Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0043167 (pertussis)
 19,595 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The present study in purified rat Leydig cells shows that arachidonic acid may act as an intratesticular factor regulating LH-mediated testicular steroidogenesis. Arachidonic acid decreased, in a dose-dependent manner, the LH-stimulated cAMP and testosterone levels, over 2 h incubation. Incubation of Leydig cells with arachidonic acid did not modify 125I-hCG binding to the cells as compared to control, showing that the action of arachidonic acid is not related to a decrease of hCG binding to the cells. Forskolin-stimulated cAMP and testosterone production were inhibited by 51.65 and 70.9%, respectively, in the presence of arachidonic acid (100 microM), although the ED50 for the diterpene was not changed. When isobutyl-methyl-xanthine was added to the incubation medium, the same percentage of inhibition was found indicating that arachidonic acid inhibition of cAMP production is not due to stimulation of Leydig cell phosphodiesterase activity. Pretreatment of the cells with pertussis toxin, to inactivate Gi, was also without effect on arachidonic acid inhibition of LH-stimulated cAMP production, but pertussis toxin abolished the inhibitory effects of arachidonic acid when adenylate cyclase was stimulated with forskolin. However, arachidonic acid addition resulted in inhibition of LH- and forskolin-stimulated testosterone production, even if the cells were pretreated with pertussis toxin. It can be concluded that: (1) The inhibitory effect of arachidonic acid is neither due to a decrease of hCG binding to Leydig cells nor to a stimulation of cell phosphodiesterase activity; (2) arachidonic acid modulates cAMP production at two different levels, either by activation of Gi protein and by inhibition of Gs protein or adenylate cyclase; (3) the effect of arachidonic acid on steroidogenesis is also beyond cAMP formation.
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PMID:Different sites of action of arachidonic acid on steroidogenesis in rat Leydig cells. 873 5

We have previously shown that the Gi protein-mediated negative modulation of FSH-stimulated cAMP production in neonatal rat Sertoli cells can be blocked by pretreatment with pertussis toxin (PT), an inhibitor of the Gi protein function. In contrast, hCG-stimulated testosterone (T) production by neonatal Leydig cells was insensitive to PT action, despite the demonstration of Gi protein in these cells by immunohistochemistry. We now tested the hypothesis that the missing Gi protein function in neonatal Leydig cells is due to absence of its endogenous activator, adenosine. It was first reconfirmed in dispersed cells of 7-day-old rats that PT preincubation enhanced FSH-stimulated cAMP production (i.e. Sertoli cell function), but had no effect on hCG-stimulated T production (Leydig cell function). The adenosine agonist n-phenylisopropyladenosine (PIA 1 mumol/l), acting through the Gi-protein, attenuated FSH-stimulated cAMP production, and this effect was abolished when the Gi protein was inactivated by preincubation with PT. PIA (1 mumol/l) also inhibited (P < 0.05-0.01) the basal and hCG-stimulated rates of Leydig cell T production, and the PIA effect was abolished by PT preincubation. In conclusion, the present data show that the apparent absence of a functional Gi protein function of neonatal Leydig cells is due to insufficient endogenous levels of the stimulating ligand, adenosine. When the Gi protein function is activated by exogenous adenosine agonist (PIA), the enhancement of hCG-stimulated T production by PT can be demonstrated. At the same time, the endogenous level of adenosine is sufficient for activation of the Gi protein function in Sertoli cells.
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PMID:Lack of endogenous adenosine receptor activation explains the insensitivity of neonatal rat Leydig cells to treatment with pertussis toxin. 880 33

This study examined the potential role of testicular opioids, a pertussis toxin (PT)-sensitive G-protein, and phosphodiesterase in mediating the inhibitory effect of immobilization stress on testicular steroidogenesis in adult rats. The experiments were initiated with enriched preparations of Leydig cells, but the stress effect was not sustained in vitro either as a result of the disruption of the morphology of the testis and/or the time required for Leydig cell isolation. Consequently, testicular fragments from control and stressed (3-hour immobilization) rats were used in these experiments. When fragments from stressed rats were incubated for 2 hours in the absence and presence of human chorionic gonadotropin (hCG) (0.1,1, or 10 mlU), testosterone (T) production in response to 1 and 10 mlU hCG was lower (P < 0.05 and 0.01, respectively) than that from control fragments. Basal T secretion did not differ between stressed and control fragments. Naloxone (1, 10, or 100 mu M), did not alter basal or hCG-stimulated T secretion from control fragments, but it normalized the T response to hCG from stressed fragments. Control fragments also showed a reduced T response (P < 0.05) to hCG in the presence of beta-endorphin (beta-E; 36 nM). Incubation of control fragments with PT (30 ng) did not alter basal or hCG-stimulated T production. However, PT normalized (P < 0.01) hCG-stimulated T secretion from stressed fragments. Methylisobutylxanthine (MIX; 0.125 mM) elevated (P < 0.01) hCG-stimulated T production from control fragments, but hCG-stimulated T secretion from stressed fragments remained subnormal in the presence of the phosphodiesterase inhibitor. The data suggest that acute immobilization stress inhibits gonadotropin-induced T production in adult male rats via a mechanism involving testicular opioids and a PT sensitive G-protein. We found no evidence to suggest that a stress induced increase in the activity of phosphodiesterase was involved in this mechanism.
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PMID:Mechanism of stress-induced attenuation of the testicular response to gonadotropin: possible involvement of testicular opioids, a pertussis toxin-sensitive G-protein, and phosphodiesterase. 883 36

