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E R Levin

Publications and source records attributed to E R Levin.

At least 37 records · Page 2Linked to original sources
PubMed1996

PGE2 and PGI2 inhibit ET-1 secretion from endothelial cells by stimulating particulate guanylate cyclase.

Prostaglandins (PG)E2 and prostacyclin (PGI2) can cause vasodilation in selective vascular beds and could act in part by inhibiting the production of the vasoconstrictor endothelin-1 (ET-1). We recently reported that these prostanoids inhibit ET-1 production/secretion from cultured endothelial cells via the generation of guanosine 3'-5'-cyclic monophosphate (cGMP). It is unclear whether this results from the stimulation of the particulate (membrane) of soluble (cytosolic) form of guanylate cyclase, and whether these effects are through an intermediate, such as nitric oxide. PGE2 and PGI2 each caused a three- to fourfold increase in both membrane and whole bovine aortic endothelial cell guanylate cyclase activity. The stimulations were significantly reversed (80-90%) by the compound LY-83583, an antagonist to cGMP generation, but were unaffected by methylene blue (MB), an inhibitor of nitric oxide-induced soluble guanylate cyclase. In contrast, the prostaglandins did not generate cGMP in cytosolic fractions. The prostaglandins inhibited ET-1 secretion from the intact cells, which was significantly prevented by LY-83583, but not by MB. Neither prostaglandin stimulated NO synthase activity, an indicator of nitric oxide generation. We conclude that PGE2 and PGI2 are likely to inhibit ET-1 secretion through the activation of the particulate guanylate cyclase, identifying a novel mechanism by which the prostanoids signal in the endothelial cell.

Aminoquinolines↗
PubMed1996

Endothelins as cardiovascular peptides.

The normal functional state of the vasculature and the events leading to the development of significant arterial disease involve the interaction of important vasoactive substances, which play important modulating or initiating roles in the development of hypertension and arteriosclerosis. Three endothelins have now been identified, of which ET-1 is the best characterized. ET-1 is produced by epithelial, mesangial, neuronal and glial, and liver cells, and is the most potent vasoconstrictor yet found. Each endothelin is derived from a different gene on separate chromosomes, and each binds to at least 2 types of receptor. The plasma half-life of ET-1 is about 7 min, and this provides a rapid mechanism for adjusting vascular resistance or blood pressure. The actions of endothelin are mediated through several pathways of postreceptor signaling, including activation of the mitogen-activated protein kinase cascade, which give rise to its growth-stimulating properties. Secretion of ET-1 from cultured endothelial cells is stimulated by a wide range of substances, and is inhibited by some prostaglandins. Endothelin in turn stimulates secretion of nitric oxide, arginine vasopressin and atrial natriuretic peptide, and participates in the hormonal control of salt and water balance. Hypoxia and ischemia augment ET-1 secretion, as does insulin, and this could play a role in the accelerated vascular disease of diabetes. ET-1 also causes bronchoconstriction and has been implicated in the development of acute asthma, primary pulmonary hypertension and pulmonary fibrosis. Its role in hypertension is still debatable, though most of the manifestations of congestive heart failure can theoretically be explained by the actions of ET-1. Endothelin also has extensive renovascular and parenchymal effects in the kidney. It is hoped that a fuller understanding of the role of endothelins in normal or pathologic vasculature will lead to effective therapy based on antagonism or augmentation of specific functions.

Animals↗
PubMed1995

Endothelins.

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Cardiovascular Diseases↗
PubMed1995

Atrial and brain natriuretic peptides stimulate the production and secretion of C-type natriuretic peptide from bovine aortic endothelial cells.

