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Biomedical subjects

J Axelrod

Publications and source records attributed to J Axelrod.

At least 73 records · Page 4Linked to original sources
PubMed1985

Inhibitors of the cytochrome P-450 enzymes block the secretagogue-induced release of corticotropin in mouse pituitary tumor cells.

A mouse pituitary tumor cell line (AtT-20) releases corticotropin (ACTH) in response to a number of secretagogues, including corticotropin-releasing factor (CRF), beta-adrenergic agents, N6,O2'-dibutyryladenosine 3',5'-cyclic monophosphate (Bt2 cAMP), and potassium. The stimulation of ACTH secretion induced by the secretagogues can be blocked by inhibitors of the enzymes that generate (phospholipase A2) and metabolize (lipoxygenase and epoxygenase) arachidonic acid. The phospholipase A2 blockers mepacrine and p-bromophenacylbromide inhibited the ACTH release induced by secretagogues. The lipoxygenase inhibitors nordihydroguaieretic acid, butylated hydroxytoluene, and icosatetraynoic acid abolished the ACTH secretion induced by secretagogues, whereas indomethacin, a cycloxygenase inhibitor, did not. Blockers of the cytochrome P-450 epoxygenase, such as SKF 525A and piperonyl butoxide, compounds that have different molecular structures, also suppressed secretagogue-induced ACTH release. These findings suggest that metabolites of arachidonic acid formed via the epoxygenase and/or the lipoxygenase pathway are involved in the stimulation of ACTH release caused by secretagogues.

Adrenocorticotropic Hormone↗
PubMed1984

Beta-adrenergic mechanism of insulin-induced adrenocorticotropin release from the anterior pituitary.

Intraperitoneal administration of insulin to control rats and to rats with pituitary stalk transections or with lesions of the median eminence resulted in increased plasma adrenocorticotropin (ACTH) levels. The insulin-induced stimulation of ACTH release was blocked in both the control and lesioned animals by prior treatment with either the beta-adrenergic antagonist propranolol or the glucocorticoid analog dexamethasone. The direct application of insulin to primary cultures of the anterior pituitary did not evoke ACTH release or affect the maximal ability of corticotropin-releasing factor or epinephrine to stimulate ACTH secretion. The results suggest that insulin stimulates ACTH release by a mechanism in which catecholamines of peripheral origin act directly on the anterior pituitary.

Adrenocorticotropic Hormone↗
PubMed1984

Stress hormones: their interaction and regulation.

Stress stimulates several adaptive hormonal responses. Prominent among these responses are the secretion of catecholamines from the adrenal medulla, corticosteroids from the adrenal cortex, and adrenocorticotropin from the anterior pituitary. A number of complex interactions are involved in the regulation of these hormones. Glucocorticoids regulate catecholamine biosynthesis in the adrenal medulla and catecholamines stimulate adrenocorticotropin release from the anterior pituitary. In addition, other hormones, including corticotropin-releasing factor, vasoactive intestinal peptide, and arginine vasopressin stimulate while the corticosteroids and somatostatin inhibit adrenocorticotropin secretion. Together these agents appear to determine the complex physiologic responses to a variety of stressors.

Adenylyl Cyclases↗
PubMed1983

Corticotropin releasing factor stimulation of protein carboxylmethylation in mouse pituitary tumor cells.

A putative role for the protein carboxylmethylase (PCM) enzyme has been suggested in exocytotic secretion. The involvement of 3H-methyl incorporation into protein carboxylmethyl esters during corticotropin releasing factor (CRF)-induced ACTH secretion from AtT-20/D16-16 mouse pituitary cells was investigated. Protein carboxylmethylation and ACTH secretion both increased as a function of extracellular CRF concentration, and both processes were temporally parallel up to 60 min incubation. The less potent [Met(O)21]-CRF also stimulated increases in protein carboxylmethylation and ACTH secretion. The free acid analogue of CRF did not alter either process. A combination of the PCM inhibitors, 3-deazaadenosine and L-homocysteine thiolactone, reduced both CRF-stimulated protein carboxylmethylation and ACTH release. Dexamethasone, known to inhibit ACTH secretion and synthesis, inhibited both CRF-stimulated protein carboxylmethylation and ACTH secretion.

