Energetic cost of sexual attractiveness: ultrasonic advertisement in wax moths

PURPOSE: The response of endothelium to ionizing radiation was studied. METHODS AND MATERIALS: The abdominal aorta in different experimental groups of rats was irradiated, and the response of arterial rings from the irradiated segments to norepinephrine, acetylcholine (ACh), and nitroglycerin (NTG) was studied. Nonirradiated thoracic segments in the same experimental animals were used as as a control for comparisons. Two age-matched nonirradiated control groups were also studied. RESULTS: A poor endothelium-dependent vasodilator response was obtained with ACh in the irradiated rings and also in those not directly irradiated; the endothelium-independent vasodilator response to NTG was preserved during the first 3 days after irradiation. By 6 months, both the endothelium-dependent response and endothelium-independent response were impaired. CONCLUSIONS: Alterations in nitric oxide synthesis and/or release by the endothelium were observed during the early phase of radiation in irradiated and nonirradiated segments. In the delayed phase of radiation, endothelium-independent muscular relaxation was also affected.     

Impaired endothelium-dependent relaxation in isolated resistance arteries of spontaneously diabetic rats

1. Previous studies have shown that endothelium-dependent relaxation in the aorta of spontaneously diabetic bio bred rats (BB) is impaired. 2. We have investigated noradrenaline (NA) contractility, endothelium-dependent acetylcholine (ACh) and bradykinin (BK) relaxation, and endothelium-independent sodium nitroprusside (SNP) relaxation in mesenteric resistance arteries of recent onset BB rats and established insulin treated BB rats, compared to their age-matched non diabetic controls. 3. There was no significant difference in the maximum contractile response or sensitivity to noradrenaline in either of the diabetic groups compared to their age-matched controls. 4. Incubation with the nitric oxide synthetase inhibitor NG-nitro-L-arginine (L-NOARG) resulted in a significant increase in maximum contractile response to noradrenaline in the recent onset age-matched control group (P < 0.05). Analysis of the whole dose-response curve (using ANOVA for repeated measures with paired t test) showed a significant left-ward shift following the addition of L-NOARG (P < 0.001). A similar but less marked shift (P < 0.01) was evident in vessels from recent onset diabetics. An overall shift in both sensitivity and maximum response was also evident in the age-matched non diabetic controls of the insulin-treated group (P < 0.05). However, by contrast, there was no significant change in sensitivity in the insulin-treated diabetic rats. 5. ACh-induced endothelium-dependent relaxation was significantly impaired in the recent onset diabetic rats compared to their age-matched controls (47 +/- 11% versus 92 +/- 2%, P < 0.05, n = 6), and in the insulin treated diabetic rats (34 +/- 5% versus 75 +/- 6%, P < 0.05, n = 6). The relaxation responses to BK also were significantly impaired in the diabetic rats compared to their age-matched controls (recent onset: 20 +/- 3% versus 72 +/- 7%, P < 0.05, n = 6; insulin treated: 12 +/- 9% versus 68 +/- 7%, P < 0.05, n = 7). 6. Incubation with either the nitric oxide synthetase substrate, U-arginine, or the free radical scavenging enzyme superoxide dismutase (150 mu ml-1) failed to improve the attenuated response of acetylcholine-induced relaxation in the diabetic vessels. 7. Endothelium-dependent relaxation mediated by ACh and BK was significantly attenuated in both the diabetic and control vessels after incubation with L-NOARG. 8. Pretreatment with a cyclo-oxygenase inhibitor, indomethacin, significantly enhanced the relaxation to ACh in both the recent onset and insulin treated diabetic rats (42 +/- 10%, n = 7 versus 64 +/- 7%, n = 7, P < 0.05, and 40 +/- 5%, n = 7 versus 65 +/- 9%, n = 6, P < 0.05). 9. Following endothelium removal, there was a marked impairment in endothelium-dependent relaxation responses to ACh and BK in both the diabetic and control vessels. 10. Incubation with the thromboxane A2 receptor antagonist SQ29548, did not significantly improve the ACh endothelium-dependent relaxation response in the diabetic vessels. 11. Endothelium-independent relaxation to sodium nitroprusside was significantly impaired in the first group of diabetic vessels studied; however, subsequent studies showed no impairment of the sodium nitroprusside response in the diabetic vessels. 12. In conclusion, the ability of the endothelium to regulate vascular contractility is reduced in recent onset diabetic vessels, and significantly impaired in established insulin treated diabetics. Relaxation to the endothelium-dependent vasodilators ACh and BK was impaired in both the recent onset and the established insulin treated diabetics, and the ACh response was significantly improved following pretreatment with indomethacin, suggesting a role for a cyclo-oxygenase-derived vasoconstrictor. Preliminary studies with a thromboxane A2, receptor antagonist, SQ29548 did not significantly improve the impaired relaxation to ACh, indicating that the vasoconstrictor prostanoid is not thromboxane A2.     