C-type natriuretic peptide (CNP) is a member of the natriuretic peptide family which is produced in vascular endothelial cells and may play an important paracrine role in the vasaculature. We sought to determine the regulation of CNP production by other vasoactive peptides from cultured aortic endothelial cells. The vasoconstrictors endothelin-1 and angiotensin II had little effect on the basal secretion of CNP. In contrast, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) strongly stimulated the secretion of CNP. BNP caused as much as a 400-fold enhancement above the basal accumulated secretion of CNP over 24 h at a concentration of 1 microM; this was 20 times greater than the stimulatory effect of ANP, BNP and ANP also significantly enhanced the production of new CNP protein (translation) and mRNA expressed in the BAEC. In contrast, C-ANP-4-23, a truncated form of ANP which selectively binds to the natriuretic peptide clearance receptor, did not stimulate CNP secretion. The enhanced production and secretion of CNP, caused by either ANP or BNP, was significantly prevented by LY 83583, an inhibitor of cGMP generation, and was also attenuated by KT 5823, an inhibitor of cGMP-dependent protein kinase. Our results indicate that ANP and BNP can stimulate CNP production through a guanylate cyclase receptor on endothelial cells. BNP is a much more potent stimulator of CNP secretion, compared to ANP. Our findings suggest that the vasodilatory, and anti-mitogenic effects of ANP and BNP in the vasculature could occur in part through CNP production and subsequent action if these interactions occur in vivo.

Angiotensin II↗
PubMed1994

Prostaglandin E2 and prostacyclin inhibit the production and secretion of endothelin from cultured endothelial cells.

Endothelin-1 (ET-1) is the most potent endogenous vasoconstrictor yet identified. This peptide plays an important role in the regulation of arterial tone, in part through its interaction with endogenous vasodilator compounds. To understand the interactions of endothelin with the vasoactive prostaglandins (PGs), we determined the effects of prostaglandin E2 (PGE2), prostacyclin (PGI2), and thromboxane A2 on ET-1 synthesis and secretion from cultured bovine aortic endothelial cells and on ET-1 action in aortic smooth muscle cells. Both PGE2 and PGI2 (vasodilator prostaglandins) caused an approximately 40% inhibition of basal ET-1 secretion and a 50% inhibition of serum-stimulated ET-1 secretion in a dose-related and time course fashion. In contrast, the vasoconstrictor prostaglandin, thromboxane A2, had no effect on ET-1 secretion. PGE2 and PGI2 similarly inhibited the basal production of new ET-1 protein (translation) by 40-50% and inhibited the basal steady-state mRNA expression of ET-1 in bovine aortic endothelial cells by 60-70%. Both prostaglandins also caused an approximately 55% inhibition of ET-1 transcription, as shown by chloramphenicol acetyltransferase reporter studies. PGE2 and PGI2 strongly stimulated cGMP generation; both the PG stimulation of cGMP and the inhibition of ET-1 secretion and translation were reversed by LY83583, a general inhibitor of cGMP generation. The PG-induced inhibition of ET-1 secretion and translation was also reversed by KT5823, an inhibitor of cGMP-dependent protein kinase, but not by (Rp)-adenosine cyclic 3':5'-monophosphate, an inhibitor of protein kinase A activation. PGE2 and PGI2 also inhibited both basal and ET-1-stimulated DNA synthesis in aortic smooth muscle cells by approximately 45% through a cGMP-dependent mechanism. Therefore, two endogenous PGs, known to be important vasodilators in vivo, significantly inhibit the transcription, translation, secretion, and action of ET-1. We propose that the vasodilator action of the PGs results, in part, from their ability to inhibit the production of this potent vasoconstrictor.

Alkaloids↗
PubMed1994

Insulin stimulates thyroid hormone receptor alpha gene expression in cultured bovine aortic endothelial cells.

