Recent studies have yielded contradictory interpretations about the influence of gram-negative endotoxin on endothelium-derived relaxing factor (EDRF). We tested the hypothesis that Escherichia coli endotoxin exerts primary facilitatory or, alternatively, inhibitory actions on EDRF release and the synthesis of either nitric oxide or a nitroso compound in cultured endothelial cells. Bovine aortic endothelial cells were grown on microcarrier beads and either exposed acutely (30 min) to E. coli endotoxin or incubated with endotoxin for 1 h followed by a 1-h wash (prolonged exposure). EDRF bioactivity was measured under basal, bradykinin-stimulated, and A23187-stimulated conditions using standard isometric tension recordings. EDRF-derived nitric oxide was quantitated using a specific chemiluminescence technique. Endotoxin (0.005-5 micrograms/ml) decreased EDRF bioactivity and nitric oxide production under both basal and bradykinin-stimulated conditions after prolonged, but not acute, exposure. A23187-stimulated EDRF bioactivity and nitric oxide production were minimally, albeit significantly, reduced after endotoxin. The present results demonstrate that EDRF activity and nitric oxide production are decreased in vascular endothelial cells exposed to endotoxin. Endotoxin itself failed to directly stimulate EDRF release from endothelium. Alternative sources of nitrovasodilators, endothelium-independent effects, or release of other vasoactive mediators by endotoxin may be responsible for systemic hypotension during in vivo endotoxemia.

Animals↗

PubMed1992

Effects of exercise training on vasomotor reactivity of porcine coronary arteries.

The purpose of this study was to determine whether exercise training induces changes in the contractile behavior of proximal coronary arteries. Female Yucatan miniature swine were either exercise trained (ET) on a motor-driven treadmill or allowed to remain sedentary (SED) for 16-22 wk. Responses to vasoactive compounds were evaluated in vitro using coronary arterial rings (approximately 2 mm diam) isolated from ET and SED pigs. Each ring was stretched to the apex of the length-active tension relationship. Concentration-response relationships for isometric contractions evoked with KCl (5-100 mM), prostaglandin F2 alpha (PGF2 alpha; 10(-8)-3 x 10(-5) M), acetylcholine (ACh; 10(-9)-10(-4) M), and endothelin (10(-10)-10(-7) M) were similar in arteries from SED and ET pigs. In contrast, arteries from the ET group developed 50-60% less maximal tension in response to norepinephrine (NE; 10(-6)-10(-4) M) than did controls. Vasodilator responses of rings precontracted with either KCl or PGF2 alpha were evaluated with adenosine (ADO; 10(-9)-10(-4) M), isoproterenol (10(-9)-10(-4) M), forskolin (10(-9)-10(-4) M), and sodium nitroprusside (NP; 10(-10)-10(-4) M). Vasodilator responses were similar in SED and ET groups for all agents except ADO and NP; arteries from ET pigs were more sensitive to ADO and less sensitive to NP. The ET-induced alterations in vasomotor responses to NE and ADO appear to be due to changes in vascular smooth muscle because they were still present after removal of endothelium. We conclude that chronic exercise training in pigs induces selective alterations in NE and ADO receptor-second messenger coupling and/or postreceptor-related events in epicardial coronary vascular smooth muscle.

Animals↗

PubMed1992

Adrenergic responsiveness and intrinsic sinoatrial automaticity of exercise-trained rats.

