Assuntos
Humanos , Inibidores da Angiogênese/uso terapêutico , Fator A de Crescimento do Endotélio Vascular/antagonistas & inibidores , Degeneração Macular/tratamento farmacológico , Doenças Retinianas/tratamento farmacológico , Taquifilaxia , Proteínas Recombinantes de Fusão/uso terapêutico , Angiofluoresceinografia , Acuidade Visual , Protocolos Clínicos , Inibidores da Angiogênese/administração & dosagem , Inibidores da Angiogênese/economia , Receptores de Fatores de Crescimento do Endotélio Vascular , Tomografia de Coerência Óptica , Aptâmeros de Nucleotídeos/uso terapêutico , Uso Off-Label , Injeções Intravítreas , Bevacizumab/uso terapêutico , Ranibizumab/uso terapêutico , Degeneração Macular/economiaRESUMO
ABSTRACT Purpose: The present study compared the efficacy of aflibercept for neovascular age-related macular degeneration (NV-AMD) in patients with complete ranibizumab resistance and tachyphylaxis. Methods: Forty-four eyes of 38 neovascular age-related macular degeneration patients were evaluated. Eyes were divided into a complete resistance group (n=23 eyes) and tachyphylaxis group (n=21 eyes). Results: After three injections, eight (38.1%) patients in the tachyphylaxis group and nine (39.1%) in the complete resistance group presented with macular dryness. After the first injection of aflibercept, the mean visual acuity improved significantly in the tachyphylaxis group (p=0.018) but remained unchanged in the complete resistance group (p=0.37). There was a non-significant trend towards improved mean visual acuity in both groups after the second and third injections relative to the acuity at the final visit for ranibizumab treatment. In the tachyphylaxis group, the presence of subfoveal pigmented epithelium detachment (PED) decreased significantly after intravitreal aflibercept treatment. Conclusions: Although treatment with aflibercept yielded generally positive anatomical results in both groups, no significant increase in visual acuity was achieved.
RESUMO Objetivo: O presente estudo comparou a eficácia do aflibercept na degeneração macular neovascular relacionada à idade (NV-AMD) com de resistência completa ao ranibizumab e taquifilaxia ao ranibizumab. Método: Quarenta e quatro olhos de 38 pacientes com degeneração macular neovascular relacionada à idade foram inscritos. Eles foram divididos em dois grupos: grupo de resistência completa (n=23 olhos) e grupo taquifilaxia (n=21 olhos). Resultados: Depois de três injeções, 8 (38,1%) olhos no grupo de taquifilaxia e 9 (39,1%) olhos no grupo de resistência completa, apresentaram mácula seca. Após a primeira injeção de aflibercept, a acuidade visual média melhorou significativamente no grupo taquifilaxia (p=0,018) e manteve-se inalterada no grupo de resistência completa (p=0,37). Houve uma tendência de melhora da acuidade visual média em ambos os grupos após a segunda e terceira injeções em comparação com a última visita do tratamento com ranibizumab, mas isso não foi estatisticamente significativo. A presença de descolamento do epitélio pimentado subfoveal (PED) em olhos com taquifilaxia ao ranibizumab diminuiu significativamente após o tratamento aflibercept intravítreo. Conclusões: Embora o tratamento com aflibercept tenha mostrado resultados anatômicos positivas em ambos os grupos, não foi obtida melhora significativa da acuidade visual.
