Acid-catalyzed formation of isoprene from a mevalonate-derived product using a rat liver cytosolic fraction

Isoprene formation in a rat liver cytosolic fraction is shown to be increased 146-fold by acid treatment. This acid catalysis is dependent upon prior incubation of the cytosolic fraction with DL-mevalonate and is stimulated when the incubation also contains ATP. Formation of isoprene proceeds linearly through 5 h of acid treatment and is nearly complete at 10 h. These results suggest that the acid-catalyzed isoprene formation arises from the decomposition of dimethylallyl pyrophosphate via a carbonium ion mechanism. Chemical model studies using 3-methyl-2-buten-1-ol and 3-methyl-3-buten-1-ol (the alcohols corresponding to dimethylallyl pyrophosphate and isopentenyl pyrophosphate, respectively) confirm this hypothesis. At a pH less than or equal to 1, an 85% decomposition of 3-methyl-2-buten-1-ol to isoprene occurred after 24 h, while 3% of 3-methyl-3-buten-1-ol was converted to isoprene under identical conditions and time. It is concluded that the predominant immediate precursor of isoprene is dimethylallyl pyrophosphate and at low pH the ultimate fate of dimethylallyl pyrophosphate is complete conversion to isoprene. These conclusions have important biochemical and methodological implications.

Autoxidation of Acholeplasma laidlawii membranes

Autoxidation of Acholeplasma laidlawii membranes (with equimolar ratio of palmitic and linoleic acid) lacks an obvious induction period, and the overall rate of disappearance of substrate does not follow closely that of typical autocatalytic kinetics. Throughout the course of autoxidation, the major oxygenated products isolated were hydroperoxides (as hydroxy esters) and compounds that gave rise to trihydroxy esters. The yield of trihydroxy esters was appreciable even at the early stage of the oxidation and eventually grew to surpass that of hydroperoxides. The positions of the three hydroxyl groups in the trihydroxy esters were determined to be mostly of the 1,2,5-type rather than 1,2,3-type arrangement. To a lesser extent, some degraded products, including dimethyl nonanedioate, methyl myristate, methyl pentadecanoate, methyl hexadecadienoate and methyl heptadecadienoate also were obtained. Dimethyl nonanedioate was a previously known degradation product from 9-hydroperoxide. The shorter chain esters presumably arise from the cleavage of alpha-hydroperoxides of palmitate and linoleate moieties.

In vitro biosynthesis of isoprene from mevalonate utilizing a rat liver cytosolic fraction

The in vitro biosynthesis of isoprene from DL-mevalonate in the cytosolic fraction of rat liver is described. Evidence is provided suggesting a non-enzymatic formation of isoprene from isopentenyl pyrophosphate and/or dimethylallyl pyrophosphate. Furthermore, the data establish an alternate fate of the mevalonate carbon skeleton providing the first evidence that breath isoprene is linked to cholesterol biosynthesis.

Exercise echocardiography

Echocardiographic assessment of changes in wall motion and ventricular dimensions with exercise may be of significant value in the evaluation of the patient with coronary artery disease. Topics covered in this article include exercise physiology, dynamic M-mode echocardiography and its limitations, two-dimensional dynamic exercise echocardiography, and echocardiography during isometric exercise.

Autoxidation of phosphatidylcholine liposomes

Autoxidation of pure soybean phosphatidylcholine liposomes at 40 C was found to proceed without an observed induction period, but otherwise, the rates of disappearance of the linoleic acid (70% of total) and linolenic acid (6% of total) followed typical autocatalytic kinetics. Incorporation of 0.05 mol % of tocopherol into the liposomes produced an induction period of about 7 hr under the condition used for the incubation. The products formed from the autoxidation of pure soybean phosphatidylcholine liposomes were mostly 9- and 13-hydroperoxyoctadecadienoates (isolated as hydroxy esters). The yield of hydroperoxides with cis,trans configuration was about the same as those with trans,trans configuration throughout incubation period. After extensive autoxidation, a large quantity of trihydroxyoctadecenoate was also produced. When a large quantity of dipalmitoyl phosphatidylcholine was incorporated into soybean phosphatidylcholine liposomes, the rate of autoxidation decreased and was found to conform to apparent first-order kinetics. In this system, the yield of trans,trans hydroperoxides was much greater than that of cis,trans isomers at all stages of autoxidation. Late in the autoxidation of the mixed liposomes, both trihydroxyoctadecenoate and hydroxyepoxyoctadecenoate were produced in substantial quantities.

