Biomedical subjects

V M Miller

Publications and source records attributed to V M Miller.

At least 73 records · Page 4Linked to original sources

PubMed1997

An arginine analog inhibits responses of both the endothelium and smooth muscle of canine in situ vein grafts.

Increased shear, pressure, and oxygen tension in vein grafts may alter production of endothelium-derived vasoactive and anti-mitogenic factors such as nitric oxide which subsequently affect development of neointimal hyperplasia. This study was designed to determine whether or not nitric oxide mediates endothelium-dependent responses in femoral in situ vein grafts. Non-reversed, canine femoral vein grafts were placed bilaterally to bypass a ligated segment of the femoral artery in dogs. After 6 weeks, the grafts were removed, cut into rings, and suspended in organ chambers for measurement of isometric force. In some rings the endothelium was removed deliberately. In the presence of indomethacin, the synthetic analog of L-arginine, L-N(G)-monomethyl-arginine (10(-4) M; L-NMMA) did not cause a significant change in baseline tension of rings with endothelium. L-NMMA reduced only contractions of rings with endothelium to the alpha-adrenergic agonist UK 14,304. The analog also reduced maximal relaxations to the calcium-ionophore, A23187 in rings with endothelium. In addition, L-NMMA reduced relaxations of rings without endothelium to adenosine diphosphate by 35%. Positive immunostaining for nitric oxide synthase was present in both the myointima and media of histological sections of grafts. In conclusion, these results suggest that in situ vein grafts exhibit two unique properties which are unlike unoperated arteries or veins: (i) alpha2-adrenergic receptors may be coupled to the release of contractile endothelium-derived factors associated with production of nitric oxide: and (ii) nitric oxide may be released by the smooth muscle in response to purinergic stimulation. The presence of nitric oxide synthase throughout the wall of the graft may result in production of nitric oxide in response to adenosine diphosphate released by platelets and to circulating catecholamines.

Adrenergic alpha-Agonists↗

PubMed1997

Adrenomedullin-mediated relaxations in veins are endothelium-dependent and distinct from arteries.

In arteries, adrenomedullin (ADM) causes relaxations of rings with and without endothelium by stimulating accumulation of cyclic nucleotides resulting from activation of the ADM and calcitonin gene-related peptide (CGRP) receptors. Experiments were designed to determine the mechanism(s) of relaxation to ADM in veins. Rings of canine femoral vein with and without endothelium were suspended in organ chambers for measurement of isometric force. Rings were contracted with prostaglandin F2alpha (2 x 10(-6) M), and cumulative dose-responses to ADM (10(-11) to 10(-7) M) were obtained in the absence or presence of indomethacin (10(-5) M), indomethacin + N(G)-monomethyl-L-arginine (10(-4) M), methylene blue (10(-5) M), particulate guanylate cyclase inhibitor HS-142-1 (10(-5) M), tetraethylammonium (TEA, 10(-2) M), CGRP-receptor antagonist (CGRP 8-37, 10(-6) M), ADM-receptor antagonist (ADM 26-52, 10(-6) M), diphenhydramine (10(-6) M), 8-phenyltheophylline (3 x 10(-6) M), or superoxide dismutase (150 U/ml) plus catalase (1,200 U/ml). ADM produced concentration-dependent relaxations only in veins with endothelium. Relaxations to ADM in rings with endothelium were significantly inhibited only by methylene blue and HS-142-1. In separate experiments, incubation of rings with ADM (10(-8) M) and 3-isobutyl-1-methyl-xanthine (10(-4) M) for 3 min did not significantly affect the accumulation of cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP). These data suggest that ADM-mediated relaxation in veins is endothelium dependent and is not associated with activation of CGRP receptors or currently defined ADM receptors. Further, relaxations are not mediated by nitric oxide, indomethacin-sensitive prostanoids, TEA-sensitive hyperpolarizing factors, oxygen free radicals, or accumulation of cyclic nucleotides.