Assuntos
Humanos , Pessoa de Meia-Idade , Idoso , Idoso de 80 Anos ou mais , Taquifilaxia , Proteínas Recombinantes de Fusão/uso terapêutico , Acuidade Visual/efeitos dos fármacos , Inibidores da Angiogênese/uso terapêutico , Receptores de Fatores de Crescimento do Endotélio Vascular/uso terapêutico , Ranibizumab/uso terapêutico , Degeneração Macular/tratamento farmacológico , Proteínas Recombinantes de Fusão/administração & dosagem , Descolamento Retiniano/etiologia , Descolamento Retiniano/tratamento farmacológico , Resistência a Medicamentos , Resultado do Tratamento , Receptores de Fatores de Crescimento do Endotélio Vascular/administração & dosagem , Epitélio Pigmentado da Retina/efeitos dos fármacos , Injeções Intravítreas , Degeneração Macular/complicaçõesRESUMO
Angiotensin II (AngII) is the final active product of the renin enzymatic cascade, which is responsible for sustaining blood pressure. To investigate the effect of N-terminal cyclization on AT1 activation and tachyphylaxis, we designed conformationally constrained analogues with an i-(i + 1) lactam bridge. All analogues presented the same binding coefficient and tachyphylactic index, but some of them such as Cyclo (0-1a) [Glu0 , endo-(Lys1a )]-AngII and Cyclo (0-1a) [Asp0 , endo-(Orn1a )]-AngII showed higher potency. The same tachyphylactic index presented by AngII and cyclic analogues was surprising. We expected a variation after the modification of AngII N-terminal region.
Assuntos
Angiotensina II/análogos & derivados , Lactamas/química , Receptor Tipo 1 de Angiotensina/metabolismo , Sequência de Aminoácidos , Angiotensina II/síntese química , Angiotensina II/metabolismo , Angiotensina II/farmacologia , Animais , Células CHO , Dicroísmo Circular , Cricetinae , Cricetulus , Ciclização , Fundo Gástrico/efeitos dos fármacos , Fundo Gástrico/fisiologia , Ligantes , Camundongos , Camundongos Endogâmicos C57BL , Peptídeos/síntese química , Peptídeos/química , Peptídeos/farmacologia , Ligação Proteica , Estrutura Secundária de Proteína , Receptor Tipo 1 de Angiotensina/química , Receptor Tipo 1 de Angiotensina/genética , Taquifilaxia/fisiologiaRESUMO
PURPOSE:: The present study compared the efficacy of aflibercept for neovascular age-related macular degeneration (NV-AMD) in patients with complete ranibizumab resistance and tachyphylaxis. METHODS:: Forty-four eyes of 38 neovascular age-related macular degeneration patients were evaluated. Eyes were divided into a complete resistance group (n=23 eyes) and tachyphylaxis group (n=21 eyes). RESULTS:: After three injections, eight (38.1%) patients in the tachyphylaxis group and nine (39.1%) in the complete resistance group presented with macular dryness. After the first injection of aflibercept, the mean visual acuity improved significantly in the tachyphylaxis group (p=0.018) but remained unchanged in the complete resistance group (p=0.37). There was a non-significant trend towards improved mean visual acuity in both groups after the second and third injections relative to the acuity at the final visit for ranibizumab treatment. In the tachyphylaxis group, the presence of subfoveal pigmented epithelium detachment (PED) decreased significantly after intravitreal aflibercept treatment. CONCLUSIONS:: Although treatment with aflibercept yielded generally positive anatomical results in both groups, no significant increase in visual acuity was achieved.
Assuntos
Inibidores da Angiogênese/uso terapêutico , Degeneração Macular/tratamento farmacológico , Ranibizumab/uso terapêutico , Receptores de Fatores de Crescimento do Endotélio Vascular/uso terapêutico , Proteínas Recombinantes de Fusão/uso terapêutico , Taquifilaxia , Acuidade Visual/efeitos dos fármacos , Idoso , Idoso de 80 Anos ou mais , Resistência a Medicamentos , Humanos , Injeções Intravítreas , Degeneração Macular/complicações , Pessoa de Meia-Idade , Receptores de Fatores de Crescimento do Endotélio Vascular/administração & dosagem , Proteínas Recombinantes de Fusão/administração & dosagem , Descolamento Retiniano/tratamento farmacológico , Descolamento Retiniano/etiologia , Epitélio Pigmentado da Retina/efeitos dos fármacos , Líquido Sub-Retiniano/metabolismo , Tomografia de Coerência Óptica , Resultado do TratamentoRESUMO
Binding of angiotensin II (DRVYIHPF, AngII) to its AT(1) receptor can trigger a process known as tachyphylaxis (loss of receptor response owing to repeated agonist stimulation). We propose a two-state binding model for tachyphylaxis where the N-terminal Asp(1) and Arg(2) residues of the peptide are supposed to initially bind to the N-terminal segment (Arg(23)) and to the EC-3 loop (Asp(281)) of an AT(1) molecule, respectively (state 1). Sequentially, a disruption of the salt bond between the AngII Asp(1) beta-carboxyl function and the receptor Arg(23) can occur with release of the peptide N-terminal segment, favoring the binding of the Arg(2) residue to the EC-3 loop (Asp(178,281), state 2). In the present study, we expanded this investigation by assaying pharmacological properties of different AngII analogs in guinea-pig ileum bearing modifications at positions 1 and 2. Most of these peptides were weak agonists but many of them had the ability to induce tachyphylaxis. These findings support the two-state model for tachyphylaxis, but alternative mechanisms were revealed where state 1 was no longer needed, depending on the chemical structure of AngII residue 1. Otherwise, any modification of the wild type AngII Arg(2) residue was deleterious for the tachyphylaxis mechanism.
