The influence of hypertonic mannitol on regional myocardial blood flow during acute and chronic myocardial ischemia in anesthetized and awake intact dogs.

The influence of hypertonic mannitol on regional myocardial blood flow and ventricular performance was studied during acute myocardial ischemia in awake, unsedated and in anesthesized dogs and after myocardial infarction in awake unsedated dogs. Regional myocardial blood flow was measured with radioactive microspheres. Generalized increases in regional myocardial blood flow occurred after mannitol in all of the different animal models studied. The increases in coronary blood flow after mannitol were just as impressive in the nonischemic regions as in the ischemic portion of the left ventricle in all of the different models that were examined in this study. Improvement in regional myocardial blood flow to the ischemic area of the left ventricle after mannitol was associated with a reduction in ST segment elevation during acute myocardial ischemia in anesthetized dogs. The increases in regional myocardial flow after mannitol were also associated with increases in contractility, but the increases in flow appeared to be more impressive than the changes in contractility. The data obtained demonstrate that mannitol increases regional coronary blood flow to both ischemic and nonischemic myocardium in both anesthetized and awake, unsedated, intact dogs with acute and chronic myocardial ischemia and that mannitol reduces ST segment elevation during acute myocardial ischemia in anesthetized dogs. Thus the results suggest that under these circumstances the increases in regional myocardial blood flow after mannitol are of physiological importance in reducing the extent of myocardial injury. Since coronary blood flow increased to nonischemic regions the increases in regional myocardial flow demonstrated in this study after mannitol cannot be entirely explained by the mechanism of reduction in ischemic cell swelling.

Effects of a false neurotransmitter, p-hydroxynorephedrine, on the function of adrenergic neurons in hypertensive patients.

Previous studies have shown that amphetamine and p-hydroxyamphetamine impair adrenergic transmission, and it has been suggested that this effect is mediated by an active metabolite, p-hydroxynorephedrine (PHN). Studies in experimental animals have shown that PHN can deplete and substitute for norepinephrine (NE) in the transmitter pool, thus meeting the criteria of a false neurotransmitter. The pharmacologic effects of PHN on adrenergic function and NE synthesis were studied in eight hypertensive patients and compared with placebo. Mean erect and supine blood pressure (BP) decreased 22/14 and 9/6 mm Hg, respectively, during PHN 600 mg daily. The post-Valsalva diastolic overshoot was abolished. The pressor sensitivity to tyramine decreased whereas the pressor response to NE was enhanced. A mild natriuresis occurred. The 24 h urinary excretion of catecholamines and catecholamine metabolites during the administration of PHN compared with placebo changed as follows: vanillylmandelic acid (VMA), 42% decrease; NE. 42% decrease; normetanephrine (NM), 400% increase: metanephrine, unchanged; dopamine, 40% decrease; while homovanillic acid was unchanged. The sum of VMA, NE, and NM decreased 23%. The posttreatment urinary excretion of PHN was biexponential with first and second phase half-lives of 13 and 55 h. respectively. The time of the second phase closely approximated the recovery of the changes in BP and excretion of VMA. No effects of PHN on the central nervous system were observed. These studies show that PHN acts peripherally to interfere with adrenergic function and NE synthesis in hypertensive patients with a resultant decrease in BP.

Urinary prostaglandins. Identification and origin.

Human urine was analyzed by mass spectrometry for the presence of prostaglandins. Prostaglandin E2 and F2alpha were detected in urine from females by selected ion monitoring of the prostaglandin E2-methylester-methoxime bis-acetate and the prostaglandin F2alpha-methyl ester-Tris-trimethylsilylether derivative. Additional evidence for the presence of prostaglandin F2alpha was obtained by isolating from female urine an amount of this prostaglandin sufficient to yield a complete mass spectrum. The methods utilized permitted quantitative analysis. The origin of urinary prostaglandin was determined by stimulating renal prostaglandin synthesis by arachidonic acid or angiotensin infusion. Arachidonic acid, the precursor of prostaglandin E2, when infused into one renal artery of a dog led to a significant increase in the excretion rate of this prostaglandin. Similarly, infusion of angiotensin II amide led to a significantly increased ipsilateral excretion rate of prostaglandin E2 and F2a in spite of a simultaneous decrease in the creatinine clearance. In man, i.v. infusion of angiotensin also led to an increased urinary eliminiation of prostaglandin E. These results show that urinary prostaglandins may originate from the kidney, indicating that renally synthesized prostaglandins diffuse or are excreted into the tubule. Thus, urinary prostaglandins are a reflection of renal prostaglandin synthesis and have potential as a tool to delineate renal prostaglandin physiology and pathology.