Effect of age on in vitro magnesium modulation of vascular reactivity in the rat aorta

Vascular reactivity and the effect of various magnesium (Mg) concentrations on it, were studied in aortic rings from adult (4-month-old) and aged (24-month-old) male Sprague-Dawley rats. Contraction induced by CaCl2 of the aortae incubated in high potassium PSS containing 1.2 mM Mg was greater in aged than in adult rats. Low Mg (0.1 mM) decreased CaCl2-induced contraction in the aortae from adult rats more than in those from aged rats. High Mg (4.8 mM) attenuated CaCl2-induced contraction in the aged but not in the adult rats. Acetylcholine- and isoproterenol-induced relaxation of the aortae incubated in normal PSS (1.2 mM) was less pronounced in aged than in adult rats, whereas sodium nitroprusside-induced relaxation was similar in both groups. Low Mg did not modify acetylcholine- and sodium nitroprusside-induced relaxation in adult and aged rats. With high Mg, acetylcholine- and sodium nitroprusside-induced relaxation was increased in both groups. The increasing effect of high Mg on acetylcholine-induced relaxation was however greater in aorta from aged rats. Low Mg decreased isoproterenol-induced relaxation in the adult but not in the aged group, whereas high Mg increased it in both groups of rats. When endothelium was intact, Mg-induced relaxation was less in aged than in adult rats. When endothelium was disrupted, relaxation was similar in both groups . Mg Removal produced an endothelium-dependent relaxation, which was significantly lower in the aged rats. In conclusion, the functional alterations of vascular smooth muscle and endothelium observed with aging modify the modulatory role of Mg on aortic responsiveness.     

Short exposure to endotoxin increases the constriction induced by angiotensin II in rat aorta

The contraction elicited by angiotensin II (ANG II) was studied by using standard isometric tension techniques in aortic rings exposed for 1 h to 1 or 10 micrograms/ml Escherichia coli lipopolysaccharide endotoxin (LPS). This contraction was 18 and 71% greater for the two doses of LPS, respectively, than in unexposed control rings. In endothelium-denuded rings, the LPS-induced increase in contraction in response to ANG II was completely abolished. Because the contraction induced by ANG II is modulated by the simultaneous release of prostaglandins, we tested the hypothesis that LPS interferes with this modulation. We found that the LPS-induced increase in contraction to ANG II was inhibited in the presence of the cyclooxygenase inhibitor indomethacin (10(-5) M) or the prostaglandin H2/thromboxane A2-receptor antagonist SQ-29548 (2 x 10(-7) M). Conversely, the LPS-induced increase in contraction in response to ANG II was not inhibited by the presence of dexamethasone (10(-6) M), which inhibits new protein synthesis. In addition, there was no loss of vasodilator response to the endothelium-dependent receptor agonist acetylcholine (10(-8)-10(-4) M) or in the constrictor responses to norepinephrine (10(-9)-10(-5) M) and KCl (20-100 mM). We conclude that short exposure to LPS produces a specific increase in the constrictor response to ANG II via mechanisms mediated by prostaglandin H2/thromboxane A2. This effect could be a LPS-induced shift in favor of constrictor prostanoids in the balance of dilator/constrictor prostanoids, the release of which is associated with stimulation by ANG II.     

