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Biomedical subjects

A M Lefer

Publications and source records attributed to A M Lefer.

At least 163 records · Page 9Linked to original sources
PubMed1990

Direct positive inotropic and vasoconstrictor effects of endothelin.

Endothelin, a newly discovered vasoconstrictor peptide, when added to isolated cat papillary muscles, induced a direct positive inotropic effect that was slow in onset but of long duration. The magnitude of the developed force was concentration dependent. Endothelin exerted a marked concentration-dependent vasoconstriction in isolated cat carotid arteries and rabbit aortic rings. In both the carotid arteries and the aortic rings, endothelin induced a similar vasoconstrictor effect in the presence or absence of an intact endothelium. Addition of propyl gallate, a 5-lipoxygenase inhibitor, ibuprofen, a cyclooxygenase inhibitor, or SKF-525A, a cytochrome P450 inhibitor, at 2 microM did not significantly attenuate the ability of endothelin to vasoconstrict aortic rings in the presence or absence of an intact endothelium. These results demonstrate that the vasoconstrictor activity of endothelin operates independently of all three pathways of arachidonic acid metabolism (i.e., lipoxygenase, cyclooxygenase, or cytochrome P450 pathways) and is not dependent upon other endothelium-derived mediators (e.g., endothelium-derived relaxing factor, or eicosanoids) in these preparations. Moreover, endothelin exerts a direct positive inotropic effect in isolated cat ventricular myocardial tissue.

Animals↗
PubMed1990

Direct cardiovascular actions of two metabolites of linoleic acid.

Two newly discovered oxidation products of linoleic acid (i.e., 9,10-epoxy-12-octadecenoate termed Leukotoxin A, and 12,13-epoxy-9-octadecenoate termed Leukotoxin B) are produced by neutrophils in a variety of species. These substances appear to combat bacterial infection although they also have detrimental effects on normal organ function. Administration of Leukotoxin A or B to isolated cat papillary muscles decreased developed force, an index of myocardial contractility, in a concentration-dependent manner. Leukotoxin B was more active in decreasing the developed force than Leukotoxin A at high concentrations. Leukotoxin A or B, when added to isolated perfused cat carotid arteries, produced a significant vasoconstriction which in vivo would result in an increased vascular resistance. Thus, leukotoxins exert significant direct effects on the cardiovascular system in cats. Leukotoxins A and B are both cardiodepressant and vasoactive independent of release of other blood borne mediators.

Animals↗
PubMed1990

Synergism between superoxide dismutase and sodium nitrite in cardioprotection following ischemia and reperfusion.

The effects of acidified sodium nitrite (NaNO2), a releaser of nitric oxide (NO), combined with human superoxide dismutase (hSOD), were investigated in a 6-hour model of myocardial ischemia (MI) with reperfusion in open-chest, anesthetized cats. Acidified NaNO2 (12.5 mmol/kg/hr) was infused intravenously in cats starting 0.5 hour after occlusion of the left anterior descending (LAD) coronary artery, which was reperfused 1.5 hour following occlusion. Significantly lower plasma creatine phosphokinase activities were observed at all times beyond 3 hours for MI cats given NaNO2 + hSOD when compared with the other MI groups. The areas-at-risk expressed as percentages of the total left ventricular weights were not significantly different among any of the MI groups. However, the necrotic area expressed as a percentage of the myocardial area-at-risk was significantly lower in the MI + NaNO2 + hSOD-treated cats compared with all other MI groups. The NaNO2-treated group also produced a significant decrease in the necrotic area relative to the area-at-risk. Cardiac myeloperoxidase (MPO) activities indicated no significant difference in number of neutrophils attracted to the ischemic zone in the NaNO2 + hSOD-treated MI cats when compared with the other MI groups. Acidified NaNO2 + hSOD together exert significant protection on the myocardium subjected to ischemia and reperfusion injury. NaNO2 may act synergistically with hSOD to prolong the action of NO by scavenging free radicals that inactivate NO.

Animals↗
PubMed1990

Protective effects of a novel nonglucocorticoid 21-aminosteroid (U74006F) during traumatic shock in rats.