Assuntos
Angiotensina II/farmacologia , Taquifilaxia , Angiotensina II/análogos & derivados , Animais , Feminino , Cobaias , Íleo/efeitos dos fármacos , Técnicas In Vitro , Masculino , Estrutura Molecular , Receptor Tipo 1 de Angiotensina/agonistasRESUMO
Tachyphylaxis, defined as the acute loss of response of some smooth muscles upon repeated stimulations with angiotensin II (Ang II), has been shown to be dependent mainly on the N-terminal region of the ligand. To further study the structural requirements for the induction of tachyphylaxis we have synthesized Ang II analogs containing the bulky and very lipophilic substituents 9-fluorenylmethyloxycarbonyl (Fmoc) and 9-fluorenylmethyl ester (OFm) at the alpha-amino (Nalpha-Fmoc-Ang II) or the beta-carboxyl ([Asp(OFm)1]-Ang II) groups of the Asp1 residue, respectively. In binding assays with Chinese hamster ovary cells transfected with the AT1 Ang II receptor, Nalpha-Fmoc-Ang II bound with high affinity, whereas [Asp(OFm)1]-Ang II showed lower affinity. In biological assays, these two analogs were full agonists and showed 30 and 3%, respectively, of the Ang II potency in contracting the guinea-pig ileum smooth muscle. The two analogs induced tachyphylaxis, in spite of the lack of a free amino group in Nalpha-Fmoc-Ang II. Thus, analogs with Fmoc- or OFm-type groups coupled to the Asp1 residue, whether at the amino or carboxyl functions, induce tachyphylaxis through an unreported mechanism. Based in these findings and those available from the literature, an alternate molecular interaction mode between Ang II N-terminal portion and the AT1 receptor is proposed to explain the tachyphylactic phenomenon.
Assuntos
Angiotensina II/análogos & derivados , Oligopeptídeos/farmacologia , Receptor Tipo 1 de Angiotensina/efeitos dos fármacos , Taquifilaxia/fisiologia , Angiotensina II/farmacologia , Animais , Ligação Competitiva , Células CHO , Cricetinae , Relação Dose-Resposta a Droga , Feminino , Cobaias , Interações Hidrofóbicas e Hidrofílicas , Íleo/efeitos dos fármacos , Técnicas In Vitro , Contração Muscular/efeitos dos fármacos , Músculo Liso/efeitos dos fármacos , Oligopeptídeos/síntese química , Ensaio Radioligante , Relação Estrutura-AtividadeRESUMO
We have previously demonstrated that Chinese hamster ovary (CHO) cells transfected with the angiotensin II AT1 receptor gene containing only the coding region, presented tachyphylaxis to the total inositol phosphate (InsPs) and Ca2+ responses mediated by angiotensin II and [2-lysine]angiotensin II ([Lys2]angiotensin II). Now we have evaluated the possible role of the 3'-untranslated region of the angiotensin AT1 receptor mRNA in modulating the angiotensin AT1 receptor-mediated cellular responses. The binding parameters, as well as the Ca2+ and InsPs responses induced by angiotensin II and [Lys2]angiotensin II were similar in cells transfected with the angiotensin AT1 receptor with or without the 3'-untranslated region sequence. In cells transfected with the receptor containing the 3'-untranslated region sequence, angiotensin II-induced Ca2+ and InsPs responses were desensitized by repeated stimulations, whereas [Lys2]angiotensin II caused desensitization of InsPs production but not of Ca2+ uptake in these cells. Our results suggest that the 3'-untranslated region plays a role in modulating cell signalling involved in the tachyphylaxis of angiotensin AT1 receptor-mediated Ca2+ responses.