Metabolism of epoxidized phosphatidylcholine by phospholipase A2 and epoxide hydrolase

The isolation and measurement of phospholipid epoxides as major peroxidation products in biomembrane preparations prompted an investigation of enzymatic mechanisms which may be responsible for their elimination. Analysis of microsomal epoxide hydrolase and phospholipase A2 activity against a phospholipid epoxide commonly encountered in tissues indicated it to be a poor substrate for epoxide hydrolase, but rapidly hydrolyzed by phospholipase A2. Microsomal and purified phospholipase A2 preparations hydrolyzed the phospholipid epoxide at rates 2-fold greater than were observed with a monoenoic phospholipid from which the epoxide would be derived. The product fatty acid epoxide, cis-9,10-epoxystearic acid, was rapidly hydrated by microsomal and cytosolic epoxide hydrolase. On the basis of earlier reports demonstrating increased phospholipase activity against oxidized phospholipids, and on the results of the present study, a model for the metabolism of oxidized membrane phospholipids is proposed.

Clinical value of early exercise testing after myocardial infarction

The clinical utility of predischarge exercise ECGs was assessed prospectively in 47 patients 17 +/- 2 days after myocardial infarction. The graded-interval ergometric exercise protocol was terminated at 450 kilopond-m/min (kpm/min), a heart rate greater than 75% of predicted maximum, or for established clinical indications. Prior to testing, the attending physician and resident indicated their clinical impressions with regard to anticipated (1) angina, (2) exercise capacity, (3) arrhythmias during limited exercise, as well as anticipated discharge medications and activity prescriptions. Ratings were compared to exercise results and consequent alterations in management noted. No complications were noted during the evaluations. Nine patients noted anginal pain during exercise; five were unsuspected by the attending physician or resident. Ten patients demonstrated significant ventricular arrhythmias. Four were receiving antiarrhythmic therapy. Severe limitation of exercise capacity (< 300 kpm/min) was noted in six patients, unanticipated in four. Where not contraindicated, routine use of predischarge exercise ECG testing is recommended.

Lipid epoxide hydrolase in rat lung preparations

The activity of rat lung epoxide hydrolase (epoxide hydrolase, EC 3.3.2.3) was studied using two lipid epoxides which can be isolated from lung tissue. These epoxides displayed different Km,app and hydration rates. Methyl cis-9,10-epoxystearate was hydrated 20-times more rapidly than cholest-5 alpha,6 alpha-epoxy-3 beta-ol. The Km for the lung microsomal enzyme was variable and dependent on the microsome concentration in the medium. A soluble epoxide hydrolase was also detected in both lung and liver. This enzyme appears similar to the microsomal enzyme in its activity toward methyl epoxystearate. The measured activities for liver microsomal epoxide hydrolase were over 8-times those for lung microsomes; activity against cholesterol epoxide was 40-times greater for liver. In spite of the slow rates measured with cholesterol epoxide in lung preparations, this compound was an effective competitive inhibitor against methyl epoxystearate over a wide concentration range. This suggests that cholesterol epoxide readily binds to epoxide hydrolase and is an effective competitive inhibitor against a much more actively metabolized substrate, methyl epoxystearate. Such circumstances indicate that cholesterol epoxide binds with a high degree of nonproductivity to lung microsomal epoxide hydrolase. This attribute of lung epoxide hydrolase may relate to the relatively high concentrations of cholesterol epoxide found in lung tissue.

Increasing pre-excitation during exercise and isoproterenol infusion. Evidence for a catecholamine sensitive bypass tract

A patient with atypical chest pain developed pre-excitation during exercise and isoproterenol infusion, with "ischemic" ST depression only during the pre-excited beats. Coronary angiography and myocardial lactate extraction showed no evidence of abnormal coronary vessels. Electrophysiologic study and pacing-induced tachycardia did not induce pre-excitation, whereas exercise induced progressive increase in pre-excitation. The data are consistent with an unusual form of pre-excitation, perhaps related to responsiveness of an accessory bypass tract to catecholamine stimulation. The data also show that the false positive exercise test in this syndrome is due to progressively increasing pre-excitation and therefore more abnormal repolarization.

Epoxides as products of lipid autoxidation in rat lungs

The nature and content of lipid epoxides in rat lung were examined in air-breathing control rats and those exposed to nitrogen dioxide. Exposure to 6.5 ppm NO2 for 24 hr resulted in significantly greater epoxide content in a number of lipid classes. It is proposed that lipid autoxidation in lung tissues may contribute to the levels of epoxide-containing lipids. Furthermore, the processes involved in epoxide formation may be predicted from autoxidation studies utilizing a system of unsaturated fatty acid monolayers on silica gel which serves as a model for biomembranes. The findings indicate that exposure to oxidizing gases can lead to an accumulation of lipid epoxides in both lung parenchymal tissue and on the alveolar surface.

Hypertrophic cardiomyopathy in the aged

Although usually considered a disease of young or middle-aged adults, hypertrophic cardiomyopathy is not infrequently seen in older patients as well. Twenty of 23 cases of hypertrophic cardiomyopathy seen in the past 2 1/2 years at our institution have been in patients whose average age was 65 years, and who ranged up to 76 years. Sixteen of these had evidence of an obstructive component at cardiac catheterization or echocardiography. Symptoms and signs were similar to those described for the younger patients in the literature, but were often attributed to other causes, including valvular aortic stenosis, arteriosclerotic or hypertensive heart disease, or cerebrovascular disease. Left ventricular hypertrophy was more consistently present on ECG than on x-ray. The not-infrequent occurrence of hypertrophic cardiomyopathy in older patients, predominantly females, indicates that the natural history of this disease includes a group who suffer few or no symptoms until late in life. Clinical management of younger patients with this diagnosis should be considered in light of this more favorable possible course.

