Glutamate blocks astroglial stellation: effect of glutamate uptake and volume changes

Neurotransmitters which increase intracellular cAMP levels can cause cultured astroglia to change from a flat, polygonal shape to a stellate morphology. Little is known about how glial stellation can be regulated by other transmitters. In the present study, we demonstrated that L-glutamate blocked isoproterenol (ISO) or dibutyryl-cAMP induced stellation in astroglia. The glutamate inhibition was concentration dependent, with its maximal effect on > 90% of cells at 500 microM. Glutamate also reversed glial stellation within a short period (< 30 min). Glutamate uptake analogues, D-glutamate and D-aspartate, rather than receptor agonists, kainate and quisqualate, mimicked the glutamate effect. Likewise, the glutamate uptake blocker, D-thero-beta-hydroxyaspartate, blocked the glutamate effect. The glutamate inhibition was not a result of inhibition of cAMP formation, since norepinephrine, which inhibited 80% of ISO-stimulated cAMP, also caused glial stellation. Increases in extracellular K+ to 50 mM also reduced glial stellation, whereas 25 mM K+ had little effect. Since 25 mM K+ caused much greater depolarization than 400 microM glutamate, it was unlikely that the effects of both glutamate and high [K+] on glial stellation were due to membrane depolarization. Hypotonic treatment (120 mOsm) enhanced, whereas hypertonic treatment (520 mOsm) prevented, the glutamate reversal of glial stellation. Thus, glial swelling appeared to be a primary mechanism for the inhibitory effect of glutamate and high [K+] on glial stellation. This mechanism could also explain the observation that glutamate inhibited stellation induced by PMA, a PKC activator. Our data suggest that glutamate released from neurons during neuronal activity or pathology can be taken up by astrocytes and alter their morphology. Changes in glial morphology may in turn affect the volume and composition of the extracellular space and, as a result, neuronal activity.

Tumor necrosis factor-alpha decreases thyrotropin-induced 5'-deiodinase activity in FRTL-5 thyroid cells

Tumor necrosis factor-alpha (TNF-alpha) exerts various effects on many cell types. Acute administration of TNF-alpha to rats decrease hepatic 5'-deiodinase activity (5'D-I) and TNF-alpha has been implicated in the pathogenesis of the low triiodothyronine syndrome in non-thyroidal illness in humans. The thyroid, liver and kidney are rich in 5'D-I. Unlike hepatic and renal 5'D-I, thyroid 5'D-I is regulated by thyrotropin. We have investigated the effects of TNF-alpha on 5'D-I in FRTL-5 cells, a cultured rat thyroid follicular cell line. Tumor necrosis factor-alpha did not significantly affect basal 5'D-I but thyrotropin markedly increased 5'D-I (p < 0.001). This TSH-induced increase in 5'D-I was attenuated by TNF-alpha in a dose-dependent manner (p < 0.001). Enzyme kinetic analysis demonstrated that thyrotropin increased 5'D-I by increasing Vmax (p < 0.01) without significantly affecting Km. Likewise, TNF-alpha decreased the thyrotropin-induced 5'D-I by decreasing Vmax (p < 0.05) but not Km. The effect of TNF-alpha on thyrotropin-induced 5'D-I in FRTL-5 cells is probably mediated through post-thyrotropin-induced generation of cyclic adenosine monophosphate (cAMP) because TNF-alpha inhibited both dibutyryl cAMP (p < 0.001) and forskolin (p < 0.001)-induced increases in 5'D-I without affecting cAMP generation stimulated by thyrotropin. In conclusion, we have demonstrated that TNF-alpha inhibits thyrotropin-induced 5'D-I activity in FRTL-5 cells by pathways distal to the generation of cAMP and that TNF-alpha may play a role in the modulation of the production of triiodothyronine by the thyroid gland. (ABSTRACT TRUNCATED AT 250 WORDS)

Lidocaine suppresses the sodium current in Euhadra neurons which is mediated by cAMP-dependent protein phosphorylation

The action of a local anesthetic, lidocaine, in association with the cyclic AMP (cAMP)-mediated intracellular biochemical process, was examined in identified Euhadra neurons. Lidocaine dose-dependently inhibited the inward current which was elicited by dibutyryl cAMP (db-cAMP) and isobutylmethylxanthine (IBMX). This inhibitory effect was transiently reversed by the intracellular injection of a catalytic subunit of a cAMP-dependent protein kinase. The inward current elicited by db-cAMP and IBMX was abolished by Na(+)-free saline but not by Ca(2+)-free saline. The data suggest that lidocaine is not acting directly on the Na+ channel, but acts at a level proximal to the catalytic subunit of cAMP-dependent protein kinase.