Diabetes-induced endothelial dysfunction is prevented by long-term treatment with the modified iron chelator, hydroxyethyl starch conjugated-deferoxamine

Oxygen radicals are believed to play a role in vascular complications of diabetes mellitus. In this study, we evaluated whether long-term treatment with an iron chelator and inhibitor of metal-catalyzed hydroxyl radicals (.OH) could prevent diabetes-induced defects in endothelium-dependent relaxation. Diabetes was induced in Sprague-Dawley rats by injection of streptozotocin. At 48 h after streptozotocin, a subgroup of diabetic rats received daily injections of 50 mg/kg hydroxyethyl starch conjugated-deferoxamine (HES-DFO) for a total of 8 weeks. Long-term treatment with HES-DFO did not modify serum insulin or blood glucose taken at the end of the study; however, a modest reduction in glycosylated hemoglobin was present. In precontracted aortic rings suspended in tissue baths, endothelium-dependent relaxation to acetylcholine was impaired in diabetic rings compared with control rings in the presence or absence of indomethacin. Endothelium-independent relaxation to nitroglycerin was unaltered. Long-term treatment with HES-DFO had no effect on relaxation to nitroglycerin but completely prevented the impaired relaxation to acetylcholine in diabetic rings in either the presence or absence of indomethacin. These data suggest that iron-catalyzed .OH formation contributes to the development of diabetes-associated endothelial dysfunction.     

Thromboxane stimulation of mesangial cell fibronectin synthesis is signalled by protein kinase C and modulated by cGMP

Thromboxane (TX) has been implicated in the pathogenesis of glomerulosclerosis in several models of glomerular injury. In the present study, we examined the role of the protein kinase C (PKC) signalling system in expression of the action of the TXA2/PGH2 analogue U-46619 to stimulate fibronectin (Fn) synthesis in cultured rat mesangial cells (MC), and the influence of cGMP on this MC response. U-46619 activated PKC and enhanced Fn synthesis in MC in a time and concentration dependent fashion. Both responses to U-46619 were blocked by GF 109203X, a selective inhibitor of PKC activity, as well as by calphostin C and staurosporine, PKC inhibitors structurally distinct from GFX. Down-regulation of PKC by prior sustained exposure of MC to 0.5 microM phorbol myristate acetate similarly blocked increases in Fn synthesis induced by U-46619. The TXA2/PGH2 receptor antagonist Sq-29548 also prevented activation of PKC and stimulation of Fn synthesis by U-46619, consistent with transduction of these responses via specific high affinity TXA2/PGH2 receptors on MC. Addition of exogenous 8-Br-cGMP or stimulation of endogenous cGMP generation with atrial natriuretic peptide (ANP) suppressed both U-46619 activation of PKC and stimulation of Fn synthesis. cGMP did not alter TXA2/PGH2 receptor number of affinity in MC, but significantly suppressed phorbol ester activation of PKC. Thus, cGMP inhibition of U-46619 actions is expressed at steps distal to TX receptor binding and may involve effects at and proximal to activation of PKC. Interactions between the PKC and cGMP cellular signalling systems may be important determinants of MC matrix protein production in response to TX.     

Effects of dietary Spirulina maxima on endothelium dependent vasomotor responses of rat aortic rings

The aim of this study was to evaluate the effects of Spirulina maxima on vasomotor responses of aorta rings from male Wistar rats fed on a purified diet. For this purpose, the animals (weighing 200-240 g) were allocated randomly in two groups. One receiving purified control diet (A) and the other receiving purified diet containing 5% Spirulina (B). Purified diets were according to American Institute of Nutrition guidelines and adjusted to Spirulina protein content. All animals were fed (20 g/day/rat) during two weeks, receiving water ad libitum and 12 h. light-dark cycles. Spirulina maxima effects were evaluated by concentration-response (CR) curves of aorta rings with or without endothelium to phenylephrine (PE), both in presence and absence of indomethacin (Indom) or indomethacin plus L-NAME (Indom. + L-NAME), and to carbachol (CCh). Aorta rings with endothelium from group B showed, relative to corresponding rings from group A: 1) a significant decrease in the maximal tension developed in response to PE. 2) this decrease was reverted by Indom. 3) Indom. + L-NAME induced an additional increase in the contractile responses to PE. 4) a significant shift to the left of the CR curve to CCh. No significant differences were observed in the tension developed in response to PE in rings without endothelium from either group. These results suggest that Spirulina maxima may decrease vascular tone by increasing the synthesis and release of both a vasodilating cyclooxygenase-dependent product of arachidonic acid and nitric oxide, as well as by decreasing the synthesis and release of a vasoconstricting eicosanoid from the endothelial cells.     