The purpose of this study was to test the hypothesis that bradycardia in exercise-trained rats results from decreased intrinsic automaticity of the sinoatrial (SA) node and/or alterations in the responsiveness of the beta-receptors of atrial pacemaker cells. Male Sprague-Dawley rats were divided into exercise trained (ET) and sedentary (SED) groups. ET rats underwent a 12-16 wk program of progressive treadmill training, during which time the SED rats were cage confined. In vivo, resting heart rates were significantly less (P less than 0.05) in ET rats (301 +/- 8 bpm) compared with the SED group (320 +/- 6 bpm). In vitro experiments were conducted on atria isolated from ET and SED rats, and the beta-adrenoceptor agonist isoproterenol was used to investigate cardiac adrenergic control of chronotropic mechanisms in spontaneously beating right atria and inotropic mechanisms in electrically paced (1 Hz) left atria. There were no significant differences between ET and SED cardiac preparations in either the efficacy (maximal response) or potency (EC50) of isoproterenol dose-response relationships for chronotropic or inotropic responses. Intrinsic right atrial beating frequency, measured in the presence of beta-adrenoceptor block by propranolol and cholinergic muscarinic block by atropine, was lower in ET rats. We conclude that training-induced bradycardia in rats is related, at least in part, to alterations in intrinsic automaticity of SA nodal pacemaker tissue, but does not appear to be associated with changes in the properties of the beta 1-adrenoceptors or their affiliated signal transduction mechanisms in either SA pacemaker cells or atrial myocytes.

Animals↗

PubMed1991

Magnesium sulfate versus phenytoin for seizure prophylaxis in pregnancy-induced hypertension.

Seizure prophylaxis is standard intrapartum therapy for patients with pregnancy-induced hypertension. Magnesium sulfate is used in the United States in spite of limited literature comparing its efficacy with other anticonvulsants. Fifty patients with pregnancy-induced hypertension were prospectively randomized to receive magnesium sulfate or phenytoin for seizure prophylaxis. Patients were observed for toxicity, side effects, and labor outcomes, and the neonates were evaluated for side effects of the therapy. Three patients were excluded with adverse reactions to medications (one in magnesium sulfate group, two in phenytoin group). No differences were found in patient tolerance, adverse reactions, or neonatal outcomes between groups. Maternal free phenytoin levels were 13.0% +/- 0.4% of total phenytoin (serum albumin, 2.5 to 3.5 gm/dl), significantly higher than in nonpregnant patients. Neither free phenytoin levels nor percentage of total phenytoin that was free correlated significantly with maternal albumin levels. The pharmacokinetics of phenytoin loading in the massively obese pregnant patient may differ and require further evaluation. Phenytoin is a well-tolerated alternative to magnesium sulfate for seizure prophylaxis in the patient with mild pregnancy-induced hypertension.

Adult↗

PubMed1991

A single column, rapid quality control procedure for 6-[18F]fluoro-L-dopa and 6-[18F]fluorodopamine PET imaging agents.

6-[18F]Fluoro-L-dopa and 6-[18F]fluorodopamine are promising PET imaging agents for visualizing cerebral dopaminergic centers and cardiac sympathetic innervation and function. Administration to humans requires a means to determine the purity before injection. We describe such a method using HPLC with u.v. and radioactivity detection and a single high-speed C-18 column with gradient elution. The procedure can resolve within 10 min these fluorinated catechols, their isomers, and dihydroxyphenylalanine. The chemical and radiochemical purity, and specific activity, can be determined before injection.

Chromatography, High Pressure Liquid↗

PubMed1991

Distribution and kinetics of 3-O-methyl-6-[18F]fluoro-L-dopa in the rhesus monkey brain.

Most attempts to model accurately [18F]-DOPA imaging of the dopamine system are based on the assumptions that its main peripheral metabolite, 3-O-methyl-6-[18F]fluoro-L-DOPA ([18F]3-OM-DOPA), crosses the blood-brain barrier but is present as a homogenous distribution throughout the brain, in part because it is not converted into [18F]DOPA in significant quantities. These assumptions were based mainly on data in rodents. Little information is available in the primate. To verify the accuracy of the above assumptions, we administered 18F-labeled 3-OM-DOPA to normal rhesus monkeys and animals with lesions of the DA nigrostriatal system. No selective 18F regional accumulation in brain was apparent in normal or lesioned animals. The plasma metabolite analysis revealed that only the negatively charged metabolites (e.g., sulfated conjugates) that do not cross the blood-brain barrier were found in significant quantities in the plasma. A one-compartment, three-parameter model was adequate to describe the kinetics of [18F]3-OM-DOPA. In conclusion, assumptions concerning [18F]3-OM-DOPA's behavior in brain appear acceptable for [18F]DOPA modeling purposes.