Lithium stimulates the first meiotic division in mouse oocytes

Cumulus enclosed oocytes, cumulus enclosed oocytes denuded of their cumulus and cumulus free oocytes from 21 day old unstimulated mice were cultured for 18 hours in control medium supplemented with lithium chloride, dbcAMP and forskolin at various concentrations. In control medium 66% of the cumulus enclosed oocytes, 93% of the denuded oocytes, and 94% of the cumulus free oocytes resumed meiosis (germinal vesicle breakdown), whereas the levels of polar body formation were 27%, 12% and 39%, respectively. In the presence of lithium significantly more cumulus enclosed oocytes and cumulus free oocytes resumed meiosis and formed a polar body, whereas lithium had no effect on the denuded oocytes. Forskolin and dbcAMP stimulated resumption of meiosis and cumulus expansion in the cumulus enclosed oocytes and inhibited resumption of meiosis in the cumulus free oocytes. Lithium more or less eliminated this inhibitory effect of both forskolin and dbcAMP in the cumulus free oocytes. The results indicate (i) that activation of the cAMP second messenger path in the cumulus cells induces them to synthesize a meiosis inducing substance(s) which stimulates the oocyte to resume meiosis, and (ii) that other second messenger systems than the cAMP pathway, e.g. the phosphatidylinositol cycle, are involved in resumption of meiosis and polar body formation. We conclude that lithium enhances the capability of mouse oocytes for resumption of meiosis and polar body formation.

General inhibition by transforming growth factor beta 1 of thyrotropin and cAMP responses in human thyroid cells in primary culture

Transforming growth factor beta 1 (TGF beta 1) mRNA has previously been identified in human thyroid cells and this agent has been shown to inhibit DNA synthesis in thyroid cells of some other species. In normal human thyroid cells in primary culture, TGF beta 1 inhibited inconstantly the low basal DNA synthesis and strongly the stimulation of DNA synthesis by epidermal growth factor (EGF) and serum, and by thyroid-stimulating hormone (TSH) acting through cAMP. This inhibition, by TGF beta 1, of the TSH and cAMP-dependent DNA synthesis was associated with an inhibition of PCNA (proliferating cell nuclear antigen) synthesis. TGF beta 1 almost completely abolished the cAMP induced stimulation of iodide uptake and thyroperoxidase synthesis. It thus, like EGF, also acts as a dedifferentiating agent. Investigation of the pattern of protein synthesis by two-dimensional gel electrophoresis revealed that while TGF beta 1, by itself, increased the synthesis of only one protein, a tropomyosin isoform, it inhibited most of the effects of cAMP on protein synthesis (35 out of 45 cAMP-regulated proteins were affected). It also reversed the effect of cAMP on the morphology of the thyrocytes. The fact that TGF beta 1 did not affect the increase in cAMP provoked by TSH in human thyroid cells while inhibiting most of the effects of dibutyryl cAMP in these cells suggests an action at a step distal to cAMP generation.(ABSTRACT TRUNCATED AT 250 WORDS)

Oligodendrocyte differentiation and progenitor cell proliferation are independently regulated by cyclic AMP

Oligodendrocytes, the glial cells specialized to synthesize myelin in the central nervous system, differentiate in primary rat brain cell cultures on a schedule similar to that observed in vivo. The schedule of oligodendrocyte differentiation and the rate of oligodendroglial progenitor cell proliferation in vitro are both modulated by 3',5'-cyclic AMP (cAMP). A 24-hour exposure to 1 mM N6,2'O-dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP) induced a wave of oligodendrocyte differentiation but inhibited proliferation of oligodendroglial progenitors, and reduced by 30-fold the proliferation of progenitors in response to platelet-derived growth factor (PDGF). When cells were grown in the presence of maximally stimulating concentrations of PDGF, the inhibitory effect of cAMP on progenitor cell proliferation was abolished while the stimulatory effect of cAMP on oligodendrocyte differentiation remained, demonstrating that these two cAMP-regulated events are independent.

