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Biomedical subjects

A L Loeb

Publications and source records attributed to A L Loeb.

At least 19 recordsLinked to original sources
PubMed2000

Cardiovascular responses to the isoprostanes iPF(2alpha)-III and iPE(2)-III are mediated via the thromboxane A(2) receptor in vivo.

BACKGROUND: Isoprostanes (iPs) are free radical-catalyzed products of arachidonic acid that reflect lipid peroxidation in vivo. Several iPs exert biological effects in vitro and may contribute to the functional consequences of oxidant stress. For example, iPF(2alpha)-III (8-iso PGF(2alpha)) and iPE(2)-III modulate platelet function and vascular tone. Although these effects are blocked by antagonists of the receptor (TP) for the cyclooxygenase product thromboxane A(2), it has been speculated that the iPs may activate a receptor related to, but distinct from, the TP. METHODS AND RESULTS: Transgenic mice (TPOEs) were generated in which the TP-beta isoform was under the control of the preproendothelin promoter. They overexpressed TP-beta in the vasculature but not in platelets and exhibited an exaggerated pressor response to infused iPF(2alpha)-III compared with wild-type mice. This was blocked by TP antagonism. The platelet response to the iP was unaltered in TPOEs compared with wild-type mice. By contrast, both the pressor response to iPF(2alpha)-III and its effects on platelet function were abolished in mice lacking the TP gene. This was also true of the effects of infused iPE(2)-III on mean arterial pressure and platelet aggregation. CONCLUSIONS: Both iPF(2alpha)-III and iPE(2)-III exert their effects on platelet function and vascular tone in vivo by acting as incidental ligands at membrane TPs rather than via a distinct iP receptor. Activation of TPs by iPs may be of importance in syndromes in which cyclooxygenase activation and oxidant stress coincide, such as in atherosclerosis and reperfusion after tissue ischemia.

Angiotensin II↗
PubMed2000

Functional evidence for inward-rectifier potassium channels in rat cremaster muscle arterioles.

Moderate increases in extracellular K(+) produce vasodilation in fourth order cremasteric arterioles in the anesthetized rat. We studied the contribution of different subtypes of K(+) channels to this response. Cremaster muscle arteriolar diameters were observed during superfusion with buffer containing 5-30 mM K(+) in the absence (control) and presence of barium (Ba(2+), 50 microM), glibenclamide (GLIB, 1 microM), or iberiotoxin (IBTX, 100 nM) to block inward-rectifier, ATP-sensitive, or Ca(2+)-activated K(+) channels, respectively. Under control conditions, vessels dilated in response to 10-25 mM K(+) and constricted at higher concentrations. At 5 mM K(+), vessel diameters were significantly decreased by GLIB and Ba(2+), but not IBTX, suggesting that basal diameter was regulated by inward-rectifier and ATP-sensitive K(+) channels. In contrast, Ba(2+), but not GLIB or IBTX, prevented K(+)-induced dilation. The data indicate that the inward-rectifier K(+) channel (blocked by low concentrations of Ba(2+), but not GLIB or IBTX) was most likely responsible for the K(+)-induced arteriolar dilation.

Adenosine↗
PubMed2000

Directed vascular expression of the thromboxane A2 receptor results in intrauterine growth retardation.

Thromboxane (Tx) A2 is a platelet agonist, smooth muscle cell constrictor, and mitogen. Urinary Tx metabolite (Tx-M) excretion is increased in syndromes of platelet activation and early in both normal pregnancies and in pregnancy-induced hypertension. A further increment occurs in patients presenting with severe preeclampsia, in whom Tx-M correlates with other indices of disease severity. TxA2 exerts its effects through a membrane receptor (TP), of which two isoforms (alpha and beta; refs. 5,6) have been cloned. Overexpression of TP in the vasculature under the control of the pre-proendothelin-1 promoter results in a murine model of intrauterine growth retardation (IUGR), which is rescued by timed suppression of Tx synthesis with indomethacin. IUGR is commonly associated with maternal diabetes or cigarette smoking, both conditions associated with increased TxA2 biosynthesis.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1998

Cerebellar nitric oxide is increased during isoflurane anesthesia compared to halothane anesthesia: a microdialysis study in rats.