Assuntos
Regiões 3' não Traduzidas/fisiologia , Angiotensina II/análogos & derivados , Angiotensina II/metabolismo , Receptor Tipo 1 de Angiotensina/fisiologia , Angiotensina II/farmacologia , Animais , Sítios de Ligação , Células CHO , Cálcio/metabolismo , Cricetinae , Fosfatos de Inositol/biossíntese , Ratos , Receptor Tipo 1 de Angiotensina/genética , Receptor Tipo 1 de Angiotensina/metabolismo , Taquifilaxia/genética , Taquifilaxia/fisiologia , TransfecçãoRESUMO
La capsaicina es un vanilloide natural que controla la inflamación neurogénica disminuyendo los neuropeptidos en la sinapsis neuronal. Nosotros determinamos el efecto de la capsaicina sobre la proliferación y el ciclo celular de fibroblastos pulpares humanos en cultivo (FPH). La dosis con la que se obtuvo el más alto porcentaje de células en proceso de división celular fue la capsaicina 10-16 M a las 24 y 96 horas. Sin embargo, con esta dosis también se observó una ruptura de la monocapa y una disminución significativa en el conteo de células, especialmente a las 24 horas. Estos mismos cambios, aunque en menor proporción, también fueron observados con capsaicina 10-8M. Con relación al tiempo, hubo un aumento significativo en el número de cèlulas en fase 24 y 72 horas. Estos efectos sobre el receptor para vanillides (VR1) dependientes del tiempo han sido descritos anteriormente en neuronas tratadas con capsaicina y se ha denominado taquifilaxis
Assuntos
Humanos , Capsaicina , Ciclo Celular , Polpa Dentária , Fibroblastos , Capsaicina , Contagem de Células , Técnicas de Cultura de Células , Meios de Cultura , Inflamação Neurogênica/fisiopatologia , Microscopia , Neuropeptídeos/fisiologia , Interpretação Estatística de Dados , Estatísticas não Paramétricas , Sinapses , TaquifilaxiaRESUMO
The manifestation of tachyphylaxis to angiotensin II in Chinese hamster ovary (CHO) cells expressing the rat angiotensin II AT(1) receptor was investigated. The cells were transfected with a cDNA fragment containing the complete coding region of the angiotensin II AT(1A) receptor gene, as well as 56 bp of its 3'- and 52 bp of its 5'-untranslated regions. These cells (CHO-AT(1)) responded to angiotensin II by increases in intracellular Ca(2+) concentration and inositol phosphate turnover, which were inhibited upon repeated administrations, characterizing the tachyphylaxis phenomenon. In contrast to smooth muscle cells, which are rendered tachyphylactic to angiotensin II but not to [2-lysine]angiotensin II ([Lys(2)]angiotensin II), this analogue induced responses in CHO-AT(1) cells that were also inhibited upon repeated administrations. A smooth muscle cell line, which showed tachyphylaxis only to angiotensin II, became tachyphylactic also to [Lys(2)]angiotensin II after transfection with the angiotensin II AT(1) receptor gene. Our findings suggest that posttranscriptional control directed by the 3'- or the 5'-untranslated regions in the angiotensin II AT(1) receptor gene may play a role in modulating the signal transduction pathways involved in the mechanism of angiotensin II tachyphylaxis.