Effects of drugs acting on Cl−HCO3− and Na+H+ exchangers on acid secretion in the rat gastric mucosa sheet preparation

The effects of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), an inhibitor of the Cl(-)-HCO3- exchanger, and amiloride, an inhibitor of the Na(+)-H+ exchanger, on gastric acid secretion under basal conditions and after stimulation with bethanechol or dibutyryl cyclic AMP were studied in rat gastric mucosa sheet preparation. DIDS inhibited bethanechol-induced acid secretion in a dose-dependent manner, but amiloride had no effect. The stimulation of acid secretion by dibutyryl cyclic AMP plus 3-isobutyl-1-methylxanthine was also inhibited by DIDs, but not by amiloride. DIDS did not reduce basal acid secretion, and neither did amiloride. These results suggest that the Cl(-)-HCO3-exchanger in the basolateral membrane of the parietal cell plays an important role in stimulated gastric acid secretion and that the Na(+)-H+ exchanger is less important. In addition, these data show that DIDS inhibits stimulated gastric acid secretion irrespective of the secretagogue, but not basal gastric acid secretion.

Signal transduction pathways leading to the production of IL-8 by human monocytes are differentially regulated by dexamethasone

Previous studies have shown that IL-8 gene expression is enhanced by various stimuli, which induce different signal transduction pathways. A lipopolysaccharide (LPS)-induced pathway has been reported to be inhibited by glucocorticoids in monocytes. We have now examined the effect of dexamethasone on the LPS-induced and other signal transduction pathways leading to the production of IL-8 by human monocytes. Dexamethasone inhibited the production of IL-8 stimulated with a cyclic adenosine monophosphate analog or LPS. In contrast, dexamethasone had no significant effect on a phorbol ester (PMA)-stimulated IL-8 production. These results suggest that the signal transduction pathways leading to the production of IL-8 by human monocytes are differentially regulated by dexamethasone.

Effects of glucagon and an analogue of cAMP on tyrosine aminotransferase in isolated chick embryo hepatocytes

Hepatocytes were isolated from 17-day-old chick embryos by the use of collagenase. Glucagon and dibutyryl cAMP (bt2cAMP), individually or in combination, stimulated tyrosine aminotransferase (TAT) activity and synthesis in the isolated hepatocytes; maximal stimulation occurred 4 h after exposure of hepatocytes to the inducers. The stimulatory effects produced by glucagon and bt2cAMP were abolished by treatment of hepatocytes with cordycepin or cycloheximide. The effects of the hormone and the cyclic nucleotide were not additive. The induction of the enzyme by glucagon suggests a physiological role for the hormone in the expression of TAT activity during chick embryonic development.

Cyclic AMP modulation of human B cell proliferative responses: role of cAMP-dependent protein kinases in enhancing B cell responses to phorbol diesters and ionomycin

The ability of cyclic AMP (cAMP) to modulate human B cell proliferative responses and the possible role of cAMP-dependent kinases (PKA) in cAMP modulation of proliferative responses were investigated. The addition of dibutyl cAMP (Bt2 cAMP) or the cAMP-elevating agent forskolin to B cells stimulated by crosslinking surface immunoglobulins (sIg) resulted in a concentration-dependent inhibition of proliferative responses. By contrast, Bt2 cAMP or forskolin enhanced the proliferative responses of B cells after direct stimulation by phorbol myristate acetate (PMA) and the calcium ionophore ionomycin. The inhibition and enhancement of B cell proliferative responses by Bt2 cAMP were observed at different incubation intervals and were not due to temporal shifts of optimal responses. Also, Bt2 cAMP caused only small changes in B cell RNA synthesis compared to modulation of proliferative responses. Exposure of B cells to Bt2 cAMP rapidly activated PKA. Blocking Bt2 cAMP activation of PKA with the kinase inhibitor HA1004 prevented Bt2 cAMP enhancement of B cell responses after direct stimulation by PMA and ionomycin. In reciprocal experiments, the kinase inhibitor H7 resulted in some inhibition of PKC activation but did not inhibit Bt2 cAMP activation of PKA or Bt2 cAMP enhancement of proliferative responses. Other experiments demonstrated that B cells treated with Bt2 cAMP had selective increases in the de novo phosphorylations of two endogenous substrates which reflected PKA activation. Furthermore, concentrations of HA1004 or H8 which inhibited Bt2 cAMP enhancement of proliferative responses also inhibited PKA phosphorylations of these substrates whereas H7 did not. Thus, elevations of cAMP can enhance or inhibit human B cell proliferative responses to different stimuli and the activation of PKA is important for cAMP enhancement of certain responses.