BACKGROUND: This study examined the influences of isoflurane versus halothane anesthesia on basal and agonist-stimulated nitric oxide in the cerebellum of intact rats. Nitric oxide was measured using the hemoglobin-trapping method in an in vivo microdialysis technique. This method uses the stoichiometric reaction of nitric oxide with oxyhemoglobin to produce methemoglobin and nitrate; the change in methemoglobin concentration is measured spectrophotometrically to estimate nitric oxide concentration. METHODS: Male Wistar rats were anesthetized with isoflurane (1.4%) or halothane (1.2%), mechanically ventilated and paralyzed (intravenous pancuronium, 1 mg/kg). Microdialysis probes were implanted into the cerebellum. Bovine oxyhemoglobin dissolved in artificial cerebrospinal fluid was pumped through the probe (2 microl/min) and assayed at 15-min intervals. The glutamatergic agonist, kainic acid (KA, 5 mg/kg, intraarterially), was used to stimulate nitric oxide production. NG-nitro L-arginine methyl ester (L-NAME, 40 mg/kg, intravenously) was used to inhibit nitric oxide synthase. RESULTS: Unstimulated cerebellar nitric oxide concentrations were stable and greater during anesthesia with isoflurane (532+/-31 nM; mean +/- SEM) than with halothane (303+/-23 nM). L-NAME pretreatment reduced nitric oxide concentrations during isoflurane, but not halothane, anesthesia. Infusion of KA increased nitric oxide in both groups; however, the increase in nitric oxide was significantly greater during isoflurane anesthesia. Pretreatment with L-NAME inhibited the response to KA in both groups. CONCLUSIONS: Nitric oxide production in the cerebellum, monitored by microdialysis, was greater during isoflurane anesthesia than during halothane anesthesia. Increased nitric oxide production during isoflurane anesthesia would be expected to impact central neuronal function and cerebral blood flow and vascular resistance.

Anesthetics, Inhalation↗
PubMed1998

Resuscitation after hemorrhage using recombinant human hemoglobin (rHb1.1) in rats: effects on nitric oxide and prostanoid systems.

OBJECTIVES: Hemoglobin-based oxygen carriers are designed to replace blood volume and to increase oxygen delivery to tissues after blood loss. The goals of the present study were two-fold: a) to determine the systemic and regional vascular effects of resuscitation with recombinant human hemoglobin (rHb1.1) in rats during controlled hemorrhage; and b) to determine whether nitric oxide (NO) or prostaglandins were involved in the observed responses. DESIGN: Paralyzed, ventilated rats were hemorrhaged (18 mL blood/kg body weight) during halothane anesthesia and allowed to stabilize for 30 mins. Systemic and regional hemodynamics and oxygen delivery were monitored at three time points, using the radioactive microsphere method. Microspheres were first infused at the end of the hemorrhage stabilization period (t=0 min). rHb1.1 (1 g/kg body weight) or rHb1.1 diluent (phosphate buffered saline, 36 mL/kg body weight) were infused over 20 mins and microspheres were administered again, 30 mins later (t=50 mins). Saline (0.5 mL), indomethacin (5 mg/kg to inhibit cyclooxygenase), or NG-monomethyl-L-arginine (L-NMMA, 100 mg/kg, to inhibit NO synthase) were then infused in rHb1.1-treated rats and microspheres injected once more (t=80 mins). SETTING: Research laboratory. SUBJECTS: Male Wistar rats (n=37). INTERVENTIONS: Recombinant human hemoglobin (rHb1.1), rHb1.1 diluent (phosphate buffered saline) resuscitation of hemorrhaged rats. Saline, L-NMMA, or indomethacin treatment after resuscitation. MEASUREMENTS AND MAIN RESULTS: Resuscitation with rHb1.1 increased mean arterial pressure (MAP), cardiac output, and systemic oxygen delivery significantly when compared with diluent. After rHb1.1 resuscitation, regional blood flows were significantly increased in skin, kidney, spleen, and heart compared with diluent resuscitation. Compared with saline treatment after rHb1.1 resuscitation, L-NMMA increased MAP and regional resistances in virtually all tissues; indomethacin did not alter MAP, but increased resistance in the brain. CONCLUSIONS: These data indicate that rHb1.1 resuscitation was more effective than diluent in improving systemic and regional hemodynamics and oxygen delivery, suggesting that rHb1.1 may be of benefit in the treatment of acute blood loss. Increased resistance after L-NMMA in the presence of rHb1.1 indicated that rHb1.1 resuscitation did not eliminate NO dependent circulatory control. Increased resistance after indomethacin in brain indicated that vasodilator prostanoids were important in regulating vascular resistance in these tissues after rHb1.1 resuscitation.

