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Cervia D, Bagnoli P. An update on somatostatin receptor signaling in native systems and new insights on their pathophysiology. Pharmacol Ther 2007; 116:322-41. [PMID: 17719647 DOI: 10.1016/j.pharmthera.2007.06.010] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2007] [Accepted: 06/28/2007] [Indexed: 12/20/2022]
Abstract
The peptide somatostatin (SRIF) has important physiological effects, mostly inhibitory, which have formed the basis for the clinical use of SRIF compounds. SRIF binding to its 5 guanine nucleotide-binding proteins-coupled receptors leads to the modulation of multiple transduction pathways. However, our current understanding of signaling exerted by receptors endogenously expressed in different cells/tissues reflects a rather complicated picture. On the other hand, the complexity of SRIF receptor signaling in pathologies, including pituitary and nervous system diseases, may be studied not only as alternative intervention points for the modulation of SRIF function but also to exploit new chemical space for drug-like molecules.
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Affiliation(s)
- Davide Cervia
- Department of Environmental Sciences, University of Tuscia, largo dell'Università snc, blocco D, 01100 Viterbo, Italy.
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2
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Ramírez JL, Gracia-Navarro F, García-Navarro S, Torronteras R, Malagón MM, Castaño JP. Somatostatin stimulates GH secretion in two porcine somatotrope subpopulations through a cAMP-dependent pathway. Endocrinology 2002; 143:889-97. [PMID: 11861510 DOI: 10.1210/endo.143.3.8685] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Somatostatin (SRIF) inhibits GH release from rat somatotropes by reducing adenylate cyclase (AC) activity and the free cytosolic calcium concentration ([Ca(2+)](i)). In contrast, we have reported that SRIF can stimulate GH release in vitro from pig somatotropes. Specifically, 10(-7) and 10(-15) M SRIF stimulate GH release from a subpopulation of high density (HD) somatotropes isolated by Percoll gradient centrifugation, whereas in low density (LD) somatotropes only 10(-15) M SRIF induces such an effect. To ascertain the signaling pathways underlying this phenomenon, we assessed SRIF effects on second messengers in cultured LD and HD cells by measuring cAMP, IP turnover, and [Ca(2+)](i). Likewise, contribution of the corresponding signaling pathways to SRIF-induced GH release was evaluated by blocking AC, PLC, extracellular Ca(2+) influx, or intracellular Ca(2+) mobilization. Both 10(-7) and 10(-15) M SRIF increased cAMP, IP turnover, and [Ca(2+)](i) in HD cells. Conversely, in LD cells 10(-7) M SRIF reduced [Ca(2+)](i), but did not alter cAMP or IP, and 10(-15) M SRIF was without effect. Interestingly, SRIF-stimulated GH release was abolished in both subpopulations by AC blockade, but not by PLC inhibition. Furthermore, SRIF-induced GH release was not reduced by blockade of extracellular Ca(2+) influx through voltage-sensitive channels or by depletion of thapsigargin-sensitive intracellular Ca(2+) stores. Therefore, SRIF stimulates GH secretion from cultured porcine somatotrope subpopulations through an AC/cAMP pathway-dependent mechanism that is seemingly independent of net increases in IP turnover or [Ca(2+)](i). These novel actions challenge classic views of SRIF as a mere inhibitor for somatotropes and suggest that it may exert a more complex, dual function in the control of porcine GH release, wherein molecular heterogeneity of somatotropes would play a critical role.
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Affiliation(s)
- José L Ramírez
- Department of Cell Biology, Physiology, and Immunology, University of Cordoba, E-14071 Cordoba, Spain
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3
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Pearse D, Mirza A, Leah J. Jun, Fos and Krox in the hippocampus after noxious stimulation: simultaneous-input-dependent expression and nuclear speckling. Brain Res 2001; 894:193-208. [PMID: 11251193 DOI: 10.1016/s0006-8993(01)01993-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Stimulation of sensory C-fibres produces extensive expression of the Fos, Jun and Krox families of inducible transcription factors (ITFs) in many nociceptive CNS areas [28]. In the hippocampus, however, c-Fos is only weakly induced by such stimulation, and expression of the other ITFs has not been studied. Here we examine the effects of single, repeated and simultaneous C-fibre inputs on ITF expressions in the rat hippocampus. A brief, strong electrical stimulation of sciatic nerve C-fibres induced little or no expression of c-Fos or Krox-20. In contrast, FosB was induced and continued to rise in all areas, whereas the basal expressions of c-Jun and Krox-24 were initially reduced but then returned during the subsequent 36 h. A weak noxious cutaneous stimulus applied to one hindpaw induced only weak expressions of the ITFs. However, if the sciatic stimulation was applied contralaterally and 6 h beforehand, this weak stimulus strongly induced Krox-24, but not other ITFs, i.e. there was a potentiation of Krox-24 expression. When these two stimuli were applied simultaneously a few c-Fos labelled cells did appear, and there was and an increased Krox-24 expression. There was also a strong potentiation of FosB and a strong reduction in c-Jun expression. This simultaneous stimulation was the only type of stimulation to induce expression of Krox-20. Also after simultaneous stimulation the majority of the nuclear labelling for FosB, but not of the other ITFs, had a speckled appearance. MK-801 blocked these changes in ITF expressions, but it could also cause the C-fibre stimulations to induce c-Fos and c-Jun in specific areas of the hippocampus. Thus C-fibre stimulation does affect transcription factor activity in the hippocampus; and the strong responses of some ITFs to simultaneous inputs points to their having a role as 'genetic coincidence detectors' in the hippocampus.
