Ergovaline binding and activation of D2 dopamine receptors in GH4ZR7 cells

Department of Animal Sciences, University of Missouri, Columbia 65201, USA.
Journal of Animal Science (Impact Factor: 2.11). 06/1995; 73(5):1396-400.
Source: PubMed

ABSTRACT Ergovaline inhibition of radioligand binding to the D2 dopamine receptor and ergot alkaloid inhibition of vasoactive intestinal peptide (VIP)-stimulated cyclic AMP production in GH4ZR7 cells, stably transfected with a rat D2 dopamine receptor, were evaluated. Ergovaline inhibition of the binding of the D2-specific radioligand, [3H]YM-09151-2, exhibited a KI (inhibition constant) of 6.9 +/- 2.6 nM, whereas dopamine was much less potent (370 +/- 160 nM). Ergot alkaloids were also effective in inhibiting VIP-stimulated cyclic AMP production, with EC50 values for ergovaline, ergonovine, alpha-ergocryptine, ergotamine, and dopamine of 8 +/- 2, 47 +/- 2, 28 +/- 2, 2 +/- 1, and 8 +/- 1 nM, respectively. Inhibition of cyclic AMP production by ergovaline was blocked by the dopamine receptor antagonist, (-)-sulpiride (IC50, 300 +/- 150 nM). Our results indicate that ergot compounds, especially ergovaline, bind to D2 dopamine receptors and elicit second messenger responses similar to that of dopamine. These findings suggest that some of the deleterious effects of consumption of endophyte-infected tall fescue, which contains several ergot alkaloids including ergovaline, may be due to D2 dopamine receptor activation.

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Available from: Monty S Kerley, Jul 31, 2014
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    • "If dopamine receptor blockade is involved in growth promotion by PhAPs, we predicted 1) that other dopamine receptor antagonists would stimulate growth, and 2) that dopamine receptor agonists might interfere with the growthpromoting ability of PhAPs. However, we found that neither the D1 antagonist SCH-23390 nor the D2 antagonist sulpiride were able to promote neurite growth of hippocampal neurons on CSPG substrates (Figure 5A, B) despite using concentrations at and well above their known IC 50 values (Iorio et al., 1983; Larson et al., 1995). The D1 agonist SKF-38393 inhibited growth when provided alone (Figure 5C and Supplemental Figure 3), and in parallel, impaired the ability of trifluoperazine to promote growth. "
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    Molecular and Cellular Neuroscience 05/2012; 50(2):125-35. DOI:10.1016/j.mcn.2012.04.008 · 3.84 Impact Factor
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    • "2005a, b; Looper et al. 2009). Pharmaceutical research suggests that ergot alkaloids can have agonistic interactions with cell membrane receptors, specifically: dopaminergic receptors (Markstein 1981; Badia et al. 1988; Larson et al. 1995), alpha-adrenergic receptors (Roquebert et al. 1984, 1985; Badia et al. 1988), and serotonergic receptors (Kalkman and Schneider 1996; Silberstein 1997; Schoning et al. 2001). Those results suggest that membrane receptormediated activities represent one possible mechanism for the observed biological effects of ergot alkaloids. "
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    ABSTRACT: There is evidence that ergot alkaloids can directly interact with mammalian spermatozoa affecting sperm functions. Ergot alkaloids exert their toxic or pharmaceutical effects through membrane receptor-mediated activities. This study investigated the signaling pathways involved in the in vitro inhibitory effects of both ergotamine (ET) and dihydroergotamine (DEHT) on the relative motility of bovine spermatozoa using specific inhibitors. Motile bovine spermatozoa were prepared using a Percoll gradient and incubated with ergot alkaloids with and without signaling pathway inhibitors. Co-incubation of ET or DHET with 100μM prazosin (alpha 1-adrenergic receptor inhibitor) decreased (p < 0.05) relative motility of spermatozoa when compared with controls. In addition, preincubation of spermatozoa with 10 or 20μM prazosin and DHET also reduced (p < 0.05) the number of motile spermatozoa. Relative sperm motility (motility of treated spermatozoa normalized to control sperm motility) was increased (p < 0.05) when co-incubations included ET and yohimbine (alpha 2-adrenergic receptor inhibitor); conversely, co-incubation of yohimbine (100μM) and DHET decreased (p < 0.05) the percentage of motile spermatozoa when compared with controls. Pertussis toxin and cholera toxin (effectors of inhibitory and stimulatory G-proteins, respectively) altered (p < 0.05) relative sperm motility in a concentration dependent manner; however, co-incubation of pertussis or cholera toxin with ergot alkaloids had no interactive (p = 0.83) effects on the relative motility of spermatozoa. Co-incubation of Rp-cAMP (a membrane-permeable cAMP inhibitor) with 50μM DHET had no effect (p > 0.05) on relative sperm motility; whereas, the co-incubation of 22.4 or 44.8μM Rp-cAMP with 50μM ET increased (p < 0.05) the percentage of motile spermatozoa when compared with 0 or 224μM Rp-cAMP (49%, 65%, 59%, and 54%, respectively, for 0, 22.4, 44.8, and 224μM of Rp-cAMP. An interaction between BAPTA-AM (a chelator of intracellular calcium) and alkaloids also impacted (p < 0.05) relative sperm motility. Generally, co-incubating spermatozoa with BAPTA-AM and ET increased the percentage of motile spermatozoa; however, co-incubation with DHET decreased relative sperm motility except with 41μM BAPTA-AM. Collectively, these observations suggest that ET and DHET decreased the percentage of motile bovine spermatozoa via alpha adrenergic receptors. However, the second messenger systems involved with ergot alkaloid inhibition of relative motility of bovine spermatozoa remain to be elucidated.
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    ABSTRACT: Symbiotic interactions of C3 grasses with fungal endo- phytes, Epichloe species and their asexual relatives Neoty- pkodium, often provide the grass hosts with major fitness enhancements (for review, see Siegel and Bush (1994)). The endophytes protect host plants from both biotic and abiotic environmental stresses. Documented enhancements to host fitness include greater resistance to mammalian and insect herbivores, pathogens, and nematodes, as well as increased drought tolerance and competitiveness. Our understand- ing of the mechanisms responsible for a11 of these effects on host fitness is not well established. However, the antiher- bivore fitness enhancements are largely attributable to the accumulation of four groups of alkaloids: lolines, peram- ine, ergot alkaloids, and lolitrems. The objective of this Update is to present the current status of knowledge on these alkaloids, focusing on their biological activities and the potential for genetically manipulating their expression in grasslendophyte symbiota.
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