Olaf Sommer

Norepinephrine constricts the canine coronary bed via postsynaptic α2-adrenoceptors

Abstract The effect of α2-blockade (0.3 mg/kg i.v. rauwolscine) and α1-blockade (1.2 mg/kg i.v. prazosin) on coronary constrictions induced by intracoronary injections of azepexole (B-HT 933, α2-agonist, 0.1–10 μg/kg), phenylephrine (0.3–3 μg/kg) and norepinephrine (0.001–0.1 μg/kg) were studied in dog hearts perfused in situ under β-blockade. Constrictions by azepexole (antagonized by rauwolscine, yet resistant to prazosin and methylsergide) demonstrated coronary α2-adrenoceptors. Norepinephrine-induced constrictions were more attenuated (22-fold) by α2-blockade than by α1-blockade (2.6-fold) and thus were mediated mainly by activation of postsynaptic α2-receptors.

Altered spectrum of nitroglycerin action in long-term treatment: nitroglycerin-specific venous tolerance with maintenance of arterial vasodepressor potency.

The study of venodilator tolerance to nitroglycerin has been complicated by reflex compensation and by problems in analyzing venous tone in the presence of multiple determinants of venous pressure. We assessed venous tone as total effective vascular compliance (TEVC) under autonomic blockade in six dogs, in the nontolerant state, and during a 5 day infusion of nitroglycerin (1.5 micrograms/kg/min). Under long-term treatment, baseline TEVC was unaffected and the nitroglycerin dose-response relationship for TEVC was shifted to greater than 10-fold higher doses, whereas baseline mean arterial pressure (MAP) was lowered by 17 +/- 3 mm Hg without any shift in nitroglycerin responsiveness. This lowering of MAP was observed only after autonomic blockade. In six additional dogs instrumented with aortic flow probes, nitroglycerin (1.5 micrograms/kg/min) induced a 15 +/- 1% decline in peripheral vascular resistance (PVR) under autonomic blockade, but with reflexes intact these dogs showed no change in PVR and a 21 +/- 10% increase in norepinephrine release rate. We conclude that modest long-term exposure to nitroglycerin results in tolerance to its venodilating effects, whereas arteriolar action is maintained. This tolerance-induced shift in action from venous toward arteriolar dilation is normally masked by compensatory reflexes.

Ergonovine-induced constrictions of epicardial coronary arteries in conscious dogs: α-adrenoceptors are not involved