Regulation of formyl peptide receptor expression and its mRNA levels during differentiation of HL-60 cells

When incubated with N6-2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (dbcAMP), HL-60 cells expressed formyl peptide receptor (FPR) (as assessed by ligand binding) and FPR transcripts in a time- and concentration-dependent fashion. Experiments using dbcAMP analogs modified at either the C-6 or C-8 position indicated that the process was mediated by a protein kinase A type I, and protein kinase A type I activity was isolated from undifferentiated HL-60 cells by DEAE-Sephacel chromatography. Forskolin mimicked the effects of dbcAMP. Forskolin and dbcAMP-dependent expression of FPR and FPR transcript was inhibited by staurosporine. Retinoic acid (but not retinal or retinol) was capable of inhibiting dbcAMP-dependent expression of FPR mRNA half-life. Dexamethasone enhanced the effects of dbcAMP and blocked the inhibitory effect of retinoic acid on expression of FPR and FPR transcripts. Phorbol 12-myristate 13-acetate (PMA) alone (1.5-15 nM) failed to induce HL-60 to express FPR and FPR transcripts. Low concentrations (1.5 nM) of PMA enhanced the ability of dbcAMP to induce HL-60 cells to express FPR and FPR transcript, whereas high (15 nM) concentrations of PMA inhibited dbcAMP effects. These results indicate that expression of FPR and FPR transcripts by HL-60 cells can be up- and down-regulated by agents that induce HL-60 cells to differentiate and that a "cross-talk" effect exists between protein kinase A and protein kinase C that modulates FPR gene transcription (and receptor expression) by these cells.

Studies on the mechanism by which galanin inhibits insulin secretion in islets

The mechanism by which the neuropeptide galanin inhibits insulin secretion in normal islets is not yet fully elucidated. Isolated rat or mouse islets were perifused in a medium containing glucose (8.3 mM) and galanin (10(-6) M) or the sulphonamide diazoxide (400 microM). In rat islets prelabelled with 86Rb+ or 45Ca2+, galanin inhibited glucose-induced insulin secretion at the same time as increasing 86Rb+ efflux and reducing 45Ca2+ efflux. The diazoxide-induced 86Rb+ efflux was not affected by galanin, indicating that galanin activates ATP-regulated K+ channels in rat islets. In mouse islets prelabelled with 86Rb+, galanin (10(-6) M) decreased 86Rb+ efflux. These results suggest that galanin inhibits insulin release in isolated islets by increasing K+ and decreasing Ca2+ permeability. The increased K+ permeability, which is probably regulated differently in rat and mouse islets, is followed by a reduced Ca2+ influx, possibly through voltage-dependent Ca2+ channels. In addition, during a 60-min incubation with isolated islets, galanin inhibited insulin secretion induced by forskolin (1 microM), dibutyryl cyclic AMP (1 mM), or TPA (12-O-tetradecanoylphorbol-13-acetate; 0.1 microM). Galanin also reduced the content of cyclic AMP in islets stimulated by 16.7 mM glucose. We therefore conclude that the inhibitory action of galanin on insulin secretion in normal islets includes increasing K+ permeability as well as interference with the activation of adenylate cyclase and the activity of protein kinase C and cyclic AMP.