Role of endothelium in the endothelin-1-mediated potentiation of the norepinephrine response in the aorta of hypertensive rats

OBJECTIVE: To investigate the role of the endothelium in the functional interaction between endothelin-1 and norepinephrine in the contractile response of aortas from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). METHODS: Thoracic aorta rings with and without endothelium from SHR and from WKY rats were suspended in an organ bath to record the isometric tension. After an equilibration period of 120 min, the preparations with and without endothelin-1 were subjected to single and cumulative additions of norepinephrine in different experiments. To characterize the mechanisms involved in the interaction between endothelin-1 and norepinephrine, the aortic rings were pretreated with a cyclooxygenase pathway inhibitor (piroxicam, SO29548), an inhibitor of NO synthase [NG-nitro-L-arginine (NLA)], or selective endothelin receptor blockers (BQ-123 or BQ-788). In some experiments we examined the contractile responses to norepinephrine in aortas pretreated either with angiotensin II (AII) or with U46619, an agonist of prostaglandin H2-thromboxane A2 receptors. Finally, we examined the effect of the combination of calcium-entry blockade by administration of nifedipine and treatment with either endothelin-1 or U46619 on the norepinephrine reactivity. RESULTS: Administration of 3 x 10(-10) mol/l endothelin-1 potentiated the contractile response to norepinephrine in SHR aortas with endothelium, irrespective of whether they had been treated with NLA. No endothelin-1-mediated enhancement of the response to norepinephrine was observed in SHR denuded rings and in untreated and NLA-treated WKY rat aortas. All did not affect the response to norepinephrine in SHR rings with endothelium. The amplification by endothelin-1 of the response to (1-100) x 10(-9) mol/l norepinephrine was abolished by blockade of the cyclooxygenase pathway with piroxicam or SO29548. In WKY rat and SHR denuded aortas, 10(-8) mol/l U46619 potentiated the contractile responses to norepinephrine. Administration of 3 x 10(-6) mol/l BQ-123 abolished the increase in reactivity to norepinephrine evoked by endothelin-1 in intact SHR aorta, whereas 3 x 10(-6) mol/l BQ-788 failed to modify this potentiating effect. Administration of 10(-8) mol/l nifedipine inhibited the potentiation of the norepinephrine-induced contractions evoked both by endothelin-1 in SHR aortic rings with endothelium and by U46619 in SHR denuded rings. CONCLUSION: Our results show that a low concentration of endothelin-1 induced potentiation of the contractile response to norepinephrine in SHR aortas but not in WKY rat aortas. This response was endothelium-dependent. Furthermore, our study affords functional arguments that both endothelial and smooth muscle pathways are involved in the potentiating interaction. We propose that endothelin-1 stimulates the production of endothelium- and cyclooxygenase-generated vasoconstrictor factors, which in turn may serve directly as priming stimuli at the vascular smooth muscle level, to activate the Ca(2+)-signal pathway and consequently to increase locally the vascular sensitivity to norepinephrine.     

Rehabilitation of Guillain-Barré syndrome

In this study, we evaluated the effects of vitamin E on the vascular reactivity and structure of thoracic aorta from streptozotocin (STZ)-diabetic rats. Plasma glucose, cholesterol, and triglyceride concentrations in rats were increased markedly by STZ-diabetes. The thiobarbituric acid (TBA) reactivity level as an index of lipid peroxidation was higher in both plasma and aorta of STZ-diabetic rats compared with controls. The rings of thoracic aorta with or without endothelium were mounted in organ chambers for measurement of isometric tension and were contracted by a single dose (10-5 mol/L) and then cumulative doses of noradrenaline ([NA] 10(-9) to 10(-5) mol/L). Pretreatment with methylene blue (MB) or removal of the endothelium resulted in a similar degree of enhancement in NA-induced contraction of control rings. STZ-diabetes increased the fast and slow components of NA-induced contraction in all experiments. The maximal contractile response of aorta to NA was also augmented by STZ-diabetes, whereas the sensitivity (pD2) remained unaltered. STZ-diabetes resulted in significant increases in the maximum contractile response and sensitivity of aorta to KCl. STZ-diabetic rats showed a significant reduction in the percentage of endothelial response (PER). A group of diabetic rats was treated from the time of diabetes induction with a 0.5% dietary supplement of vitamin E. Vitamin E supplementation of STZ-diabetic rats eliminated accumulation of lipid peroxides and returned plasma triglycerides toward normal levels. Diabetes-induced abnormal contractility and endothelial dysfunction were significantly but not completely prevented by vitamin E treatment. The endothelium-independent relaxation response to sodium nitroprusside (SNP) was not affected by diabetes or vitamin E treatment. Electron microscopic examination of thoracic aorta revealed that normal tissue organization was disrupted in STZ-diabetic rats, and that vitamin E treatment can protect the morphological integrity of aorta against STZ-diabetes. The results suggest the following: (1) The increased triglycerides/lipid peroxides may be an important reason for morphological or functional disruption of endothelium and enhanced activation of contractile mechanisms of vascular smooth muscle in STZ-diabetic rats. Both contribute to an increased responsiveness of diabetic aorta to vasoconstrictor agents. (2) Vitamin E treatment of STZ-diabetic rats can prevent the development of abnormal contractility and structure and endothelial dysfunction in aorta. (3) The triglyceride- and/or lipid peroxidation-lowering effect of vitamin E may be crucial for the protective effect of this vitamin on the vasculature.     