Assuntos
Angiotensina II/análogos & derivados , Receptores de Angiotensina/fisiologia , Taquifilaxia/fisiologia , Trifosfato de Adenosina/farmacologia , Angiotensina II/farmacologia , Animais , Células CHO , Cálcio/metabolismo , Cricetinae , DNA Recombinante/genética , Expressão Gênica , Glicina/farmacologia , Fosfatos de Inositol/metabolismo , Soluções Isotônicas/farmacologia , Músculo Liso Vascular/citologia , Músculo Liso Vascular/efeitos dos fármacos , Músculo Liso Vascular/metabolismo , Coelhos , Ratos , Receptor Tipo 1 de Angiotensina , Receptores de Angiotensina/efeitos dos fármacos , Receptores de Angiotensina/genética , TransfecçãoRESUMO
Angiotensin II (AII) analogs bearing n-Leu, Met or S-substituted groups for cysteine at position 5 were studied regarding their agonistic and tachyphylactic properties. It was shown that these analogs lowered the relative affinity towards the AT1 receptor as determined by contractile responses, which could be due to the removal of the beta-branching residue at position 5. Insertion of a sulfur atom in a different position away from the attached backbone carbon atom presented no significant difference in EC50 values for these analogs. Interestingly, the S-bearing analogs at position 5 were full agonists but the tachyphylactic property was lost, in contrast to [n-Leu5]AII, which still induced reduction of the contractile responses. Nevertheless after replacing the Asp with Sar in position 1 (Sar1) tachyphylaxis was again established. It is concluded that the insertion of Met or an S-substituted cysteine into the side chain at position 5 of AII may promote interactions with its receptor due to the slight electronegative character of the sulfur atom and changes in the restricted conformational freedom of the Ile5 residue in the AII molecule. This was overcome by Sar1, probably through interactions due to its fully protonated N-terminal amino group and favoring the conformation responsible for the tachyphylaxis phenomenon.
Assuntos
Angiotensina II/química , Angiotensina II/farmacologia , Enxofre/química , Taquifilaxia , Vasoconstritores/química , Vasoconstritores/farmacologia , Substituição de Aminoácidos , Angiotensina II/análogos & derivados , Animais , Feminino , Cobaias , Íleo/efeitos dos fármacos , Masculino , Sarcosina/química , Relação Estrutura-AtividadeRESUMO
In the guinea-pig ileum, both sarafotoxin S6c and IRL1620 (Suc-[Glu9,Ala11,15]endothelin-1-(8-21) induced a concentration-dependent biphasic effect (relaxation and contraction), but distinct tachyphylaxis of the tissue. Cross-tachyphylaxis and additivity experiments evidenced distinct receptors for these agonists. BQ-123 (cyclo[D-Trp-D-Asp-Pro-D-Val-Leu]), an endothelin ET(A) receptor antagonist, did not affect the response induced by either agonist. PD145065 [Ac-(D-Bhg-Leu-Asp-Ile-Ile-Trp) (D-Bhg = 5H-dibenzyl[a,d]cycloheptene-10,11-dihydroglycine)], an endothelin ET(A)/ET(B) receptor antagonist, inhibited the contractions induced by IRL1620 and sarafotoxin S6c in competitive and noncompetitive manner, respectively. RES-701-1 [cyclic(Gly1-Asp9)(Gly-Asn-Trp-His-Gly-Thr-Ala-Pro-Asp-Trp-P he-Phe-Asn-Tyr-Tyr-Trp)], an endothelin ET(B1) receptor antagonist, inhibited both components of the response induced by IRL1620, whereas it inhibited mainly the relaxation induced by low sarafotoxin S6c doses. Apamin and suramin had different effects towards the agonists. Our results suggest that two endothelin ET(B) receptors with distinct signal transduction mechanism mediate the biphasic response: (1) the endothelin ET(B1) receptor: sensitive to RES-701-1 and PD145065 and (2) the endothelin ET(B2) receptor: less sensitive to RES-701-1 and PD145065.