The present investigation was designed to study the direct role of PRL on testicular Leydig cell steroidogenesis, using the MA-10 murine Leydig tumor cell line as a model system. We have previously reported on the presence of specific PRL binding sites in those cells, and we now demonstrate the functionality of those sites and the biological responses induced by the binding of PRL. When cultured MA-10 cells were exposed for 24 h to increasing concentrations of PRL, washed, and then subjected to a 3-h human CG (hCG) stimulation test, a clear dose-dependent biphasic effect of PRL on the steroidogenic response was observed, even though PRL had no effect on MA-10 cell proliferation: at low PRL concentrations (0.1-10 ng/ml), hCG-induced steroidogenesis was stimulated (maximal stimulation by 1 ng/ml PRL being 200-250% of control); at higher concentrations, hCG-induced steroidogenesis was inhibited (60% inhibition was achieved by 1000 ng/ml PRL). When steroidogenesis was induced with various concentrations of cholera toxin, instead of hCG, no effect of the prior exposure to increasing concentrations of PRL was observed, indicating that PRL acts either at the level of the LH/hCG receptor or at some stage proximal to adenylate cyclase. Indeed, further study revealed that 24 or 72 h exposure of MA-10 cells to PRL caused a dose-dependent reduction in hCG binding. Thus, the maximal inhibition of 62% after 72 h with 500 ng/ml PRL, may explain, at least in part, the inhibitory effects of high PRL concentrations on hCG-induced progesterone secretion. Evidence demonstrating possible involvement of a pertussis toxin-(PT-)sensitive G protein in the signal transduction mechanism of PRL receptors is also presented: 1. GTP caused a dose-dependent reduction in affinity (Ka) of PRL binding by its receptors (from Ka = 1.66 +/- 0.2 x 10(9) M(-1) for control MA-10 cell membranes to Ka 3.03 +/- 0.6 x 10(8) M(-1) for membranes incubated with 8 mM GTP). 2. Prior exposure of MA-10 cells to PRL (10 pg/ml) caused a significant reduction in the ability of a 44-kDa membrane protein to undergo PT-induced [32P]ADP-ribosylation. These results demonstrate that MA-10 Leydig cells possess highly specific and biologically functional PRL receptors mediating direct and dose-dependent biphasic effects of PRL on hCG-induced progesterone secretion. These cells thus offer a suitable model to study the mechanism(s) of PRL action and signal transduction of its receptor on a physiologically relevant differentiated function.
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PMID:Prolactin and MA-10 Leydig cell steroidogenesis: biphasic effects of prolactin and signal transduction. 894 Mar 78

Previous studies have suggested that melatonin (MLT) acts directly on rat Leydig cells by modulating androgen production. In the present study, the site of action of MLT was investigated. The binding of 2-[125I]iodomelatonin (125I-MLT; 7-240 pmol/l) to Leydig cell membrane fragments was tested in the presence or absence of guanosine 5'-O-(3-thiotriphosphate) (GTP-gamma-S; 50 mumol/l). Saturation studies and Scatchard analysis revealed the existence of a high-affinity binding site with a Bmax of 46.70 +/- 3.50 fmol/mg protein and a Kd of 88.70 +/- 6.20 pmol/l; treatment with GTP-gamma-S reduced the concentration of 125I-MLT binding sites (Bmax 34.03 +/- 4.50), while increasing the Kd to 106.5 +/- 2.61 pmol/l. Pretreatment of the cells with pertussis toxin (PTX; 10 ng/ml for 16 h) resulted in a decreased binding of 125I-MLT and a lack of effect of GTP-gamma-S. Moreover, the effect of MLT on testosterone secretion induced by LH (30 mIU/ml), forskolin (1 mumol/l) and LHRH (100 nmol/l) was studied after 3-h incubation of cells which had been precultured with or without PTX. The inhibition of testosterone secretion due to MLT administration was eliminated by PTX pretreatment during forskolin and LH, but not during LHRH administration. However, 17-hydroxyprogesterone levels were higher in all groups incubated in the presence of MLT, irrespective of PTX pretreatment. Our data suggest that: (a) MLT receptors are present on the membranes of adult rat Leydig cells; (b) they couple through PTX-sensitive G-protein-coupled binding sites; (c) the mechanism by which MLT blocks 17-20 desmolase enzymatic activity (thus leading to increased 17-hydroxyprogesterone levels), and testosterone secretion during LHRH stimulation is likely to depend on one or more different mechanism(s) of action.
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PMID:Melatonin receptors are present in adult rat Leydig cells and are coupled through a pertussis toxin-sensitive G-protein. 922 28

