[Ala1,3,11,15]-Endothelin

Solid-phase synthesis of [Ala1,3,11,15]-endothelin-1 by a modified double-coupling procedure.[Pubmed:8320042]

Int J Pept Protein Res. 1993 May;41(5):492-8.

[Ala1,3,11,15]-Endothelin-1, a linear analogue of endothelin-1 in which alanines replace the cystine residues, has been prepared by solid-phase synthesis in approximately 17% yield. Fmoc amino acids were coupled using an economical modified double-coupling (symmetrical anhydride followed by O-benzotriazolyl ester) procedure under fully automated conditions. Conditions for synthesis and purification were closely monitored and should be applicable to other endothelin analogues.

[Ala1,3,11,15]endothelin-1 analogs with ETB agonistic activity.[Pubmed:1652952]

Biochem Biophys Res Commun. 1991 Aug 30;179(1):286-92.

A linear peptide analog of endothelin (ET)-1, [Ala1,3,11,15]ET-1 (4AlaET-1), and its truncated peptide analogs were synthesized to study the structural requirements of ET-1 for the recognition of ETs-nonselective ETB receptors. ET-1 exhibited sub-nanomolar binding to two distinct ET receptor subtypes (ETA and ETB), but 4AlaET-1 bound to ETB with an affinity 1,700 times higher than that seen during binding to ETA. The truncated linear peptides 4AlaET-1(6-21), 4AlaET-1(8-21) and N-acetyl-4AlaET-1(10-21) still had high affinity for ETB, whereas 4AlaET-1(6-20) and 4AlaET-1(11-21) displayed remarkably reduced affinity for ETB. Therefore, ET-1 requires the Glu10-Trp21 sequence for ETB binding, but not the disulfide bridges. These ETB-binding peptides elicit endothelium-dependent vasorelaxation of porcine pulmonary arteries in parallel with the binding affinity for ETB, suggesting that they are ETB agonists.

Different distribution of endothelin receptor subtypes in pulmonary tissues revealed by the novel selective ligands BQ-123 and [Ala1,3,11,15]ET-1.[Pubmed:1310013]

Biochem Biophys Res Commun. 1992 Jan 15;182(1):144-50.

We have demonstrated the different distribution of two distinct endothelin (ET) receptor subtypes in porcine pulmonary tissues using a radioligand binding assay. The clear differentiation of the subtypes was made possible by the discovery of two compounds, BQ-123 and [Ala1,3,11,15]ET-1 (4AlaET-1), that are highly selective for ETA and ETB receptors, respectively. In the bronchus and lung parenchyma, BQ-123 inhibited 65% and 30% of [125I]ET-1 binding on the sensitive sites, while 4AlaET-1 displaced 25% and 60%, respectively. The combination of the two compounds completely inhibited ET-1 binding in both tissues. An autoradiographic study of [125I]ET-1 binding using BQ-123 and 4AlaET-1 also supported the different localization of two ET receptor subtypes in pulmonary tissues. In particular, the blood vessels and bronchi are rich in ETA, but the lung parenchyma is rich in ETB.

Discrimination between ETA- and ETB-receptor-mediated effects of endothelin-1 and [Ala1,3,11,15]endothelin-1 by BQ-123 in the anaesthetized rat.[Pubmed:1467841]

Br J Pharmacol. 1992 Dec;107(4):912-8.

1. The influence of BQ-123 (a selective ETA-receptor antagonist) on the haemodynamic response elicited by endothelin-1 (ET-1) and [Ala1,3,11,15]ET-1 (a selective ETB-receptor agonist) was studied in anaesthetized rats instrumented with ultrasonic Doppler flow probes on the carotid, coeliac, mesenteric, renal and iliac arteries. 2. BQ-123 alone (1.6 mumol kg-1, i.v.) induced a decrease in femoral mean arterial pressure (AP), accompanied by a systemic vasodilatation. The response was maximal after 3 min and then returned slowly to baseline. None of these effects was observed after a 0.016 mumol kg-1 dose of BQ-123. 3. ET-1 (1 nmol kg-1, i.v.) induced a biphasic response characterized by a transient initial decrease in AP accompanied by regional vasodilatation (mainly in the carotid and iliac beds) and by immediate mesenteric and renal vasoconstrictions. This was followed, within 1 min, by a marked and prolonged increase in AP accompanied by systemic vasoconstriction. Pretreatment with BQ-123 (1.6 mumol kg-1, i.v., 8 min before ET-1) increased and prolonged the vasodilator effect of ET-1 (mainly in the carotid, coeliac, mesenteric and iliac beds) and reduced its systemic vasoconstrictor effects with marked regional differences (the coeliac, mesenteric and renal beds being poorly affected). 4. [Ala1,3,11,15]ET-1 (3 nmol kg-1, i.v.) induced an initial and marked decrease in AP accompanied by regional vasodilatation (mainly in the carotid, coeliac and iliac beds) and by mesenteric and renal vasoconstrictions. This was followed, within 5 min, by a small increase in AP and systemic vasoconstriction. All these effects were dose-dependent. Pretreatment with BQ-123 (1.6 tmol kg'; 8 min before ET-1) did not modify the early effect of [Ala'3""5]ET-l, but abolished its secondary vasoconstrictor effect except in the mesenteric bed.5. This study demonstrates that pretreatment with BQ-123 not only reduced a large part of the sustained vasoconstrictor activity of ET-1, suggesting the involvement of ETA-receptors, but also enhanced the early vasodilator activity of ET-1 revealing a functional antagonism between the two effects. The vasodilator effect of [Ala1"3""l '5]ET-1 was not affected by BQ-123 and ET-1 induced a similar vasodilatation, that was potentiated by BQ-123, suggesting the involvement of ETB-receptors in this vasodilator response. Marked regional differences were however observed which might be partly related to different levels of functional antagonism between ETB- and ETA-mediated effects, but differences in receptor types, or subtypes, cannot be excluded, mainly in the mesenteric and renals beds.

Endothelin and structurally related analogs distinguish between endothelin receptor subtypes.[Pubmed:1312833]

Biochem Biophys Res Commun. 1992 Mar 16;183(2):566-71.

The endothelin (ET) analog ET-1[1,3,11,15-Ala] was compared with ET-1, ET-2, ET-3 and sarafotoxins (SRTX) S6b and S6c for receptor binding and function. All the peptides exhibited high affinity binding and contracted rabbit pulmonary artery with near equal potency. In rat aorta both ET-3 and ET-1 [1,3,11,15-Ala] bound with much lower affinity than ET-1 while ET-3 displayed weak contractile potency and ET-1 [1,3,11,15-Ala] and SRTX-c were inactive. In rat left atria, ET-1 [1,3,11,15-Ala] and SRTX-c were weak inhibitors of binding and were also functionally inactive, whereas ET-1, ET-2, ET-3, and SRTX-b were equipotent in producing contractile responses. The data support the idea of there being a predominance of ETA receptors in rat aorta and ETB receptors in rabbit pulmonary artery. In rat left atria, the ET receptor could not be readily classified into ETA or ETB and suggests the existence of a new receptor subtype.