Animals↗

PubMed1991

Coronary vascular smooth muscle function in E. coli endotoxemia in dogs.

The purpose of this study was to determine whether intrinsic contraction-relaxation properties of coronary arteries are altered during acute gram-negative endotoxemia. Coronary vascular smooth muscle (VSM) was evaluated in vitro using large and small left circumflex coronary ring preparations isolated from dogs 4 h after administration of either saline (control; C) or 1.5 mg/kg Escherichia coli endotoxin (ET). ET dogs exhibited marked systemic hypotension and cardiovascular depression throughout the 4-h in vivo phase of the study accompanied by reduction in total left ventricular myocardial blood flow. Isolated coronary vessels were stretched to the apex of the length-contractile tension curve; no differences were observed in length-active or length-passive tension (vessel compliance) relationships between C and ET vessels. Isometric contractions produced by K+ and prostaglandin F2 alpha (PGF2 alpha) were similar in C and ET coronary arteries. VSM relaxant responses to nitroprusside (NP; 10(-10) to 10(-4) M) were also similar in C and ET vessels. In contrast to the apparent lack of effect of ET on directly acting VSM agents, relaxation responses to the endothelial-dependent vasodilator acetylcholine (ACh) were significantly less in ET vessels. Impaired vasodilator response to ACh was not improved by in vivo treatment with the combination antioxidant therapy of allopurinol, superoxide dismutase, and catalase. We conclude that both depolarization (K+) and receptor (PGF2 alpha)-mediated contractile mechanisms, as well as basal cGMP (NP)-mediated vasodilator mechanisms, remained functional in coronary vasculature during acute endotoxemia. Inhibition of ACh-mediated relaxation in ET vessels suggests altered endothelial-dependent vasodilation in coronary arteries during endotoxemia, but this change did not seem to be associated causally with oxygen free radicals.

Acetylcholine↗

PubMed1991

Systolic and diastolic dysfunction of the left ventricle induced by dietary taurine deficiency in cats.

Isovolumic left ventricular (LV) preparations were used to assess myocardial failure associated with dietary taurine deficiency in cats. Adult female cats (n = 12) were fed a purified diet devoid of taurine for 6-8 mo. Six of the cats received 1,000 mg of crystalline taurine orally once daily. The remaining six cats were not provided taurine replacement. Compared with control preparations, hearts isolated from taurine-deficient cats generated significantly lower values for developed LV systolic pressure (107 +/- 6 vs. 66 +/- 15 mmHg; P less than 0.05), maximal rate of LV pressure rise (+dP/dtmax; 1,103 +/- 38 vs. 718 +/- 172 mmHg/s; P less than 0.05), and fall (-dP/dtmax; 930 +/- 46 vs. 587 +/- 129 mmHg/s; P less than 0.05). LV function curves generated by hearts from taurine-deficient cats were shifted downward and to the right of control curves, demonstrating inotropic depression. In addition, end-diastolic pressure-volume (compliance) relationships in hearts from taurine-deficient cats were shifted downward and to the right of controls in the direction of increased chamber compliance or distensibility. Ten millimolar taurine significantly improved inotropic indexes only in hearts from taurine-deficient cats but failed to affect diastolic compliance. Myocardial contractile dysfunction and LV chamber dilatation in hearts from taurine-deficient cats verify a causal association between dietary deficiency of this amino acid and dilated cardiomyopathy in this species.

Animals↗

PubMed1991

Postinjection L-phenylalanine increases basal ganglia contrast in PET scans of 6-18F-DOPA.

The sensitivity of 18F-DOPA positron emission tomography for imaging presynaptic dopamine systems is limited by the amount of specific-to-nonspecific accumulation of radioactivity in brain. In rhesus monkeys, we have been able to increase this ratio by taking advantage of the lag time between 18F-DOPA injection and the formation of its main metabolite, the amino acid 18F-fluoromethoxydopa, the entrance of which into brain is responsible for most of the brain's nonspecific radioactivity. By infusing an unlabeled amino acid, L-phenylalanine, starting 15 min after 18F-DOPA administration, we preferentially blocked the accumulation of 18F-fluoromethoxydopa by preventing its entrance into brain through competition at the large neutral amino acid transport system of the blood-brain barrier. This method appears as reliable as the original and more sensitive, as demonstrated by the comparison of normal and MPTP-treated animals under both conditions.