The purpose of this study was to investigate the effect of the nonglucocorticoid steroid U74006F in the pathogenesis of a murine traumatic shock model. Pentobarbital-anesthetized (40 mg/kg) rats were subjected to Noble-Collip drum trauma and developed a lethal shock state characterized by a decreased mean arterial blood pressure (MABP) to 67 +/- 2 mm Hg and survival time (1.5 +/- 0.2 h). In contrast, sham trauma rats exhibited a MABP of 122 +/- 4 mm Hg at 5 h postanesthesia. Administration of U74006F at doses of 22.5 mg/kg at 15 to 20 min following trauma significantly maintained a higher MABP and prolonged survival compared to those trauma rats receiving only the vehicle for U74006F (0.002 N HCl). U74006F at 15 and 22.5 mg/kg prolonged survival time to 2.6 +/- 0.3 (p less than 0.05) and 3.1 +/- 0.6 h (p less than 0.02), respectively. U74006F also significantly attenuated the plasma accumulation of cathepsin D (p less than 0.02 to p less than 0.01) and free amino-nitrogen compounds (p less than 0.01) compared to the rats receiving only vehicle. Additionally, U74006F at 15 and 22.5 mg/kg blunted the production of the cardiotoxic peptide, myocardial depressant factor (MDF) (p less than 0.01 to p less than 0.001). Moreover, U74006F is a steroid without significant glucocorticoid or mineralocorticoid activity. These results suggest that U74006F may be useful as a therapeutic agent in traumatic shock.

Animals↗
PubMed1990

Beneficial effects of two forms of NO administration in feline splanchnic artery occlusion shock.

We studied the effects of nitric oxide (NO) solution and acidified sodium nitrite (NaNO2), which produces NO, in splanchnic artery occlusion (SAO) shock in cats. NO is thought to be endothelium-derived relaxing factor (EDRF), a labile substance having several potentially valuable biological effects. Anesthetized cats subjected to total occlusion of the celiac, superior mesenteric, and inferior mesenteric arteries for 120 min, followed by reperfusion, usually died approximately 60 min after reperfusion. NO infusion significantly improved survival time in SAO-shock cats compared with those receiving vehicle (P less than 0.005). Administration of NO also attenuated the increase in plasma activities of the lysosomal hydrolase cathepsin D (P less than 0.05), total amino-nitrogen (P less than 0.001), and of the cardiotoxic peptide, myocardial depressant factor (MDF) (P less than 0.001). SAO-shock cats treated with NaNO2 at pH 2.0 also exhibited lower plasma cathepsin D (P less than 0.001), amino-nitrogen (P less than 0.05), and MDF activities (P less than 0.01), and survival time was also significantly improved (P less than 0.02). The same dose of NaNO2 infused at pH 7.4 failed to exert any significant protective effect. These results indicate that NO exerts beneficial effects in SAO shock in cats and suggest that exogenously administered NO may be a potentially useful therapeutic agent in splanchnic ischemic shock, probably via a cytoprotective rather than a vasodilator effect.

Amines↗
PubMed1990

Time course and mechanism of endothelial dysfunction in isolated ischemic- and hypoxic-perfused rat hearts.

Isolated perfused rat hearts were subjected to global ischemia for 30 min followed by reperfusion for 2.5, 5, 10, or 20 min and then were tested for responsiveness to the endothelium-dependent vasodilator acetylcholine (ACh) and the endothelium-independent vasodilator nitroglycerin (NTG). ACh relaxation was impaired 2.5 min after reperfusion (32 +/- 3% of initial control, P less than 0.01) and remained comparably depressed at every time thereafter. No significant decrease in vasodilator response to NTG occurred at any time. Endothelial dysfunction was prevented by recombinant human superoxide dismutase (hSOD, 5 mg/heart) but not by the hydroxyl radical scavenger N-(2-mercaptopropionyl)-glycine (8 mg/heart). Comparable effects and a similar time course were observed in hypoxic hearts reoxygenated for periods up to 20 min. Chemiluminescence of perfusion effluent employed as an index of free radical production was measured at all postreperfusion times in ischemic hearts. Ischemia alone produced small increases in chemiluminescence. Reperfusion, however, produced significantly higher increases in chemiluminescence, with a large burst of activity at 0.25 min, which was blocked by hSOD. These findings suggest that endothelial dysfunction resulting in decreased release of endothelium-derived relaxing factor occurs very early after reperfusion or reoxygenation and may be due to the action of superoxide free radicals.