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Affiliation(s)
- D Pearse
- School of Biomedical and Biomolecular Sciences, Griffith University, Nathan, Australia
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Izquierdo-Claros RM, del Boyano-Adánez M, Arilla-Ferreiro E. Activation of D1 and D2 dopamine receptors increases the activity of the somatostatin receptor-effector system in the rat frontoparietal cortex. J Neurosci Res 2000; 62:91-8. [PMID: 11002291 DOI: 10.1002/1097-4547(20001001)62:1<91::aid-jnr10>3.0.co;2-d] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The role of dopamine D1 and D2 receptor subtypes in the regulation, in vivo, of the somatostatin (SRIF) receptor-effector system in rat frontoparietal cortex was investigated. The D1-receptor agonist SKF 38393 (4 mg/kg) or the D2-receptor agonist bromocriptine (2 mg/kg), administered intraperitoneally to rats, increased the number of SRIF receptors without altering the affinity constant, an effect antagonized by both SCH 23390 (0.25 mg/kg) and raclopride (5 mg/kg), D1 and D2 receptor antagonists, respectively. These antagonists alone had no effect on [(125)I]Tyr(3) octreotide binding to its receptors. No change in binding was detected when the dopamine agonists were added in vitro. Basal adenylyl cyclase (AC) activity was increased by SKF 38393 treatment and decreased by bromocriptine. Octreotide (SMS 201-995)-mediated inhibition of basal and forskolin-stimulated AC was increased by SKF 38393 or bromocriptine treatment. In frontoparietal cortical slices, basal inositol-1,4, 5-triphosphate (IP(3)) levels were decreased by bromocriptine treatment but were unaffected by SKF 38393. SMS 201-995 increased the IP(3) accumulation in control, SKF 38393-, and bromocriptine-treated rats. Insofar as SRIF and dopamine appear to be involved in motor regulation and could well modulate somatosensory functions in frontal and parietal cortex, respectively, heterologous receptor regulation may have important repercussions regarding the control exerted by these neurotransmitters on frontal and parietal cortical function in the intact animal.
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MESH Headings
- 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine/pharmacology
- Animals
- Benzazepines/pharmacology
- Binding, Competitive/drug effects
- Bromocriptine/pharmacology
- Cell Membrane/chemistry
- Cell Membrane/metabolism
- Colforsin/pharmacology
- Dopamine Agonists/pharmacology
- Dopamine Antagonists/pharmacology
- Dopamine D2 Receptor Antagonists
- Frontal Lobe/chemistry
- Frontal Lobe/drug effects
- Frontal Lobe/metabolism
- Male
- Octreotide/pharmacology
- Parietal Lobe/chemistry
- Parietal Lobe/drug effects
- Parietal Lobe/metabolism
- Raclopride/pharmacology
- Rats
- Rats, Wistar
- Receptors, Dopamine D1/agonists
- Receptors, Dopamine D1/antagonists & inhibitors
- Receptors, Dopamine D1/metabolism
- Receptors, Dopamine D2/agonists
- Receptors, Dopamine D2/metabolism
- Receptors, Somatostatin/metabolism
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Affiliation(s)
- R M Izquierdo-Claros
- Departamento de Bioquímica y Biología Molecular, Facultad de Medicina, Universidad de Alcalá, Alcalá de Henares, Madrid, Spain
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5
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Pittaluga A, Bonfanti A, Raiteri M. Somatostatin potentiates NMDA receptor function via activation of InsP(3) receptors and PKC leading to removal of the Mg(2+) block without depolarization. Br J Pharmacol 2000; 130:557-66. [PMID: 10821783 PMCID: PMC1572105 DOI: 10.1038/sj.bjp.0703346] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
