Rat Blood Vessels Research Articles

P-329 - Insulin acts on calcitonin gene-related peptide (CGRP) receptors in mesenteric resistance blood vessels of rats

P-329 - Insulin acts on calcitonin gene-related peptide (CGRP) receptors in mesenteric resistance blood vessels of rats

Quantitative Analysis of Calcitonin Gene-Related Peptide- and Neuropeptide Y-Immunoreactive Nerve Fibers in Mesenteric Blood Vessels of Rats Irradiated with Cobalt-60 Gamma Rays

The effects of 60Co gamma rays on calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers and neuropeptide Y (NPY)-immunoreactive nerve fibers were examined in mesenteric blood vessels of rats. Using a free-floating immunostaining streptavidin-biotin peroxidase complex method combined with a nickel-enhancement technique, we found that the distribution pattern of these two peptidergic nerve fibers in superior mesenteric arteries and superior mesenteric veins did not change, while the densities of CGRP-immunoreactive nerve fibers and NPY-immunoreactive nerve fibers in superior mesenteric arteries and veins varied with the time after irradiation. The results suggested that CGRP and NPY may be important in the development and elimination of radiation-induced injury.

A quantitative study on vascular angiotensin II receptors in rats with portal hypertension.

Angiotension-II (A-II) receptor maximal binding capacity (Bmax) and dissociation constants (Kd) of different blood vessels in rats with prehepatic portal hypertension were studied by radioligand binding analysis. The results showed that the A-II receptor Bmax in the thoracic aorta, superior mesenteric artery and portal vein of portal hypertensive animals (113.7 +/- 19.4 fmol/mg protein, 206.9 +/- 39.3 fmol/mg protein and 31.5 +/- 9.2 fmol/mg protein respectively) was all significantly lower than that of controls (146.8 +/- 24.5 fmol/mg protein, 297.2 +/- 44.7 fmol/mg protein and 53.4 +/- 12.1 fmol/mg protein respectively, P < 0.01). The A-II receptor Kd in the superior mesenteric artery was markedly increased in portal hypertensive animals (1.03 +/- 0.11 nmol/L) compared with that in controls (0.88 +/- 0.08 nmol/L, P < 0.05). In the thoracic aorta and portal vein, the A-II receptor Kd in portal hypertensive animals was slightly higher than that in controls, but no significant difference was observed between the two groups. The results suggested that the vascular hyporesponsiveness to A-II in portal hypertension was caused partially by a reduction in number and a decrease in affinity of vascular A-II receptors, and these changes might possibly lead to the formation of hyperdynamic circulation.

Reduced vascular beta-adrenergic receptors and catecholamine response in rats with lead induced hypertension.

Beta-adrenergic receptor-mediated relaxation of blood vessels declines in lead induced hypertension although the mechanism is unknown. We have utilized the aorta of lead hypertensive rats to investigate this problem. In an effort to elucidate the mechanism responsible for this alteration we examined plasma catecholamine levels, vascular beta-adrenergic receptor density, and cyclic adenosine monophosphate (cAMP) production in lead hypertensive rats. The density of beta-adrenergic receptors was 41% lower in the blood vessels of lead hypertensive rats compared with control rats. The corresponding apparent Kd values were not significantly different between two groups. The plasma catecholamine level was significantly higher in lead hypertensive rats compared with controls (P < 0.001). Stimulation of the vascular beta-adrenoceptor resulted in significantly lower levels of cAMP in lead hypertensive rats compared with controls (P < 0.001). The present results suggest that there is reduced beta-adrenoceptor density and diminished cAMP accumulation in blood vessels from lead hypertensive rats. Plasma catecholamine may play a role in the diminished beta-adrenoceptor and responsiveness to cAMP-mediated vascular relaxation in lead exposure.

Detection and characterization of a protein isoaspartyl methyltransferase which becomes trapped in the extracellular space during blood vessel injury.