Animals↗
PubMed1990

Leukocyte-dependent and leukocyte-independent mechanisms of impairment of endothelium-mediated vasodilation.

Leukocytes release cytokines and oxygen derived free radicals upon activation. Both superoxide (O2) and tumor necrosis factor (TNF) inhibit endothelium-dependent vasodilation in the intact circulation as well as in isolated blood vessels. Superoxide inactivates endothelium-derived relaxing factor (EDRF) rapidly, whereas TNF required 2 h to block EDRF release due to synthesis of adhesive proteins on the surface of neutrophils and/or the expression of their ligands on endothelial cells. Thus, vasodilation to acetylcholine is markedly attenuated by either O2 or TNF, whereas the vasodilation to NaNO2 at pH 2.0 or to nitroglycerin is not affected. Superoxide dismutase restores acetylcholine responses to myocardial ischemia followed by reperfusion, whereas cycloheximide restores acetylcholine responses to TNF. This occurs both in the isolated perfused rat heart (perfused without plasma or blood cells) and in isolated perfused cat carotid arteries. EDRF may be important in preserving integrity of vital tissues during ischemic states.

Acetylcholine↗
PubMed1990

Time course of endothelial dysfunction and myocardial injury during myocardial ischemia and reperfusion in the cat.

Myocardial ischemia and reperfusion have been shown to impair coronary vasorelaxation to endothelium-dependent vasodilators. To examine the time course of this dysfunction, occlusion of the left anterior descending (LAD) coronary artery (90 minutes) was followed by reperfusion for 0, 2.5, 5, 20, 180, or 270 minutes. Coronary arterial rings from the ischemic LAD and control left circumflex (LCx) arteries were tested for responsiveness to the endothelium-dependent receptor-mediated vasodilator, acetylcholine (ACh), and the endothelium-dependent nonreceptor-mediated vasodilator, A23187, as well as the endothelium-independent vasodilator, NaNO2. ACh relaxation was not impaired after 90 minutes of ischemia without reperfusion. However, 2.5 minutes of reperfusion resulted in depressed ACh responses (36 +/- 10% of control) that was further reduced to 16 +/- 6% at 20 minutes, and remained comparably depressed at every time thereafter. A23187 vasodilator responses were also attenuated after reperfusion, although the reduced response occurred later (that is, at 20 minutes). There was no significant decrease in response to NaNO2 in the LAD at any time or to any vasodilator in LCx control rings. Treatment with recombinant human superoxide dismutase (hSOD, 5 mg/kg/hr, that is, 15,545 SOD units/kg/hr), starting 10 minutes before reperfusion, preserved the vasodilator response to ACh (82 +/- 6%) and A23187, but treatment with the hydroxyl ion scavenger N-(2-mercapto proprionyl)-glycine (MPG) (8 mg/kg/hr) only protected the A23187 response. No damage to the surface of the endothelium was observed by scanning electron microscopy at any time point. Myocardial cell damage increased with time of reperfusion as assessed by increasing plasma CK activities and amounts of necrotic tissue indexed to area at risk. Significant myocardial injury occurred at 3 hours after reperfusion. These findings suggest that endothelial dysfunction resulting in reduced endothelium-derived relaxing factor release occurs before the development of myocardial cell necrosis and may be due to oxygen-derived free radicals produced rapidly on reperfusion.

Animals↗
PubMed1990

Endothelium and myocardial protecting actions of taprostene, a stable prostacyclin analogue, after acute myocardial ischemia and reperfusion in cats.

