Apamin-sensitive K+ currents mediate arachidonic acid-induced relaxations of rabbit aorta

Arachidonic acid induces an endothelium-dependent relaxation of the rabbit aorta that is blocked by lipoxygenase inhibitors. The cellular vasodilatory mechanisms activated by arachidonic acid metabolites remain undefined. In rabbit thoracic aortic rings pretreated with indomethacin (10 micromol/L) and contracted with phenylephrine, arachidonic acid (0.1 to 100 micromol/L) induced concentration-dependent relaxations. Maximal relaxations averaged 45+/-3% and were inhibited by increasing extracellular K+ (30 mmol/L, 15+/-5%; P<0.001) or incubation with apamin (100 nmol/L, 26+/-7%; P<0.05) but not incubation with charybdotoxin (100 nmol/L, 41+/-5%). In aortic strips with an intact endothelium that were treated with phenylephrine, arachidonic acid (10 micromol/L) increased the membrane potential from -28.7+/-1.3 to -37.8+/-3.0 mV (P<0.01). Preincubation with apamin did not alter basal membrane potential but inhibited arachidonic acid-induced hyperpolarization (-31.5+/-1.5 mV). Incubation of rabbit aortic segments with apamin or charybdotoxin did not alter [14C]arachidonic acid metabolism. Whole-cell outward K+ currents from isolated rabbit aortic smooth muscle cells averaged 43.0+/-4.8 pA/pF at 60 mV and were significantly decreased to 35.7+/-4.2 pA/pF by apamin (P<0.001). Subsequent addition of charybdotoxin further decreased maximal currents to 14.4+/-2.3 pA/pF. Addition of 11,12,15-trihydroxyeicosatrienoic acid increased the outward whole-cell K+ current. In inside-out patches of aortic smooth muscle, apamin inhibited the calcium activation (100 to 300 nmol/L; P<0.001) of a small-conductance K+ channel (approximately 24 pS). These results suggest that arachidonic acid induces endothelium-dependent hyperpolarization and relaxation of rabbit aorta through activation of smooth muscle, apamin-sensitive K+ currents.     

Arachidonic acid- and acetylcholine-induced relaxations of rabbit aorta.

The present study investigated the role of arachidonic acid and acetylcholine in mediating endothelium-dependent relaxations of rabbit aorta. Isolated thoracic aortic rings were precontracted with a submaximal concentration of norepinephrine, and the effect of various agents on arachidonic acid- and acetylcholine-induced relaxations was examined. Arachidonic acid elicited a concentration-related relaxation that was potentiated by the cyclooxygenase inhibitor indomethacin. Treatment with the lipoxygenase inhibitor nordihydroguaiaretic acid completely blocked but the cytochrome P450 inhibitor metyrapone had no effect on arachidonic acid-induced relaxation. NG-Monomethyl-L-arginine and nitro-L-arginine, compounds that inhibit the nitric oxide-like endothelium-derived relaxing factor, had little or no effect on arachidonic acid-induced relaxations. In contrast, nordihydroguaiaretic acid, metyrapone, NG-monomethyl-L-arginine, and nitro-L-arginine all attenuated the relaxation to acetylcholine; however, indomethacin had no effect on acetylcholine-induced relaxations. Arachidonic acid and acetylcholine had no effect on denuded rabbit aorta. Incubation of rabbit aorta with [14C]arachidonic acid resulted in the synthesis of major radioactive metabolites that comigrated with the prostaglandins and hydroxyeicosatetraenoic acids. Indomethacin selectively inhibited prostaglandin formation, nordihydroguaiaretic acid attenuated both prostaglandins and hydroxyeicosatetraenoic acids, and metyrapone blocked the epoxyeicosatrienoic acids. Additionally, acetylcholine elicited a twofold increase in tissue cyclic guanosine monophosphate content in contrast to a 59% reduction in cyclic guanosine monophosphate content observed with arachidonic acid. Therefore, these data suggest that in rabbit aorta, arachidonic acid-induced relaxations are mediated by an endothelium-dependent factor (or factors) that differs from the factor (or factors) released by acetylcholine. These results support the existence of multiple endothelium-derived relaxing factors.     