Injury to rat blood vessels in vivo was found to release intracellular pools of protein D-aspartyl/L-isoaspartyl carboxyl methyltransferase (PIMT) into the extracellular milieu, where it becomes trapped. This trapped cohort of PIMT is able to utilize radiolabeled S-adenosyl-L-methionine (AdoMet) introduced into the circulation to methylate blood vessel proteins containing altered aspartyl residues. As further shown in this study, methylated substrates are detected only at the specific site of injury. In vitro studies more fully characterized this endogenous PIMT activity in thoracic aorta and inferior vena cava. Methylation kinetics, immunoblotting, and the lability of methylated substrates at mild alkaline pH were used to demonstrate that both types of blood vessel contain an endogenous protein D-aspartyl/L-isoaspartyl carboxyl methyltransferase (PIMT). At least 50% of the PIMT activity is resistant to nonionic detergent extraction, suggesting that the enzyme activity becomes trapped within or behind the extracellular matrix (ECM). Quantities of lactate dehydrogenase (LDH), another soluble enzyme of presumed intracellular origin, were found to be similarly trapped in the extracellular space of blood vessels.

Salmeterol reduces early- and late-phase plasma leakage and leukocyte adhesion in rat airways.

We examined the effect of salmeterol, a long-acting beta2-adrenergic receptor agonist, on ovalbumin-induced plasma leakage and leukocyte adhesion in tracheal blood vessels of unanesthetized brown Norway rats. Ovalbumin challenge of sensitized rats resulted in both early and late phases of plasma leakage as measured with Evans blue. The early phase occurred during the challenge. The late phase began 2 h after the challenge, peaked at 4 h, and ended by 24 h. Ovalbumin challenge also increased the number of adherent leukocytes in mucosal blood vessels at 4 h. Nebulized salmeterol (5 mg/ml for 10 min) administered before the challenge inhibited the early-phase leak by 26%, 58%, or 85%, depending upon whether the interval between pretreatment and challenge was 0.5, 1, or 4.5 h, respectively. Similarly, salmeterol pretreatment (0.05 to 5 mg/ml for 10 min) reduced the late-phase leak at 4 h. Late-phase leakage was completely blocked at concentrations of 0.5 mg/ml or greater. This inhibitory effect was prevented by prior injection of the beta2-adrenergic receptor antagonist ICI-118,551. Salmeterol pretreatment also reduced the adherence of neutrophils, eosinophils, monocytes, and lymphocytes in mucosal blood vessels at 4 h. We conclude that salmeterol pretreatment can reduce the plasma leakage and leukocyte adhesion in early- and late-phase responses after antigen challenge through its action on beta2 receptors.

Alcohol dehydrogenase of human and rat blood vessels: Role in ethanol metabolism

Alcohol dehydrogenase (ADH) activity has been detected in all arteries and veins examined from humans and rat. In distinct human autopsy vessels, activity values range from 0.9±0.2 to 9.9±7.7 mU/mg. Distribution of the activity in human aorta was: intima (23.5%), media (74%) and adventia (2.5%). In most of the samples the β1β1 isozyme of class I ADH was the only form responsible for the ADH activity. Class IV ADH (σσ-ADH) was present in three of the 28 individuals examined. The rat blood vessels showed class IV, but not class I, ADH localized in endothelium and media. The physiological role of vascular ADH is probably related to retinoid metabolism and elimination of lipid peroxidation aldehydes. A contribution to human ethanol metabolism is supported by the significant amount of low- K m activity and the extension of the vascular system. © 1997 Federation of European Biochemical Societies.

Enhanced expression of endothelin-1 gene in resistance arteries in severe human essential hypertension.