Adrenomedullin↗

PubMed1997

Gender and transcriptional regulation of NO synthase and ET-1 in porcine aortic endothelial cells.

Experiments were designed to determine whether normal fluctuations in sex steroid hormones alter gene transcription for endothelial nitric oxide synthase (NOS) and preproendothelin-1 (prepro-ET-1). Aortic endothelial cells were removed from adult, gonadally intact male and female or ovariectomized Yorkshire pigs. Endothelial cells were prepared for Northern blot analysis, Western blot analysis or enzyme activity. Nitric oxide products (NOx) and endothelin-1 (ET-1) in plasma were measured by chemiluminescence and radioimmunoassay, respectively. Northern blot analysis identified single bands corresponding to endothelial NOS and prepro-ET-1. Quantification of the blots showed an increase in expression of mRNA for both endothelial NOS and prepro-ET-1 in ovariectomized pigs compared with gonadally intact male and female pigs. There were no differences in amount of endothelial NOS protein identified by Western blot analysis among groups. On the contrary, plasma concentrations of NOx were significantly decreased in ovariectomized pigs, and there were no differences either in the concentrations of ET-1 in the plasma or extracts from the coronary arteries. These results suggest that expression of endothelial NOS and prepro-ET-1 may be regulated at transcriptional level by ovarian hormones. In addition, the ovarian hormones may regulate production of these endothelium-derived factors at the posttranscriptional level.

Animals↗

PubMed1997

Gender differences in endothelium-dependent relaxations do not involve NO in porcine coronary arteries.

Experiments were designed to determine whether normal fluctuations in endogenous sex steroid hormones and/or gender affect endothelium-dependent relaxations in coronary arteries, and, if so, to identify endothelium-derived factors contributing to these differences. Coronary arteries from sexually mature, gonadally intact male and female pigs or ovariectomized pigs were prepared either for study of isometric force in organ chambers or for measurement of prostanoids and activity of nitric oxide (NO) synthase. In organ chamber studies, neither the magnitude nor the sensitivity of endothelium-dependent relaxations correlated with endogenous estrogen or progesterone in female pigs. However, relaxations to bradykinin and UK-14304 were significantly greater and/or shifted leftward in arterial rings from female compared with male pigs. Indomethacin (10(-5) mol/l) increased endothelium-dependent relaxations only in arteries from male pigs. N(G)-monomethyl-L-arginine reduced endothelium-dependent relaxations to a similar extent in coronary arteries from either sex. Neither production nor response to thromboxane A2 or prostacyclin differed in coronary arteries from male compared with female pigs. Activity for calcium-dependent or -independent NO synthase was similar in both sexes. These results suggest that normal fluctuations in endogenous sex steroid hormones do not affect endothelium-dependent relaxations in coronary arteries from female pigs. There are, however, gender differences in endothelium-dependent relaxations that are indomethacin sensitive and may be due to cyclooxygenase products other than thromboxane A2 or prostacyclin.

Adrenergic alpha-Agonists↗

PubMed1997

Effects of mononuclear cells on pulmonary arteries from rejecting transplanted lungs.

Experiments were designed to determine responses of pulmonary arteries from an acutely rejecting, transplanted lung to rejection-activated mononuclear cells. Pulmonary arteries and macrophage-depleted mononuclear cells were obtained from unoperated dogs (control) and dogs with rejecting single lung allotransplants (transplanted, rejecting). In some arteries, the endothelium was removed deliberately. Pulmonary arteries were suspended for measurement of isometric force in organ chambers. Contractions to potassium chloride (60 M) were greater in rings of pulmonary arteries from rejecting compared with control dogs. Mononuclear cells from both control and transplanted dogs caused cell number-dependent contractions of autogenous pulmonary arteries. Contractions to cells were decreased when the endothelium was present only in arteries from control dogs; these contractions were increased by the L-arginine analog N(G)-monomethyl-L-arginine (10(-4) M) but not by indomethacin (10(-5) M). Contractions to mononuclear cells were reduced by superoxide dismutase (150 U/ml) and catalase (1,200 U/ml) in arteries without endothelium from control but not transplanted dogs. In arteries from transplanted dogs, contractions to mononuclear cells were reduced by desferoxamine (10(-3) M). Results suggest that interactions between mononuclear cells and pulmonary arteries are modified during rejection of lung allografts so that, during rejection, 1) endothelium-derived nitric oxide no longer antagonizes contractions to substances produced by the mononuclear cells and 2) contractions of smooth muscle from rejecting arteries to mononuclear cells may be mediated by radicals other than superoxide.