Arachidonic acid elicits endothelium-dependent release from the rabbit aorta of a constrictor prostanoid resembling prostaglandin endoperoxides

This study was designed to investigate the mediator(s) of endothelium-dependent arterial constrictor responses evoked by arachidonic acid in vitro. A segment of descending rabbit thoracic aorta was isolated and perfused (1-2 ml/min) with oxygenated Krebs' bicarbonate buffer. Changes in the vascular smooth muscle-contracting activity of the aortic effluent were detected by superfusion bioassay using either strips of rabbit aorta or rings of dog saphenous vein, both denuded of endothelium and exposed to indomethacin (10 microM). Arachidonic acid (5-50 micrograms) injected into the inflow of the perfused aorta caused a dose-related increase in the vascular smooth muscle-contracting activity of the aortic effluent, whereas arachidonic acid added directly into the aortic effluent did not. The arachidonic acid-induced elevation of vascular smooth muscle-contracting activity in the aortic effluent was not apparent when indomethacin (10 microM) was added to the aortic inflow to inhibit cyclooxygenase, when the endothelium of the perfused aorta was removed by rubbing, or when the thromboxane A2/prostaglandin H2 receptors of the vascular tissues used for bioassay were blocked with an antagonist (1 microM SQ29548), and was unaffected when an inhibitor of thromboxane synthase (10 microM CGS 13080) was added to the aortic inflow. This effect of arachidonic acid was accompanied by release of prostaglandin H2 (measured as prostaglandin F2 alpha after reduction with SnCl2) in amounts sufficient to elicit contraction of the vascular tissues used for bioassay and was attenuated when a reducing agent (2 mM FeCl2) that converts prostaglandin H2 to 12-heptadecatrienoic acid was added to the aortic effluent. Collectively, these observations suggest that arachidonic acid stimulates endothelium-dependent release from the perfused aorta of a prostanoid that contracts vascular smooth muscle via interaction with thromboxane A2/prostaglandin H2 receptors. The study also suggests that the prostanoid responsible for the vascular smooth muscle-contracting activity of the aortic effluent is a prostaglandin endoperoxide(s) rather than thromboxane A2.     

Histamine-induced rhythmic contraction of hog carotid artery smooth muscle

Smooth muscle strips isolated from the hog common carotid artery can contract rhythmically, exhibiting low frequency, large amplitude oscillations in tension when stimulated with 10 microM histamine. Strips required at least 1.45 mM calcium and 2.5 mM potassium to exhibit this rhythmic activity. Rhythmic contractions could be converted to tonic contractions by removal of potassium or ouabain treatment. Relaxation by 2 mM lanthanum, 1 mM manganese, or 1 microM verapamil implies that the external medium is the source of calcium mediating the contractions. The involvement of adrenergic nerve terminals in this response was ruled out, since propranolol, phentolamine, tetrodotoxin, bretylium, or 6-hydroxydopamine treatment did not alter the oscillations. Blockade of H1 receptors with 0.1 microM diphenhydramine relaxed the muscle strips. The H2 receptor antagonist cimetidine (5 microM) had no effects. Attempts to obtain rhythmic contractions by stimulating with other vasoactive agents (norepinephrine, acetylcholine, 5-hydroxytryptamine, angiotensin II, and elevated potassium concentrations) were unsuccessful, suggesting that this is a specific histamine response mediated solely by H1 receptors. These results show that this large artery, commonly considered a multi-unit smooth muscle, can sometimes exhibit single-unit behavior.     

Beta-endorphin and adrenocorticotropin release from rat adenohypophysis in vitro: evidence for local modulation by arachidonic acid metabolites of the cyclooxygenase and lipoxygenase pathway

This study was performed to examine an involvement of adenohypophysial arachidonic acid metabolites in the local mechanisms controlling the release of peptide hormones from the corticotrope cells of the anterior pituitary gland. Therefore, we investigated the effect of blockers of the lipoxygenase (nordihydroguaiaretic acid, NDGA), cyclooxygenase (indomethacin) or both of these enzyme systems (BW755C; eicosatetraynoic acid, ETYA) on the release of beta-endorphin-like (beta-E-IR) and adrenocorticotropin-like immunoreactivity (ACTH-IR) from rat anterior pituitary quarters incubated in vitro. NDGA and ETYA did not influence the basal release of beta-E- and ACTH-IR. However, upon stimulation by arginine-vasopressin (AVP) or synthetic ovine corticotropin-releasing factor (CRF(1-41], NDGA inhibited beta-E-IR release by 40%. ETYA inhibited AVP-induced release of beta-E- and ACTH-IR by 75%. Indomethacin and BW755C (lower concentration) enhanced beta-E-IR release, induced by AVP, by about 100%, whereas BW755C (higher concentration) had no effect. When indomethacin was present, NDGA, ETYA and BW755C (higher concentration) inhibited AVP-induced release of beta-E- and ACTH-IR. Prostaglandin E2 (PGE2) inhibited beta-E-IR release in response to AVP but failed to do so in the presence of NDGA. 12-OH-5,8,10,14-eicosatetraenoic acid (12-HETE) had no effect. When anterior pituitary quarters were incubated with 3H-arachidonic acid (3H-AA), NDGA and BW755C (higher concentration) but not indomethacin and BW755C (lower concentration) blocked the formation of a metabolite which co-migrated with 12-HETE on thin-layer chromatography.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of indomethacin on prostanoid synthesis and vasomotor responsiveness in endothelium-denuded abdominal and thoracic aortas of Wistar rats