SummaryThe effect of i.v. ergonovine tartrate infusions (0.05–20 μg/kg/min, 12 minutes duration) on coronary arteries was studied in 14 conscious dogs instrumented to continuously measure vascular diameter by an ultrasonic dimension gauge using 10-MHz piezoelectric crystals.Ergonovine induced a biphasic coronary response: small, transient dilation during the first minutes of infusion, followed by slowly developing constriction reaching its maximum 5 to 15 minutes after the end of the infusion and persisting at this level for at least 10 minutes. The threshold dosage for significant constriction was 0.05 μg/kg/min. A dosage of 5 μg/kg/min (cumulative 60 μg/kg, corresponding to 35 μg/kg ergonovine maleate) caused a decline in mean left circumflex artery diameter by 137±15 μm (=4.6%) without significantly altering heart rate, plasma catecholamines or plasma renin activity. Coronary venous O2 saturation did not decline, indicating the absence of coronary resistance vessel constriction. The epicardial artery constriction was not attenuated by a vasopressin antagonist. Under adrenergic blockade (2 mg/kg phentolamine and 2 mg/kg nadolol) or under ganglionic blockade (5 mg/kg pentolinium tartrate), ergonovine (5 μg/kg/min) caused substantial elevation in mean arterial pressure, while the decline in coronary artery diameter was attenuated. When this increase in arterial pressure was prevented by appropriate bleeding, the ergonovine-induced coronary constriction was not diminished by adrenergic or ganglionic blockade. The serotonin antagonist methysergide (0.5 mg/kg) completely abolished the ergonovine-induced coronary artery vasomotion.It is concluded that ergonovine in dogs causes an epicardial coronary artery constriction comparable to the diffuse coronary artery narrowing in men not suffering from variant angina pectoris. These constrictions are not mediated by an adrenergic mechanism.ZusammenfassungDie Wirkung intravenöser Infusionen von Ergonovitartrat (0.05–20 μg/kg/min, 12 Minuten Dauer) auf die Koronararterien wurde in 14 wachen Hunden untersucht. Die Tiere waren für eine kontinuierliche Messung des Gefäßdurchmessers mit einem Ultraschall-Verfahren mittels implantierten piezoelektrischen 10-MHz-Kristallen ausgerüstet.Ergonovin verursachte eine biphasische Koronarreaktion: eine geringgradige, vorübergehende Dilatation während der ersten Minuten der Infusion, anschließend eine allmählich einsetzende Konstriktion, die ihr Maximum erst 5–15 Minuten nach Ende der Infusion erreichte und für mindestens 10 Minuten bestehen blieb. Die Schwellendosis für signifikante Konstriktion betrug 0,05 μg/kg/min. Die Dosis von 5 μg/kg/min (kumulativ 60 μg/kg, was 35 μg/kg Ergonovin-Maleat entspricht) verursachte eine Abnahme des mittleren Durchmessers der linken umschlingenden Koronararterie um 137±15 μm (=4,6%) ohne signifikante Wirkungen auf Herzfrequenz, Plasma-Katecholamine oder Plasma-Renin-Aktivität. Die koronarvenöse O2-Sättigung nahm nicht ab, demnach erfolgte also keine Konstriktion von koronaren Widerstandsgefäßen. Die Konstriktion der epikardialen Gefäße war nicht durch einen Vasopressin-Antagonisten abschwächbar. Unter adrenerger Blockade (2 mg/kg Phentolamin und 2 mg/kg Nadolol) oder unter Ganglienblockade (5 mg/kg Pentoliniumtartrat) verursachte Ergonovin (5 μg/kg/min) eine erhebliche Zunahme des arteriellen Mitteldruckes, während die Verminderung des Koronararterien-Durchmessers abgeschwächt war. Wurde dieser arterielle Druckanstieg durch entsprechende Blutentnahme verhindert, so war die Ergonovin-induzierte Koronarkonstriktion weder durch adrenerge Blockade noch durch Ganglienblockade abgeschwächt. Der Serotonin-Antagonist Methysergid (0,5 mg/kg) hob die ergonovininduzierten Koronarreaktionen vollständig auf.Ergonovin verursacht in Hunden eine Konstriktion epikardialer Koronararterien ähnlich der diffusen Koronarverengung in Menschen, die nicht an “Variant”-Angina-pectoris leiden. Diese Konstriktionen werden nicht durch einen adrenergen Mechanismus bewirkt.

Angiotensin Receptor Blocker Losartan Suppresses Platelet Activity by Interfering with Thromboxane Signaling

AbstractEnhanced platelet activity and platelet endothelial interaction are hallmarks of different vascular and metabolic diseases with subsequent thrombus formation. In atherosclerosis, coronary artery disease, congestive heart failure, nitrate tolerance, chronic inflammation, or diabetic states, platelet activation may in part be due to a stimulation of the renin-angiotensin-aldosteron system, which also contributes to enhanced oxidant stress in these conditions. Aims. We examined the putative role of the angiotensin receptor (AT1) and of phospholipase A2 (PLA2) in mediating platelet activation under defined in vitro conditions using the AT1 receptor antagonists losartan, EXP 3174, candesartan, and the PLA2 inhibitor arachidonyltrifluoromethyl ketone (AACOCF3), respectively. Results. In washed human or canine platelet suspensions, losartan (10−4–10−6 mol/L) dose-dependently suppressed thrombin-induced calcium transients as well as thromboxane (TxA2) release. In both species, aggregation of washed platelets in response to thrombin or ADP was substantially diminished by different doses of losartan. This inhibition of platelet aggregation was even maintained in ADP-stimulated platelet-rich plasma. While the PLA2 inhibitor AACOCF3 effectively inhibited thrombin-induced TxA2 release from washed human or canine platelets (similar to the effects observed with losartan), the AT1 agonist angiotensin II elicited platelet TxA2 release only at high supra-physiological doses (e.g., at 10−4 mol/L). The AT1 specific antagonist candesartan did not diminish stimulated platelet aggregation, TxA2 formation, or calcium transients. By contrast, the active losartan metabolite EXP 3174 dose-dependently inhibited stimulated platelet calcium transients as well as TxA2 release at 1–100 μmol/L. Conclusions. Losartan significantly counteracts ex vivo platelet activation, probably via the blockade of TxA2 receptor-dependent signaling (e.g. implying activation of phospholipase A2) rather than acting at the AT1 receptor itself. This implies that the TxA2 signaling pathway plays a significant role during platelet activation, which may be successfully antagonized in vivo under different pathological states with enhanced thrombus formation or platelet-endothelium interactions.

