Experiments were designed to examine the effect of oxidized low density lipoproteins (Ox-LDLs) on the expression and the release of endothelin from cultured endothelial cells and intact blood vessels. Ox-LDLs (30-300 jtg/ml), but not native low density lipoproteins (200 ,ug/ml), stimulated the expression of preproendothelin mRNA in porcine and human endothelial cells, leading to a time-and concentrationdependent release of the peptide into the culture medium. The Ox-LDL-stimulated release of endothelin was mimicked by acetylated low density lipoprotein and abolished by downregulation of protein kinase C by phorbol ester. In the intact porcine aorta, Ox-LDLs, but not native low density lipoproteins, also increased the release of peptide in an endothelium-and concentration-dependent manner. The maximal effect was observed at a concentration of 100 ,g/ml. Incubation of the intact porcine aorta with the scavenger receptor antagonist dextran sulfate decreased the formation of endothelin evoked by Ox-LDLs. The Ox-LDL-stimulated production of the peptide was further augmented in the presence of thrombin (4 units/ml) and was unaffected by nitric oxide-generating compound 3-morpholinosydnonimine (10`M).These results suggest that Ox-LDL may be an endogenous mediator of the augmented release of endothelin observed in hyperlipidemia and atherosclerosis. The increased production of the peptide could contribute to vasospastic events and may promote vascular smooth muscle proliferation and progression of atherosclerotic vascular disease.

This study has investigated the ability of the vasoconstrictor peptide angiotensin II to activate human peripheral blood monocytes. Activation was monitored by measuring both the release of tumor necrosis factor a from monocytes and their adhesion to monolayers of human endothelial cells. Angiotensin II-elicited activation of monocytes was dose-dependent (half-maximally effective concentration =0.2 nM), saturable (maximally effective concentration =5 nM), and sensitive to inhibition by the angiotensin type 1 receptor antagonist ZD 7155. Such direct actions imply that angiotensin II is an important candidate stimulus for the subendothelial infiltration of monocytes observed in atherogenesis and hypertension.

Endothelin (ET), a peptide originally isolated from the supernatants of cultured endothelial cells, exerts a wide variety of biological effects in different tissues. Endothelial-cell-synthesized ET-1 has been proposed to act in a paracrine manner on adjacent smooth muscle cells (SMC) in vivo, with effects that include both vascular reactivity (vasodilation/vasoconstriction) and mitogenesis. This study, by the use of immunocytochemically characterized SMC (rVSMC) isolated from the aortas of spontaneously hypertensive rats, has investigated a possible autocrine role for ET in regulation of the vasculature. Although quiescent cultures of rVSMC apparently did not constitutively express prepro ET-1mRNA, ET-specific transcripts could be induced by a variety of growth factors (transforming growth factor beta [TGF-beta]; platelet-derived growth factor-AA homodimer [PDGF-A chain]) and vasoactive hormones (angiotensin II [Ang II], arginine-vasopressin, and ET-1 itself). The kinetics for prepro ET-1mRNA induction in rVSMC were characteristically rapid in onset and transient. Down-regulation of protein kinase C by 48 h pretreatment of rVSMC with phorbol ester markedly reduced the subsequent ability of rVSMC to express ET-1 transcripts and secrete ET-1 peptide in response to Ang II. Inducible prepro ET-1mRNA expression was accompanied by a cycloheximide-inhibitable release of ET-1 peptide into the medium of rVSMC. ET-1 peptide was determined by both radioreceptor- and radioimmunoassay. Stimulated rVSMC accumulated ET-1 (approximately 200 pg.10(6) cells-1 x 4 h-1) at levels that attained biological relevance (approximately 10(-10) M). Sep-pak C18 extracts of medium from stimulated rVSMC elicited contraction of isolated endothelium-denuded rat mesenteric resistance vessels, and this response was characteristically protracted and difficult to "wash out." Synthetic (porcine) ET-1 promoted the expression of transcripts for PDGF-A chain, TGF-beta, and thrombospondin in quiescent rVSMC. Such effects of ET-1 on gene expression may be relevant to the mitogenic potential of ET-1 on VSMC. Our findings imply a role for ET-1 in the control of vascular function via both paracrine and autocrine regulatory mechanisms. The expression of prepro ET-1mRNA and peptide biosynthesis by rVSMC may have both short-term (e.g., vasoconstriction) and long-term (e.g., structural remodeling) consequences. A sustained loop of autocrine stimulation by ET-1 in SMC could contribute toward the pathogenesis of vasospasm and/or atherosclerosis.

In cultured endothelial cells, endothelin is produced after stimulation with angiotensin II. The effects of angiotensin II and endothelin-1 on vascular sensitivity to norepinephrine were studied in perfused rat mesenteric resistance arteries. Expression of endothelin messenger RNA (mRNA) was determined in endothelial cells obtained from the mesenteric circulation.

Cardiac hypertrophy is largely due to cardiac fibroblast growth and increased synthesis of extracellular matrix. This study has investigated the contribution of the vasoactive hormone, angiotensin II, toward Invest. 1994Invest. . 93:2372Invest. -2378