In endothelium-denuded abdominal (but not thoracic) aortas of rats, the nonselective cyclooxygenase (COX) inhibitor, indomethacin, suppressed contractions evoked by α-adrenergic agonists hypothetically mediated by prostanoids. We aimed to identify these non-endothelial-derived contractile prostanoids released by α-adrenergic receptors activation. Endothelium-denuded abdominal and thoracic aortas of Wistar rats were used for biochemical and functional analyses. Western blot analysis showed that COX-1 and COX-2 protein levels were respectively equivalent in endothelium-denuded abdominal and thoracic aortas. Enzyme immunoassay data supported direct evidence of phenylephrine-stimulated release of prostanoids (PGI₂, PGE₂, and PGF_2α) by thoracic and abdominal aortas without endothelium, and their almost complete inhibition by 1 μM indomethacin. Isometric force measurements established that 10 μM indomethacin—but no lower concentrations—inhibited the contractions evoked by phenylephrine in endothelium-denuded abdominal aorta. In this preparation, 10 μM indomethacin also depressed the contractions provoked by angiotensin II and high K⁺ (80 mM). In fact, indomethacin (up to 1 mM) caused concentration-dependent reductions in all abovementioned contractile responses. In endothelium-denuded thoracic aortas, however, only 1 mM indomethacin significantly depressed the contractile activity stimulated by either phenylephrine, angiotensin II, or high K⁺. Hence, there was a clear quantitative difference in response to indomethacin between abdominal and thoracic aortas without endothelium. Altogether, the results indicate that prostanoids induced by phenylephrine in abdominal and thoracic aortas were derived from non-endothelial COX-mediated metabolism; notably, the decrease in prostanoid synthesis could not account for the inhibition of vasoconstrictor responses by indomethacin: Through COX-independent actions, indomethacin inhibited aortic smooth muscle contractility.     

Cytotoxic effects of cytokines on islet beta-cells: evidence for involvement of eicosanoids

Arachidonic acid metabolites (eicosanoids) have been implicated in mediating actions of cytokines in different tissues. In this study, we tested inhibitors of arachidonate metabolism for possible protection against the toxic effects of the cytokine combination of tumor necrosis factor (TNF, 100 U/ml) and interferon-gamma (IFN-gamma, 100 U/ml) in rat islet cell monolayer cultures, using a 51Cr release cytotoxicity assay to measure islet cell lysis (% 51Cr release). The toxic effect of TNF/IFN-gamma (26.6 +/- 3.7%) was inhibited partially by both a cyclooxygenase inhibitor, indomethacin and a lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA), and combination of maximally effective concentrations of Indo and NDGA (30 microM) produced further protection against TNF/IFN-gamma-induced lysis (3.5 +/- 0.9%). Also, the combined cyclo/lipoxygenase inhibitors, oxyphenbutazone and eicosa 5,8,11,14 tetrynoic acid, as well as the phospholipase A2 inhibitor, bromophenacyl bromide, significantly inhibited the cytotoxic effect of TNF/IFN-gamma. Whereas indomethacin and NDGA did not prevent TNF/IFN-gamma-induced inhibition of insulin release, this recovered after cytokine removal from cultures protected by the cyclo/lipoxygenase inhibitors. These results suggest that arachidonate metabolites may be involved in mediating the cytotoxic and not the functional inhibitory effects of TNF and IFN-gamma in islet cells.     