Local stimulation of the adenosine A2B receptors induces an increased release of IL-6 in mouse striatum: an in vivo microdialysis study.

Both adenosine and interleukin‐6 (IL‐6) have been implicated in the pathophysiology of, e.g., epileptic seizures, traumatic brain injury, and affective disorders. Stimulation of adenosine A2B receptors on astrocytes in vitro leads to the increased synthesis and secretion of IL‐6. We investigated whether or not activation of adenosine receptors evokes an increase of IL‐6 release also in vivo. 5′‐N‐ethylcarboxamidoadenosine, a non‐specific adenosine‐agonist or vehicle was administered into the striatum of freely moving mice by reverse microdialysis. A statistical significant increase of the IL‐6 concentration in the perfusate was detected already 60 min after 5′‐N‐ethylcarboxamidoadenosine administration. IL‐6 increased progressively and reached a maximum after 240 min. This effect appears to be mediated through adenosine A2B receptors since it was counteracted by the specific A2B receptor antagonist MRS1706 but not by the specific A1 receptor antagonist DPCPX. We conclude that adenosine via activation of A2B receptors evokes IL‐6 release also in vivo.

Matrix metalloproteinase-9 derived from polymorphonuclear neutrophils increases gut barrier dysfunction and bacterial translocation in rat severe acute pancreatitis

BACKGROUND The role of polymorphonuclear neutrophil granulocytes (PMNs) and the PMN-derived protease, which is called matrix metalloproteinase-9 (MMP-9), for the gut barrier dysfunction in severe acute pancreatitis (SAP) has not yet been clarified. The aim of this study was to evaluate the effects of PMNs and MMP-9 on gut barrier dysfunction in rat SAP. METHODS SAP was induced by the injection of 5% sodium taurocholate, and anti-rat PMN serum or BB-94 were administered 48 h and 24 h, respectively, before the induction of acute pancreatitis. Twenty-four hours after the induction of acute pancreatitis, the gut barrier dysfunction and the incidence of bacterial translocation (BT) and PMN transmigration were investigated by bacterial, histologic, and biochemical (MPO) analysis. Inhibition of MMP-9 was achieved by depletion of PMNs or inhibition of MMP-activity by a broad-spectrum MMP inhibitor and confirmed by zymography. In addition, reactive oxygen species were evaluated by spin trap assay. RESULTS The mucosal injury and the infiltration of PMNs into the gut tissue of rats with SAP were significantly increased in comparison with rats treated with anti-rat PMN serum or BB-94. The levels of MMP-9 and reactive oxygen species in the gut of rats with SAP were significantly higher than those of the rats treated with anti-rat PMN serum or BB-94. Pretreatment with anti-rat PMN serum or BB-94 reduced the incidence of BT in SAP. CONCLUSION The incidence of BT in SAP was prevented by the depletion of PMNs or less pronounced by the injection of the MMP inhibitor BB-94. PMNs play an important pathophysiologic role in the occurrence of BT, and MMP-9 is involved in both BT and PMN transmigration in rat SAP.

Effects of antipsychotics and vitamin C on the formation of reactive oxygen species

There is evidence that reactive oxygen species (ROS) are involved in the pathophysiology of psychiatric disorders such as schizophrenia. Indirect biochemical alterations of ROS formation have been shown for patients treated with antipsychotics as well as for untreated patients. Only one study measured directly the ROS formation after treatment with antipsychotics by using electron spin resonance spectroscopy. The aim of the present examination was to demonstrate the effects of haloperidol, clozapine and olanzapine in concentrations of 18, 90 and 180 μg/mL on the formation of ROS in the whole blood of rats by using electron spin resonance spectroscopy after incubation for 30 min. To test the protective capacity of vitamin C we incubated the highest concentration of each drug with vitamin C (1 mM). Under all treatment conditions, olanzapine led to a significantly higher formation of ROS compared with control conditions, whereas in the cases of haloperidol and clozapine the two higher concentrations induced a significantly enhanced formation of ROS. Vitamin C reduced the ROS production of all drugs tested and for haloperidol and clozapine the level of significance was reached. Our study demonstrated that antipsychotics induce the formation of ROS in the whole blood of rats, which can be reduced by the application of vitamin C.