Endothelins are potent vasoconstrictors, and may also act as mitogens and hypertrophic agents. Expression of a member of this family of peptides, endothelin-1, is enhanced in the endothelium of blood vessels of rats with severe forms of hypertension, even in the absence of elevated plasma endothelin levels. In some of these hypertensive models enhanced endothelin-1 gene expression may contribute to vascular hypertrophy of small arteries and to elevation of blood pressure. To establish whether endothelin-1 may play a role in essential hypertension in humans, in whom plasma levels are known to be usually within normal limits, by examining the expression of the endothelin-1 gene in resistance-size arteries of normotensive subjects, and in humans with mild and severe hypertension. Using in-situ hybridization, the abundance of endothelin-1 messenger RNA transcripts was evaluated in small arteries of subcutaneous gluteal fat obtained by biopsy in normotensive and hypertensive patients. Vessels from five normotensive subjects and four untreated mild essential hypertensive patients did not exhibit topographically localized specific labeling with the antisense human endothelin-1 probe. Biopsies from four untreated hypertensive patients with moderate-to-severe blood pressure elevation, in contrast, showed a heavy density of grains on endothelial cells of small arteries of gluteal subcutaneous fat, corresponding to hybridization of the antisense human endothelin-1 complementary RNA probe with endothelin-1 messenger RNA. Some patients with moderate-to-severe essential hypertension, similar to some experimental rat models with severe blood pressure elevation, exhibit enhanced endothelial expression of the endothelin-1 gene. This is the first demonstration that overexpression of the endothelin-1 gene may occur in the vascular wall in a small sample of this subset of hypertensive patients. This pathophysiologic phenomenon could play a role in blood pressure elevation and perhaps in the pathogenesis of vascular hypertrophy. Treatment with endothelin receptor antagonists may offer a novel therapy for these moderate-to-severe hypertensive patients.

Specific adrenomedullin binding sites and hypotension in the rat systemic vascular bed

The potent vasodilator peptide, adrenomedullin, has been shown to be present in plasma, suggesting a physiological role in cardiovascular control. Here we investigated the hypotensive action of adrenomedullin in vivo, using the anaesthetised rat as the bioassay model, and adrenomedullin binding sites using ligand binding assays on rat blood vessel membranes. Rat αCGRP and both human and rat adrenomedullins induced dose-dependent, powerful and long-lasting hypotensive effects. At peptide doses used in this study (0.02–2 nmol/kg), the efficacy of both human and rat adrenomedullins was lower than that of rat αCGRP. The CGRP 1-receptor antagonist, human CGRP(8–37) (200 nmol/kg) was able to completely inhibit the hypotensive effect of rat αCGRP (0.2 nmol/kg) but not that of rat adrenomedullin (2 nmol/kg), implying that the adrenomedullin action is independent of CGRP 1-receptors. Ligand binding assays confirmed the presence of both CGRP and adrenomedullin binding sites in rat blood vessels. The 125I-rat adrenomedullin binding site has a K d = 0.32 ± 0.12 nM ( n = 4) for rat adrenomedullin but has a K i > 10 −6M for rat αCGRP. Chemical cross-linking and SDS-PAGE analysis revealed theadrenomedullin binding protein to have a M r of 83 000 with a minor band of M r = 99 000. The results suggest that the hypotensive effect of adrenomedullin may be mediated via specific adrenomedullin binding sites, in vivo.

Effect of NG-nitro-L-arginine methylester (L-NAME) on functional and biochemical alpha 1-adrenoceptor-mediated responses in rat blood vessels.