The aim of the present study was to evaluate the effects of pituitary adenylate cyclase activating polypeptide (PACAP) on testosterone production in isolated adult rat Leydig cells and its possible mechanisms of action. PACAP-38 stimulated testosterone secretion in a dose-dependent manner with a minimal and a maximal efficacious dose of 1.0 nM and 100 nM, respectively. PACAP-27 was without effect on testosterone secretion at any dose tested. Similarly, vasoactive intestinal peptide did not stimulate steroidogenesis nor interfere with PACAP-38 activity, as well as preincubation of Leydig cells with the vasoactive intestinal peptide-antagonist [Lys(1), Pro(2,5), Arg(3,4), Tyr(6)]-vasoactive intestinal peptide. Removal of extracellular Ca2+ did not inhibit the stimulatory effects of PACAP-38 on Leydig cell testosterone production. Neither PACAP-38 nor PACAP-27 modified intracellular free Ca2+ and cAMP levels at any dose tested thus excluding a role for Ca2+ and cAMP in the stimulatory effects of PACAP. PACAP-38 was able to induce a plasma membrane depolarization that was dependent on an influx of Na+ from the extracellular medium as confirmed by the monitoring of intracellular Na+ with the Na+-sensitive fluorescent dye sodium benzofuran isophtalate. When Na+ was removed from the extracellular medium, PACAP-38 did not stimulate testosterone production, demonstrating that Na+ influx through the plasma membrane is strictly related to the stimulatory effects of this peptide. In addition, preincubation of Leydig cells in the presence of pertussis-toxin (500 ng/ml for 5 h) significantly reduced PACAP-38-stimulated effects both on plasma membrane depolarization and testosterone secretion. These results demonstrate that PACAP-38 stimulates testosterone secretion in isolated adult rat Leydig cells through the interaction with a novel PACAP receptor subtype coupled to a pertussis toxin sensitive G protein whose activation induces a Na+-dependent depolarization of the plasma membrane and testosterone production.
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PMID:Pituitary adenylate cyclase activating polypeptide stimulates rat Leydig cell steroidogenesis through a novel transduction pathway. 923 72

Previous results from our group have indicated that arachidonic acid decrease cAMP production through a modification of heterotrimeric G proteins. In the present study, we have characterized the high affinity GTPase activity present in Leydig cell membranes and its regulation by fatty acids. The high-affinity GTPase activity, measured as [gamma32P] GTP hydrolysis rate, was both time and protein concentration dependent. Arachidonic acid elicited a dose-dependent inhibition of enzyme activity with an IC50 = 26.7+/-1.1 microM. The existence of only two double bonds in linoleic acid is reflected by a decrease in its inhibitory activity (IC50 = 34+/-2.3 microM). Saturated fatty acids showed no effect at this level. The kinetic analysis as interpreted by Lineweaver-Burk plots, indicated that 50 microM arachidonic acid had no effect on the apparent affinity for GTP, but resulted in a 40% decreases in the maximal velocity of the reaction. Arachidonic acid modulation of GTPase activity was not attenuated by blocking eicosanoid metabolism with inhibitors of 5'-lipoxygenase, cyclooxygenase, or epoxygenase P-450. The addition of arachidonic acid to pertussis toxin-treated membranes had no effect on the enzyme activity, indicating that arachidonic acid does not modify the GTPase activity present in Galphas protein. However, ADP-ribosylation with cholera toxin followed by arachidonic acid treatment led to a further 40% inhibition when compared with cholera toxin treatment alone. These results allowed us to postulate that arachidonic acid inhibits the GTPase activity of Gi protein family. To further analyze the mechanism of arachidonic acid inhibition of GTPase activity, the effect of arachidonic acid on the [35S]GTPgammaS binding was studied. No effect of this fatty acid on GTP binding was found. Combining our previous results with those found here, we can conclude that arachidonic acid maintains Gi proteins in their active state, which in turn inhibit adenylate cyclase and results in decrease cAMP levels.
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PMID:Modulation of guanosine triphosphatase activity of G proteins by arachidonic acid in rat Leydig cell membranes. 1069 85


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