Animals↗

PubMed1990

Potentiation by glycine of anticonvulsant drugs in maximal electroshock seizures in rats.

This study evaluated the potentiation by glycine of anticonvulsant drugs in maximal electroshock seizures in rats. Administered alone, glycine (40 mmol/kg, p.o.) induced no anticonvulsant effect or neurotoxicity. Administered together with the anticonvulsants, glycine significantly enhanced the anticonvulsant potency of phenobarbital and carbamazepine. Glycine also potentiated the anticonvulsant actions of MK-801 and diazepam but did not improve the selectivity of the drugs, as effective doses were still associated with neurotoxicity. Glycine did not potentiate phenytoin or sodium divalproate. Administration together with glycine had no significant effect on the concentrations of phenobarbital or carbamazepine in the brain. Administration together with phenobarbital had no relevant effect on the concentration of glycine in the brain but administration of glycine and carbamazepine together resulted in an increased concentration of glycine in the hippocampus and brainstem. These findings indicate a possible glycine-sensitive component in the mechanism of action of phenobarbital, carbamazepine and diazepam in maximal electroshock seizures. Although the mechanism may not be mediated by a glycine-GABA interaction, the evidence does implicate a possible interaction between glycine and anticonvulsant drugs at NMDA receptors.

Animals↗

PubMed1990

Inotropic and chronotropic profile of MCI-154: comparison with isoproterenol and imazodan in guinea pig cardiac preparations.

Although recent studies indicate that MCI-154 exerts novel positive inotropic actions in heart muscle, the chronotropic properties of this new drug remain undefined. The present study compared the inotropic/chronotropic profile of MCI-154 with those of a nonselective beta 1/beta 2-agonist (isoproterenol, Iso) and a type III phosphodiesterase inhibitor (imazodan, CI-914) in cardiac preparations isolated from guinea pigs. The inotropic efficacy of MCI-154 was approximately equal to that of Iso and CI-194 in electrically paced (1 Hz) atrial muscle, with each agent increasing isometric contractile tension approximately 170% above basal (predrug) values. The inotropic EC50 for Iso (2.9 +/- 0.7 x 10(-9) M) was several orders of magnitude less than that for MCI-154 (1.4 +/- 0.4 x 10(-4) M) and CI-914 (1.1 +/- 0.2 x 10(-4) M). The inotropic potency of MCI-154 was equivalent in atrial and left ventricular myocardium. Both Iso and CI-194 substantially increased spontaneous beating frequency of sinoatrial preparations, and the inotropic/chronotropic potency ratio for each was unity. In contrast, MCI-154 exerted a slight negative chronotropic action on basal sinoatrial rate. Moreover, the negative chronotropic influence of MCI-154 was increased several-fold in the presence of Iso-stimulated maximal increases in heart rate (HR), and this inhibitory chronotropic action of MCI-154 was not prevented by muscarinic receptor blockade with atropine. These findings indicate that MCI-154 has a unique inotropic/chronotropic profile in cardiac tissues of guinea pigs in that this drug (a) efficaciously increased myocardial contractility, (b) had minimal effect on basal sinoatrial automaticity and yet (c) markedly inhibited sympathetically mediated sinus tachycardia.

Animals↗

PubMed1990

Left ventricular dysfunction in early E. coli endotoxemia: effects of naloxone.