1. The modulation by NG-nitro-L-arginine methylester (L-NAME) of alpha 1-adrenoceptor-mediated contraction was investigated on isolated segments of rat tail artery and aorta. The influence of L-NAME on inositol phosphates accumulation by alpha 1-adrenoceptor agonists was also investigated to elucidate the intracellular mechanism responsible for this modulation. 2. In aorta but not in tail artery L-NAME (30 microM) enhanced the sensitivity (3.3 times) and the maximum contraction (Emax) induced by the full agonist, phenylephrine. 3. St-587, a partial alpha 1-adrenoceptor agonist, behaved as a weak agonist in the aorta (22.2% of phenylephrine Emax). However, when the same agonist was studied in tail artery rings a maximum contraction that was 78.4% of the phenylephrine induced Emax was reached. 4. L-NAME increased (3.3 times) the Emax for St-587 contraction in the aorta but not in the tail artery. Sensitivity to St-587 was slightly but significantly (P < 0.001) enhanced (1.9 times) by L-NAME in tail artery segments. 5. Contractile responses to phenylephrine after partial alkylation with phenoxybenzamine were analyzed by the nested hyperbolic null method. To elicit 50% of Emax for contraction only 1.1% of the receptors in the tail artery and 21% of the receptors in the aorta need to be occupied. These results indicate a higher receptor reserve for the tail artery than the aorta. 6. In the tail artery but not in the aorta, St-587 activates phosphoinositide turnover. The presence of L-NAME was without effect on inositol phosphates accumulation induced by this partial alpha 1-adrenoceptor agonist. 7. The maximum contraction induced by phenylephrine, after partial alpha-adrenoceptor alkylation, was enhanced by L-NAME in tail artery rings. However, the NO synthase inhibitor was unable to modify the phenylephrine-induced accumulation of inositol phosphates in the presence of phenoxybenzamine. 8. These results indicate that the differences in St-587-induced contraction and the modulation by L-NAME of alpha 1-adrenoceptor-mediated contraction observed between the tail artery and aorta are associated with differences in receptor reserve. In addition, our biochemical studies indicate that the potentiating effect of L-NAME is independent of intracellular calcium release via phosphatidylinositol turnover.

Enhanced expression of the endothelin-1 gene in blood vessels of DOCA-salt hypertensive rats: correlation with vascular structure.

Endothelin (ET)-1 is a potent vasoconstrictor peptide which is also endowed with hypertrophic and mitogenic properties. Enhanced ET-1 gene expression in blood vessels of rats with hypertension induced by deoxycorticosterone acetate (DOCA)-salt has been previously demonstrated. The objective of this study was: (1) to investigate the individual effects of salt and DOCA, and of the development of hypertension in DOCA-salt-hypertensive rats, on ET-1 gene expression in blood vessels; and (2) to correlate the presence of enhanced ET expression and the severity of vascular hypertrophy. By providing salt and/or DOCA to rats which were or were not unilaterally nephrectomized, groups of rats with variable degrees of blood pressure elevation were generated. Increased abundance of ET-1 mRNA and a greater content of immunoreactive ET-1 were found with progression of hypertension in aorta and the mesenteric arterial bed only in unilaterally nephrectomized DOCA-salt-treated rats (DOCA-salt-hypertensive rats). Vascular expression of ET-1 was not enhanced in other DOCA-or salt-treated rats, even when blood pressure rose to a mean systolic pressure of 180 mm Hg. The wet weight of aorta and the mesenteric arterial bed, the media thickness, the media cross-sectional area, and the media-to-lumen ratio of mesenteric small arteries of all groups of rats exhibited a close correlation with systolic blood pressure. In DOCA-salt-hypertensive rats after 5 weeks, in which overexpression of ET-1 was maximal, the vascular morphometric parameters were excessive for the level of systolic blood pressure. However, in DOCA-salt-hypertensive rats treated with the combined ETA/ETBET receptor antagonist bosentan, vascular morphometry correlated closely with blood pressure, even though blood pressure was only slightly lower than than of untreated DOCA-salt-hypertensive rats. These data support the hypothesis that ET-1 gene overexpression in blood vessels may accentuate vascular hypertrophy in some forms of hypertension.