Impairment of endothelium-dependent vasorelaxation in experimental atherosclerosis is dependent on gender

OBJECTIVE: Nitric oxide (NO) has been suggested to have antiatherosclerotic effects. It has also been demonstrated that there is a greater basal release of endothelium derived relaxing factor (EDRF) in female as compared to male rabbit aorta, which also might have beneficial effects in atherosclerosis. We thus sought to determine if gender influences the severity of atherosclerosis. METHODS: We studied 18 female and 18 male New Zealand White rabbits that were randomly divided in two groups of 9 animals each and fed either a standard or a cholesterol diet (0.75%) for 15 weeks. RESULTS: In cholesterol-fed rabbits the percentage of atherosclerotic lesions in the aorta was identical in females and males and was inversely correlated with the maximal aortic relaxation to acetylcholine as assessed in organ chamber experiments (females: P < 0.0008, males: P < 0.0002). Importantly, the cholesterol diet induced a significantly (P < 0.025) more severe impairment of maximal vasorelaxation to acetylcholine in males from 78.4 +/- 1.2% to 29.4 +/- 10.2%) compared to females (from 84.4 +/- 1.2% to 60.7 +/- 8.5%). Both male gender (P < 0.0001) and the extent of impairment of endothelium-dependent relaxation (P < 0.0002) were associated with a reduced aortic sensitivity to S-nitroso-N-acetyl-D,L-penicillamine, which releases NO into the organ bath. In contrast, the aortic sensitivity to the organic nitrates pentaerythritol tetranitrate and isosorbide 5-nitrate, which release NO after enzymatic metabolization within the smooth muscle, was not reduced. CONCLUSIONS: These results suggest that the impairment of endothelium-dependent vasorelaxation induced by atherosclerosis is dependent on gender. This may be due to a greater degradation of extracellular NO in the vessel wall of males.     

Effects of en bloc esophagectomy on nutritional and immune status in patients with esophageal carcinoma

We tested the hypothesis that extravascular adenosine induces the release of vasodilatory products from endothelial cells lining skeletal muscle vessels. Endothelium-intact (n = 35) and -denuded (n = 5) dog semitendinosus intramuscular arteries were isolated, cannulated, and placed in 100-mL baths containing Krebs-Henseleit bicarbonate buffer (Krebs) at 37 degrees C and gassed with 95% O2--5% CO2. Each vessel, as well as a parallel tubing segment (avascular control), was perfused at 3.5 +/- 0.2 mL/min (inflow pressure 94 +/- 2 mmHg; 1 mmHg = 133.3 Pa) with Krebs containing 100 microM phenylephrine, 6% dextran, and 15 units/mL superoxide dismutase. Perfusate from all segments dripped onto endothelium-denuded dog femoral artery rings. The addition of 10 microM acetylcholine to the perfusate to test the functional integrity of endothelium-intact donor segments did not alter resistance in vessel segments or change force in rings. The addition of 100 microM adenosine to the extravascular bath decreased resistance 1.5 +/- 0.4 mmHg.mL-1.min-1 in vessel segments but was without effect on downstream rings. When acetylcholine was retested in the presence of extravascular adenosine, a relaxation (16 +/- 6%) occurred in rings receiving perfusate from endothelium-intact segments but not endothelium-denuded or tubing segments. This relaxation was eliminated by N omega-nitro-L-arginine (10 microM), a nitric oxide synthase inhibitor, and was attenuated to 4 +/- 1% by 8-phenyltheophylline (10 microM), an adenosine receptor antagonist. Thus adenosine, in conjunction with acetylcholine, acting through a receptor-mediated event, resulted in the release of nitric oxide from the endothelium of perfused intramuscular arteries, indicating the potential for extravascular conditions to influence the release of endothelium-derived products.     