Aprotinin impairs endothelium-dependent relaxation in rat aorta and inhibits nitric oxide release from rat coronary endothelial cells

OBJECTIVE: Aprotinin, a non-specific serine protease inhibitor, reduces postoperative bleeding after coronary artery surgery. The mechanism of action for this 'blood-sparing' effect of aprotinin is only partially clarified. We therefore aimed to investigate the effect of aprotinin on the release of nitric oxide (NO), a vasodilator and antiaggregant factor, from rat coronary microvascular endothelial cells and on the NO-mediated endothelium-dependent relaxation of rat thoracic aorta. METHODS: Endothelium-intact and endothelium-denuded thoracic aortic rings from Wistar rats (250-300 g) were suspended in organ chambers. Contractile and relaxant responses in the absence and presence of aprotinin (125, 250 and 500 KIU/ml) were recorded via a mechanotransducer. Coronary microvascular endothelial cells (CMEC) were isolated on a Langendorff system by collagenase perfusion of the hearts from the same rats. Calcium ionophore- (1 microM) induced release of NO from confluent cells was determined spectrophotometrically by measuring its stable metabolites, nitrite and nitrate, via Griess reaction. RESULTS: Aprotinin selectively enhanced phenylephrine-induced contractions in endothelium-intact rat thoracic aortic rings, but not in the endothelium-denuded rings. The use of a nitric oxide synthesis inhibitor Nomega-nitro-L-arginine methyl ester (100 microM) on endothelium-intact rings produced a similar increase in phenylephrine-induced contractions. KCl-induced contractions remained unaltered. Aprotinin inhibited acetylcholine-, calcium ionophore- and L-arginine-induced endothelium-dependent relaxations, but not sodium nitroprusside-induced endothelium-independent relaxation. Aprotinin had no significant effect on basal nitrite-nitrate release from CMEC, while it inhibited calcium ionophore-induced total nitrite accumulation in the supernatants. CONCLUSION: Aprotinin selectively impairs endothelium-dependent relaxation as well as basal NO availability in rat thoracic aortic rings and inhibits NO release from rat CMEC. This effect of the drug may contribute to its 'blood-sparing' action and may also account for the increase in perioperative restenosis risk observed in clinical practice during aprotinin therapy.     

Growth inhibition and eicosanoid metabolism in the R3230AC mammary adenocarcinoma by interferon

The mode of action of rat interferon (IFN) on growth of the R3230AC mammary adenocarcinoma was studied in vivo in Fischer female rats. A dose of 1 X 10(4) units of rat IFN given thrice weekly inhibited the growth of the transplanted mammary tumors. Of the five eicosanoids measured in the tumor, the content of four arachidonate products, prostaglandin (PG) E2, PGF2 alpha, 6-keto-PGF1 alpha, and thromboxane (TX) B2, was higher in mammary tumors from IFN-treated rats than the control rats. PGE2 was the major eicosanoid. In vitro PG synthesis (PGE1, PGE2, and PGF2 alpha) was lower in tumor microsomes prepared from IFN-treated tumors. These data suggest that the tumor content of four arachidonate products in the IFN-treated tumors was related to the in vivo effects of rat IFN. Indomethacin, a cyclooxygenase inhibitor, also inhibited tumor growth. Furthermore, when indomethacin was administered daily in combination with rat IFN, the tumor-inhibiting effect of rat IFN was reduced. These observations suggest that the effects of eicosanoids appear to be biphasic in this tumor model. Inhibition of arachidonic acid metabolism resulted in tumor growth inhibition, a finding consistent with the view that eicosanoid production is required for tumor enhancement. Conversely, in the experiments with rat IFN, retardation of tumor growth is associated with a greater amount of arachidonic acid metabolism, and indomethacin prevents this effect. Eicosanoids appear to be required for tumor-inhibiting effects of rat IFN, and yet inhibition in vivo of eicosanoid synthesis also resulted in retardation of tumor growth. Although the precise mechanism of action in each situation is unclear, these apparently contradicting results are consistent with the biphasic actions of eicosanoids reported in some normal tissues and transformed tumor cell lines.     