Blockade of angiotensin signaling improves myocardial function in hypercholesterolemia independent of changes in eicosanoid release.

In hypercholesterolemia in the presence or absence of atherosclerosis, cardiovascular dysfunction and altered signaling of angiotensin, nitric oxide, or prostanoids are closely related to enhanced oxidant stress. We analyzed the potentially beneficial effects of the specific angiotensin-converting enzyme inhibitor enalapril and the specific angiotensin receptor blocker losartan on cardiac performance, eicosanoid metabolism, and parameters of oxidant stress in hypercholesterolemic animals. Guinea pigs were fed a 1% cholesterol diet for 8 weeks (Chol) with or without equieffective doses of either enalapril (1.5 mg/kg/d; Ena) or losartan (3 mg/kg/d; Los). Hemodynamics were analyzed in Langendorff hearts. Detection of eicosanoids was by enzyme immunoassay. Estimation of plasma xanthine oxidase (XO) activity was determined by spectrophotometry. In hypercholesterolemic guinea pigs, enhanced oxidant stress (e.g., increased plasma XO activities) was associated with profound myocardial and coronary (e.g., endothelial) dysfunction. Both enalapril and losartan lowered plasma cholesterol levels slightly, but only the angiotensin receptor antagonist effectively suppressed the increased plasma XO activities (from 11.4 ± 0.7 to 7.6 ± 2.2 U/L), and at the same time decreased the augmented coronary flow (from 26.0 ± 1.0 to 23.0 ± 1.0 mL/min/g tissue) observed in hypercholesterolemic animals. Assessment of left ventricular pressure and contractility (e.g., dp/dtmax) as well as the diastolic relaxation parameter (τ) revealed substantial myocardial dysfunction (systolic and diastolic) in Chol that was more substantially (and comparably) improved during administration of losartan (Los) than during enalapril (Ena). Surprisingly, angiotensin signaling blockade by either antagonist further suppressed the diminished coronary dilator responses to bradykinin (BK; not significant for enalapril) or adenosine (Ado) that was demonstrated in Chol Langendorff hearts [ΔCPPBK/Ado: from 5.0 ± 0.5/0.9 ± 0.1 to 4.4 ± 1.5/0.4 ± 0.1 (Ena) or to 1.9 ± 0.5/0.4 ± 0.1 (Los) cm2 (area under the curve), respectively]. Finally, as expected from control studies using heart preparations from normocholesterolemic guinea pigs, enhanced cardiac release of eicosanoids, prostacyclin, and thromboxane in Chol (0.48 ± 0.03 and 0.6 ± 0.1 ng/min/g) was augmented even further by treatment with enalapril (Ena: 1.6 ± 0.4 and 1.0 ± 0.1 ng/min/g), but was significantly reduced to or below control levels in losartan-treated animals (Los: 0.4 ± 0.1 and 0.2 ± 0.1 ng/min/g). Blockade of angiotensin signaling via angiotensin-converting enzyme inhibition or receptor antagonism—although differentially acting on enhanced cardiac prostanoid metabolism and oxidant stress—efficiently restored proper systolic and diastolic myocardial performance (losartan was more beneficial than enalapril), probably by counterbalancing altered angiotensin II → angiotensin receptor signaling in the cardiovascular system of hypercholesterolemic animals. Impaired coronary vasodilator capacity seems to be irreversible after 8 weeks of a high-cholesterol diet, as shown by the unexpected lack of a dilator effect with both enalapril and losartan.

Sympathoadrenal inhibition by atrial natriuretic peptide is not attenuated during development of congestive heart failure in dogs.