Acute Disease↗

PubMed1997

Increased levels of circulating nitrates and impaired endothelium-mediated vasodilation suggest multiple roles of nitric oxide during acute rejection of pulmonary allografts.

Experiments were designed to determine whether changes in pulmonary artery function could be reduced by treatment with a lipid peroxidation inhibitor (H 290/51) during acute rejection of pulmonary allografts. Single lung transplantation was performed in three groups of dogs: group 1 was maintained on immunosuppression for 8 days after operation (immunosuppressed, n = 5); in group 2, immunosuppression was discontinued on postoperative day 5, so that rejection occurred on postoperative day 8 (rejecting, n = 6); in group 3, immunosuppression was discontinued after 5 days, and the lipid peroxidation inhibitor H 290/51 (25 mg/kg) was given perorally for 3 days (rejecting + H 290/51, n = 6). Plasma nitric oxide (NO(x)) was measured by use of chemoluminescence. On postoperative day 8 rejection was observed in groups 2 and 3. Contractions to angiotensin I and endothelium-dependent relaxations to adenosine diphosphate were reduced in pulmonary arteries from rejecting lungs. Responses of rings from dogs treated with H 290/51 were similar to those from rejecting lungs. Rejection did not alter relaxations to exogenous nitric oxide. However, plasma levels of NO(x) increased significantly during rejection independently of treatment with H 290/51. Results of this study confirm that endothelium-dependent relaxation of pulmonary arteries is reduced during acute rejection of lung allografts. The result extends these observations to suggest that treatment with a lipid peroxidation inhibitor neither protects the pulmonary artery function nor affects levels of circulating NO(x). Therefore mechanisms other than lipid peroxidation participate in vascular changes associated with allograft rejection.

Acute Disease↗

PubMed1996

Endothelin-1 and cell proliferation in lung organ cultures. Implications for lung allografts.

Endothelin-1 (ET-1) is found in bronchoalveolar lavage fluid in patients following lung transplantation. ET-1 causes contraction of isolated pulmonary vessels and bronchi and stimulates proliferation of smooth muscle cells in culture. Therefore, ET-1 could contribute to the smooth muscle hyperplasia and stromal proliferation seen in chronic rejection of lung allografts. Experiments were designed to determine whether (1) ET-1 stimulates proliferation of pulmonary tissue, (2) proliferation is increased in rejecting allotransplanted lungs, (3) endothelin-A receptors mediate the proliferative response, and (4) ET-1 is produced by activated infiltrating immunocompetent cells. Lung organ cultures were prepared from unoperated dogs and dogs with rejecting single lung allografts. Incubation of organ cultures from unoperated dogs with ET-1 (10(-9) to 10(-7) M)) increased positive staining for proliferation cell nuclear antigen (PCNA) in lung parenchyma. PCNA staining was not decreased by the endothelin-A antagonist BQ123 (10(-6) M). In addition, immunostaining for endothelin-B receptors was present in sections of unoperated but not rejecting lungs. PCNA staining in lung cultures from rejecting allotransplanted dogs was significantly greater than that from unoperated dogs. Positive immunohistochemical staining for ET-1 was found in mononuclear cells infiltrating rejecting transplanted lungs. In conclusion, exogenous ET-1 is mitogenic in lung organ cultures through receptors other than endothelin-A. Proliferation in rejecting transplanted lungs is increased compared with unoperated lungs. Mononuclear cells may be a source of endothelin-1 in the rejecting lung. ET-1, therefore could, in synergism with other cytokines, contribute to acute and chronic pathological changes seen in pulmonary rejection.