Animals↗
PubMed1997

Anesthetics alter relative contributions of NO and EDHF in rat cremaster muscle microcirculation.

The contributions of the vasodilators nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) were investigated in the rat cremaster muscle microcirculation during halothane, isoflurane, or ketamine anesthesia. After inhibition of prostaglandin synthesis with indomethacin, changes in diameter of fourth-order arterioles to acetylcholine (ACh) or bradykinin (BK) were studied in the presence or absence of NG-monomethyl-L-arginine (L-NMMA), an inhibitor of NO synthase, and/or 20 mM K+, an inhibitor of EDHF action. L-NMMA inhibited ACh- and BK-induced vasodilation during isoflurane but not halothane or ketamine anesthesia. Superfusion of the muscle with buffer containing 20 mM K+ dilated arterioles. EDHF was responsible for most of the NO-independent response to ACh, because 20 mM K+ unmasked ACh-stimulated, NO-dependent relaxation during halothane or ketamine anesthesia. However, 20 mM K+ did not inhibit BK-induced vasodilation during halothane or ketamine anesthesia. Our data suggest that anesthetics can alter the balance between NO and EDHF vasodilation in the microcirculation and that NO-dependent mechanisms are enhanced and EDHF action inhibited during isoflurane anesthesia.

Abdominal Muscles↗
PubMed1996

Isoflurane enhances glutamatergic agonist-stimulated nitric oxide synthesis in cultured neurons.

The purpose of this study was to determine how halothane, isoflurane, and enflurane, three commonly used volatile anesthetic agents, affect glutamate receptor-modulated nitric oxide signaling in cultured cortical neurons. Primary cultures of cortical neurons were prepared from fetal Sprague-Dawley rats and experiments were performed after 11-13 days in culture. Cyclic GMP was measured as an indicator of nitric oxide production. Glutamate (100 microM), N-methyl-D-aspartate (100 microM), quisqualate (300 microM), or kainate (100 microM) increased cyclic GMP production. At clinically relevant concentrations, isoflurane enhanced responses to each of these agonists, while halothane or enflurane had no effect. Thus, isoflurane, but not halothane or enflurane, enhanced nitric oxide signaling stimulated by glutamatergic agonists.

Anesthetics, Inhalation↗
PubMed1996

Effect of chronic cocaine exposure on carotid artery reactivity in neonatal rabbits.