The feedback control of neuroendocrine activity by cardiopulmonary blood volume is disturbed in congestive heart failure. By analyzing plasma catecholamine kinetics, we tested in 11 chronically instrumented conscious dogs whether attenuations in the sympathoadrenal inhibition induced by atrial natriuretic peptide (ANP) contributed to this disturbance. Low-output failure was brought about by continuous ventricular pacing at 265 beats/min for 2 weeks. This resulted in a decline in aortic flow by 37 +/- 5% (SEM), an increase in peripheral vascular resistance by 48 +/- 4%, a 13 +/- 3-fold elevation in plasma ANP, a 9 +/- 3-fold elevation in plasma renin activity, and an augmentation of the norepinephrine-release rate into plasma by 132 +/- 17%. During ANP infusion, the epinephrine-release rate declined by 26 +/- 5% per 10-fold elevation in plasma ANP before pacing and by 31 +/- 7% (not significantly different) after 2 weeks of pacing. Before pacing, ANP attenuated plasma renin activity and caused hypotension without a rise in norepinephrine-release rate. After 2 weeks of pacing, ANP lowered norepinephrine release (by 16 +/- 6%) without affecting blood pressure or plasma renin activity, and vascular nonresponsiveness to ANP was verified under autonomic blockade. These data indicate that, during the development of heart failure, an inhibitory action of ANP on norepinephrine release is unmasked by an ANP-specific vascular desensitization, whereas the inhibition of epinephrine release is observed throughout. It is concluded that ANP-induced sympathoadrenal inhibition is not attenuated and, therefore, does not contribute to the disturbed regulation observed early in the development of failure.

Cardiovascular Dysfunction in Hypercholesterolemia Associated With Enhanced Formation of ATI-Receptor and of Eicosanoids

Background: In hypercholesterolemia with or without atherosclerosis cardiovascular dys function and altered signalling of angiotensin (Ang II), nitric oxide (NO), or prostanoids are intimately related to enhanced oxidant stress and concomitant changes in gene expression. We analyzed cardiac angiotensin receptor (AT1) expression and metabolism of Ang II, eicosanoids, and NO in hypercholesterolemic animals. Methods: Guinea pigs were fed a 1% cholesterol diet for 8 weeks (Chol). Hemodynamics were analyzed in Langendorff hearts. Spectrophotometric determination of plasma lipids and radioimmunological detection of eicosanoids/cyclic guanosine monophosphate (cGMP). Ac tivities of NO synthase III (NOS-III) or angiotensin converting enzyme (ACE) were deter mined by enzymatic assays. AT1 receptor density was assessed by radioligand binding assay. NOS-III mRNAs were quantitated by reverse transcription polymerase chain reaction. Results: Hypercholesterolemia was associated with fatty degeneration of the liver and pro found myocardial and coronary (e.g., endothelial) dysfunction. In Chol Langendorff hearts we observed significant increases in coronary flow (26.0 ± 1.0 vs. 17.5 ± 0.5 mL/min/g tissue) but diminished coronary responses to bradykinin (Bk, 250 ng bolus) or adenosine (Ado, 250 μg bolus) (ΔCPPBk/Ado: 5 ± 0.5 vs. 7.2 ± 1/0.9 ± 0. 1 vs. 1.9 ± 0.3 cm2 (area under the curve)). AT1 receptor expression was significantly increased in Chol hearts (72 ± 6.8 vs. 45 ± 5.6 fmol/mg protein), whereas marked suppression of cardiac activities of ACE (1.96 ± 0.34 vs. 4.90 ± 0.20 nmol/min/mg tissue) and of the entire cardiac nitric oxide-cGMP axis (e.g., NOS-III activity: 1.9 ± 0.4 vs. 3.1 ± 0.1 pmol/min/mg tissue; NOS-III mRNA: 0.82 ± 0.16 vs. 1.20 ± 0.12 arbitrary units; cGMP release: 0.41 ± 0.02 vs. 0.54 ± 0.04 pmol/min/g tissue) were shown in Chol. Finally, cardiac release of eicosanoids prostacyclin (PGI2) and throm boxane (TxA2) were significantly enhanced (0.48 ± 0.05 vs. 0.38 ± 0.05 and 0.60 ± 0.10 vs. 0.24 ± 0. 10 ng/min/g tissue, respectively). Enhanced cardiac PGI2 release and suppression of cGMP synthesis in Chol were even more pronounced on stimulation with Bk (38.2 ± 3.0 vs. 28.2 ± 2.0 ng/min/g tissue and 1.9 ± 0.3 vs. 3.0 ± 0.3 pmol/min/g tissue, respectively). Conclusions: Altered angiotensin-mediated signal transduction probably related to aug mented eicosanoid formation does not compensate for the limited endogenous NO production and for cardiovascular dysfunction in hypercholesterolemic guinea pigs. In this context, changes in redox-sensitive regulation of gene expression (ATI receptor, NOS-III—caused by enhanced oxidant stress—coutd play a pivotal role.