1. Metabolism of Big endothelin-1 (1-38) and (22-38) in the human circulation in relation to production of endothelin-1 (1-21)
A Hemsén, G Ahlborg, A Ottosson-Seeberger, J M Lundberg Regul Pept. 1995 Feb 14;55(3):287-97. doi: 10.1016/0167-0115(94)00119-i.
Healthy male volunteers received intravenous infusions of Big endothelin (ET)-1 (1-38) or Big ET-1 (22-38). Blood samples were drawn from catheters in the brachial and pulmonary arteries and the hepatic, renal, jugular and deep forearm veins. The in vivo half-lives of circulating plasma Big ET-1 (1-38) were 6.6 +/- 0.3 min for the initial phase and 23 +/- 1.4 min for the late phase. The corresponding half-lives of Big ET-1 (22-38) were considerably shorter, being 0.9 +/- 0.03 min (P < 0.01) and 3.1 +/- 0.4 min (P < 0.01), respectively. This was concordant with the efficient regional clearance of Big ET-1 (22-38), which was most prominent in the forearm muscle (51 +/- 3%), liver (44 +/- 5%) and kidney (43 +/- 3%) and less pronounced in the lungs (14 +/- 2%) and brain (22 +/- 5%). Significant fractional extraction of Big ET-1 (1-38) was only found for the liver (30 +/- 2%) and kidney (44 +/- 3%). During the infusion of Big ET-1 (1-38) a positive veno-arterial gradient of ET-1-LI was noted only for the kidney, indicating production of ET-1. In conclusion, whereas Big ET-1 (22-38) is eliminated in skeletal muscle, splanchnic, renal, pulmonary and cerebral vascular beds, Big ET-1 (1-38) is extracted mainly in the renal and splanchnic vasculature. Furthermore, plasma half-life of Big ET-1 (1-38) is much longer than that of both ET-1 and Big ET-1 (22-38) in man. Thus, for investigation of the secretory activity of the ET-1-system measurements of Big ET-1 (1-38) levels may be a better approach.
2. Hydrolysis of big endothelin-1 by a serine protease in the membrane fraction of human lung
G C Hanson, K E Andersson, E Gyllstedt, E D Högestätt, B F Lindberg Regul Pept. 1997 Jan 15;68(1):63-9. doi: 10.1016/s0167-0115(96)02105-2.
The hydrolysis of human big endothelin 1-38 (bigET-1) was investigated in the membrane fractions from three human lung specimens. The hydrolysis products were identified by HPLC or by amino acid analysis, peptide sequencing and mass spectrometry, and the contractile effects of synthetic bigET-1, synthetic ET-1 and the major metabolite were tested on isolated rabbit pulmonary arteries. The dominating hydrolysis product was identified as bigET1-31, formed by a chymostatin-sensitive enzyme. Soybean trypsin inhibitor also suppressed bigET1-31 formation, while two other serine protease inhibitors, 3,4-dichloroisocoumarin and aprotinin, had no (or a limited) inhibitory effect. Through a partly phosphoramidon-sensitive enzymatic activity, endothelin-1 (ET-1) was formed independently of bigET1-31. On isolated pulmonary arteries, bigET1-31 had a contractile effect similar to that of synthetic bigET-1, with pEC50% values of 7.3 +/- 0.1 (n = 6) and 7.1 +/- 0.1 (n = 8), respectively. The pEC50% value of ET-1 was 9.2 +/- 0.3 (n = 6). These results indicate that human pulmonary membranes, besides hydrolysing bigET-1 to ET-1, also express serine protease activity that is responsible for the formation of the biologically active product, bigET1-31.
3. Different pressor and bronchoconstrictor properties of human big-endothelin-1, 2 (1-38) and 3 in ketamine/xylazine-anaesthetized guinea-pigs
J P Gratton, G A Rae, A Claing, S Télémaque, P D'Orléans-Juste Br J Pharmacol. 1995 Feb;114(3):720-6. doi: 10.1111/j.1476-5381.1995.tb17198.x.
1. In the present study, the precursors of endothelin-1, endothelin-2 and endothelin-3 were tested for their pressor and bronchoconstrictor properties in the anaesthetized guinea-pig. In addition, the effects of big-endothelin-1 and endothelin-1 were assessed under urethane or ketamine/xylazine anaesthesia. 2. When compared to ketamine/xylazine, urethane markedly depressed the pressor and bronchoconstrictor properties of endothelin-1 and big-endothelin-1. 3. Under ketamine/xylazine anaesthesia, the three endothelins induced a biphasic increase of mean arterial blood pressure. In contrast, big-endothelin-1, as well as big-endothelin-2 (1-38), induced only sustained increase in blood pressure whereas big-endothelin-3 was inactive at doses up to 25 nmol kg-1. 4. Big-endothelin-1, but not big-endothelin-2, induced a significant increase in airway resistance. Yet, endothelin-1, endothelin-2 and endothelin-3 were equipotent as bronchoconstrictor agents. 5. Big-endothelin-1, endothelin-1 and endothelin-2, but not big-endothelin-2, triggered a marked release of prostacyclin and thromboxane A2 from the guinea-pig perfused lung. 6. Our results suggest the presence of a phosphoramidon-sensitive endothelin-converting enzyme (ECE) which is responsible for the conversion of big-endothelin-1 and big-endothelin-2 to their active moieties, endothelin-1 and 2. However, the lack of bronchoconstrictor and eicosanoid-releasing properties of big-endothelin-2, as opposed to endothelin-2 or big-endothelin-1, suggests the presence of two distinct phosphoramidon-sensitive ECEs in the guinea-pig. The ECE responsible for the systemic conversion of big-endothelins possesses the same affinity for big-endothelin-l and 2 but not big-endothelin-3. In contrast, in the pulmonary vasculature is localized in the vicinity of the sites responsible for eicosanoid release, an ECE which converts more readily big-endothelin-1 than big-endothelin-2.