Adrenocorticotropic Hormone↗
PubMed1983

Desensitization of beta 2-adrenergic receptors and adrenocorticotropin release.

Pre-exposure of mouse anterior pituitary tumor cells (A+T-20/D16-16) to (-) isoproterenol reduces the ability of this beta-adrenergic agonist to restimulate cyclic AMP synthesis or adrenocorticotropin hormone (ACTH) release from these cells. This beta-adrenergic receptor desensitization is time and dose-dependent, recoverable and specific for beta-receptors. Longer pretreatment times are required to decrease beta-receptor density than to induce receptor desensitization. This initial beta-receptor refractoriness involves an uncoupling of the receptor from adenylate cyclase since (-) isoproterenol treatment does not alter forskolin-activated cyclic AMP formation or ACTH release. In addition to diminishing beta-receptor responsiveness, (-) isoproterenol treatment induces a prolonged elevation of basal ACTH release. This finding indicates that the intracellular events leading to ACTH secretion may also be altered during the desensitization process.

Adrenocorticotropic Hormone↗
PubMed1983

Direct stimulation of beta 2-adrenergic receptors in rat anterior pituitary induces the release of adrenocorticotropin in vivo.

Previous work in our laboratory has shown that stimulation of beta 2-adrenergic receptors on mouse anterior pituitary tumor cells causes the secretion of immunoreactive adrenocorticotropin (ACTH). The present study was designed to test the hypothesis that catecholamines can cause the release of ACTH in vivo by the direct stimulation of beta 2-adrenergic receptors in the rat anterior pituitary. Systemic administration of a beta-adrenergic receptor agonist (-)-isoproterenol resulted in an increase in plasma ACTH levels in intact animals and in rats with transected pituitary stalks. This effect could be blocked by the beta-adrenergic receptor antagonist, propranolol, but not by the specific beta 1-adrenergic receptor antagonist, practolol. Salmefamol, a beta 2-adrenergic receptor agonist also elevated plasma ACTH levels in stalk-sectioned animals. Dexamethasone, a glucocorticoid that inhibits the synthesis and release of ACTH from the anterior pituitary but not the intermediate lobe, prevented the elevation of ACTH secretion by (-)-isoproterenol in stalk-transected rats. These data indicate that beta 2-adrenergic receptors are present on anterior pituitary cells and suggest that catecholamines can directly stimulate ACTH secretion.

Adrenocorticotropic Hormone↗
PubMed1983

Bradykinin stimulates phospholipid methylation, calcium influx, prostaglandin formation, and cAMP accumulation in human fibroblasts.

The biochemical events that lead to bradykinin stimulation of cAMP accumulation in human fibroblasts were examined. Treatment of human fibroblasts with bradykinin increases phospholipid methylation, Ca2+ influx, arachidonic acid release, prostaglandin formation, and cAMP content. The dose-response curves of bradykinin for the increase in the above changes were similar. In human fibroblasts, exogenous arachidonic acid was mainly incorporated into phosphatidylcholine, followed by phosphatidylserine, phosphatidylethanolamine, and phosphatidylinositol. Bradykinin caused a release of arachidonic acid from methylated phospholipids (phosphatidylcholine) and phosphatidylinositol. 3-Deazaadenosine, a methyltransferase inhibitor, almost completely inhibited bradykinin-stimulated phospholipid methylation and Ca2+ influx and partially reduced arachidonic acid release and prostaglandin formation but had no effect on cAMP formation. Mepacrine, a phospholipase inhibitor, blocked bradykinin-induced arachidonic acid release, prostaglandin release, and cAMP accumulation. Indomethacin, a cyclooxygenase inhibitor, blocked the effect of bradykinin on cAMP accumulation. Prostaglandins E1 and E2, but not F2 alpha, increased accumulation of cAMP. These observations indicate that bradykinin generates cAMP via arachidonic acid release and subsequent formation of prostaglandins. Our findings suggest that arachidonic acid can arise from either phosphatidylcholine synthesized by the methylation pathway or phosphatidylinositol.