Animals↗

PubMed1996

Endothelin induces vasoconstriction in the bone vasculature in vitro: an effect mediated by a single receptor population.

The aim of this study was to define the types of endothelin receptors present in the canine tibial vasculature. Endothelin receptor agonists and antagonists were used in two different models: isolated nutrient tibial arteries in organ bath and in vitro-perfused canine tibial bones. In isolated nutrient tibial arteries, endothelin-1 caused concentration-dependent contractions of rings with and without endothelium. BQ-123, a selective endothelin-A antagonist, induced a significant rightward shift of endothelin-1 concentration-response curves. No contractions were observed with sarafotoxin S6c, a selective endothelin-B agonist. The responses of endothelin-1 were not affected by the presence of NG-monomethyl-L-arginine acetate plus indomethacin or by removal of the endothelium. In perfused tibial bones, endothelin-1 was more potent than endothelin-3 in causing concentration-dependent contractions. Neither endothelin-1, endothelin-3, nor sarafotoxin S6c caused relaxations. Neither the inhibition of nitric oxide nor the inhibition of prostaglandins significantly altered contractions to endothelin-1. These concordant data indicate that endothelin is a vasoconstrictor in the bone vasculature, an effect that appears to be mediated only through endothelin-A receptors.

Animals↗

PubMed1996

Endothelin-A receptors mediate vascular smooth-muscle response to moderate acidosis in the canine tibial nutrient artery.

Perfusate pH may influence the tone of vascular smooth muscle by affecting the release of endothelium-derived vasoactive factors or by directly modulating function of the smooth muscle. This study was designed to investigate the role of endothelium-derived factors on acidosis-induced responses of isolated canine tibial nutrient artery suspended in an organ chamber for the measurement of isometric contractile force. To investigate the specific role of the endothelium in half the rings, the endothelium was removed mechanically. Concentration-response curves to KCl were obtained in the absence or presence of inhibition of two important endothelium-derived relaxing factors, nitric oxide and prostacyclin, and an inhibitor of receptors for the endothelium-derived contracting factor, endothelin-1. Acidification of the perfusate from pH 7.45 to 7.0 significantly attenuated the contractions to KCl in arterial rings with endothelium (the mean of the effective concentration causing 50% of the maximal response for KCl at pH 7.45 and 7.0 was 12.31 +/- 0.40 nM and 14.60 +/- 0.55 nM, respectively). This difference was abolished by mechanical removal of the endothelium. In rings with endothelium, inhibition of nitric oxide or prostacyclin did not abolish the attenuation of KCl-induced contractions occurring with acidosis (the mean of the effective concentration causing 50% of the maximal response for KCl at pH 7.45 and 7.0 was 11.18 +/- 0.60 nM and 13.60 +/- 0.60 nM, respectively). Inhibition of endothelin-A receptors did not alter contractions to KCl at pH 7.45. However, the acidosis-induced attenuation of contractions with KCl was abolished by the endothelin-A-receptor antagonist BQ-123 (the mean of the effective concentration causing 50% of the maximal response at pH 7.45 and 7.0 was 13.8 +/- 1.34 nM and 13.2 +/- 1.34 nM, respectively). These results suggest that acidosis-induced relaxation of canine tibial nutrient artery is endothelium dependent and that activation of endothelin-A receptors during acidosis is coupled to a release of an endothelium-derived relaxing factor.

Acidosis↗

PubMed1996

Contractile properties of enteric smooth muscle after small bowel transplantation in rats.