The effects of taprostene, a synthetic prostacyclin analogue, were investigated in a 6-hour model of myocardial ischemia (MI) with reperfusion in anesthetized cats. Taprostene (100 ng/kg/min) was infused intravenously starting 30 minutes postocclusion of the left anterior descending coronary artery followed by reperfusion 1 hour later, and the cats were observed for an additional 4.5 hours. Taprostene infusion resulted in significantly lower plasma creatine phosphokinase activities at every time from 3 to 6 hours for the MI + taprostene group compared with the MI + vehicle group and were not significantly different when compared with sham MI controls. The areas at risk, expressed as a percentage of the total left ventricular weights, were not significantly different between the MI groups. However, the necrotic area expressed as a percentage of the myocardial area at risk was significantly lower in the taprostene-treated cats compared with the untreated MI group (p less than 0.01). Cardiac myeloperoxidase activities indicated that significantly fewer neutrophils were attracted to the area at risk and to the ischemic zone of the MI + taprostene cats when compared with the MI cats given only the vehicle. Data from isolated left anterior descending coronary artery ring preparations removed from hearts after 6 hours of ischemia indicated that the endothelium was damaged by ischemia-reperfusion injury in the untreated cats. However, endothelial dysfunction was not observed in circumflex coronary arteries of ischemic cats or in coronary rings isolated from MI + taprostene cats. Thus, taprostene exerted a significant cardioprotection in cats subjected to ischemia and reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1990

Daltroban, a thromboxane receptor antagonist, protects the myocardium against reperfusion injury following myocardial ischemia without protecting the coronary endothelium.

The effects of daltroban, a specific thromboxane receptor antagonist, were investigated in a model of myocardial ischemia consisting of 1.5 h of coronary artery occlusion followed by reperfusion for 4.5 h in anesthetized cats. Daltroban (1 mg/kg) was infused as a bolus 10 min prior to reperfusion of the left anterior descending (LAD) coronary artery. Daltroban infusion resulted in a significantly lower necrotic area expressed as a percentage of the myocardial area-at-risk compared to the MI + vehicle group. However, daltroban failed to retard increases in myeloperoxidase activity in the ischemic myocardium, indicating no reduction in neutrophil accumulation. Moreover, left anterior descending coronary artery ring preparations isolated from daltroban treated MI cats exhibited endothelial dysfunction following ischemia reperfusion. Thus, daltroban significantly protected the myocardium from reperfusion injury without protecting the coronary endothelium or retarding neutrophil accumulation.

Animals↗
PubMed1990

Protective effects of the specific thromboxane receptor antagonist (+)-S145Na in splanchnic artery occlusion shock in rats.

We studied the effects of a new potent thromboxane A2 receptor antagonist as a protective measure in circulatory shock induced by splanchnic artery occlusion and reperfusion. The celiac and superior mesenteric arteries of anesthetized rats were occluded for 40 min followed by reperfusion, resulting in a large decrease in mean arterial blood pressure usually leading to a fatal outcome within 60 to 90 min. Rats were treated with the specific thromboxane A2 receptor antagonist, (+)-S145Na, at one of three doses (50, 200 or 500 micrograms/kg) or with its vehicle (0.9% NaCl). In isolated rat aortic rings, (+)-S145Na was found to be a highly specific and potent thromboxane receptor antagonist having an IC50 of 1 ng/ml. The highest dose of the drug exhibited protection characterized by an attenuation in the increases in hematocrit (P less than .05), plasma cathepsin D activity (P less than .05), plasma aminonitrogen concentration (P less than .05), and plasma myocardial depressant factor activity (P less than .01) as well as increased survival rate and time (P less than .01), compared to the splanchnic artery occlusion shock group given the vehicle. The lowest dose of (+)-S145Na failed to provide protection, whereas the intermediate dose (i.e., 200 micrograms/kg) exerted less dramatic protective effects than the 500 micrograms/kg dose. These findings suggest an important role of thromboxane A2 in the pathogenesis of splanchnic artery occlusion shock, and that (+)-S145Na may be a useful agent in the treatment of bowel ischemia and its complications.

Animals↗
PubMed1990

Cardioprotective actions of the specific thromboxane receptor antagonist (+)-S145Na following coronary occlusion and reperfusion in the rat.