Effect of indomethacin on electrical field stimulation-induced contractions of isolated transverse and longitudinal rat gastric fundus strips

AIM: To study the effects of indomethacin on the isolated transverse and longitudinal rat gastric fundus strips. METHODS: The strips were suspended in an organ bath containing oxygenated Krebs solution, and contractile responses to electrical field stimulation were recorded on a physiograph in an isotonic manner after administration of cumulative concentrations of indomethacin. The effects of indomethacin on the strips pretreated with K_(ATP) channel modulators, diazoxide and glybenclamide were studied. RESULTS: Treatment of the transverse strips with indomethacin resulted in a concentration-dependent inhibitory response. In longitudinal strips, biphasic responses were seen, which included a stimulatory response at low concentrations of indomethacin, followed by an inhibitory response at higher concentrations. Diazoxide pre-treatment inhibited the stimulatory response of longitudinal strips. Glybenclamide pre-treatment not only blocked inhibitory effect of the low concentrations of indomethacin on transverse strips, but also increased the amplitude of contractions. Moreover, the drug decreased the amplitude of contractions in longitudinal strips. CONCLUSION: Responses of the isolated longitudinal and transverse rat gastric fundus strips to indomethacin are not similar, and are influenced by K_(ATP) channel modulators.     

Angiotensin II-induced relaxation of vascular smooth muscle

The effects of angiotensin II (AII) on contractile tension were studied in vascular smooth muscle from dogs, pigs and rabbits. Helically cut strips of renal veins were mounted in organ chambers and isometric contractions were recorded. Contraction of the venous strips was induced by application of 10(-8) g/ml norepinephrine (NE). Subsequent addition of 5 X 10(-8) g/ml AII caused a triphasic response: (1) there was an initial contraction (subsequent contractions were tachyphylactic in all species); (2) the contraction was followed by a relaxation below the contraction induced by NE (subsequent relaxation responses were tachyphylactic in dog and pig veins), and (3) there was a return from the relaxation to the level of the NE-induced contraction. The duration of the entire response was approximately 5 min. The magnitude of the relaxation varied inversely with the level of the NE contraction when the contractile state was altered by changing the NE concentration. Conditions which inhibit the sodium pump (potassium-free solution and ouabain) and beta-adrenergic blockade with propranolol had no effect on the AII-induced relaxation. The relaxation was temperature sensitive. Inhibitors of prostaglandin synthesis (indomethacin and aspirin) and saralasin attenuated the relaxation in response to AII. Prostaglandins E1 and E2 and arachidonic acid caused relaxation of renal vein strips contracted with NE; the relaxant effect of arachidonic acid was blocked by indomethacin. These results suggest that: (1) All stimulates the synthesis of prostaglandins in isolated venous smooth muscle, and (2) endogenous prostaglandins modulate the response of venous smooth muscle to AII.     

Role of arachidonate metabolism on the in vitro release of luteinizing hormone and prolactin from the anterior pituitary gland: possible involvement of lipoxygenase pathway

The aim of the present study was to evaluate whether arachidonic acid metabolism may play a role on luteinizing hormone (LH) and prolactin (PRL) release directly at the pituitary level. To this purpose, exogenous arachidonic acid, alone or in presence of inhibitors of cyclooxygenase (indomethacin:IND) and lipoxygenase pathways (nordihydroguaiaretic acid:NDGA), was added to perfused rat anterior pituitary cells. PGE, PGF alpha, LH and PRL levels present in the eluate were assayed with specific RIA methods. Both PGE and PGF alpha show a dose-related response after the addition of increasing doses of arachidonic acid. The addition of 0.05 mM arachidonic acid induces an increase of LH and PRL. The addition of IND to the perfusion medium highly potentiates the stimulatory effects induced by arachidonic acid on LH and PRL release. On the contrary, the addition to the medium of either NDGA or IND plus NDGA completely reverses the stimulatory action induced by arachidonic acid alone. The present results suggest that: adenohypophyseal cells are able to metabolize exogenous arachidonic acid; arachidonic acid induces an elevation in LH and PRL levels; lipoxygenase pathway metabolite(s) are likely involved in these activities, and the site of action of arachidonic acid is at the pituitary level.     