Regulation of the immune response--lessons from transgenic models

Volatile anaesthetics induce hypotension by both indirect and direct effects; they have been reported to inhibit vasoconstriction produced by a variety of agonists. These studies were performed to see if halothane, enflurane and isoflurane attenuate endothelin-1-evoked contraction and if they interact with endothelium-dependent or -independent vasoactive substances. Rat aortic rings were suspended in aerated Krebs' solution (37 degrees C) and contracted by incremental doses of endothelin-1 5 x 10(-10) to 5 x 10(-8) mol litre-1. Volatile anaesthetics at 1 and 2 MAC were tested on endothelium intact and denuded rings. They were tested also on L-NAME incubated endothelium intact and indomethacin-incubated endothelium intact and denuded rings. Responses to endothelin-1 were compared in the presence and absence of volatile anaesthetics. Isoflurane at 1 and 2 MAC concentration, and enflurane at 2 MAC, induced a rightward shift of the dose-response curve obtained with endothelin-1 in both endothelium denuded and intact rings, associated with a decrease in maximal tension generated in the latter rings. In L-NAME-incubated endothelium intact rings and in indomethacin endothelium denuded rings, the anaesthetics induced a rightward shift of the dose-response curve without modification of maximal tension. In indomethacin-incubated endothelium intact rings there was significant attenuation of endothelin-1 contraction in control rings which was not enhanced by volatile anaesthetics in treated rings. The present study indicates that isoflurane at 1 and 2 MAC, and enflurane at 2 MAC, significantly decreased endothelin-1-induced contraction of isolated rat aorta. This inhibition was observed in both intact and denuded rings and probably involves mechanisms within the smooth muscle. Nevertheless, our results suggest that part of the anaesthetic-induced inhibition of endothelin-1-evoked vasocontraction involves an "indomethacin-like" effect on an endothelial-derived vasoconstricting cyclo-oxygenase product.     

Effects of adrenomedullin and calcitonin gene-related peptide on contractions of the rat aorta and porcine coronary artery

1. Effects of adrenomedullin and alpha-calcitonin gene-related peptide (CGRP) on the contractions and cytosolic Ca2+ concentrations ([Ca2+]i) of the rat aorta and porcine coronary artery were investigated. Characteristics of the receptors mediating the effects of adrenomedullin and alpha-CGRP were also investigated. 2. Adrenomedullin and alpha-CGRP caused a concentration-dependent relaxation in the rat aorta contracted with noradrenaline. The IC50 values for adrenomedullin and alpha-CGRP were 2.4 nM and 4.0 nM, respectively. The relaxant effects of these peptides were abolished by removal of the endothelium and significantly attenuated by an inhibitor of nitric oxide synthase, NG-monomethyl-L-arginine (L-NMMA, 100 microM), but not by a cyclo-oxygenase inhibitor, indomethacin (10 microM). 3. Adrenomedullin and alpha-CGRP increased the endothelial [Ca2+]i in the rat aorta with endothelium, whereas they did not change [Ca2+]i in the smooth muscle. 4. An antagonist of the CGRP1 receptor, CGRP (8-37), antagonized the relaxant effects of alpha-CGRP and the beta-isoform of CGRP (beta-CGRP) but not those of adrenomedullin in the rat aorta. 5. In the porcine coronary artery contracted with U46619, adrenomedullin and alpha-CGRP caused a concentration-dependent relaxation with an IC50 of 27.6 and 4.1 nM, respectively. Removal of the endothelium altered neither the IC50 values nor the maximal relaxations induced by adrenomedullin or alpha-CGRP. When the artery was contracted with high K+ solution (72.7 mM), these peptides caused a small relaxation. 6. Adrenomedullin and alpha-CGRP increased cyclic AMP content and decreased the smooth muscle [Ca2+]i in the porcine coronary artery. 7. CGRP (8-37) significantly antagonized the relaxant effects of adrenomedullin and alpha-CGRP in the porcine coronary artery. However, it had little effect on the relaxations induced by the beta-isoform of CGRP (beta-CGRP). 8. These results suggest that in the rat aorta, adrenomedullin and alpha-CGRP increase the endothelial [Ca2+]i, activate nitric oxide synthase and release nitric oxide, without a direct inhibitory action on smooth muscle. In the porcine coronary artery, in contrast, adrenomedullin and alpha-CGRP directly act on smooth muscle, increase cyclic AMP content, decrease the smooth muscle [Ca2+]i and inhibit contraction. The rat aortic endothelium seems to express the CGRP receptor which is sensitive to alpha-CGRP, beta-CGRP and CGRP (8-37) and the adrenomedullin specific receptor. The porcine coronary smooth muscle, in contrast, seems to express two types of CGRP receptor; one of which is sensitive to alpha-CGRP, CGRP (8-37) and adrenomedullin and the other is sensitive only to beta-CGRP.     