Arachidonic Acid↗
PubMed1983

Protein carboxyl methylation increases in parallel with differentiation of neuroblastoma cells.

Cells of mouse neuroblastoma clone N1E-115 in the confluent phase of growth can catalyze the formation of endogenous protein carboxyl methyl esters, using a protein carboxyl methylase and membrane-bound methyl acceptor proteins. The enzyme is localized predominantly in the cytosol of the cells and has a molecular weight of about 20,000 daltons. Treatment of the cells with dimethylsulfoxide (DMSO) or hexamethylene-bisacetamide (HMBA), agents that induce morphological and electrophysiological differentiation, results in a marked increase in protein carboxyl methylase activity. Maximal levels are reached 6-7 days after exposure to the agents, a time course that closely parallels the development of electrical excitability mechanisms in these cells. Serum deprivation also causes neurite outgrowth but does not enhance electrical excitability or enzyme activity. The capacity of membrane-bound neuroblastoma protein(s) to be carboxyl methylated is increased by the differentiation procedures that have been examined. However, the increase in methyl acceptor proteins induced by DMSO or HMBA is the largest, and its time course parallels electrophysiological differentiation. In contrast, serum deprivation induced a small increase that reached maximal levels within 24 h. The data suggest that increased protein carboxyl methylation is a developmentally regulated property of neuroblastoma cells and that at least two groups of methyl acceptor proteins are induced during differentiation: a minor group related to morphological differentiation, and a major group that may be related to ionic permeability mechanisms of the excitable membrane.

Animals↗
PubMed1983

Prolonged somatostatin pretreatment desensitizes somatostatin's inhibition of receptor-mediated release of adrenocorticotropin hormone and sensitizes adenylate cyclase.

Addition of somatostatin-14 (SRIF) inhibits corticotropin releasing factor (CRF) and forskolin-stimulated cyclic AMP formation and ACTH release from tumor cells of the mouse anterior pituitary (AtT-20/D16-16). After long-term pretreatment of these cells with SRIF, the ability of SRIF to inhibit CRF and forskolin-stimulated cyclic AMP accumulation or ACTH secretion is markedly reduced. SRIF pretreatment also increases the formation of cyclic AMP in response to forskolin. This increase is delayed in onset, slow to recover, and blocked by the protein synthesis inhibitor, cycloheximide. SRIF pretreatment did not affect basal cyclic AMP and cyclic GMP levels or phosphodiesterase activity. It is proposed that prolonged treatment of AtT-20 cells with SRIF desensitizes SRIF receptors and induces a compensatory sensitization of adenylate cyclase through a process requiring protein synthesis.

Adenylyl Cyclases↗
PubMed1983

Activation of beta 2-adrenergic receptors on mouse anterior pituitary tumor cells increases cyclic adenosine 3':5'-monophosphate synthesis and adrenocorticotropin release.

AtT-20 cells comprise a mouse anterior pituitary tumor cell line that synthesizes and secretes adrenocorticotropin hormone (ACTH). beta-Adrenergic receptors were characterized on AtT-20 cells using receptor binding methodology and the ability of beta-receptor agonists to stimulate intracellular cyclic adenosine 3':5'-monophosphate (cAMP) formation and the release of ACTH immunoreactivity. The density of beta-receptors on membrane preparations of these cells is 64 fmol/mg of protein and their affinity constant (KD value) for tritiated dihydroalprenolol is 11 nM. The binding of [3H] dihydroalprenolol to AtT-20 cells is stereoselectively inhibited by propranolol and isoproterenol but is not affected by phentolamine. The beta-receptors on these cells appear to be of the beta 2-receptor subtype since a selective beta 2-receptor agonist, salmefamol, can inhibit [3H]dihydroalprenolol binding, whereas practolol, a beta 1-receptor blocker, is ineffective. (-)-Isoproterenol stimulates cAMP formation in AtT-20 cells and this effect is blocked by dl-propranolol. Both l-epinephrine and l-norepinephrine induce dose-dependent increases in cAMP formation with the former agonist being more potent. Salmefamol also stimulates cAMP formation in these cells. The secretion of ACTH from AtT-20 cells is induced by (-)-isoproterenol as well as by other adrenergic agonists. The isoproterenol effect on ACTH release is stereoselective, calcium dependent, and blocked by dl-propranolol but not by phentolamine or practolol.