Although the opiate receptor antagonist naloxone (NAL) has been reported to improve in vivo systolic performance of the heart in different circulatory shock syndromes, the influence of this drug on intrinsic cardiac mechanical function during hypodynamic circulatory states is unknown. The present study was designed to determine the effects of in vivo NAL on contraction-relaxation properties of isovolumic left ventricular (LV) preparations isolated from guinea pigs 4 h after induction of gram-negative endotoxemia. Animals were given a 1 mg/kg ip injection of Escherichia coli endotoxin and immediately treated intravenously with either NAL (4 mg/kg iv bolus plus 4 mg.kg-1.h-1 infusion) or an equivalent volume of saline. Endotoxin produced significant reduction of LV contractile function in coronary-perfused hearts, a response unaffected by NAL therapy. For example, LV systolic pressure at approximately 10 mmHg end-diastolic pressure averaged 78 +/- 3 and 82 +/- 6 mmHg in hearts from saline and NAL control animals, respectively, but only 41 +/- 2 and 40 +/- 2 mmHg in endotoxin and endotoxin plus NAL groups, respectively. LV end-diastolic pressure-volume relationships in endotoxin hearts were shifted upward and to the left of controls in the direction of decreased diastolic compliance (P less than 0.05). Importantly, in vivo NAL prevented the endotoxin-induced decrease in LV compliance of the isolated heart preparations (P less than 0.05). Thus intrinsic cardiac complications of early (4 h) nonhypotensive endotoxemia included decreased diastolic compliance as well as diminished contractility of the left ventricle. Only the diastolic compliance changes were NAL responsive and therefore may involve endogenous opioid systems in their pathophysiological expression.

Animals↗

PubMed1990

Intrinsic myocardial dysfunction during endotoxemia: dependent or independent of myocardial ischemia?

The cardiac mechanisms responsible for endotoxin-mediated disruptions in left ventricular (LV) contraction-relaxation dynamics have been controversial. Recently, a combination of clinical cardiodynamic studies in patients along with experimental cardiodynamic studies in endotoxemic/septic animals and isolated heart tissue has yielded corroborating evidence for a consistent deleterious alteration(s) of intrinsic LV contractility during shock syndromes. Cardiac dysfunction in shock patients and intact animals was characterized by reduced LV ejection fraction in the presence of unchanging LV stroke volume, or by reduced LV end-systolic pressure-volume ratio. In hearts isolated from experimental shock subjects, LV contractile abnormality was characterized by reduced isovolumetric intraventricular pressure development and stroke volume, even in the presence of maximally effective increments in end-diastolic volume or preload. Cardiodynamic changes developed early in experimental septicemic shock syndromes (less than 4 hr) and were not irreversible. Furthermore, and this is a key element, both clinical and experimental study indicated that coronary perfusion inadequacy was not an obligatory etiologic factor in the shock-associated loss of cardiac contractile function. Thus, clinical and experimental data are now available to assemble a consensus that 1) intrinsic LV contractile reserves are diminished early during endotoxemia and sepsis and 2) this diminution is not simply a consequence of global myocardial ischemia.

Animals↗

PubMed1989

6-18F-L-dopa imaging of the dopamine neostriatal system in normal and clinically normal MPTP-treated rhesus monkeys.

Positron emission tomography following intravenous administration of 6-[18F]-L-fluorodopa was used to investigate the usefulness of PET for the assessment of normal and abnormal dopaminergic function. For this purpose, the incracerebral distribution of 6-[18F]-L-fluorodopa and its metabolites was evaluated in normal control and asymptomatic MPTP-treated rhesus monkeys. MPTP is a neurotoxic compound which destroys selectively the dapaminergic neurons of the nigrostriatal pathways in primates. The 18F accumulation was found to be significantly reduced in the striatum, putamen more than caudate, of the MPTP-treated animals compared to the normal controls. The 18F accumulation in dopamine-poor areas did not differ between the two groups. The ratios of striatum to dopamine-poor brain area were highly correlated to the concentrations of the dopamine metabolite, homovanillic acid, in the cerebrospinal fluid of the same animals. The findings are consistent with the hypothesis that "silent damage" to the dopaminergic nigral neurons may precede the onset of parkinsonism by many years and that PET scanner examination using 6-[18F]-L-fluorodopa may be useful in the detection of subtle dopaminergic dysfunctions as may exist in DA-related motor syndromes and neuropsychiatric disorders.

Animals↗