Effects of the enantiomers of lansoprazole (AG-1749) on (H+ + K+)-ATPase activity in canine gastric microsomes and acid formation in isolated canine parietal cells

The effects of the enantiomers of 2-[[[3-methyl-4-(2,2,2-trifluoroethoxy)-2-pyridyl]methyl]-sulfinyl ]- 1H-benzimidazole (lansoprazole, AG-1749) on acid formation in isolated canine parietal cells and (H+ + K+)-ATPase activity in canine gastric microsomes were investigated. Both the (+)-and the (-)-enantiomer of lansoprazole inhibited the acid formation stimulated by dibutyryl cyclic AMP (db-cAMP) in isolated canine parietal cells in a concentration-dependent manner with IC50 values of 59 and 82 nM, respectively. The enantiomers showed concentration-dependent inhibition of (H+ + K+)-ATPase with IC50 values of 4.2 and 5.2 microM, respectively. On the other hand, the IC50 values of lansoprazole for db-cAMP-stimulated acid formation and (H+ + K+)-ATPase were 59 nM and 2.1 microM, respectively. These results suggest that the two enantiomers of lansoprazole have antisecretory action due to inhibition of (H+ + K+)-ATPase.

D-(-)-beta-hydroxybutyrate inhibits catecholamine-stimulated lipolysis and decreases beta-adrenoceptors' affinity in human fat cells but not in lymphomonocytes

The effect of D-(-)-beta-hydroxybutyrate, at concentrations commonly achieved during ketoacidosis in humans (10 mmol/l), on human fat cell lipolysis in vitro was the aim of this study. The basal lipolysis was not modified and beta-hydroxybutyrate did not affect forskolin- or dibutyryl-cAMP-stimulated glycerol release, whereas it markedly inhibited isoproterenol-stimulated lipolysis. In membranes of intact adipocytes exposed to D-(-)-beta-hydroxybutyrate for 1 h, we found a decrease in beta-adrenoceptor affinity in saturation experiments and a shift to the right of the isoproterenol-mediated radioligand [( 125I]-cyanopindolol) displacement curve. These findings suggest that beta-hydroxybutyrate inhibits catecholamine-stimulated lipolysis by decreasing beta-adrenoceptor affinity. No effect of beta-hydroxybutyrate was found on beta-adrenoceptor binding of intact mononuclear cells of peripheral blood. In conclusion, the beta-adrenoceptor affinity lowering effect of beta-hydroxybutyrate is seemingly specific to human fat cells and might represent a feed-back mechanism that prevents an uncontrolled breakdown of triglycerides and indirectly regulates its own production rate.

Direct inhibitory action of glucocorticoid on glycoconjugate secretion from airway submucosal glands

The precise mechanism by which glucocorticoids inhibit airway mucus secretion is still unknown. To study directly the effect of glucocorticoid on submucosal gland secretion, we examined the effects of dexamethasone on the precursor uptake, biosynthesis, and release of mucus glycoprotein in isolated feline tracheal submucosal glands. Mucus glycoprotein release from isolated glands was estimated by measuring [3H]glucosamine-labeled trichloroacetic acid (TCA)-precipitable glycoconjugates secreted into the medium. Released glycoconjugate per hour per dry weight of gland tissue was less than 7% of the total intracellular content, where intracellular content is defined as total 3H activity in the dissolved gland tissue. Treatment with 10(-9) to 10(-5) M dexamethasone for 24 to 72 h significantly reduced basal glycoconjugate secretion up to 22% of control (a 78% decrease) in a dose-dependent fashion, whereas the total intracellular 3H content was reduced to 70% of control (a 30% decrease) with no statistically significant differences from controls. The ratio of released glycoconjugates to the total intracellular content decreased significantly to 31% of control (a 69% decrease) after the treatment with 10(-10) to 10(-5) M dexamethasone. Further, ratio of radioactivity of TCA-precipitable glycoconjugates in the dissolved gland tissue to the total intracellular 3H content increased from 40% in nontreated controls to 46% after the treatment with dexamethasone (10(-5) M). Dexamethasone also inhibited the glycoconjugate secretion stimulated by dibutyryl cyclic AMP and alpha- and beta-adrenergic agonists. Simultaneously, the ratio of released to total intracellular content also decreased significantly after dexamethasone treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible mechanism for the inhibition of acid formation by the proton pump inhibitor AG-1749 in isolated canine parietal cells