Adrenocorticotropic Hormone↗
PubMed1982

Enzymatic methylation of the membrane-bound nicotinic acetylcholine receptor.

The acetylcholine receptor of the Torpedo electric organ acts as substrate for the enzyme protein carboxyl methyltransferase within receptor-enriched membranes and after it is purified. In right-side-out receptor-enriched vesicles, protein of the membrane. All four receptor subunits were found to be methylated from the inside as well outside of the membrane vesicles. The higher molecular weight subunits were found to be methylated to a greater degree than the lower molecular weight subunits.

Animals↗
PubMed1982

The relationship between phospholipid methylation and calcium influx in murine lymphocytes stimulated with native and modified Con A.

Native Con A and two chemical derivatives, divalent dimeric Con A and monovalent dimeric Con A. induced a transient increase of phospholipid methylation, Ca2+ influx, and also increased DNA synthesis in murine lymphocytes. For each of the individual mitogens, the dose-response curves for these three activities were very similar. However, there were major differences between the dose-response curves for Con A and each of its two chemical derivatives. On the other hand, the time course of phospholipid methylation for each lectin reached a maximum at about 10 min after the addition of lectin, and then gradually decreased to control levels. In like manner, Ca2+ influx reached its maximum at approximately 5 min. The lectin-stimulated increase in phospholipid methylation occurred in calcium-free medium, while the inhibitor of phospholipid methylation, 3-deaza-SIBA, also suppressed the increased calcium influx. This suggests that the Ca2+ influx might be regulated by early phospholipid methylation. Further, in the absence of calcium, the methylated phospholipids do not undergo Con A-accelerated breakdown by phospholipase A2. This suggests that the increased influx of calcium is necessary for the activation of phospholipase A2, an enzyme that hydrolyses methylated phospholipids to yield arachidonic acid and lysolecithin. Blocking any of these biochemical steps also blocked subsequent DNA synthesis, suggesting that the pathway may be required for the activation of lymphocytes.

Animals↗
PubMed1982

Corticotropin-releasing factor stimulates phospholipid methylation and corticotropin secretion in mouse pituitary tumor cells.

The 41-residue synthetic ovine corticotropin-releasing factor (CRF; corticoliberin) has been shown to stimulate release of corticotropin (adrenocorticotropic hormone; ACTH) and beta-endorphin from AtT-20/D16-16 mouse pituitary tumor cells. Phospholipid methylation of phosphatidylethanolamine to phosphatidylcholine with S-adenosylmethionine as methyl donor has been suggested as a possible membrane transduction mechanism for some receptor-induced events. CRF increased phospholipid methylation in pituitary tumor cells at concentrations that also stimulated immunoreactive ACTH secretion, and both processes increased linearly and in parallel with time. The methionine sulfoxide derivative of CRF was less potent than CRF was in stimulating both phospholipid methylation and hormone secretion, and the COOH-terminal free acid analogue of CRF had no effect on either process. CRF-induced increases in phospholipid methylation and ACTH secretion were reduced when cells were treated with the phospholipid methyltransferase inhibitors 3-deazaadenosine and L-homocysteine thiolactone. These CRF-stimulated effects were also blocked by the glucocorticoid dexamethasone. It is suggested that phospholipid methylation may be a CRF receptor-mediated event associated with ACTH release in pituitary tumor cells.

Adrenocorticotropic Hormone↗