Thyroid hormones and insulin regulate numerous cell processes and potentially interact through the transcriptional regulation of key genes. For instance, thyroid hormones stimulate the transcription of the fatty acid synthase and malic enzyme genes in chick embryonic hepatocytes, while insulin amplifies these effects. It is possible that insulin augments these actions of thyroid hormone by stimulating production of the thyroid hormone nuclear receptor (TR). In these studies, we examined the regulation of TR production/gene expression by insulin in bovine aortic endothelial cells (BAEC). We demonstrate that insulin significantly stimulates the gene expression of the TR alpha receptor, from BAEC. Insulin causes a maximal threefold induction above control TR alpha steady state mRNA levels in time and dose-related fashion in these cells. The increased mRNA mainly resulted from a twofold increase in transcription, as determined by nuclear run on. Insulin also increases thyroid receptor number and thyroid hormone binding, determined by Scatchard analysis of competitive inhibition binding studies. An established observation is that insulin can synergistically augment thyroid hormone-induced transcriptional activation of several important genes. It has also been previously determined that thyroid hormone action correlates closely to TR nuclear receptor number. Therefore, our studies, which show that insulin stimulates TR alpha production, suggests a potential mechanism whereby insulin can augment thyroid hormone transcriptional action.

Animals↗
PubMed1994

High density lipoproteins stimulate the production and secretion of endothelin-1 from cultured bovine aortic endothelial cells.

The concentration of HDL in the blood inversely correlates with the incidence of cardiovascular disease, probably related to the ability of these lipoproteins to efflux cholesterol from vascular cells. it is also possible that HDL affect the production or action of vasoactive peptides implicated in the development of vascular diseases. Therefore, we determined the effects of human HDL on the production and secretion of endothelin-1 (ET-1) from cultured bovine aortic endothelial cells. HDL produced a highly significant stimulation of endothelin secretion (maximum 240% of control), even at very low levels of lipoproteins (1 microgram/ml). HDL also stimulated the translation of ET-1 by twofold in the bovine aortic endothelial cells. In contrast, HDL had no significant effect on steady state mRNA levels, transcript degradation, or transcription. Stimulation of ET-1 secretion by HDL was dependent on protein kinase C activation. Purified apo A-I, the major apoprotein of HDL, increased ET-1 secretion and translation approximately 85% as potently as HDL. Our results indicate that low concentrations of human HDL strongly stimulate the production of ET-1, a powerful vasoconstrictor and mitogen for the vascular smooth muscle cell. We propose that HDL may participate in the regulation of vasomotor tone through this potentially important effect in the vasculature.

Animals↗
PubMed1994

Astrocyte growth is regulated by neuropeptides through Tis 8 and basic fibroblast growth factor.

The important intracellular mechanisms of astrocyte growth are not well defined. Using an inhibitor of astrocyte proliferation, atrial natriuretic peptide (ANP), and the glial mitogen endothelin (ET-3), we sought a common pathway for growth regulation in these neural cells. In cultured fetal rat diencephalic astrocytes, ANP selectively and rapidly inhibited the Tis 8 immediate early gene and protein. After 4 h, ANP selectively inhibited the basic fibroblast growth factor (bFGF) gene and protein. ET-3 significantly stimulated both Tis 8 and bFGF mRNAs and protein, but also stimulated several other immediate early and growth factor/receptor genes. An antisense oligonucleotide to Tis 8 strongly prevented ET-stimulated thymidine incorporation, while the inhibitory action of ANP was enhanced. The Tis 8 antisense oligonucleotide also significantly reversed ET-stimulated bFGF transcription and enhanced the bFGF inhibition caused by ANP. In addition, an antisense oligonucleotide to bFGF significantly reversed the ET-stimulated thymidine incorporation and enhanced the ANP inhibition of DNA synthesis. The sequential modulation of Tis 8, followed by bFGF, provides a novel mechanism for both positive and negative regulation of astrocyte growth by endogenous neuropeptides.

Astrocytes↗
PubMed1993

Natriuretic peptide C-receptor: more than a clearance receptor.

The natriuretic peptide family of proteins acts through two distinct classes of receptors that signal through entirely different mechanisms. The elucidation of the structure of the guanylate cyclase-containing receptor proteins has provided a better understanding of the mechanisms by which the natriuretic peptides regulate diverse functions of salt and water balance, in conjunction with other vasoactive peptides. A second receptor class was named for the originally described function of this protein to clear the natriuretic peptides from plasma. The mechanism of signaling for the natriuretic peptide clearance receptor is not firmly established. All known members of the natriuretic peptide family bind to, and can theoretically act through, the clearance receptor. This review summarizes the known features of the natriuretic peptide clearance receptor, a protein that contains extracellular and transmembrane domains and a short cytoplasmic segment. Recent studies have pointed to new and potentially important functions for this protein in mediating the actions of the natriuretic peptides.