We have reported previously that 2-[[[3-methyl-4-(2,2,2-trifluorethoxy)-2-pyridyl]methyl] sulfinil]- 1H-benzimidazole (AG-1749) inhibits (H+ + K+)-adenosine triphosphatase after being transformed into its cyclic sulfenamide form (AG-2000) or disulfide form (AG-1812) under acidic conditions. In this study, mechanisms related to the inhibition of acid formation by AG-1749 were investigated in isolated canine parietal cells. AG-1749 suppressed the acid formation stimulated by histamine, carbachol or dibutyryl cyclic AMP with IC50 values of approximately 0.09 microM: AG-1749 being twice as potent as omeprazole. The inhibitory effect of AG-1749 was antagonized by dithiothreitol (1 mM). 2-Cyclo-hexen-1-one (3 mM) decreased cytosolic glutathione to less than 10% of control value, and caused a 3-fold increase in the inhibitory effect of AG-1749. Glutathione, however, when added exogenously, did not affect the action of AG-1749. The inhibition was reversed by removing AG-1749 from the medium or by adding dithiothreitol (1 mM). The reversal of inhibition by these two procedures was hardly affected by puromycin (100 microM) or cycloheximide (300 microM) but significantly prevented by 2-cyclo-hexen-1-one (1 mM). Exogenously added AG-2000 (10 microM) or AG-1812 (5 microM), active forms of AG-1749, did not inhibit acid formation.(ABSTRACT TRUNCATED AT 250 WORDS)

[Effect of cyproterone acetate on aromatase activity in cultured human genital skin fibroblasts: intracellular control of aromatase activity]

Cyproterone acetate(CA), a well-known competitive antiandrogen, has been used for the treatment of precocious puberty, prostatic adenocarcinoma, hirsutism and hypersexuality. However, there have been some reports of troublesome gynecomastia developing during the use of this drug. It was, therefore, of interest to investigate the effect of CA on peripheral aromatization, since it is the major source of circulating estrogens in men. Our recent studies of aromatase activity in human skin fibroblasts demonstrated that the skin is an important site of extraglandular aromatase activity in men and suggested that these cells might provide a valuable new system in which to study the enzyme. Estrogen formation was assayed by the [3H]H2O technique, after 3h incubation of the cells with androstenedione. The initial experiment was designed to test the effect of CA (10(-8) to 10(-5) M) on baseline aromatase activity during a 12h preincubation in the presence of fetal bovine serum (FBS). Baseline aromatase activity was not affected by the presence of CA, whereas medroxyprogesterone acetate, a similar synthetic progestogen, induced a 2-fold stimulation of aromatase activity at a concentration of 10(-5) M. In cells preincubated with dexamethasone (DEX) in the presence of FBS, aromatase activity was stimulated markedly. When the cells were preincubated in the medium containing FBS with DEX (2.5 X 10(-7) M) in the presence of CA (10(-7) to 10(-4) M), DEX-stimulated levels of aromatase activity were inhibited by CA in a dose-dependent fashion. A competitive binding assay using [3H]DEX, showed that CA was able to compete with DEX for glucocorticoid receptor and the relative binding affinity of CA was approximately 50 times less than DEX. This suggested that the inhibitory effect of CA was due to competition with DEX for receptor binding. Aromatase activity was also stimulated by (Bu)2cAMP (1mM) in the absence of FBS. The stimulatory effect of (Bu)2 cAMP was maximal after 12-24h of preincubation, and this level was maintained for 60h. Similar to the DEX stimulation, stimulation of aromatase activity by (Bu)2cAMP required both RNA and protein synthesis, since the stimulatory effect of (Bu)2cAMP was abolished by co-preincubation with cycloheximide or actinomycin D. When CA was present during either the 12h preincubation or assay incubation, no difference was found in the (Bu)2cAMP-stimulated levels of aromatase activity. On the other hand, the non-aromatizable androgen dihydrotestosterone (DHT) (10(-8) to 10(-6) M) inhibited the stimulation of aromatase activity by (Bu)2cAMP in a dose-dependent fashion.(ABSTRACT TRUNCATED AT 400 WORDS)

Phorbol ester inhibits luteinizing hormone-, forskolin-, and dibutyryl cyclic AMP-induced progesterone production in chicken granulosa cells