Assuntos
Endotelinas/farmacologia , Contração Muscular/efeitos dos fármacos , Músculo Liso/efeitos dos fármacos , Fragmentos de Peptídeos/farmacologia , Receptores de Endotelina/fisiologia , Taquifilaxia , Venenos de Víboras/farmacologia , Animais , Apamina/farmacologia , Relação Dose-Resposta a Droga , Interações Medicamentosas , Antagonistas dos Receptores de Endotelina , Feminino , Cobaias , Íleo/efeitos dos fármacos , Técnicas In Vitro , Contração Isométrica/efeitos dos fármacos , Masculino , Relaxamento Muscular/efeitos dos fármacos , Receptores de Endotelina/agonistas , Venenos de Serpentes/química , Suramina/farmacologiaAssuntos
Animais , Cobaias , Angiotensina II , Relaxamento Muscular , Técnicas de Patch-Clamp , Canais de Potássio , TaquifilaxiaRESUMO
Angiotensin II (AII) tachyphylaxis occurs in the guinea pig ileum, but is not induced by analogs lacking the N-terminal amino group or the Arg2 guanidino group. Both AII and Lys2AII increased cell inositol trisphoshate content in cultured intestinal smooth muscle cells. Protein kinase C inhibition by staurosporine or downregulation by prolonged incubation with phorbol reverted tachyphylaxis of the inositol trisphoshate response, but not that of the Na+ uptake response, indicating that the uncoupling of the phosphoinositide signal system by protein kinase C did not involve all processes distal to receptor activation. Tachyphylaxis of the Na+ uptake response was prevented when receptor internalization was blocked by reduction of the temperature (4 degrees C) or by pretreatment of the cells with phenylarsine oxide. Acid washings, which prevented tachyphylaxis of the 24Na+ influx response, also prevented tachyphylaxis of the contractile response of the guinea pig ileum to AII. Although these findings suggest that sequestration or internalization of the AII receptor might be involved in AII tachyphylaxis, binding of [125I]AII and of [125I]Lys2AII to the cells was equally unaffected by repeated administrations of the peptides. The results suggest that conformational change of the AII-receptor complex within the plasma membrane, but not internalization, is the most important factor responsible for tachyphylaxis.
Assuntos
Angiotensina II/farmacologia , Íleo/efeitos dos fármacos , Taquifilaxia , Alcaloides/farmacologia , Angiotensina II/análogos & derivados , Angiotensina II/metabolismo , Animais , Arsenicais/farmacologia , Cálcio/metabolismo , Células Cultivadas , Temperatura Baixa , Feminino , Cobaias , Íleo/citologia , Íleo/metabolismo , Íleo/fisiologia , Inositol 1,4,5-Trifosfato/metabolismo , Masculino , Contração Muscular/efeitos dos fármacos , Proteína Quinase C/antagonistas & inibidores , Sódio/metabolismo , EstaurosporinaRESUMO
El conocimiento básico de la farmacología de las drogas promueve un uso más racional de las mismas por parte del anestesiólogo. En la presente revisión se actualizan conceptos farmacodinámicos y farmacocinéticos. (AU)
Assuntos
Humanos , Anestésicos Locais/farmacologia , Anestésicos Locais/farmacocinética , Bloqueio Nervoso , Bupivacaína/administração & dosagem , Lidocaína/administração & dosagem , Raquianestesia , Taquifilaxia , Fatores de RiscoRESUMO
El conocimiento básico de la farmacología de las drogas promueve un uso más racional de las mismas por parte del anestesiólogo. En la presente revisión se actualizan conceptos farmacodinámicos y farmacocinéticos.
Assuntos
Humanos , Anestésicos Locais/farmacocinética , Anestésicos Locais/farmacologia , Bloqueio Nervoso , Raquianestesia , Bupivacaína/administração & dosagem , Lidocaína/administração & dosagem , Fatores de Risco , TaquifilaxiaRESUMO
The importance of residues 9 and 10 in endothelin-1 was assessed by studying the responses of the guinea-pig ileum to [Ala9]endothelin-1 and [Ala10]endothelin-1. Both analogues induced relaxation followed by contraction. [Ala9]Endothelin-1 showed similar ED50 values and maximum response to those of endothelin-1, whereas [Ala10]endothelin-1 showed a larger ED50 value and was a partial agonist. Endothelin-1 and [Ala10]endothelin-1 induced similar degrees of tachyphylaxis, whereas [Ala9]endothelin-1 induced very little tachyphylaxis, indicating that Lys9 is important for inducing tachyphylaxis. Apamin inhibited the relaxation induced by endothelin-1 and [Ala9]endothelin-1 but not that induced by [Ala10]endothelin-1. BQ-123 (cyclo[D-Trp-D-Asp-Pro-D-Val-Leu), a specific endothelin ETA receptor antagonist, inhibited [Ala9]endothelin-1-, but not [Ala10]endothelin-1-induced contraction. Cross-tachyphylaxis and additivity studies indicated that [Ala9]endothelin-1, like endothelin-1, acts at the endothelin ETA receptor, whereas [Ala10]endothelin-1 behaved as an endothelin ETB receptor agonist, like sarafotoxin S6c. Thus, the residue at position 10 plays a significant role in receptor activation and is a candidate for further exploration of receptor antagonism.
