium-mediated enhancement of the cyclic AMP response in cultured bone cells

Effect of Calcium Ions on Steroid‐Binding Spectra and Pregnenolone Formation in Rat–Adrenal Mitochondria

Mechanism of Corticotropin Action on Adrenal Protein Synthesis

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