Autoxidation of fatty acid monolayers adsorbed on silica gel: II. Rates and products

Unsaturated fatty acid monolayers on silica gel have been autoxidized, and the rate of fatty acid disappearance and products obtained from those membrane-like assemblies have been studied. Fatty acid monolayers consisting of pure linoleic acid, linolelaidic acid, and oleic acid were autoxidized at 60 C. The rates of autoxidation of linoleic acid and linolelaidic acid monolayers followed by the disappearance of substrates are considerably faster than that in bulk phase, and the rates conform to apparent first order kinetics. Autoxidation of linoleic and linolelaidic acid monolayers, unlike bulk phase, produced only a small amount of diene conjugation, and the major products formed were identified as 9,10-epoxy and 12,13-epoxyoctadecenoic acid in roughly equal quantities. The epoxidation is stereospecific, with cis and trans olefins giving cis and trans epoxides, respectively. Oleic acid was autoxidized to only a small extent during 27 hr and produced no detectable amount of epoxide.

The effect of exercise training on heart rate during coitus in the post myocardial infarction patient

The effect of interval exercise training on the peak coital heart rate in post myocardial infarction patients was studied. Sixteen men (ages 46-54) underwent a 16-week bicycle ergometer training program 12 to 15 weeks following their first myocardial infarction. Portable ECG tape recorders were used to record the ECG during coitus twice before and twice after the training program. The maximum minute oxygen consumption (VO2max) was measured in each subject during bicycle ergometer ECG examinations before and after the training program. A control group of six post myocardial infarction patients who were not trained was evaluated in the same manner. The exercise-trained group had an average increase in VO2max of 11.5%(2.7 to 3.0 L/min) and an average decrease in peak coital heart rate of 5.5%(127/min to 120/min). The control group demonstrated a 2% increase in VO2max and no significant change in peak coital heart rate. The increase in aerobic capacity (VO2max) and the consequent reduction in peak coital heart rate in our trained group suggests the potential value of exercise training in improving sexual function in the patient with angina during coitus.

Labeled metronidazoles as potential new agents for amebic hepatic abscess imaging

Two new radiopharmaceuticals were developed as possible agents for demonstrating the presence of hepatic amebic abscesses by selective accumulation of these agents in the abscess contents. These agents are: 131I-labeled Bromometronidazole, that has been shown to possess some of the antibiotic activity of metronidazole or Flagyl; and a Technetium 99m-penicillamine-Flagyl complex. A method of radioiodination has been devised which can be performed in radiopharmaceutical laboratories. Both radiopharmaceuticals are of very low toxicity. Distribution studies in animals show accumulation in the liver and elimination by way of the gallbladder. Scintillation camera studies depict a rapid uptake by the liver with subsequent biliary excretion. Animal models for the study of hepatic amebic abscesses are not available. A human patient with suspected amebic abscesses has been studied with negative findings that were confirmed at surgery. Collaborative studies are now in progress in several areas of the world where amebiases is endemic.

Ahmad-Strong synthesis of 8-, 9-, and 10-pentadecynoic acids

Three pentadecynoic acids, with the triple bond in the 8-, 9-, and 10-positions, have been synthesized on a gram scale in over-all yield of 65% by refinements of the five-step Ahmad-Strong method; isolation of intermediates was shown to be unnecessary prior to purification of the acetylenic nitriles by column chromatography on silicic acid. The melting points of the pentadecynoic acids alternate regularly and widely with position of unsaturation, in marked contrast to behavior of the homologous octadecynoic acids described by Huber.

Synthesis oftrans-3-hexadecenoic acid and oftrans-3-hexadecenoic-1-C14 acid

Thetrans-3-hexadecenoic acid has been synthesized. Physical properties and chemical degradation prove its identity with the acid earlier isolated from several plant lipids. In the sequence of the synthesis, the introduction of a terminal triple bond into commercially available 1-tetradecene was performed by bromination and debromination with KOH and NaNH(2). Chain elongation by a Grignard reaction with CO(2) gave a carboxylic acid with a triple bond in the 2-position. Reduction with LiAlH(4) yielded the corresponding alcohol, and reduction of the triple to thetrans double bond was accomplished with Na in ethanol. Bromination of the alcohol with PBr(3) and conversion of the bromide to the nitrile with KCN or KC(14)N elongated the carbon chain to the desired length. Methanolysis with HCl in methanol and saponification with KOH formed the acid with acceptable yields, and in the case of the C(14)-labeled carboxyl, group, with high specific activity.