BACKGROUND: The effects of small bowel transplantation (SBTx) on the function of enteric smooth muscle are not understood. PURPOSE: To study the contractile properties of enteric smooth muscle after SBTx in rats. METHODS: Five groups of inbred Lewis rats (n > or = 8 each group) were studied: unoperated, naive controls; operated controls 1 week (OC1) and 8 weeks after intestinal transection/reanastomosis of the proximal jejunum and distal ileum; and 1 week (TX1) and 8 weeks (TX8) after syngeneic orthotopic SBTx. Contractile activity of circular muscle strips of jejunum was evaluated in tissue chambers. Spontaneous contractile activity (force per wet weight tissue) increased in TX1, TX8, and OC1 rats (P < or = 0.01). Frequency of contractions doubled in OC1 rats (P < or = 0.001) but was unchanged in the other groups. In the presence of nonadrenergic noncholinergic (NANC) blockade, spontaneous contractile activity increased in TX1 and OC1 (P < or = 0.005) without a change in frequency of contractions. Inhibition of neural activity with tetrodotoxoin increased amplitude and frequency in all groups. Bethanechol (3 x 10(-6) to 3 x 10(-4) mol/L) increased, and norepinephrine (1 x 10(-6) to 1 x 10(-4) mol/L) dose-dependently decreased the amplitude and frequency of contractions in all groups; equi-effective concentrations, however, did not differ among groups. CONCLUSIONS: The increase in contractile activity after intestinal transection/reanastomosis is secondary to an increase in frequency of contractions and not amplitude. SBTx increases contractile amplitude of circular muscle due, in part, to downregulation of NANC nerves but not via muscarinic or adrenergic hypersensitivity. These alterations in enteric physiology of intestinal contractile activity may have important implications in clinical SBTx.

Animals↗

PubMed1996

Effects of acute rejection and antirejection therapy on arteries and veins from canine single lung allografts.

Experiments were designed to compare the function of the endothelium and smooth muscle in intralobar pulmonary arteries and veins of transplanted lungs during acute rejection and after treatment of rejection. Single lung allografts were performed in dogs. Dogs were monitored for 5 days to allow good recovery from the operation and resolution of early chest radiographic changes. In group I, immunosuppression (cyclosporine A, azathioprine, and methylprednisone) was withdrawn to allow rejection, which typically occurred after 3 days. In group II, immunosuppression was reinstituted at this time during acute rejection until the chest roentgenograms again cleared (approximately after 6 days). The blood vessels were studied at this time. Rings were cut from intralobar pulmonary arteries and veins of the allotransplanted lungs and suspended for the measurement of isometric force in organ chambers. Contractions of arteries and veins to phenylephrine but not endothelin-1 were significantly reduced during acute rejection. In arteries and veins, endothelium-dependent relaxations to bradykinin but not the calcium ionophore A23187 were reduced with rejection. Relaxations of the smooth muscle to histamine increased with rejection in both blood vessels. Relaxations to nitric oxide were reduced with rejection in veins but not arteries. Treatment of rejection reversed all responses toward those observed in arteries and veins in lungs from dogs not undergoing transplantation. These results suggest that responses of the endothelium and smooth muscle of pulmonary arteries and veins of transplanted lungs are altered similarly during rejection. Further, treatment of rejection restores function of the pulmonary blood vessels of lung allografts toward that observed in unoperated lungs.

Animals↗

PubMed1996

Increased levels of endothelin-1 in bronchoalveolar lavage fluid of patients with lung allografts.