N-methyl-D-aspartate (NMDA) receptors exist on noradrenergic axon terminals and mediate enhancement of noradrenaline (NA) release. We here investigated modulation by somatostatin (SRIF, somatotropin release inhibiting factor) of the NMDA-induced release of NA using superfused hippocampal synaptosomes. The NMDA response was increased by SRIF-28 and SRIF-14, but not SRIF-28((1 - 14)), whereas the release of [(3)H]-NA elicited by alpha-amino-3-hydroxy-5-methylisoxazide-4-propionic acid (AMPA) was unaffected. SRIF-14 did not mimic glycine at the NMDA receptor but activated SRIF receptors sited on noradrenergic terminals. The SRIF-14 effect was blocked by pertussis toxin but mimicked by mastoparan, a G-protein activator. BIM-23056, but not Cyanamid 154806, antagonized the SRIF-14 effect. This effect was mimicked by L362855, a partial agonist at the sst(5) subtype, but not by the new selective sst(1) - sst(4) receptor agonists L797591, L779976, L796778 and L803087. Protein kinase C (PKC) inhibitors (H7, staurosporine, GF 209103X, cheleritrine and sphingosine) prevented the SRIF-14 effect, while phorbol 12-myristate 13-acetate enhanced the NMDA response. SRIF-14 permitted NMDA receptor activation in the presence of 1.2 mM Mg(2+) ions, both in hippocampal synaptosomes and slices. Blockade of inositol-1,4,5-trisphosphate (InsP(3)) receptors with heparin abolished the effect of SRIF-14. It is concluded that SRIF receptors, possibly of the sst(5) subtype, can exert a permissive role on NMDA receptors colocalized on hippocampal noradrenergic terminals: activation of sst(5) receptors is coupled to pertussis toxin-sensitive G proteins enhancing phosphoinositide metabolism with activation of InsP(3) receptors and PKC; NMDA receptor subunits might be phosphorylated with consequent removal of the Mg(2+) block in absence of depolarization.
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Affiliation(s)
- A Pittaluga
- Dipartimento di Medicina Sperimentale, Sezione di Farmacologia e Tossicologia, Università di Genova, Viale Cembrano 4, 16148 Genova, Italy
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6
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Bokkala S, Rubin E, Joseph SK. Effect of Chronic Ethanol Exposure on Inositol Trisphosphate Receptors in WB Rat Liver Epithelial Cells. Alcohol Clin Exp Res 1999. [DOI: 10.1111/j.1530-0277.1999.tb04086.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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7
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Wilkinson GF, Feniuk W, Humphrey PP. Homologous and heterologous desensitisation of somatostatin-induced increases in intracellular Ca2+ and inositol 1,4,5-trisphosphate in CHO-K1 cells expressing human recombinant somatostatin sst5 receptors. Eur J Pharmacol 1997; 340:277-85. [PMID: 9537824 DOI: 10.1016/s0014-2999(97)01430-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The mechanisms responsible for somatostatin (SRIF)-induced increases in intracellular Ca2+ concentration ([Ca2+]i) and subsequent desensitisation were studied in CHO-K1 cells expressing human sst5 receptors (CHOsst5 cells). To study the nature of the desensitisation, interactions with uridine triphosphate (UTP) were examined. SRIF (pEC50 7.10) and UTP (pEC50) 5.14) caused concentration-dependent increases in [Ca2+]i but the SRIF maximum was about 40% of that to UTP. SRIF-, but not UTP-, induced increases in [Ca2+]i were transient and abolished by pertussis toxin. SRIF and UTP caused sustained increases in Ins(1,4,5)P3 but the SRIF maximum was about 30% of that to UTP. Removal of [Ca2+]e attenuated the SRIF-induced peak rise in [Ca2+]i but had no effect on the peak increases in Ins(1,4,5)P3. UTP-induced increases in [Ca2+]i and Ins(1,4,5)P3 were attenuated in the absence of [Ca2+]e. Following pre-exposure to SRIF (1 microM) or UTP (100 microM) for 5 min, subsequent SRIF responses were desensitised. Similar results were obtained in the absence of [Ca2+]e. Pre-exposure to SRIF had no effect on subsequent responses to UTP but in the absence of [Ca2+]e, responses to UTP were attenuated. The results suggest that SRIF but not UTP-induced increases in [Ca2+]i in CHOsst5 cells are mediated by pertussis toxin sensitive G proteins and are caused by an entry of extracellular Ca2+ and release from an Ins(1,4,5)P3 sensitive Ca2+ store. Homologous or heterologous desensitisation of agonist-induced increases in [Ca2+]i could be demonstrated in the presence or absence of extracellular Ca2+ respectively, and the latter appeared to involve depletion of a common intracellular Ca2+ store.