A novel methodology for assignment of disulfide bond pairings in proteins.

A novel methodology is described for the assignment of disulfide bonds in proteins of known sequence. The denatured protein is subjected to limited reduction by tris(2-carboxyethyl)phosphine (TCEP) in pH 3.0 citrate buffer to produce a mixture of partially reduced protein isomers; the nascent sulfhydryls are immediately cyanylated by 1-cyano-4-dimethylamino-pyridinium tetrafluoroborate (CDAP) under the same buffered conditions. The cyanylated protein isomers, separated by and collected from reversed-phase HPLC, are subjected to cleavage of the peptide bonds on the N-terminal side of cyanylated cysteines in aqueous ammonia to form truncated peptides that are still linked by residual disulfide bonds. The remaining disulfide bonds are then completely reduced to give a mixture of peptides that can be mass mapped by MALDI-MS. The masses of the resulting peptide fragments are related to the location of the paired cysteines that had undergone reduction, cyanylation, and cleavage. A side reaction, beta-elimination, often accompanies cleavage and produces overlapped peptides that provide complementary confirmation for the assignment. This strategy minimizes disulfide bond scrambling and is simple, fast, and sensitive. The feasibility of the new approach is demonstrated in the analysis of model proteins that contain various disulfide bond linkages, including adjacent cysteines. Experimental conditions are optimized for protein partial reduction, sulfhydryl cyanylation, and chemical cleavage reactions.

Trapping of intermediates during the refolding of recombinant human epidermal growth factor (hEGF) by cyanylation, and subsequent structural elucidation by mass spectrometry.

Human epidermal growth factor (hEGF) contains 53 amino acids and three disulfide bonds. The unfolded, reduced hEGF is allowed to refold under mildly alkaline conditions. The folding is quenched at different time points by adjusting the pH to 3.0 with an acetic acid solution of 1-cyano-4-dimethylamino-pyridinium (CDAP) which traps folding intermediates via cyanylation of free sulfhydryl groups. The mixture of cyanylated intermediates is separated by reversed-phase HPLC; the fractions collected are identified by mass spectrometry. The disulfide structures of the intermediates are then determined by specific chemical cleavage and mass-mapping by MALDI-MS, a novel approach developed in our laboratory. The procedure of quenching and trapping of disulfide intermediates in acidic solution minimizes sulfhydryl-disulfide exchange, and therefore provides a good measure of folding kinetics and preservation of intermediate species. Our cyanylation methodology for disulfide mapping is simpler, faster, and more sensitive than the more conventional approach. Among 18 folding intermediates isolated and identified at different time points, disulfide structures of seven well-populated intermediates, including two non-native isomers with scrambled disulfide structures, one 2-disulfide intermediate, and four 1-disulfide intermediates, have been characterized; most of them possess non-native disulfide structures.

Preliminary studies of 6 beta-hydroxydexamethasone and its importance in the DST.

The role of the metabolites of dexamethasone (DEX) in the dexamethasone suppression test (DST) has never been fully elucidated. We report here our preliminary studies of 6 beta-hydroxydexamethasone (6 OH-Dex), a known metabolite of DEX, on the hypothalamic-pituitary-adrenal (HPA) axis of the rat; its activity in the most commonly used radioimmunoassay for plasma DEX; and its plasma concentrations in a normal human subject during the standard 1.0 mg DST. Six OH-Dex administered subcutaneously to rats at a dose of 1 mg/kg was able to completely suppress corticosterone production for at least 3 hr. In the IgG Corp. radioimmunoassay for plasma DEX, 6 OH-Dex was moderately cross-reactive yielding a 50% cross-reactivity of 10%. Gas chromatographic coupled mass spectroscopic analysis of human plasma samples, obtained 12 to 20 hr after the oral ingestion of 1.0 mg DEX, demonstrated similar plasma concentrations for both the parent compound and the 6-hydroxyl metabolite. The relevance of these findings, particularly to pharmacokinetic studies of the DST, is discussed.

