Modulation of contractions to and receptors for endothelins in canine veins

Abstract

Experiments were designed to characterize endothelin receptors in canine femoral veins and to determine whether their distribution or sensitivity could be altered by chronic changes in blood flow and oxygen tension in veins proximal to an arteriovenous fistula. Endothelium was removed from unoperated or fistula-operated femoral veins of anesthetized dogs. Veins were cut into rings and suspended in organ chambers for the measurement of isometric force or frozen for isolation of membrane proteins. Endothelin-1, endothelin-3, and sarafotoxin S6c caused concentration-dependent increases in tension in all rings. In rings of unoperated veins, maximal tensions were significantly less to endothelin-3 and sarafotoxin S6c than to endothelin-1. In rings of fistula-operated veins, maximal tensions to endothelin-1 and endothelin-3 were the same. Contractions to endothelin-1 or endothelin-3 in unoperated veins were not inhibited by an antagonist of endothelin-A receptors, BQ-123. Binding of 125I-labeled endothelin-1 (125I-endothelin-1) to membranes from veins without endothelium increased as a function of membrane protein. Affinity of receptors, as determined by competitive inhibition of 125I-endothelin-1 was as follows: endothelin-1 > endothelin-3 > sarafotoxin S6c. Competitive inhibition of 125I-endothelin-1 by endothelin-3 and sarafotoxin S6c was significant for a two-site binding model in all veins. The total number of binding sites was reduced significantly in fistula-operated veins; the relative proportions of high- and low-affinity binding sites did not change. Affinity of high- and low-affinity receptors increased in fistula-operated veins.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased expression of endothelin receptors in the vasculature of portal hypertensive rats: Role in splanchnic hemodynamics

“…ET-B receptors are present on splanchnic vessels and mediate both endothelial-dependent vasodilation 11 and endothelial-independent vasoconstric- tion. [12][13][14] Indeed, we and others 12 demonstrate that 25% of the arterial pressor response to ET-1 in vitro is mediated via ET-B receptors present on the vascular smooth muscle of these vessels. It is possible therefore that the pressor response to ET-1 following activation of smooth muscle ET-B receptors is offset by the enhanced NO production following activation of ET-B receptors on endothelial cells.…”

“…However, it is known that chronic increases in blood flow in vivo 14,15 and in vitro 25 are associated with an enhanced response to the contractile effects of ET-1 in vivo concomitant with an increase in the number of ET-B receptors on these hyperemic vessels. 14,15 Moreover, the magnitude of the ET-1-induced contractions exceeded that which could be explained by activation of an elevated ET-B receptor population alone, suggesting that the ET-A receptor population may also be up-regulated in these vessels. 14,15 Of note, we have recently shown that NO-generating drugs are capable of dosedependently increasing the expression of ET receptors on vascular smooth muscle cells in vitro.…”

“…Total RNA (1-5 µg) was converted to cDNA using the Superscript II reverse-transcriptase (RT) system and oligo-dT primers (Life Technologies, Inc.). Briefly, total RNA (in Diethylpyrocarbonate water) was incubated with 200 U/µL Superscript II RNase H -RT in buffer containing 20 mmol/L Tris-HCl [pH 8.4], 2.5 mmol/L MgCl 2 , 0.5 mmol/L dNTP mix, 10 mmol/L dithiothreitol, and oligo-dT [12][13][14][15][16][17][18] (0.5 µg/mL) for 50 minutes at 42°C. Reactions were terminated with Escherichia coli RNase H (2 U/µL).…”

“…5,6,9,11 ET-B receptors are also present on vascular smooth muscle cells and have been shown to mediate vasoconstriction in veins 12,13 and some arteries. [14][15][16] The possible role of ET in the pathophysiology of PHT has recently been addressed in humans and animal models of PHT with or without parenchymal dysfunction. [17][18][19][20][21][22][23][24] While an overwhelming number of clinical studies have demonstrated increased ET levels in cirrhotic patients, 20,21 several studies have also reported decreased circulating levels of ET-1 in PHT.…”

“…20,21 Previous studies have also demonstrated that if blood flow is chronically increased locally, e.g., following an arteriovenous fistula, ET receptors are significantly up-regulated concomitant with an enhanced pressor responsiveness of the vasculature to the contractile effects of ET. 14,15 Moreover, chronic increases in flow induce an increase in ET receptor expression in vascular smooth muscle cells that is endothelium-dependent and is in part mediated by NO. 25 Finally, that enhanced NO production typical of PHT may contribute to the regulation of ET receptors in vivo is evident from studies that demonstrate NO-mediated up-regulation of ET receptors on vascular smooth muscle in vitro.…”