Chronic cocaine abuse by pregnant women results in chronic neonatal drug exposure. In adults, chronic cocaine use alters neurotransmitter concentrations and receptor dose-response relationships. Similar changes may also occur in the neonatal cerebrovasculature after in utero cocaine exposure. This study examined the effect of chronic cocaine exposure on internal carotid artery reactivity to norepinephrine, serotonin, acetylcholine, sodium nitroprusside, adenosine, and cocaine in neonatal rabbits. Internal carotid artery rings were isolated from 16 to 20 day old rabbits that had received cocaine (20 mg/kg IP BID, n = 8) or saline (n = 8) from 5 days of age and were studied in organ baths using standard in vitro techniques. Chronic treatment with cocaine decreased the half-maximal relaxant response (ED50) to adenosine (control 6.9 +/- 1.8 vs cocaine 3.5 +/- 0.99 microM, p = 0.05). The half-maximal contractile responses (EC50) to norepinephrine and serotonin and the half-maximal relaxant responses (ED50) to acetylcholine and sodium nitroprusside were similar between groups. The threshold concentration of cocaine that induced vessel contraction was altered by chronic cocaine exposure (control group 10(-6) M vs chronic cocaine group 10(-4) M). We conclude that chronic cocaine exposure sensitizes carotid arteries to the relaxant effects of adenosine. In addition, chronic cocaine exposure desensitizes carotid arteries to the contractile effects of acute cocaine. These vasoreactivity changes may underlie altered cerebrovascular responses to asphyxia and play a role in the pathogenesis of postnatally acquired brain injury in critically ill "crack" babies.

Acetylcholine↗
PubMed1995

Ketamine inhibits glutamate-, N-methyl-D-aspartate-, and quisqualate-stimulated cGMP production in cultured cerebral neurons.

BACKGROUND: Glutamatergic signaling has been linked to the recently discovered neurotransmitter/neuromodulator nitric oxide (NO), and several classes of anesthetics block some step in glutamatergic signaling. This study was designed to determine whether or not ketamine would prevent NO-dependent cGMP production stimulated by glutamate (GLU) and the GLU analogs NMDA, quisqualate (QUIS), and kainate (KAIN). METHODS: Primary cultures of cortical neurons and glia (prepared from 16-day gestational rat fetuses) were used after 12-16 days in culture. Reactions were carried out in magnesium-free buffer containing 100 microM 3-isobutyl-1-methylxanthine, and cGMP content of cultures was used as a bioassay of NO production. RESULTS: Cyclic GMP production stimulated by sodium nitroprusside (100 microM) occurred predominately in neurons and not in glia. Neurons were spontaneously active in these cultures; basal cGMP production was decreased by 50% in the presence of 1 microM tetrodotoxin (TTX). Glutamate (100 microM), NMDA (100 microM), QUIS (300 microM), and KAIN (100 microM) each increased cGMP content of neuronal cultures. L-NMMA (100 microM), a NO synthase inhibitor, prevented the stimulation of cGMP production by GLU or its analogs. Pretreatment with MK-801 (1 microM) or ketamine (10-100 microM) inhibited GLU-, NMDA-, and QUIS-stimulated cGMP production. Quisqualate-stimulated responses were the most sensitive to inhibition by ketamine and NMDA-stimulated responses were the least sensitive to inhibition. MK-801 and ketamine did not significantly inhibit KAIN-stimulated cGMP production. CNQX (10 microns) blocked KAIN-stimulated cGMP production only. CONCLUSIONS: The authors' data demonstrate that ketamine inhibited NO synthesis stimulated by NMDA- and non-NMDA-receptor specific analogs. Our findings indicate that blockade of QUIS- as well as NMDA-subtypes of GLU- receptor may be important in the development of ketamine-induced anesthesia.

Animals↗
PubMed1994

Halothane inhibits bradykinin-stimulated prostacyclin production in endothelial cells.