Relation between plasma concentration of indomethacin and its effect on prostaglandin synthesis and platelet aggregation in man.

The dose and plasma levels of indomethacin correlated with inhibition of prostaglandin synthesis as measured both by urinary excretion of the major metabolite of prostaglandin E2 (PGE-M) and by the release of prostaglandin E2 from thrombin-stimulated platelets. Considerable intersubject variability was observed in the suppression of PGE-M excretion. In some patients 37.5 mg indomethacin daily, usually considered subtherapeutic, caused suppression. Maximal suppression (greater than 90%) occurred in some after a daily dose of 75 mg, whereas 150 mg was required to achieve this level of inhibition in others. Suppression of the excretion of PGE-M by 60% occurred when the end of the dosage interval plasma levels of indomethacin were in the range 0.05 to 0.3 microgram/ml, which implies that a somewhat higher average steady-state concentration during the dosage interval was required to achieve this effect. A similar degree of inhibition of the release of PGE2 on thrombin-stimulated platelets was associated with the same range of plasma levels. Upon discontinuation of the drug, the levels of indomethacin in plasma decreased exponentially; inhibition of the release of PGE2 from platelets by indomethacin declined linearly with time and in parallel with the logarithm of the diminishing plasma levels.

Gentisuric acid: metabolic formation in animals and identification as a metabolite of aspirin in man.

Gentisuric acid was synthesized from gentisic acid and glycine ethyl ester. NMR, mass spectrometric and elemental analysis confirmed the product as GU, and physicochemical characteristics were determined. A TLC-densitometric technique was developed to estimate GU and other metabolites of aspirin. Conjugation of gentisic acid with glycine to form GU was catalyzed by a mitochondrial fraction of rat and beef liver. GU was also formed by the rat liver microsomal hydroxylation of salicyluric acid, and phenobarbital pretreatment increased this formation. A random survey showed GU in 76% of SA-positive urines from aspirin-treated patients. Identity of GU in urine from two aspirin-treated patients was confirmed by TLC and mass spectrometric analysis, and hydrolysis of the compound from one patient yielded glycine and gentisic acid. Urine from controls or post-aspirin treatment patients did not show GU by TLC analysis. These results demonstrate for the first time the metabolic formation of GU in animals and its occurrence as a metabolite of aspirin in man.

Autoradiographic localization of nicotinic acetylcholine receptors in the brain of the zebra finch (Poephila guttata).

We have localized nicotinic acetylcholine receptors in the zebra finch brain by using three 125I-labelled ligands: alpha bungarotoxin and two monoclonal antibodies to neuronal nicotinic receptors (MAb 35 of Tzardos et al., J. Biol. Chem., 250: 8635-8645, '81; and MAb 270 of Whiting and Lindstrom: J. Neurosci. 6: 3061-3069, '86). Unfixed brains from intact adult male and female zebra finches were prepared for in vitro autoradiography. Low-resolution film autoradiograms and high-resolution emulsion autoradiograms were prepared for each of the three ligands. The major brain structures that bind all three of the ligands are hippocampus; hyperstriatum dorsalis; hyperstriatum ventralis; nucleus lentiformis mesencephali; nucleus pretectalis, some layers of the optic tectum; nucleus mesencephalicus lateralis; pars dorsalis; locus ceruleus; and all cranial motor nuclei except nucleus nervi hypoglossi. The major structures labelled only by [125I]-alpha bungarotoxin binding included hyperstriatum accessorium and the nuclei: preopticus medialis, medialis hypothalami posterioris, semilunaris, olivarius inferior, and the periventricular organ. Of the song control nuclei, nucleus magnocellularis of the anterior neostriatum; hyperstriatum ventralis, pars caudalis; nucleus intercollicularis; and nucleus hypoglossus were labelled. The binding patterns of the two antibodies were similar to one another but not identical. Both labelled nucleus spiriformis lateralis and nucleus geniculatus lateralis, pars ventralis especially heavily and also labelled the nucleus habenula medialis; nucleus subpretectalis; nucleus isthmi, pars magnocellularis; nucleus reticularis gigantocellularis; nucleus reticularis lateralis; nucleus tractus solitarii; nucleus vestibularis dorsolateralis; nucleus vestibularis lateralis; nucleus descendens nervi trigemini; and the deep cerebellar nuclei. Lobus parolfactorius and nucleus vestibularis medialis were labelled by only MAb 270, whereas only MAb 35 labelled nucleus laminaris and the medial and lateral pontine nuclei. These data extend previous reports of cholinergic participation in the song system (Ryan and Arnold: J. Comp. Neurol. 202: 211-219, '81) to suggest that the zebra finch song system may contain several closely related nicotinic receptors. In several brain nuclei it appeared that certain anatomical portions of a nucleus or a certain class of neurons were specifically labelled. Furthermore, in certain cases, the labelling appeared to be clustered around Nissl-stained cell nuclei, thus suggesting that the receptors are concentrated on or in somata.