Endothelin in hypertension

The endothelins, 21-amino-acid peptides produced by the endothelium of blood vessels and many other tissues such as the kidney, brain, endocrine organs, etc., are potent vasoconstrictors, and are also endowed with mitogenic and cell hypertrophic properties. Endothelin may be involved in the pathogenesis of hypertension through vascular, renal, endocrine, and neural effects. Although many studies have been performed to test the hypothesis that these peptides have a pathophysiologic role in hypertension, it is only recently that evidence has been found of enhanced production of endothelin-1 in some models of hypertension, particularly in blood vessels in deoxycorticosterone acetate-salt hypertensive rats. Vascular responses to endothelin-1 have been shown to be normal or depressed in many models of experimental hypertension, and also in humans with essential hypertension. Elevation of blood pressure and development of vascular hypertrophy is blunted in deoxycorticosterone acetate-salt hypertensive rats treated chronically with endothelin receptor antagonists. Spontaneously hypertensive rats do not overexpress vascular endothelin, and do not exhibit a hypotensive response to chronic endothelin receptor antagonism. Malignant spontaneously hypertensive rats treated with deoxycorticosterone acetate and salt exhibit vascular overexpression of endothelin-1 and respond to endothelin antagonists with lowering of blood pressure. A genetic role of components of the endothelin system has been suggested in Dahl salt-sensitive rats. In human essential hypertension, there is as yet little evidence of activation of the endothelin system. A role of endothelins in hypertension is thus becoming increasingly apparent in severe forms of experimental hypertension, but further studies are required to establish whether these peptides are involved in the human disease.

Expression of serotonin receptor mRNAs in blood vessels

Using RT-PCR we distinguished mRNAs for all known G-protein coupled serotonin receptors expressed in various rat and porcine blood vessels. Nearly all vessels expressed 5HT1 dβ , 5-HT 2A, 5-HT 2B, 5-HT 4, and 5-Ht 7 receptor mRNA to different extents. New splice variants of the porcine 5-HT 4 receptor were observed. Similar PCR assays were performed with endothelial and smooth muscle cells from human pulmonary artery, aorta, and with endothelial cells from human coronary artery and umbilical vein. All endothelial cells expressed 5-HT 1 dβ , 5-HT 2b, and 5-HT 4 receptor mRNA, whereas in smooth muscle cells 5-HT 1 dβ , 5-HT 2A, 5-HT 7, and in some experiments 5-HT 2B receptor mRNA were found. A model for the regulation of vascular tone by different 5-HT receptors is proposed.

Endothelin: potential role in hypertension and vascular hypertrophy.

The endothelins are a family of 21-amino acid peptides that are powerful vasoconstrictors. They may also induce vascular hypertrophy. These peptides may participate through these two mechanisms in the pathogenesis of the elevation of blood pressure and/or in the maintenance of hypertension in both experimental animal models and human essential hypertension. This review presents evidence both in favor and against the involvement of endothelins in hypertension. Plasma levels of endothelin-1 are either normal or slightly elevated in experimental and human essential hypertension. Responses of blood vessels to endothelin-1 may be normal or depressed in many models of experimental hypertension and also in essential hypertension in humans. It has recently been demonstrated that endothelin content and mRNA are increased in blood vessels of deoxycorticosterone acetate-salt hypertensive rats. When endothelin receptor antagonists are administered chronically, elevation of blood pressure and development of vascular hypertrophy are blunted in this experimental model of hypertension. In contrast, spontaneously hypertensive rats do not exhibit any increase in either endothelin-1 mRNA or immunoreactive endothelin in blood vessels and fail to respond with lowering of blood pressure to longterm treatment with endothelin receptor antagonists. Blood pressure development in young spontaneously hypertensive rats is also unaffected by long-term administration of endothelin antagonists. Molecular genetic studies appear to support a genetic role of components of the endothelin system in Dahl salt-sensitive rats. In human essential hypertension, there is some evidence of activation of the endothelin system despite depressed responses of small arteries to endothelin-1 and normal circulating levels of endothelin-1 in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural investigation of nitric oxide synthase-immunoreactive nerves associated with coronary blood vessels of rat and guinea-pig.