BACKGROUND: Halothane and isoflurane alter signal transduction and function in several cell types. Vascular responses to these anesthetics may be attributable to agent-specific effects on vasoactive mediator production. This study investigated the effects of halothane and isoflurane on basal and agonist-stimulated prostacyclin production by endothelial cells. METHODS: Prostacyclin production by cultured bovine aortic endothelial cells was monitored by radioimmunoassay of 6-keto-prostaglandin F1 alpha, the stable breakdown product of prostacyclin. RESULTS: Neither halothane nor isoflurane (0.3-1 mM), altered prostacyclin production. Bradykinin (1 microM), adenosine triphosphate (ATP) (10 microM), and melittin (1 microgram.ml-1) stimulated prostacyclin production. Isoflurane had no effect on responses to bradykinin, ATP, or melittin. Halothane inhibited the response to bradykinin but not the response to ATP or melittin. Pretreatment with pertussis toxin (100 ng.ml-1), to inhibit the function of the guanosine triphosphate-binding protein G alpha i, did not alter the response to bradykinin in the presence or absence of halothane. Pretreatment with phorbol 12-myristate 13-acetate (100 nM), to stimulate protein kinase C activity, did not alter bradykinin-stimulated prostacyclin production and prevented the inhibition of the response to bradykinin by halothane. CONCLUSIONS: Isoflurane had no effect on the increase in prostacyclin production stimulated by bradykinin. Halothane inhibited the bradykinin-stimulated prostacyclin production but not that stimulated by ATP or melittin. These results suggest that the halothane-mediated inhibition of bradykinin-stimulated prostacyclin production does not involve a pertussis toxin-sensitive G-protein and may result from an interaction of halothane at some other step in the signal transduction pathway, including the inhibition of protein kinase C.

Adenosine Triphosphate↗
PubMed1993

Alteration of calcium mobilization in endothelial cells by volatile anesthetics.

Halothane and isoflurane have different effects on the peripheral vasculature. Halothane decreases blood pressure primarily by decreasing cardiac contractility, whereas isoflurane acts primarily as a peripheral vasodilator. These peripheral vascular actions may result from different effects of the anesthetics on endothelial cell function and the release of endothelium-derived vasoactive mediators. The ability of these agents at clinically relevant concentrations to alter agonist-induced calcium mobilization in single cultured bovine aortic endothelial cells was tested using the fluorescent indicator fura-2. Neither halothane (0.3, 0.5, and 2 mM) or isoflurane (0.5 and 2 mM) altered basal calcium ([Ca]i = 49 +/- 5 nM); however, the calcium transient normally elicited by 10 nM bradykinin (peak [Ca]i = 307 +/- 22 nM) was inhibited significantly by halothane but not isoflurane. Neither anesthetic altered the calcium response to ATP (10 microM). These findings suggest that anesthetics may have specific effects on receptor-mediated endothelial cell functions that could influence hemodynamics.

Adenosine Triphosphate↗
PubMed1993

Marked regional heterogeneity in the magnitude of EDRF/NO-mediated vascular tone in awake rats.

The systemic and regional hemodynamic effects of inhibition of endothelium-derived relaxing factor/nitric oxide (EDRF/NO) were studied in awake, indomethacin-treated rats. The radiolabeled microsphere method was used to determine the cardiac output, systemic vascular resistance (SVR), and regional blood flows and regional vascular resistances in 12 tissues before and after infusion of the EDRF/NO synthesis inhibitor, NG-monomethyl-L-arginine (NMMA, 100 mg/kg), and after reversal of NMMA by infusion of L-arginine (300 mg/kg). NMMA infusion resulted in increases in the blood pressure and SVR. After NMMA, blood flows were decreased to the cerebrum, heart, kidney, spleen, gastrointestinal tract, skin, ear, and white fat, whereas flow in the hepatic artery was increased. Vascular resistances were increased in every tissue studied except the hepatic artery, in which the resistance decreased after NMMA. L-arginine restored the vascular resistance to control values in 8 of the 12 tissues. The magnitude of the increase in the regional resistance was not uniform among the organs studied, and ranged from a maximum of 253% in brown fat to 22% in heart. These results indicate that EDRF/NO is an important mediator of regional hemodynamic control in numerous tissues of the intact rat. The marked heterogeneity in the magnitude of basal EDRF/NO-dependent tone suggests that the mechanisms mediating this cardiovascular control system are regulated locally.

Animals↗
PubMed1992

Endothelium-dependent circulatory control--a mechanism for the differing peripheral vascular effects of isoflurane versus halothane.