Animals↗
PubMed1993

Insulin stimulates endothelin binding and action on cultured vascular smooth muscle cells.

Hyperinsulinemia has been implicated as a separate risk factor for the development of accelerated cardiovascular disease, but the mechanism is unknown. Recently, we and several other groups have shown that insulin stimulates the production and secretion of the vasoconstrictor peptide endothelin-1 (ET-1) from vascular endothelial cells, and hyperinsulinemia results in increased plasma ET levels in vivo. However, the interactive effects of diabetes, insulin, and glucose on ET target tissues, like those on vascular smooth muscle cells (VSMC), are not well defined. In these studies, we examined the effects of the diabetic factors on ET receptors and [3H]thymidine incorporation into cultured cells prepared from control, streptozocin-diabetic, insulin-treated diabetic, and hyperinsulinemic rats. Scatchard analysis of saturation binding studies revealed a 2-fold increase in ET receptor number in normal VSMC treated in vitro with insulin, whereas glucose had no significant effect. Neither treatment affected receptor affinity. Similarly, aortic smooth muscle cells, brain capillary pericytes, and kidney afferent arteriolar smooth muscle cells from rats made hyperinsulinemic in vivo each showed approximately a 2-fold increase in receptor number. This increase in receptor density probably resulted from the stimulation of receptor protein production, because insulin caused a maximal 2.3 +/- 0.3 (+/- SEM) fold increase in the ETA receptor mRNA expressed in cultured VSMC by 4 h. Both insulin and ET significantly increased thymidine incorporation in aortic VSMC, but ET-1 was much more potent in this regard. However, the combined effects of insulin plus ET-1 resulted in a 10-fold increase in this index of cell proliferation, significantly different from the effects of either peptide alone. We postulate that hyperinsulinemia in vivo may potentiate ET release and receptor-mediated action, thereby contributing to vascular disease in the setting of diabetes.

Animals↗
PubMed1993

Insulin stimulates production and secretion of endothelin from bovine endothelial cells.

Endothelin, a vasoconstrictor peptide secreted from endothelial cells, has been thought to play a role in various forms of vascular disease. Diabetes mellitus is well known for its association with accelerated atherosclerosis and microvascular damage. Although the basis for the vessel insult is multifactorial, hyperinsulinemia is thought to contribute by an unknown mechanism. In this study, we sought to determine whether insulin stimulates the production and secretion of ET-1 as a possible basis for the association of hyperinsulinemia and vascular disease. We demonstrated that insulin significantly stimulates the gene expression and secretion of ET-1 from cultured BAEC, and that insulin increases ET-1 mRNA expressed in BBCEC. Insulin caused a maximal twofold inducement above control ET-1 mRNA expression in a dose-related fashion in BAEC. The increased mRNA resulted from increased transcription, as determined by nuclear run-off studies. Increased ET-1 mRNA was seen after 4 h of incubation with insulin: the peak occurred at 6-8 h and persisted for 24 h. Insulin caused as much as a fourfold stimulation of ET-1 secretion from BAEC in a dose-related fashion, including a twofold increase at a physiological concentration (10(-9) M): The increase began at 1 h of incubation and continued for the entire 24-h incubation period. The insulin-induced increases in both ET-1 mRNA and ET-1 protein secretion were significantly attenuated by genistein, a tyrosine kinase inhibitor. This stimulation probably occurred through the insulin receptor, because IGF-1 had no effect on ET-1 gene expression or secretion from these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1992

Atrial natriuretic peptide inhibits the production and secretion of endothelin from cultured endothelial cells. Mediation through the C receptor.