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Affiliation(s)
- G F Wilkinson
- Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge, UK
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8
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Izquierdo-Claros RM, Boyano-Adánez MC, Larsson C, Gustavsson L, Arilla E. Acute effects of D1- and D2-receptor agonist and antagonist drugs on somatostatin binding, inhibition of adenylyl cyclase activity and accumulation of inositol 1,4,5-trisphosphate in the rat striatum. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1997; 47:99-107. [PMID: 9221906 DOI: 10.1016/s0169-328x(97)00063-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
A recent study carried out by our group demonstrated that exogenous dopamine increases the somatostatin (SS) receptor-effector system in the rat striatum. The present study examined the participation of the D1- and D2-dopaminergic systems in the modulation of the rat striatal SS receptor-effector system by use of the D1-receptor agonist and antagonist SKF 38393 and SCH 23390, respectively, and the D2-receptor agonist and antagonist bromocriptine and raclopride, respectively. In view of the rapid onset of dopamine action, the effect of dopaminergic agents on the SS mechanism of action were studied 3 h after their administration. SKF 38393 (4 mg/kg i.p.) or bromocriptine (2 mg/kg i.p.) administered to male Wistar rats increased the number of 125I-Tyr3-SMS receptors in the striatum (52 and 30%, respectively) without changing the affinity constant. The effect of SKF 38393 on 125I-Tyr3-SMS binding was antagonized by the D1-specific antagonist SCH 23390 (0.25 mg/kg i.p.) whereas the effect of bromocriptine was abolished by the D2-specific antagonist raclopride (5 mg/kg i.p.). No change in binding was produced when SKF 38393 or bromocriptine were added directly to the incubation medium. The acute systemic administration of SCH 23390 or raclopride alone had no effect on the binding of 125I-Tyr3-SMS to its receptors. The increase of the number of 125I-Tyr3-SMS receptor induced by SKF 38393 or bromocriptine was accompanied by an increase in the capacity of SMS 201-995 to inhibit basal and forskolin (FK)-stimulated adenylyl cyclase (AC) activity when compared to the control groups. In addition, the effect of SMS 201-995 on the mass accumulation of inositol 1,4,5-trisphosphate (IP3) was investigated. SKF 38393 as well as bromocriptine increased the capacity of SMS 201-995 to accumulate IP3 in the rat striatum although this effect was only statistically significant in the case of SKF 38393. These results suggest that the activation of D1 and D2 receptors increases the activity of the SS receptor-effector system, the effect being greater in the case of D1 receptors. These findings are consistent with a functional interaction between dopamine and SS in the rat striatum.
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Affiliation(s)
- R M Izquierdo-Claros
- Departamento de Bioquímica y Biología Molecular, Universidad de Alcalá, Alcalá de Henares, Madrid, Spain
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9
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Wilkinson GF, Feniuk W, Humphrey PP. Characterization of human recombinant somatostatin sst5 receptors mediating activation of phosphoinositide metabolism. Br J Pharmacol 1997; 121:91-6. [PMID: 9146892 PMCID: PMC1564659 DOI: 10.1038/sj.bjp.0701116] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
1. We have functionally characterized the human recombinant somatostatin (SRIF) sst5 receptor in Chinese hamster ovary-K1 (CHOsst5) cells by measuring total [3H]-inositol phosphate ([3H]-InsPx) accumulation, in the presence of 10 mM LiCl, in cells labelled with [3H]-myo-inositol. 2. In CHOsst5 cells, SRIF, SRIF-28 and the cyclic hexapeptide, L-362,855, produced time- and concentration-related increases in [3H]-InsPx accumulation, with similar potency (pEC50 values of 6.5, 6.8 and 7.2, respectively). L-362,855 behaved as a partial agonist, producing approximately 30% of the SRIF maximum response. The other peptide analogues of SRIF, BIM-23027 and BIM-23056, were inactive as agonists. 3. Increasing concentrations of L-362,855 increased [3H]-InsPx accumulation and simultaneously produced rightward shifts of SRIF concentration-effect curves, with an estimated pKp value of 7.6, confirming that it was acting as a partial agonist. 4. BIM-23056, but not BIM-23027, potently antagonized SRIF-induced [3H]-InsPx accumulation, with an estimated pKB value of 7.4. BIM-23056 did not antagonize [3H]-InsPx accumulation induced by uridine 5'-triphosphate (UTP). 5. SRIF- but not UTP-induced [3H]-InsPx accumulation was inhibited by increasing concentrations of pertussis toxin (0.01-100 ng ml-1), indicating the involvement of pertussis toxin-sensitive G-proteins. 6. These findings show that the human recombinant sst5 receptor, when stably expressed in CHO-K1 cells, is able to mediate activation of phosphoinositide metabolism in a pertussis toxin-sensitive manner. In this system L-362,855 behaved as a partial agonist while BIM-23056 was a specific antagonist. These agents should provide useful tools for functionally characterizing endogenous SRIF receptors.
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Affiliation(s)
- G F Wilkinson
- Glaxo Institute of Applied Pharmacology, Department of Pharmacology, University of Cambridge
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