Several studies have suggested that halothane and isoflurane modify responses to endothelium-dependent vasodilators, indicating that the differing circulatory effects of these anesthetics may be, in part, attributable to alterations in endothelial cell control of vascular tone. This study was designed to determine the contribution of endothelium-derived relaxing factor (EDRF/NO) to circulatory control in indomethacin-treated rats anesthetized with equipotent concentrations (1 MAC) of either isoflurane (n = 6) or halothane (n = 8). Using radiolabelled microspheres, systemic and regional hemodynamics were measured in cerebrum, cerebellum, heart, kidney, gastrointestinal tract, spleen, liver, skeletal muscle, skin, ear, and white and brown fat. Cardiac output, mean arterial pressure (MAP), systemic vascular resistance (SVR), regional blood flows, and regional vascular resistances were determined before (control) and after administration of NG-monomethyl-L-arginine (L-NMMA, 100 mg/kg) to inhibit EDRF/NO synthesis, and following L-arginine (300 mg/kg) to reverse the effects of L-NMMA. In both anesthetic groups, L-NMMA decreased cardiac output and increased MAP, SVR, and regional resistances in brain, heart, kidney, spleen, gastrointestinal tract, hepatic artery, skeletal muscle, skin, and white fat. L-arginine returned SVR and MAP to or below control values in both groups, although cardiac output remained decreased. During isoflurane as compared to halothane anesthesia, L-NMMA caused significantly greater increases in blood pressure (54 +/- 7% vs. 24 +/- 2%) and SVR (143 +/- 22% vs. 79 +/- 11%). In addition, rats anesthetized with isoflurane had significantly greater increases in vascular resistance in heart, kidney, gastrointestinal tract, hepatic artery, and skin after L-NMMA than did rats anesthetized with halothane.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, Inhalation↗
PubMed1992

Inhibition of endothelium-derived relaxing factor-dependent circulatory control in intact rats.

The effects of the endothelium-derived relaxing factor (EDRF) inhibitors NG-monomethyl-L-arginine (L-NMMA) and methylene blue (MB) on resting hemodynamics and responses to vasodilators were studied in the intact rat anesthetized with pentobarbital sodium. L-NMMA infusions (100 mg/kg) significantly increased mean blood pressure by 48%; this effect was rapidly reversed by L-arginine (300 mg/kg). MB (50 mg/kg) decreased mean blood pressure by 24%. Both MB and L-NMMA significantly attenuated the vasodepressor responses to acetylcholine, ATP, and adenosine. By use of radiolabeled microspheres, it was determined that the blood pressure increase after L-NMMA was due to a marked increase in systemic vascular resistance (SVR; from 1.3 +/- 0.1 to 3.1 +/- 0.3 mmHg.ml-1.min-1) and decreased cardiac output. L-NMMA increased vascular resistance in brain, cerebellum, skin, skeletal muscle, ear, white and brown fat, kidney, spleen, hepatic artery, and gastrointestinal tract. Flow decreased in the skin, kidneys, ear, white and brown fat, gastrointestinal tract, portal venous circulation, and liver in response to L-NMMA. In contrast, MB decreased heart rate, blood pressure, and SVR significantly. MB increased blood flow and decreased vascular resistance in several organs, including the brain, and skeletal muscle. These results indicate that both MB and L-NMMA can inhibit agonist-induced EDRF-mediated vasodepressor responses. However, inhibition of agonist-induced responses did not predict the general and regional hemodynamic responses to L-NMMA or MB infusion.

Animals↗
PubMed1990

Microcirculatory responses to exogenous endothelial cell-derived relaxing factor.