Atrial natriuretic peptide (ANP) and endothelin-1 (ET-1) are vasoactive peptides produced in cells of the cardiovascular system. We examined the effects of ANP on ET-1 transcription, production (translation), and secretion in cultured bovine aortic endothelial cells (BAEC). ANP and C-ANP 4-23 (a specific ligand for the C or non-guanylate cyclase receptor) equipotently inhibited the synthesis of prepro-ET-1 and ET-1 proteins in BAEC by at least 50%. Both of these forms of ANP and another C receptor specific ligand, nanopiperazine ANP (11-15)-NH2, inhibited ET-1 secretion by as much as 55%. LY 83583, an inhibitor of ANP-induced cGMP generation, failed to reverse the ANP-induced inhibition of ET-1 secretion. This further indicated that the guanylate cyclase-linked B receptor is not involved. The decreased ET-1 secretion caused by C-ANP 4-23 was reversed by 8-bromo-cAMP or amiloride, which prevents ANP-induced inhibition of cAMP. We also found that ANP and C-ANP 4-23 augmented ET-1 mRNA levels in BAEC by prolonging the mRNA half-life. ANP or cycloheximide comparably inhibited ET-1 translation while increasing ET-1 mRNA levels, suggesting that the two events are related. These results indicate that ANP inhibits ET-1 protein production and secretion while stabilizing the ET-1 mRNA. The effects of ANP are mediated through the C receptor and are probably the result of ANP inhibiting the generation of cAMP. These findings suggest a potentially important new function for this receptor to mediate, in part, the interactions of ANP and ET in the vasculature.

Animals↗
PubMed1992

Endothelin receptors on cultured fetal rat diencephalic glia.

The recently described family of proteins, the endothelins, are produced in neurons and bind to extravascular sites in the CNS. To characterize these receptors, we carried out studies on cultures of fetal rat diencephalic glia. Scatchard analysis of saturation binding studies was done for astrocytes (greater than 95% glial fibrillary acidic protein positive). For endothelin 3 (ET-3) and ET-1, respectively, a single receptor class of KD 0.41 +/- 0.05 and 0.62 +/- 0.04 nM and a receptor density of 42 +/- 0.8 and 58 +/- 1.1 fmol/mg of glial protein was found. Bound and cross-linked 125I-ET-3 or ET-1 showed a single predominant receptor band at Mr 52,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis; a minor band at 50,000 was also seen. At concentrations equal to the receptor KD, the major brain form of ET, ET-3, stimulated a nearly 200% increase in the incorporation of tritiated thymidine into glia. ET-3 and ET-1 significantly impaired the ability of atrial natriuretic peptide (ANP) to generate cyclic GMP, and isoproterenol to generate cyclic AMP. The ability of ET to inhibit ANP-induced cyclic GMP generation was reversed by cycloheximide and actinomycin-D, whereas the inhibition of isoproterenol-induced cyclic AMP generation was partially and significantly blocked by inhibitors of calcium influx, protein kinase C action, or G protein activation, as well. Astrocytes from this part of the brain are a potential target cell for endothelin, assuming these findings are present in vivo. This neuropeptide may serve as a growth stimulator for astrocytes and modulator of the actions of catecholamines or ANP on glia by inhibiting second messenger generation.

Affinity Labels↗
PubMed1992

Arginine vasopressin stimulates atrial natriuretic peptide gene expression and secretion from rat diencephalic neurons.