The aim of the present study was to determine levels of endothelin-1 in bronchoalveolar lavage fluid and in plasma in patients with lung and heart-lung allografts. The aim was based on the hypothesis that levels of endothelin-1 are elevated in the bronchoalveolar lavage fluid of patients with lung allografts. Patients (n = 23) undergoing heart-lung (n = 8), single-lung (n = 10), or bilateral lung (n = 5) transplantation were included in the study. In patients with single-lung allografts, endothelin-1 levels were analyzed in bronchoalveolar lavage fluid from both the transplanted and the nontransplanted, native lung. The level of endothelin-1 was also analyzed in bronchoalveolar lavage fluid from 12 patients who did not undergo transplantation. Transbronchial biopsies and bronchoalveolar lavage were done routinely or when clinically indicated on 64 different occasions, between 2 and 104 weeks after transplantation. The level of endothelin-1 was measured in bronchoalveolar lavage fluid and plasma by radioimmunoassay. Immunoreactive endothelin-1 was detectable in bronchoalveolar lavage fluid from all patients. The concentration of endothelin-1 in bronchoalveolar lavage fluid from transplanted lungs (2.94 +/- 0.30 pg/ml, n = 64) was significantly higher compared with that in bronchoalveolar lavage fluid from patients without allografts (0.86 +/- 0.20 pg/ml, n = 12, p < 0.01). In patients who received single-lung transplantation because of emphysema, the level of endothelin-1 in bronchoalveolar lavage fluid from the transplanted lung was significantly greater than that from the native lung (5.61 +/- 1.9 versus 0.39 +/- 0.05 pg/ml, p < 0.05). Concentrations of endothelin-1 in bronchoalveolar lavage fluid did not correlate with grade of rejection, infection, or time after transplant. Plasma levels of endothelin-1 were unchanged with pulmonary rejection. These results indicate that endothelin-1 is released into bronchi of transplanted human lungs. The release is not associated with rejection or infection. Because of its potent mitogenic properties, endothelin-1 may have a potential impact in the development of posttransplant complications such as bronchiolitis obliterans.

Adult↗

PubMed1996

Experimental evaluation of bleeding complications, thrombogenicity and neointimal characteristics of prosthetic patch materials used for carotid angioplasty.

Experiments were designed to compare perioperative blood loss, early thrombogenicity and morphologic and functional characteristics of the neointima of three types of prosthetic materials used for carotid artery patch angioplasty. Bilateral carotid patch angioplasties were performed in 20 dogs, using 20 gelatin-impregnated fluoropassivated Dacron (GIF), 10 untreated knitted Dacron and 10 expanded polytetrafluoroethylene (PTFE) patches (5 cm2). Intraoperative blood loss, platelet deposition at 24 h and neointimal morphology at 6 weeks after the operation were assessed. Bioassay of the neointima was performed at 6 weeks in 16 patches. Mean (s.e.m.) blood loss was significantly less in GIF patches (14.7 (2.7) ml) compared with either PTFE (75.6 (24) ml) or untreated Dacron (64.3 (9.5)) (P < 0.005). Mean (s.e.m.) platelet deposition in GIF patches (1380 (328) platelets/cm2) was approximately 50% less at 24 h than in untreated Dacron (2562 (1035) platelets/cm2) or PTFE (2140 (998( platelets/cm2) patches (P < 0.05). Neointimal coverage was greater in PTFE (94 (1.3%)) compared with GIF (79 (2.7%)) or untreated Dacron (86 (2.4%)) patches (P < 0.05). The thickness of the neointimal layer of PTFE (0.5 (0.01) mm) patches was greater than other patch types; GIF (0.2 (0.01) mm) or untreated Dacron (0.3 (0.01) mm) (P < 0.50). Under bioassay conditions, acetylcholine caused release of vasoactive relaxing factor(s) from all patches. However, relaxations from baseline were less with GIF patches (-37.9 (11.7)% versus -54.5(9.6( for untreated Dacron; -50.2 (15.2)% for PTFE) (P = n.s.). Endothelin-1 release occurred from all patches and was increased with the extent of neointimal coverage. These data demonstrate that GIF patches caused the least perioperative bleeding, were the least thrombogenic at 24 h and developed the thinnest neointima at 6 weeks. All patch materials developed a functioning neointima.

Angioplasty↗

PubMed1996

Gender differences in response to endothelin-1 in coronary arteries: transcription, receptors and calcium regulation.