Effect of Red Blood Cells and Hemoglobin on Spontaneously Hypertensive and Normotensive Rat Aortas

Experiments were designed to compare the contractile effect of red blood cells (RBC) on aortic rings with and without endothelium from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Red blood cells of 4 week old WKY and SHR rats induced a negligible increase in tension of aortic rings, either with or without endothelium, being slightly more effective in SHR rats. However, red blood cells of 16 week old rats increased tension of WKY and SHR aortic rings, with endothelium at this age being more pronounced then red blood cells in 4 week old animals. The contractions induced by WKY and SHR red blood cells both in WKY and SHR aortic rings without endothelium at this age are significantly greater compared to the effect on aortic rings with endothelium. Red blood cell ghosts of rats of both strains increased the tension of the rings without endothelium of SHR aorta to near 50% of those induced by red blood cells, whereas they were ineffective in aortic rings without endothelium of WKY rats. Oxyhemoglobin increased the tension of 16 week SHR aortic rings both with and without endothelium, whereas the effect on the rings of WKY rats was negligible. This increase in tension was inhibited by BM 13505, nordihydroguaiaretic acid, and indomethacin in SHR rings both with and without endothelium, demonstrating an eicosanoid involvement in oxyhemoglobin-induced contractions. Hemoglobin or its metabolites may be involved in development or in maintenance of spontaneous hypertensin.     

Effects of nesfatin-1 on atrial contractility and thoracic aorta reactivity in male rats

Background: This study aimed to examine the effects of nesfatin-1 on thoracic aorta vasoreactivity and to investigate the inotropic and chronotropic effects of nesfatin-1 on the spontaneous contractions of the isolated rat atria.

Methods: Isolated right atria and thoracic aorta were used in organ baths. The reactivity of the thoracic aorta was evaluated by potassium chloride (KCl), phenylephrine (Phe), acetylcholine (ACh), and sodium nitroprusside (SNP). The effects of nesfatin-1 on the spontaneous contractions of the rat atria were also examined.

Results: Nesfatin-1 (0.1–100 ng/ml) produced a concentration-dependent relaxation response in rat thoracic aorta. The relaxant responses to nesfatin-1 were inhibited by the removal of endothelium, NO synthase blocker N-nitro-L-arginine methyl ester (L-NAME, 10^?4 M), and soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10^–5 M). Nesfatin-1 (10 ng/ml, 30 min) increased the relaxation responses to either ACh or SNP, and the contractile response to both Phe and KCl did not significantly change in the arteries that were incubated with nesfatin-1 compared with the controls. The thoracic aorta contractions induced by the stepwise addition of Ca²⁺ to a high KCl solution with no Ca²⁺ were not significantly changed by nesfatin-1. Under calcium-free conditions, the contractions of the thoracic aorta rings incubated with nesfatin-1 in response to Phe were not significantly lower than those of the rings from the control rats. Nesfatin-1 showed positive inotropic and chronotropic effects on rat atria.

Conclusion: Nesfatin-1 significantly changed the vascular responsiveness in rat thoracic aorta and produced positive inotropic and chronotropic effects on rat atria.     

Receptor-mediated release of endothelium-derived relaxing factor and prostacyclin from bovine aortic endothelial cells is coupled

Bovine aortic endothelial cells were grown on microcarrier beads and were perfused with Krebs-Ringer solution. Endothelium-derived relaxing factor (EDRF) was bioassayed on a cascade of four strips of rabbit aorta, and prostacyclin was analyzed by RIA of 6-oxo-prostaglandin F1 alpha. The endothelial cells released EDRF and prostacyclin when stimulated with bradykinin and its analogues, or with ADP, ATP, arachidonic acid, and phospholipase C (phosphatidylcholine cholinephosphohydrolase, EC 3.1.4.3). The detection of EDRF was potentiated by superoxide dismutase, and the relaxation of rabbit aortic strips induced by EDRF was antagonized by methylene blue. The release of EDRF and prostacyclin was inhibited by phorbol myristate acetate, R59022 (a diacylglycerol kinase inhibitor), and gentamycin. We suggest that the release of EDRF and prostacyclin is coupled and the initial common step is activation of a phospholipase C.     

二甲基亚砜对离体大鼠胸主动脉的舒张作用

目的探讨二甲基亚砜（DMSO）对离体大鼠胸主动脉环的作用及其可能机制。方法观察离体大鼠胸主动脉环血管张力的变化，探讨DMSO对血管的作用。结果高浓度DMSO可降低动脉环的基础张力；DMSO对去氧肾上腺素（PE）和KCl预收缩的血管环均有浓度依赖性的舒张作用。左旋硝基精氨酸甲酯（LNAME）预处理血管环后，DMSO对PE预收缩的血管的舒张作用明显减弱。DMSO对PE诱发的依赖内钙释放和外钙内流的血管环收缩反应均有浓度依赖性抑制作用。DMSO预处理可使CaCl2量效曲线右移。结论DMSO可能通过抑制血管平滑肌细胞膜及胞内的Ca^2＋通道引起血管舒张。内皮源性的NOS通路可能部分参与DMSO诱导的血管舒张作用。     

Progression of induced aortic atherosclerosis in rabbits fed a high cholesterol diet

In this study we have evaluated the progression of atheromatosis in aortic arch, thoracic aorta and abdominal aorta in rabbits fed a high cholesterol diet. The aortic atheromatosis decreased progressively from the aortic arch to the abdominal aorta after 6 months of high cholesterol diet. It is possible that a different segmental resistance to hypercholesterolemic damage may be involved in the cranio caudal progression of atheromatosis in rabbits.     