The possible role of protein kinase C in avian granulosa cell steroidogenesis was studied in vitro by examining the effect of tumor-promoting phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) on progesterone synthesis in chicken granulosa cells in short-term (3h) incubations. TPA (1-100 nM) caused a marginal but nonsignificant increase in progesterone production in granulosa cells isolated from the largest preovulatory follicle. When incubated in combination with luteinizing hormone (5-100 ng/mL), TPA suppressed the stimulatory effects of submaximally and maximally effective doses of the gonadotropin in a concentration-related manner. Similarly, the phorbol ester inhibited the steroidogenic responses to forskolin and dibutyryl cyclic AMP. By comparison, TPA had no appreciable effect on the metabolism of exogenous pregnenolone substrate to progesterone. Our data indicate that the tumor-promoting phorbol ester influences steroidogenic steps distal to cyclic AMP generation but at or before pregnenolone formation, and that protein kinase C may be a negative regulator of steroid biosynthesis in chicken granulosa cells.

[The study of direct effect of methimazole on thymidine incorporation in FRTL-5 cells]

During the course of treatment of Graves' disease with the anti-thyroid drug, methimazole (MMI), a decrease in a patient's goiter size is sometimes observed. Using rat thyroid cell strain, FRTL-5, the direct effect of MMI on thyroid cell growth was investigated. FRTL-5 cells (2 X 10(5)) were cultured for 48 hours with TSH, (Bu)2 cAMP or forskolin in the presence of [3H]-thymidine. All three stimulators increased cell growth, expressed as [3H]-thymidine incorporation into DNA in a dose-dependent fashion. When FRTL-5 cells were cultured for 48 hours in the presence of MMI at 10(-6)-10(-3) M with these stimulators (TSH 250 microU/ml, (Bu)2 cAMP 10(-3) M, forskolin 10(-5) M), [3H]-thymidine incorporation was suppressed in dose-dependent fashions (MMI 10(-5) M-10(-3) M). From the present study, it is suggested that methimazole directly modulates thyroid cell growth induced by thyroid growth stimulators which are involved in adenylate cyclase-cyclic AMP system and that the site of its action exists beyond cAMP production.

Phorbol 12-myristate 13-acetate prevents isoproterenol-induced morphological change in cultured vascular smooth muscle cells

The effect of phorbol 12-myristate 13-acetate (PMA) on isoproterenol (ISO)- and dibutyryl cAMP (dBcAMP)-induced morphological change and cytoskeletal reorganization was studied in cultured vascular smooth muscle cells (VSMC) using the fluorescence staining of actin and microtubules. The treatment of VSMC with 1.0 microM of ISO or with 1.0 mM of dBcAMP for 90 min induced the disruption of actin-containing stress fibers followed by cytoplasmic arborization. The addition of 100 or 10 nM of PMA prevented both the destruction of actin fibers and cell arborization induced either by ISO or by dBcAMP. However, PMA rather enhanced cAMP production stimulated by ISO. 1-Oleoyl-2-acetyl-sn-glycerol (100 micrograms/ml) mimicked this inhibitory effect of PMA whereas 4 alpha-phorbol 12,13-didecanoate (100 nM) failed to block the arborization. These results indicated that the inhibition of arborization by PMA was mediated through the activation of protein kinase C. Colchicine at 5.0 microM also had an inhibitory effect on ISO- and dBcAMP-induced cell arborization. However, immunofluorescence studies revealed that colchicine but not PMA elicited the reorganization of microtubules, suggesting that the effect of PMA was mediated through a mechanism different from that of colchicine. These observations indicated that the morphology of VSMC was regulated through the alteration of cytoskeletal organization induced by cAMP-mediated and by protein kinase C-dependent systems.

K-252a, a potent protein kinase inhibitor, blocks nerve growth factor-induced neurite outgrowth and changes in the phosphorylation of proteins in PC12h cells