We studied the effects of a novel thromboxane receptor antagonist (+)-S145Na, on the loss of myocardial creatine kinase activity in the rat myocardium after 10 minutes of coronary artery ligation, followed by 24 hours of reperfusion. (+)-S145Na (500 micrograms/kg), or its vehicle, was administered 10 minutes after occlusion (just prior to reperfusion) intravenously. Myocardial creatine kinase activity was significantly reduced in the ischemic areas of hearts obtained from rats receiving vehicle when compared to sham operated control rats. This loss in creatine kinase activity was significantly attenuated in hearts obtained from rats receiving (+)-S145Na. These findings further support the important role of thromboxane A2 in the pathogenesis of reperfusion injury following myocardial ischemia, and that (+)-S145Na may be a useful agent in the treatment of myocardial reperfusion injury.

Animals↗
PubMed1990

Cardioprotective effects of acidified sodium nitrite in myocardial ischemia with reperfusion.

The effects of acidified sodium nitrite (NaNO2) which releases nitric oxide, a substance which is thought to be indistinguishable from endothelium-derived relaxing factor, were investigated in a 6-h model of myocardial ischemia (MI) with reperfusion in open-chest, anesthetized cats. Acidified NaNO2 (12.5-50 mmol/kg/hr) was infused i.v., starting 30 min postocclusion followed by reperfusion 1 hr later, in cats subjected to MI by occlusion of the left anterior descending coronary artery. Acidified NaNO2 infusion (25 and 50 mmol/kg/hr) resulted in significantly lower plasma creatine kinase activities at every time beyond 1 hr for the MI + vehicle group, and was not significantly different when compared to sham MI + NaNO2 controls. The areas at risk expressed as percentage of the total left ventricular weights were not significantly different between the MI + vehicle and MI + acidified NaNO2 groups. However, the necrotic area expressed as a percentage of the myocardial area at risk was significantly lower in the 25 and 50 mmol/kg/hr NaNO2-treated cats. Cardiac myeloperoxidase activities indicated that significantly fewer neutrophils were attracted to the ischemic zone of the NaNO2-treated MI cats when compared to the vehicle-infused MI cats. Acidified NaNO2 significantly inhibited platelet aggregation in a dose-dependent manner in cat platelet-rich plasma. Thus, acidified NaNO2 exerts a significant protective action during ischemia and reperfusion injury, which suggests that endothelium-derived relaxing factor has a cardioprotective effect in MI.

Animals↗
PubMed1990

Beneficial actions of BN 50739, a new PAF receptor antagonist, in murine traumatic shock.

We studied the effects of BN 50739, a novel PAF antagonist, in a rat model of traumatic shock. Pentobarbital anesthetized rats subjected to Noble-Collip drum trauma developed a shock state characterized by marked hypotension, significant increases in plasma cathepsin D (4.2-fold), free amino-nitrogen (2.8-fold) and myocardial depressant factor (4.7-fold) activities and a survival time of 1.62 +/- 0.16 h. Treatment with BN 50739 (10 mg/kg, i.v.) 10 min post-trauma prolonged survival time to 3.14 +/- 0.44 h (p less than 0.01) and attenuated the accumulations of cathepsin D (5.8 vs. 12.5 U/ml, p less than 0.01), free amino-nitrogen (4.6 vs. 12.5 U/ml, p less than 0.001) and myocardial depressant factor (19.4 vs. 65.1 U/ml, p less than 0.001). Moreover, in washed rabbit platelets, BN 50739 inhibited PAF (1.85 nM)-induced aggregation (IC50: 50 nM) without affecting ADP (5 microM)-induced aggregation. In anesthetized rats, BN 50739 (10 mg/kg, i.v.) attenuated PAF (10-30 ng/kg, i.v.)-induced hypotension for longer than 5 h, without influencing acetylcholine (10 micrograms/kg, i.v.)-induced hypotension. These findings indicate that BN 50739 is a specific PAF receptor antagonist with a long duration of action in vivo. The beneficial effects of PAF antagonism on traumatic shock are significant in the present study, and are consistent with the concept that PAF is involved in the pathogenesis of traumatic shock.

Animals↗
PubMed1990

Protective effects of a novel 21-aminosteroid during splanchnic artery occlusion shock.