Two mechanisms for platelet-mediated killing of tumour cells: one cyclo-oxygenase dependent and the other nitric oxide dependent

We have tried to identify the cytotoxic effectors in platelet-mediated tumour cell killing, using two tumour cell lines K562 (a chronic myelogenic leukaemic cell line) and LU99A (a lung cancer cell line), which are both sensitive to platelet cytotoxicity. Cyclo-oxygenase inhibitors, acetylsalicylic acid (ASA) and indomethacin, effectively inhibited the platelet-mediated killing of K562 cells, but not that of LU99A cells. In contrast, inhibitors of the nitric oxide (NO) pathway. NG-nitro-1-arginine (L-NA), haemoglobin and methylene blue, reduced the cytotoxic activity of platelets against LU99A, but not against K562. Synthetic analogues of platelet cyclo-oxygenase products thromboxane A2/ prostaglandin H2(TXA2/PGH2) exerted cytotoxicity against K562 cells but not against LU99A cells. Electron microscopic study showed that TXA2/PGH2 analogues induced bleb formation and disruption of the plasma membrane of K562 cells. K562 cells enhanced the production of TXA2 by platelets, as inferred from the accumulation of thromboxane B2 (TXB2), a spontaneous hydrolysis product of TXA2. LU99A cells had no such effects. These results indicate that platelets kill these two tumour cell lines through different mechanisms. In K562, the cyclooxygenase products TXA2/PGH2 possibly play a significant role but in LU99A the NO pathway seems to be involved.     

Characterization of signal transduction events stimulated by 8-epi-prostaglandin(PG)F2 alpha in rat aortic rings

One of the most abundant F2 isoprostanes formed under pathological conditions is 8-epi-prostaglandin F2 alpha (8-epi-PGF2 alpha), a potent vasoconstrictor. The purpose of this study was to determine the signal transduction events initiated by 8-epi-PGF2 alpha-induced vasoconstriction. Isolated arterial rings from male Sprague-Dawley rats were suspended in tissue baths containing Krebs-Henseleit salt solution, stretched to optimal resting tension and stimulated. 8-epi-PGF2 alpha induced concentration-dependent contractions in pulmonary arteries (EC50: 7.7 +/- 2.1 microM; n = 3) and aortas (EC50: 0.9 +/- 0.1 microM; n = 4) which were blocked by the TXA2 receptor antagonists SQ29548, L657925 and L657926. The contractile response to 8-epi-PGF2 alpha was significantly (*p < 0.05; n = 4) diminished by: 1) indomethacin and ibuprofen; 2) Ca++ free media; 3) verapamil, a voltage gated Ca++ channel blocker; 4) flunarizine, a T-type Ca++ channel blocker; and 5) calphostin C, a protein kinase C inhibitor. These data suggest that the contractile response to 8-epi-PGF2 alpha is: 1) mediated via activation of TXA2 receptors; 2) partially dependent on the synthesis and release of other cyclooxygenase derived products; 3) dependent on an influx of extracellular Ca++ possibly via Ca++ channels; and 4) may be PKC dependent.     