Endothelium-derived relaxing factor (EDRF) plays an important role in the vasodilatory responses of large blood vessels. However, such a role has yet to be conclusively shown for the microvasculature. In this study we tested the sensitivity of arterioles in the cheek pouch of pentobarbital-anesthetized hamsters to the EDRF-dependent agonists bradykinin and A23187, as well as to exogenous EDRF from cultured bovine aortic endothelial cells. The pouch superfusion fluid was arranged to first pass through a column containing endothelial cells and then on to the tissue. Bradykinin (10-30 nM) or A23187 (0.3 microM) was introduced either upstream or downstream to the endothelial cells, and the resultant responses were measured with video microscopy. Bradykinin and A23187 both caused a dose-dependent release of a microvessel dilator from cultured endothelial cells. We take this dilator to be EDRF based on the characteristics of the responses to the stimuli. Indomethacin (7.7 microM) was present in the superfusate to eliminate the production of cyclooxygenase products from the endothelial cells, and the magnitude of the response was diminished if the superfusate was first passed through a 3-min delay coil before arrival at the pouch. The arterioles dilated to the direct application of bradykinin in a dose-dependent fashion. They did not respond however to the direct application of A23187. These studies demonstrate that arteriolar smooth muscle is able to respond to exogenous EDRF and support the premise that EDRF may play an active role in the regulation of blood flow in the microcirculation.

Animals↗
PubMed1989

Endothelium-dependent potentiation of human platelet aggregation.

The endothelium produces many substances which have the potential to alter hemostasis. We examined the influence of a substance(s) released by cultured bovine aortic endothelial cells on very early events (less than 5 sec) in platelet function, using a new quenched-flow approach. Contributions of the endothelial cell surface to alterations in platelet function were avoided by separating the endothelium and platelets. Superfusates from endothelial cells were allowed to interact with platelets for several seconds, followed by challenge with ADP to induce aggregation. Single-particle counting provided a sensitive index of aggregation kinetics. In this system, unstimulated endothelial-cell superfusate had no effect on aggregation induced by ADP. Stimulation of the endothelial cells with bradykinin produced an unstable factor(s) that potentiated ADP-induced platelet aggregation, was not affected by hemoglobin or cyclooxygenase inhibitions, and had no platelet aggregatory activity on its own. Nitric oxide inhibited aggregation and its effect was blocked by hemoglobin. The identity of the potentiating factor is unknown, but it does not appear to be platelet activating factor, thrombin, ADP, thromboxane, nitric oxide, or endothelium-derived relaxing factor.

Adenosine Diphosphate↗
PubMed1988

Endothelium-derived relaxing factor release associated with increased endothelial cell inositol trisphosphate and intracellular calcium.

The release of eicosanoids and endothelium-derived relaxing factor (EDRF) from endothelial cells is thought to involve a calcium-dependent step. Using cultured bovine aortic endothelial cells as a model system, we have examined the relation between agonist-induced changes in inositol polyphosphates and calcium levels within the endothelial cells and extracellular calcium on EDRF release. In a superfusion-cascade system, EDRF was detected by the relaxation of a rabbit aortic ring without endothelium suspended beneath a column of cultured endothelial cells. Endothelial cell stimulation by bradykinin or melittin induced dose-dependent relaxation of the bioassay ring. In addition, bradykinin and melittin stimulated an increase in intracellular calcium concentration in fura-2 loaded endothelial cells and an increase in inositol 1,4,5-trisphosphate (Ins[1,4,5]P3) in cells prelabeled with 3H-myoinositol. Bradykinin stimulation produced transient increases in Ins(1,4,5)P3, fura-2 fluorescence and transient EDRF release. Melittin stimulation induced more prolonged release of EDRF from the endothelial cell column, which was correlated with sustained increases in the fura-2 signal and the level of Ins(1,4,5)P3. Omission of calcium from the cell superfusate attenuated, but did not eliminate, bradykinin-induced EDRF release and the calcium transient, whereas the melittin-induced responses were only slightly attenuated. Endothelial cells clearly demonstrate receptor-activation of phospholipase C and release of sequestered calcium from subcellular sites in response to Ins(1,4,5)P3. These results imply that EDRF release is correlated with increased intracellular calcium levels seen in the absence of extracellular calcium. However, sustained release of EDRF does require influx of extracellular calcium via an undefined mechanism.

Animals↗