Intraaortic balloon counterpulsation in patients in cardiogenic shock, medically refractory left ventricular failure and/or recurrent ventricular tachycardia.

Of the 27 patients described, 23 were in cardiogenic shock, 2 had severe left ventricular failure, and 2 had medically refractory ventricular tachycardia. Utilizing intraaortic counterpulsation, adequate systemic blood pressure was initially restored in 19 patients. Nine of these were subsequently weaned from circulatory assistance, but only three were discharged from the hospital and are currently alive. The remaining 10 patients who derived initial benefit from circulatory assistance were balloon-dependent in that they could not be weaned from circulatory assistance. Eight of these patients subsequently underwent cardiac catheterization; four had inoperable disease. The remaining four patients underwent surgery for either resection of the area of infarction and/or for myocardial revascularization; only one survived to subsequently leave the hospital. Ventricular volumes were abnormal and ejection fractions were below 30 per cent in all the patients in cardiogenic shock except one who underwent cardiac catheterization and ultimately died. Ejection fractions were greater than 30 per cent in the two patients with cardiogenic shock who were weaned from balloon support and survived to leave the hospital without surgery. Both of these patients had inferior myocardial infarction. The data obtained from this experience suggest that intraaortic counterpulsation is a very useful adjunct to currently existing medical measures to treat both cardiogenic shock and medically refractory left ventricular failure but that most patients have such extensive disease that they can neither be weaned from balloon support nor undergo successful infarctectomy or myocardial revascularization.

Axial lengths and refractive errors in kittens reared with an optically induced anisometropia.

An anisometropia was simulated in kittens during the critical period of development by securing a high-powered negative lens in front of one eye. Refractive error measurements obtained with an objective infrared optometer indicated that the deprived eyes of the anisometropic kittens were significantly more myopic than the normal eyes. A-scan ultrasonography showed that these differences in refractive error were correlated with an increase in the axial dimensions of the deprived eyes. The results of this experiment demonstrate that form deprivation associated with a habitually defocused retinal image produces an experimental myopia which is similar in nature to the refractive error changes produced by lid fusion and corneal opacification.

Effect of hypertonic mannitol and intraaortic counterpulsation on regional myocardial blood flow and ventricular performance in dogs during myocardial ischemia.

Studies were performed to determine if intervention with hypertonic mannitol and intraaortic balloon counterpulsation increases regional myocardial blood flow during acute myocardial ischemia. Anesthetized dogs on right heart bypass were studied. Heart rate was kept constant by atrial pacing. Myocardial ischemia was provided by ligating the proximal left anterior descending coronary artery for 12 minute periods. Infusion of hypertonic mannitol begun immediately after ligation increased coronary blood flow to the ischemic area by 36 +/- 9.0% (standard error) (P less than 0.01) and to the nonischemic left ventricle by 21 +/- 8.8% (P less than 0.05) as compared with flow in the same regions during the control coronary ligation. Intraaortic balloon counterpulsation begun immediately after ligation increased regional coronary flow to the ischemic region by 20 +/- 8.4% (P less than 0.05) but did not significantly alter flow to the nonischemic left ventricle as compared with levels during the control ligation. Combined intraaortic counterpulsation and hypertonic mannitol increased coronary flow to the ischemic region by 46 +/- 13% (P less than 0.02) and to the nonischemic left ventricle by 59 +/- 22% (P less than 0.05) as compared with flow during occlusion of the left anterior descending artery with mannitol alone. The data demonstrate that both hypertonic mannitol and intraaortic counterpulsation increase left ventricular ischemic regional flow and that combined hypertonic mannitol and intraaortic balloon counterpulsation provide a greater increase in regional coronary blood flow to both the ischemic and nonischemic regions of the left ventricle than mannitol alone.