The central nervous system modulates cardiovascular function and fluid and electrolyte balance in part through the actions of vasoactive peptides/neurotransmitters. The presence of several vasoactive peptides and their receptors in the hypothalamus suggests a possible interaction at this site. One level at which vasoactive peptides such as arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) might interact is through the mutual regulation of production and secretion in the hypothalamus. To determine whether AVP modulates ANP gene expression and secretion, we cultured fetal rat diencephalic neurons in the presence of AVP. AVP induced a significant increase in ANP secretion in dose-related fashion (mean +/- SEM basal ANP, 87 +/- 4 pg/ml; maximal mean AVP-stimulated ANP, 146 +/- 6 pg/ml; P less than 0.05, by analysis of variance). Neither oxytocin nor the vasoactive neuropeptide angiotensin-II had any effect on ANP secretion. The stimulatory effect of AVP was significantly blocked by coincubation with a V1 receptor antagonist, but was unaffected by a V2 receptor antagonist. The immunoreactive ANP secreted in response to AVP was the major brain isoform, ANP-(103-126). Coincubation with a calcium channel antagonist, nifedipine, had no effect on AVP-induced ANP secretion, while ryanodine, an inhibitor of intracellular calcium mobilization, significantly reduced the stimulatory effect of AVP. AVP induced a dose-related, nearly 3-fold maximal increase in ANP mRNA expression at 4 h. Coincubation of the neurons with a V1 receptor antagonist also significantly attenuated the increased ANP gene expression induced by AVP. These results indicate that AVP acts directly through V1 receptors on cultured fetal rat diencephalic neurons to augment ANP gene expression and secretion of the peptide. The effects are probably related to AVP-stimulated mobilization of intracellular calcium and not the result of calcium influx into the cell. These studies provide the first evidence that AVP modulates ANP production from cultured neurons. In the central nervous system, these two vasoactive neuropeptides might interact in part through the regulation of ANP production by AVP.

Analysis of Variance↗
PubMed1991

Natriuretic peptides inhibit rat astroglial proliferation: mediation by C receptor.

The processing and secretion of atrial natriuretic peptide (ANP) from neurons and the expression of high-affinity receptors on astroglia from primary cultures of fetal rat diencephalon have recently been demonstrated. Thus natriuretic peptides may play a role in neuronal-glial signaling, but a physiological role has not been characterized. In these studies, we show that ANP and brain natriuretic peptide significantly (P less than 0.05) decrease the incorporation of [3H]thymidine into astroglia in the presence of fetal bovine serum and inhibit the proliferation of these cells in the presence or absence of serum. These effects were evident at concentrations of natriuretic peptides (10(-10) M) characteristic of the receptor Kd and were not seen in cultured bovine brain capillary endothelial cells, another brain cell expressing high-affinity receptors for the natriuretic peptides. The antiproliferative effects were potently produced by ANP-(4-23), a ring-deleted analogue of ANP-(1-28), which at the concentrations used in this study binds only to the C or low-molecular-weight natriuretic peptide receptor. Thymidine incorporation was not affected by adenosine 3',5'-cyclic monophosphate (cAMP), the inhibition of which has been proposed to mediate postbinding signaling of the C receptor. Epidermal growth factor (10(-9) M) produced an 87% increase in thymidine incorporation, which was not significantly inhibited by either form of ANP. Thus natriuretic peptides in the brain may serve as antigrowth factors for glia through binding to a receptor previously felt to function solely in peptide clearance. The inhibitory effects are not the result of inhibiting the proliferative effects of an endogenous growth factor and are cAMP independent.

Animals↗
PubMed1991

Endothelin increases atrial natriuretic peptide production in cultured rat diencephalic neurons.

The vasoactive peptides atrial natriuretic peptide (ANP) and endothelin have been localized to several areas of the extravascular brain where they are produced in neurons, often overlapping in distribution. Since endothelin has been found to increase ANP secretion from the heart, we examined a possible regulation by endothelin of the secretion and production of ANP in fetal diencephalic cultures of neurons from gestational day 16 rats. Endothelin produced a concentration-related increase in the secretion of ANP. The ability of endothelin to induce ANP secretion was dependent upon calcium, since added nifedipine, a calcium channel blocker, significantly reversed the effects of this vasoconstrictor peptide. ANP 103-126 was the predominant form secreted, as determined by HPLC followed by RIA. The production of this peptide, assessed by specific mRNA expression, was increased more than 2-fold, in dose-related fashion. These studies provide the first evidence that endothelin regulates ANP gene expression in the brain. Additionally, our secretion studies from neurons are consistent with the known stimulatory effects of endothelin on ANP release from the heart. The regulation of ANP production and secretion by the vasoconstrictor peptide endothelin is one level at which ANP and endothelin might interact in the in vivo brain.

Animals↗