Nerve growth factor (NGF) promotes neuronal differentiation of PC12 pheochromocytoma cells. One of the most prominent and distinguishing features of neuronal differentiation is neurite outgrowth. The mechanism by which NGF causes the cells to elaborate neurites is unknown. This study shows that K-252a, a potent protein kinase inhibitor, blocks NGF-induced neurite outgrowth and the changes in protein phosphorylation elicited by NGF. In the experiment with intact cells phosphorylated with 32P-orthophosphoric acid, an exposure of PC12h cells to NGF (50 ng/ml) caused an increase in the phosphorylation of tyrosine hydroxylase and a 35,000-D protein and a decrease in a 36,500-D protein. Pretreatment of PC12h cells with K-252a (100 nM) inhibited the effects of NGF on the phosphorylation of these three proteins. In the phosphorylation of cell-free extracts with [gamma-32P] ATP, treatment of PC12h cells with NGF (50 ng/ml) caused a decrease in the phosphorylation of Nsp100. Pretreatment of the cells with K-252a (30 nM) almost completely blocked the NGF effect on the phosphorylation of Nsp100 elicited by subsequent treatment of the cells with NGF. Treatment of PC12h cells with NGF promoted outgrowth of neurites. The addition of K-252a (100 nM) into the culture almost completely blocked the generation of neurites elicited by NGF. Earlier studies demonstrated that NGF-induced neurite outgrowth in PC12 cells involves at least two components: the first of these is transcription-dependent and the second is transcription-independent. To determine the component on which K-252a acts, experiments were carried out on NGF-induced priming or regeneration of neurites. When K-252a was present in the priming step, NGF induced only actinomycin D-sensitive neurites, showing that K-252a interferes with the transcription-dependent actions of NGF. When already primed cells were treated with NGF, actinomycin D-resistant neurites were formed and these were blocked by K-252a, showing that the inhibitor interferes with the transcription-independent actions of NGF as well. Although the exact mechanism of inhibition of NGF-promoted neurite formation by K-252a is unknown, the most probable explanation is that both transcription-dependent and -independent components are involved in at least one step of the activation of some specific protein kinase(s) that can be suppressed by K-252a.

Catecholamine inhibition of Ca2+-induced insulin secretion from electrically permeabilised islets of Langerhans

Noradrenaline (1-10 microM) inhibited Ca2+-induced insulin secretion from electrically permeabilised islets of Langerhans with an efficacy similar to that for inhibition of glucose-induced insulin secretion from intact islets. The inhibition of insulin secretion from permeabilised islets was blocked by the alpha 2-adrenoreceptor antagonist, yohimbine. Adenosine 3',5'-cyclic monophosphate (cAMP) did not relieve the noradrenaline inhibition of Ca2+-induced secretion from the permeabilised islets, although noradrenaline did not affect the secretory responses to cAMP at substimulatory (50 nM) concentrations of Ca2+. These results suggest that catecholamines do not inhibit insulin secretion solely by reducing B-cell adenylate cyclase activity, and imply that one site of action of noradrenaline is at a late stage in the secretory process.

Modulation of stimulatory action of follicle stimulating hormone (FSH) and inhibitory action of epidermal growth factor (EGF) on aromatase activity in Sertoli cells by calcium

Aromatization of testosterone by cultured Sertoli cells isolated from immature rats was stimulated more than 7-fold by follicle stimulating hormone (FSH) or dcAMP. The effects of FSH and dcAMP could be partly inhibited by epidermal growth factor (EGF) in a dose-dependent manner (ID500.5 nM). The phorbol ester 4 beta-phorbol-12-myristate-13-acetate (PMA) could also inhibit aromatase activity in a fashion similar to EGF. When 3 mM EGTA was present in the culture medium, the inhibitory effect of EGF was abolished but the stimulatory effect of FSH or dcAMP was magnified. These results suggest that EGF exerts a negative control on aromatase via calcium and protein kinase C. The abolishment of the inhibitory effect of EGF and the enhancement of the stimulatory effect of FSH or dcAMP by a calcium deficiency may be an indication that growth factors produced by Sertoli cells negatively controls FSH-induced responses in an autocrine fashion.

Effects of sodium ions and monensin on amylase secretion from rat parotid cells

The role of sodium ions in amylase secretion from rat parotid cells was studied using various Na+-free media and monensin. In a sucrose medium, amylase secretion was not stimulated by isoproterenol but was significantly stimulated by dibutyryl cAMP. In choline chloride and LiCl media, both isoproterenol and dibutyryl cAMP clearly evoked amylase release. Monensin itself elicited amylase secretion slightly, but significantly inhibited the secretion stimulated by isoproterenol or dibutyryl cAMP. The inhibitory effect of monensin was detectable even in choline chloride, LiCl and KCl media. These results indicate that sodium ions are not essential for amylase secretion from rat parotid cells and that the inhibitory effect of monensin is independent of influx of sodium ions or efflux of potassium ions.