1. Experiments were designed to determine how sex hormonal status may influence production and response to endothelins. 2. Circulating concentrations of endothelin-1 were not different between sexually mature male and female pigs and did not differ between females of low- and high-oestrogen status. 3. Expression of messenger RNA for preproendothelin was not different in aortic endothelial cells derived from sexually mature male and female pigs. 4. Endothelin-1, endothelin-3 and sarafotoxin S6c caused concentration-dependent contractions of rings of coronary arteries suspended for the measurement of isometric force. Only in response to endothelin-1 were contractions greater in arteries from female than in male pigs. This difference was not related to oestrogen levels in females. 5. The intrinsic force-calcium relationship defined in smooth muscle cells permeabilized with either triton-X or beta-escine was not different in coronary arteries from male and female pigs. The calcium sensitivity was increased to the same extent by endothelin-1 in smooth muscle from male and female pigs. 6. Competitive inhibition of radiolabelled endothelin-1 by unlabelled endothelin-1 was not different in membranes prepared from coronary arteries from male and female pigs. However, competitive inhibition of radiolabelled endothelin-1 by unlabelled endothelin-3 showed two binding sites. The affinity of the high affinity binding site was increased only in females with high oestrogen levels. 7. These results suggest that there are gender differences in contractions of porcine coronary arteries to endothelin-1. These differences may not relate to transcriptional regulation for the production of the peptide in endothelial cells, to the regulation of the number or affinity of endothelin receptors or to intrinsic calcium-sensitivity of the contractile proteins. Rather they are probably due to differences in the regulation of intracellular calcium.

Animals↗

PubMed1996

Chronic increases in blood flow upregulate endothelin-B receptors in arterial smooth muscle.

Experiments were designed to characterize endothelin receptors in arteries after chronic increases in blood flow. A fistula was created between the femoral artery and vein in one hindlimb of dogs; contralateral blood vessels were sham operated. Sham- and fistula-operated arteries were removed 6 wk postoperatively. Some arteries were prepared for measurement of isometric force or for isolation of membrane proteins. Other arteries were used for histological staining with an endothelin-B (ETB) receptor antibody. In arteries suspended for the measurement of isometric force, endothelin-1 produced concentration-dependent increases in tension that were significantly greater in fistula- than in sham-operated arteries without endothelium. The ETB-receptor-selective peptide sarafotoxin S6c produced concentration-dependent increases in tension only in fistula-operated arteries. In receptor-binding studies of membrane proteins, Scatchard analysis of saturation binding with 125I-labeled endothelin-1 (125I-endothelin-1) indicated that the total number of receptors was greater in fistula-operated arteries; affinity was threefold less in fistula- than in sham-operated arteries. Competitive displacement of 125I-endothelin-1 by endothelin-3 was significant for a two-site model in membranes prepared from sham-and fistula-operated arteries. Competitive inhibition of 125I-endothelin-1 binding by sarafotoxin S6c was significant for a one-site binding model in all arteries. Sarafotoxin S6c binding sites were elevated significantly in fistula-operated arteries. Immunohistochemical staining for the ETB receptor was significantly greater in both the endothelium and smooth muscle of fistula- than in sham-operated arteries. These results suggest that chronic increases in blood flow upregulate endothelin receptors, including ETB receptors in arterial smooth muscle.

Animals↗

PubMed1996

Effects of prolonged exposure to oxygen-derived free radicals in canine pulmonary arteries.