We investigated the effects of a novel, non-glucocorticoid 21-aminosteroid, U74006F, in the pathogenesis of splanchnic artery occlusion (SAO) shock in rats. Pentobarbital-anesthetized (40 mg/kg) rats were subjected to 40 min of occlusion of both the celiac and superior mesenteric arteries followed by reperfusion, which resulted in a severe shock state characterized by a markedly lower mean arterial blood pressure (MABP) and a survival time of 40-80 min post-reperfusion. In contrast, infusion of U74006F (22.5 mg/kg) during the occlusion period resulted in a significantly higher MABP following reperfusion which prolonged survival (117 +/- 3 min vs. 66 +/- 10, P less than .01) compared to those rats receiving only the vehicle for U74006F (0.002 N HCl). Hematocrits measured at the end of each experiment were significantly lower in the treated shock rats compared to the untreated group (55.7 +/- 1.8 vs. 63.0 +/- 1.7, P less than .01). SAO shock rats treated with U74006F also exhibited significantly attenuated plasma accumulation of cathepsin D (P less than .05) and myocardial depressant factor (MDF) (P less than .01). Six of 7 SAO shock rats treated with U74006F survived for 120 min following reperfusion, while none of 7 SAO shock rats given the vehicle survived for 120 min (P less than .01). These results suggest that U74006F has therapeutic utility in SAO shock.

Animals↗
PubMed1989

Beneficial effects of a specific leukotriene receptor antagonist in splanchnic artery occlusion shock.

The purpose of this study was to examine the effects of a new potent peptidoleukotriene receptor antagonist, SK&F 104353, in splanchnic artery occlusion shock. SK&F 104353 was administered as a 1 mg/kg initial bolus followed by an infusion of 3 mg/kg per h for the entire 2 h post-reperfusion observation period. In a group of conscious rats, this dose of SK&F 104353 shifted the LTD4 dose response curve rightward 10-fold, indicating effective antagonism of peptidoleukotriene responses in the rat. Anesthetized rats subjected to splanchnic artery occlusion shock survived an average of only 98 +/- 8 min whereas all animals receiving SK&F 104353 survived the 2 h reperfusion period (P less than 0.02 from vehicle). Therefore, the survival rate of the splanchnic artery occlusion shock group of rats receiving SK&F 104353 was improved to 100% compared with 50% survival for the vehicle-treated splanchnic artery occlusion shock group (P less than 0.025). In the splanchnic artery occlusion shock + SK&F 104353 group the increase in the plasma activities of the lysosomal hydrolase, cathepsin D, and the cardiotoxic peptide, myocardial depressant factor, were significantly attenuated in comparison to the splanchnic artery occlusion shock + vehicle group (P less than 0.025). These data indicate that the peptidoleukotriene receptor antagonist, SK&F 104353 is beneficial in splanchnic artery occlusion shock, and furthermore suggests that it may be a therapeutically useful agent in bowel ischemic shock.

Animals↗
PubMed1989

Pharmacologic profile of lipoxins A5 and B5: new biologically active eicosanoids.

In this study, we have investigated the biological activities of LxA5 and LxB5 in isolated smooth muscle preparations of the guinea pig. LxA5 slowly contracted pulmonary parenchymal strips isolated from guinea pigs in a concentration-dependent manner over the range of 0.1-2.2 microM. This bronchoconstrictor effect was not associated with release of peptide leukotrienes (i.e. LTC4, LTD4 and LTE4) and only a slight increase in thromboxane B2. Furthermore, the bronchoconstrictor effect was not blocked by lipoxygenase inhibitors, suggesting the pulmonary effect is not mediated by lipoxygenase products. However, a peptide leukotriene receptor antagonist (e.g. SK&F-104353) inhibited or reversed the LxA5 response indicating that LxA5 and the peptide leukotrienes may share the same receptor. In contrast to LxA5, LxB5 displayed no significant bronchoconstrictor effect at concentrations up to 2.2 microM. Moreover, LxA5 and LxB5 did not exert a significant endothelium-dependent vasorelaxation in aortic vascular smooth muscle as do LxA4 and LxB4. Thus, LxA5 and LxB5 display a unique biological profile which differs from LxA4 and LxB4. LxA4 may be a mediator in circulatory disease states (e.g. myocardial ischemia, circulatory shock), but LxA5 and LxB5 are not as likely candidates as mediators of disease.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