Trandolapril inhibits atherosclerosis in the Watanabe heritable hyperlipidemic rabbit.

The effects of trandolapril (0.25 mg/kg body wt per 48 hours) on aortic atherosclerosis were examined in the Watanabe heritable hyperlipidemic rabbit treated from 3 to 12 months of age. Trandolapril caused a significant decrease in atherosclerotic involvement of the intimal surface of total aorta from 56.3 +/- 5.0% in control Watanabe rabbits to 35.0 +/- 4.1% with treatment (p less than 0.01). The largest reductions were observed in descending thoracic aorta where 21.8 +/- 5.7% of intimal surface was involved in the trandolapril-treated animals versus 54.4 +/- 7.7% in the control group (p less than 0.01). Significant decreases also occurred in ascending aorta/arch and abdominal aortic segments. Cholesterol content of descending thoracic aorta was also significantly reduced in the trandolapril-treated rabbits. The atherosclerotic plaques in aorta from trandolapril-treated rabbits appeared to contain less foam cells and relatively greater amounts of connective tissue than those from control animals. These studies indicate that trandolapril inhibits aortic atherosclerosis in the Watanabe heritable hyperlipidemic rabbit. The similarity in results between the current study and that using captopril suggests that the antiatherosclerotic action of trandolapril and captopril represents a class effect related to angiotensin converting enzyme inhibition.     

Endothelium-dependent contractions in arteries and veins

Endothelium-dependent contractions of isolated veins can be induced with arachidonic acid and thrombin. Anoxia causes endothelium-dependent contractions in a variety of isolated arteries and veins. Rapid stretch and acetylcholine contract cerebral arteries with, but not those without endothelium. Acetylcholine (and serotonin) cause endothelium-dependent contractions in the aorta of the spontaneously hypertensive, but not that of the normotensive rat.     

Effect of various blockers of arachidonic acid metabolism on release of beta-endorphin- and adrenocorticotropin-like immunoreactivity induced by phospholipase A2 from rat adenohypophysis in vitro

Anterior pituitary quarters were incubated in vitro and the release of beta-endorphin-like (beta-End-IR) and adrenocorticotropin-like immunoreactivity (ACTH-IR) was determined. The effect of phospholipase A2 as well as the effect of various compounds known to influence arachidonic acid metabolism under certain conditions were examined. Phospholipase A2 increased the release of beta-End-IR and ACTH-IR. This effect was reversible, concentration-dependent (1-400 ng/ml) and inhibited in calcium-free medium and in the presence of CoCl2 (5 mM) or phospholipase A2 inhibitors (p-bromophenacylbromide, 21 microM; mepacrine, 1 mM). The phospholipase A2-induced beta-End-IR release was accompanied by the release of prostaglandin E2. Inhibition of cyclooxygenase activity by indomethacin (14 or 140 microM) did not change beta-End-IR release induced by phospholipase A2 (5 ng/ml). The effects of blockers of lipoxygenase (nordihydroguaiaretic acid, NDGA; AA861) or lipoxygenase plus cyclooxygenase (BW755C; eicosatetraynoic acid, ETYA) on phospholipase A2-induced release of beta-End-IR were diverse. BW755C (up to 250 microM) and AA861 (up to 100 microM) produced no effect. However, NDGA or ETYA inhibited phospholipase A2-induced beta-End-IR release. NDGA (100 microM) produced a maximum inhibition by about 40% (p less than 0.05), whereas ETYA (100 microM) produced a maximum inhibition by about 85% (p less than 0.001). These data are consistent with the view that phospholipase A2 releases endogenous arachidonic acid which is transformed into products which stimulate ACTH and beta-endorphin release from the corticotrophs; the metabolizing enzyme (possibly a lipoxygenase or epoxygenase) is sensitive to NDGA and especially to ETYA.