Ultrastructural investigation of nitric oxide synthase-immunoreactive nerves closely associated with blood vessels in rat and guinea-pig hearts revealed many labelled nerve fibres in the walls of the main branches of the coronary arteries, and in arterioles, capillaries and post-capillary venules. The number of nitric oxide synthase-containing nerve fibres associated with different vessels, even those of the same calibre, varied. Terminal regions of nitric oxide synthase-immunoreactive fibres were observed in the endocardium and myocardium. Nitric oxide synthase-labelled fibres displayed electron-dense immunoproduct in both varicose and intervaricose regions. Immunoreactive axonal varicosities contained both small and large synaptic vesicles. The characteristics of the nitric oxide synthase-immunoreactive nerve fibres observed in the heart and the possibility that these fibres represent the processes of intracardiac neurones and/or sensory neurones of extrinsic origin are discussed.

Ultrastructural investigation of nitric oxide synthase-immunoreactive nerves associated with coronary blood vessels of rat and guinea-pig

Ultrastructural investigation of nitric oxide synthase-immunoreactive nerves associated with coronary blood vessels of rat and guinea-pig

Differential effects of phosphoramidon on contractile responses to angiotensin II in rat blood vessels.

1. Cumulative concentration-tension response (C-R) curves to angiotensin II (AII), big endothelin-1 (big ET-1), ET-1 and arginine vasopressin (AVP) were determined in endothelium intact-ring preparations of aorta, mesenteric artery and tail artery isolated from adult male Sprague-Dawley rats in the presence or absence of the neutral metalloprotease inhibitor, phosphoramidon. 2. The order of sensitivity of the three rat vascular smooth muscle preparations to AII, big ET-1 and ET-1 was aorta > mesenteric artery > tail artery whereas that for AVP was reversed, namely, tail artery > mesenteric artery > aorta. 3. Phosphoramidon blocked the responses to AII in a concentration-dependent manner, whereas even very high concentrations of phosphoramidon (100 microM) failed to affect the tension responses evoked by ET-1 and AVP in all three preparations. Low concentrations of phosphoramidon (10 microM) produced significant increases in EC50 values for AII in tail artery (P < 0.01) and mesenteric artery (P < 0.05) but not in aorta. The rank order of sensitivity to the inhibition by phosphoramidon was tail artery > mesenteric artery > aorta. Phosphoramidon-evoked rightward shifts in the C-R curves to AII were much higher than those to big ET-1 in both mesenteric artery and tail artery. 4. In endothelium-denuded preparations, AII failed to evoke any increases in tension in tail artery while the responsiveness of the mesenteric artery to AII was reduced significantly relative to endothelium-intact tissues with a rightward shift in the C-R curve and a decrease in the maximal response. On the other hand, the C-R curve to AII was shifted to the left in aorta following removal of the endothelium.Importantly, ET-1 and AVP evoked vasoconstrictor responses were unaffected by the inclusion of a high concentration of phosphoramidon (100 microM) in endothelium-denuded aorta and mesenteric artery.5. The results suggest that AII-evoked tension responses of blood vessels such as tail artery are completely endothelium-dependent; in relatively larger blood vessels such as mesenteric artery they are partially endothelium-dependent while in much bigger conduit type blood vessel such as aorta, they are endothelium-independent. It is concluded that the vasoconstrictor responses to AII in mesenteric artery and tail artery may be mediated by the release of endothelins from the endothelium by increased formation from big ET, an effect that is blocked by phosphoramidon.

Endothelin-1 expression in blood vessels of DOCA-salt hypertensive rats treated with the combined ETA/ETB endothelin receptor antagonist bosentan