Somatostatin-induced contraction mediated by endothelial TXA2 production in canine cerebral arteries

Whether somatostatin causes endothelium-dependent contraction (EDC) in isolated canine basilar arteries was examined. Somatostatin (10(-8)-10(-6) M) caused transient contractions in a dose-dependent manner. These contractions were abolished by removal of the endothelium, while the contractile response to neuropeptide Y occurred even after removal of the endothelium. The EDC induced by somatostatin (10(-7) M) was affected by neither atropine (10(-6) M) nor cyclo-somatostatin (10(-5) M), which suggests that the EDC is not due to release of endogenous acetylcholine and that the endothelial somatostatin receptor is different from hormonal somatostatin receptors. The somatostatin-induced EDC was attenuated by cyclooxygenase inhibitors (aspirin and indomethacin), thromboxane A2 (TXA2) synthetase inhibitors (OKY-064 and RS-5186), and TXA2 antagonists (ONO-3708 and S-145), which suggests that the endothelium-derived contracting factor is TXA2. These findings demonstrate that somatostatin causes EDC via activation of TXA2 synthesis in canine cerebral arteries.     

Tissue response to covered Wallstents

8-epi prostaglandin F2alpha(8-epi PGF2alpha) contracted rat thoracic aorta rings in a concentration-dependent manner in the presence or absence of functional endothelium [median effective concentration (EC50) values, 455+/-52 and 268+/-34 nM, respectively; Student's t test; p=0.006]. U46619 was a more potent agonist with or without functional endothelium (EC50 values, 6.8+/-1.6 and 4.5+/-1.0 nM, respectively). SQ29548 [a thromboxane (TP)-receptor antagonist] inhibited contractions to both 8-epi PGF2alpha and U46619 in a competitive manner, with mean pA2 values of 8.3 and 7.9, respectively. 8-Epi PGF2alpha had a further contractile effect in vessels that had been contracted with noradrenaline and had been shown to possess a functional endothelium. Inhibition of thromboxane synthesis with OKY-046 or blockade of endothelin receptors with bosentan had no effect on responses to 8-epi PGF2alpha or U46619. Preincubation with 8-epi PGF2alpha or noradrenaline shifted the concentration-response curves to U46619 upward at low concentrations of U46619 with no significant change in EC50 values or maximal responses. Reduction of TP-receptor number in rat aorta with dithiothreitol caused a concentration-dependent inhibition of responses to both U46619 and 8-epi PGF2alpha, with no effect on maximal responses and or on the responses to U46619 after the preincubation with 8-epi PGF2alpha. These results indicate that 8-epi PGF2alpha is a potent vasoconstrictor in the rat aorta and are suggestive of an action of 8-epi PGF2alpha at the TP receptor.     

Thromboxane A2 stimulated signal transduction in vascular smooth muscle

Thromboxane A2 (TXA2) is a potent, labile vasoconstrictor which stimulates vessel contraction through vascular smooth muscle TXA2 receptors differing from those in platelets. We studied TXA2-stimulated events in cultured adult rat aortic smooth muscle cells. The stable TXA2 mimetic (15S)-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5Z, 13E-dienoic acid (U46619) competed for TXA2 agonist binding to vascular smooth muscle cells with an IC50 of 10 +/- 1 nM. In fura-2-loaded cells, U46619 increased free cytosolic Ca++ concentration with an EC50 of 49 +/- 14 nM. The increase in free cytosolic Ca++ was rapid, transient and independent of extracellular Ca++ or Ca++ antagonists and thus was due to release from intracellular stores. U46619-mediated Ca++ release was temporally associated with phosphorylation of myosin light chains, increased accumulation of 1,4,5-inositol trisphosphate (EC50 = 32 +/- 4 nM) and cytoplasmic acidification from pH 7.06 +/- 0.01 to 7.00 +/- 0.02 (P = .02). Ca++ release was 53% attenuated by the phospholipase C inhibitor, 1-[6-[[17 beta-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H- pyrrole-2,5-dione. In rat aortic rings U46619 caused TXA2 receptor-mediated contractions (EC50 of 28 +/- 2 nM) which were not attenuated by removal of extracellular Ca++ from the superfusion buffer. Together, these results suggest that agonist occupation of TXA2 receptors produces vascular smooth muscle contraction through initial activation of phospholipase C with production of 1,4,5-inositol phosphate, release of intracellular calcium stores and phosphorylation of myosin light chains associated with cellular acidification, presumably via activation of Ca++ ATPase.