Experiments were designed to evaluate endothelium-dependent responses of pulmonary arteries following prolonged exposure to oxygen-derived free radicals. Rings of canine pulmonary arteries with and without endothelium were suspended for measurement of isometric force in organ chambers and incubated with xanthine (10(-4)M) plus xanthine oxidase (0.015 U/ml) for 1 h in the absence and presence of either superoxide dismutase (SOD, 150 U/ml), catalase (1,200 U/ml), deferoxamine (10(-3)M), or a combination of all three scavengers. Xanthine plus xanthine oxidase caused significantly greater contractions of rings without compared with those with endothelium. In rings with endothelium, contractions were reduced by SOD or catalase but not by deferoxamine. Following 1 h of exposure to xanthine plus xanthine oxidase, endothelium-dependent relaxations to ADP were reduced but not those to bradykinin or the calcium ionophore A-23187 (calcimycin). Relaxations to ADP were not corrected by incubation with the antioxidants used singly or in combination during the exposure to xanthine plus xanthine oxidase. These results suggest that oxygen-derived free radicals generated from exogenously applied xanthine plus xanthine oxidase cause contractions of canine pulmonary arteries. In addition, even when contractions of rings with endothelium were prevented by SOD and catalase, subsequent expression of some but not all endothelium-dependent relaxations were reduced. Therefore, scavenging of oxygen-derived free radicals may prevent some but not all of the vascular injury caused by oxygen-derived free radicals.

Adenosine Diphosphate↗

PubMed1996

Systemic vascular effects during acute rejection of lung allografts.

Circulating leukocytes activated during rejection of organ allografts could potentially have generalized effects on systemic blood vessels of the transplant recipient. Experiments were designed, therefore, to determine the function of the endothelium and smooth muscle of arteries from nontransplanted organs in dogs who received single lung transplants. Dogs underwent single lung allotransplantation and were immunosuppressed for 5 days. Immunosuppression was then withheld for 3 days, allowing rejection to occur. Dogs were studied at this time (rejecting) or following treatment for rejection for an additional 6-8 days (treated). Arteries from unoperated, untreated dogs also were studied to provide baseline responses of healthy tissue. Rings cut from left circumflex coronary, nonoperated native pulmonary, and renal arteries were suspended in organ chambers for measurement of isometric force. Endothelium-dependent relaxations to the calcium ionophore A23187 were not affected by rejection in any of the arteries. Contractions to angiotensin I were reduced significantly only in native pulmonary arteries. Contractions to KCI and endothelin-1 increased in renal arteries with endothelium during rejection. These contractions in renal arteries were reduced following treatment of rejection. None of the responses of the coronary arteries were affected significantly by rejection of the lung allograft. These results demonstrate that contractions of arteries in the transplant recipient's native organs are altered during rejection of lung allografts. The effects are organ specific, may include production of endothelium-derived contractile factors in renal arteries, and can be partially reversed by treatment of rejection.

Angiotensin I↗

PubMed1996

Modulation of endothelium-derived nitric oxide in canine femoral veins.

Experiments were designed to determine whether nitric oxide was the mediator of increased endothelium-dependent relaxations in veins proximal to an arteriovenous fistula. A fistula was prepared between femoral arteries and veins in dogs. After 6 wk, veins proximal to the fistula were removed, cut into rings, and suspended for the measurement of isometric force in organ chambers. In some rings the endothelium was removed deliberately. NG-monomethyl-L-arginine (L-NMMA) caused contraction in three of six fistula-operated veins with and without endothelium. In rings contracted submaximally with prostaglandin F2 alpha, acetylcholine and the alpha 2-adrenergic agonist UK-14,304 cause e tylcholine and the alpha 2-adrenergic agonist UK-14,304 caused endothelium-dependent, concentration-dependent relaxations that were greater in fistula compared with sham-operated veins. These relaxations were reduced by L-NMMA. Calcium ionophore A23187 caused comparable endothelium-dependent relaxations in fistula- and sham-operated veins that were unaffected by L-NMMA. There were no differences in either calcium-dependent or -independent activity of nitric oxide synthase isolated from fistula- and sham-operated veins. Positive staining for nitric oxide synthase was present in both the endothelium and media of fistula-operated veins. These results indicate that nitric oxide mediates increased endothelium-dependent relaxations to acetylcholine and alpha 2-adrenergic agonists in fistula-operated veins. Therefore, chronic increases in blood flow and oxygen tension modify selectively receptor-coupled production of nitric oxide in endothelium and smooth muscle of veins.

Adrenergic alpha-Agonists↗