Assuntos
Endotelinas/química , Endotelinas/farmacologia , Receptores de Endotelina/efeitos dos fármacos , Sequência de Aminoácidos , Animais , Apamina/farmacologia , Antagonistas dos Receptores de Endotelina , Endotelina-1/análogos & derivados , Feminino , Cobaias , Íleo/efeitos dos fármacos , Técnicas In Vitro , Contração Isométrica/efeitos dos fármacos , Contração Isotônica/efeitos dos fármacos , Masculino , Dados de Sequência Molecular , Contração Muscular/efeitos dos fármacos , Peptídeos Cíclicos/farmacologia , Receptores de Endotelina/agonistas , Sódio/metabolismo , Taquifilaxia/fisiologiaRESUMO
1. In the guinea-pig ileum the C-terminal hexapeptide of the endothelins, endothelin (16-21), induced a biphasic effect (relaxation followed by contraction) qualitatively similar to that seen in the responses to endothelins 1 and 3. Both components of the response were concentration-dependent in the range studied (2-100 microM). 2. The response induced by endothelin (16-21) was inhibited in low-sodium (80 mM) medium. 3. Repeated administration of endothelin (16-21) induced no desensitization of the preparation, contrasting with the tachyphylaxis induced by endothelin-1 and endothelin-3 in the guinea-pig ileum. 4. Tissues rendered tachyphylatic to endothelin-1 or endothelin-3 responded normally to endothelin (16-21). 5. The results suggest that the C-terminal tail of the endothelins contains the message for the biphasic response, whereas the N-terminal domain may be responsible for the strong binding to the receptor and for the tachyphylactic properties of endothelin-1 and endothelin-3, in the guinea-pig isolated ileum. However, the possibility that endothelin (16-21) may be acting on a site other than the endothelin receptor cannot be ruled out.
Assuntos
Endotelinas/farmacologia , Músculo Liso/efeitos dos fármacos , Fragmentos de Peptídeos/farmacologia , Sequência de Aminoácidos , Animais , Feminino , Cobaias , Íleo/efeitos dos fármacos , Técnicas In Vitro , Contração Isométrica/efeitos dos fármacos , Masculino , Dados de Sequência Molecular , Receptores de Endotelina/efeitos dos fármacos , Sódio/fisiologia , Taquifilaxia/fisiologiaRESUMO
Simultaneous recordings of the tension and intracellular Ca2+ concentration of guinea-pig ileum longitudinal smooth muscle strips, as well as 24Na+ and 45Ca2+ influx measurements in cultured myocytes from the same tissue, were used to investigate the mechanisms underlying angiotensin-induced desensitization and tachyphylaxis. Angiotensin II and [2-lysine]-angiotensin II (Lys2All), incubated for prolonged periods (10 min) with muscle strips, induced fading of the contractile response (desensitization) and reappearance of the intracellular Ca2+ concentration oscillations, which were inhibited during the initial increase in cytosolic Ca2+. The desensitization was paralleled, in cultured myocytes, by inhibition of the 45Ca2+ but not of the 24Na+ influxes which were initially stimulated by the peptides. On the other hand, repeated administrations of angiotensin II (but not of Lys2All) caused gradual reduction of the contractile response and of the 24Na+ influx stimulation evoked by the agonist (tachyphylaxis). Treatment with phorbol 12-13 dibutyrate accelerated the desensitization induced by both angiotensin II and by Lys2All and aggravated the tachyphylaxis to angiotensin II. The results support the hypothesis that activation of protein kinase C is responsible for the desensitization and that tachyphylaxis is due to the slow dissociation of angiotensin II from a postulated Na(+)-dependent regulatory site on the receptor.