In previous studies it has been shown that blood vessels of deoxycorticosterone acetate (DOCA) salt hypertensive rats present significantly higher immunoreactive ET-1 (ir-ET-1) content and increased ET-1 gene expression. DOCA-salt hypertensive rats respond to treatment with the combined ETA/ETB endothelin receptor antagonist bosentan with lowering of blood pressure. In the present study, we investigated the ir-ET-1 levels and the expression of the ET-1 gene in blood vessels of DOCA-salt hypertensive rats treated or not treated with bosentan. Blood pressure was significantly lower in bosentan-treated rats (185 +/- 6 mmHg; 1 mmHg = 133.3 Pa) compared with DOCA-salt hypertensive rats (203 +/- 4 mmHg; p < 0.01). Plasma ir-ET-1 concentration was slightly but significantly elevated (p < 0.01) in DOCA-salt hypertensive rats compared with uninephrectomized control rats, and was further increased (p < 0.01) in bosentan-treated rats. The tissue wet weight and ir-ET-1 content of segments of thoracic aorta were significantly increased (p < 0.01) in DOCA-salt hypertensive rats in comparison with control rats, but were similar in bosentan-treated DOCA-salt rats. The abundance of ET-1 mRNA measured by Northern blot analysis in thoracic aorta and the ir-ET-1 content were attenuated by bosentan treatment. Tissue wet weight and ir-ET-1 content in the mesenteric vascular bed were similar in bosentan-treated and -untreated DOCA-salt rats, and were significantly higher in both groups than in control rats (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

In situ hybridization shows increased endothelin-1 mRNA levels in endothelial cells of blood vessels of deoxycorticosterone acetate-salt hypertensive rats

Endothelin-1 is a potent vasoconstrictor peptide produced in blood vessels and other tissues that may play an important role in the control of local blood flow and could be involved in the pathogenesis of hypertension. Our previous studies have documented increases in endothelin-1 peptide content and gene expression in mesenteric arteries and thoracic aorta of deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Although changes in endothelin-1 were observed in the blood vessels of hypertensive rats, the exact cellular sites of these changes were not identified clearly. In the present study we investigated endothelin-1 gene expression in DOCA-salt hypertensive rats by in situ hybridization histochemistry using a high specific activity 35S-labeled complementary RNA probe. Robust increases in endothelin-1 mRNA levels were observed in both mesenteric blood vessels and aorta of DOCA-salt hypertensive rats as compared with the vessels from the uninephrectomized control rats. In both cases it was shown clearly that these increased endothelin-1 mRNA levels only originated in the endothelial cell layer, not in the underlying smooth muscle cells. Higher expression levels of endothelin-1 mRNA by the endothelial cells of DOCA-salt hypertensive rats may play an important role in vascular hypertrophy and in the maintenance of elevated blood pressure in this and perhaps other models of experimental hypertension.

Arginine Vasopressin Stimulates Protein Synthesis but Not Proliferation of Cultured Vascular Endothelial Cells

We previously showed that rat and cow blood vessels contain arginine vasopressin (AVP) of local origin. In the present study, to investigate potential roles for this locally produced peptide, we examined the effects of AVP on growth of cultured vascular endothelial and smooth muscle cells (EC, SMC). Treatment of cultured bovine aortic endothelial (BAE), murine cerebral microvascular endothelial (MME), or murine cerebral microvascular smooth muscle (MMSM) cells with AVP produced dose-dependent increases in total protein content with maximum increases of 11, 46, and 33% over vehicle-treated controls, respectively. AVP also dose-dependently increased new protein synthesis, as reflected by [3H]leucine incorporation into BAE and MME cell protein, with maximal increases of 34 and 24%, respectively. In addition, the AVP-stimulated increase in protein synthesis could be significantly attenuated in both BAE and MME cells by simultaneous addition of a specific AVP V1 receptor antagonist. In contrast, AVP did not affect total cell number or DNA synthesis, as reflected by [3H]thymidine incorporation, in any cell type. Neither was cell size, as measured by forward light scatter with a fluorescence-activated cell sorter (FACS), changed by treatment with AVP. However, the density of individual cells, as measured by orthogonal light scatter with FACS, was increased by AVP. These data demonstrate that AVP stimulates protein synthesis but not proliferation of cultured vascular EC and SMC and suggest that locally produced AVP may function as a growth factor for these cells.