Charge-remote fragmentation during FAB-CAD-B/E linked-scan mass spectrometry of aminoethyl-triphenylphosphonium derivatives of fatty acids.

The carboxyl group of fatty acids is derivatized by aminoethyl triphenylphosphonium (AETPP) bromide. Fast atom bombardment (FAB) collision-activated dissociation (CAD) B/E linked-scan mass spectrometry of these fixed-charge derivatives shows typical charge-remote fragmentation (CRF). Locations of various structural modifications in fatty acids can be recognized easily from CAD spectra of the AETPP derivatives. Because the triphenylphosphonium group localizes positive charge in the molecule, and because a key requirement for CRF is a tightly localized charge site, these preionized molecules fragment under FAB-CAD conditions more effectively than other derivatives that involve ionic bonding with metal cations or protonation of basic sites. Thus, CAD of AETPP derivatives is likely to produce more structurally informative spectra and provide an opportunity to gain additional under-standing of the CRF process. The most profound difference between the AETPP derivatives and other cations in positive mode FAB-CAD-B/E-MS is reflected in the substantial improvement of detection limits for the AETPP derivatives over those for the metal cation adducts. For several fatty acids (C10-C22) tested, the detectability can be enhanced by one to two orders of magnitude when the analysis is performed on the AETPP derivative. In addition, for the analysis of fatty acid mixtures, the FAB mass spectrum of AETPP derivatives produces a relative intensity of the molecular ion peak for each component of the mixture that more closely represents its mole fraction than does that of metal ion adducts.

Investigation of the tris(trimethoxyphenyl)phosphonium acetyl charged derivatives of peptides by electrospray ionization mass spectrometry and tandem mass spectrometry.

Charged derivatives of peptides are useful in obtaining simpler collision-activated dissociation (CAD) mass spectra. An N-terminal charge-derivatizing reagent capable of reacting with picomole levels of peptide has been recently reported (Huang et al. Anal. Chem. 1997, 69, 137-144) in the contexts of analyses by fast atom bombardment (FAB) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. Electrospray ionization (ESI) mass spectrometric investigation of these tris(trimethoxyphenylphosphonium) acetyl derivatives are described in this article, including studies by in-source fragmentation (ISF) and tandem mass spectrometry (MS/MS). Results from ISF are compared with those from MS/MS. Similarities and differences between ESI-ISF, MALDI-post-source decay (PSD), and FAB-CAD data are presented. Differences in fragmentation of these charged derivatives in the triple quadrupole and ion trap mass spectrometers also are discussed. Application of this derivatizing procedure to tryptic digests and subsequent analysis by liquid chromatography-mass spectrometry is also shown.

Mass spectrometric evidence for mechanisms of fragmentation of charge-derivatized peptides.

Mass spectrometry of charged derivatives of peptides has been a growing area of interest in the past decade. Fragmentation of charged derivatives of peptides is believed to be different from than that of protonated peptides when analyzed by collisionally activated dissociation-tandem mass spectrometry (CAD-MS/MS). The charged derivatives fragment by charge-remote fragmentation mechanisms, which are usually classified as high-energy (HE)-CAD processes. Our objective in the present study is to investigate the mechanism of fragmentation of charged derivatives of peptides when analyzed by matrix-assisted laser desorption/ionization-postsource decay-mass spectrometry (MALDI-PSD-MS) and electrospray ionization (ESI)-CAD-MS/MS (ion trap), which involve low-energy processes. Three major types of hydrogens (alpha, beta, and amide) are available for migration during the formation of the *a(n) ions (the predominant ion series produced from these charged derivatives). To pinpoint which of the three hydrogens is involved in the formation of the *a(n) ions, deuterium-labeled peptide derivatives with labels at specific sites were synthesized and analyzed by MALDI-PSD-MS and ESI-CAD-MS/MS. Our results suggest that the amide hydrogen of the residue at which the cleavage occurs shifts during the formation of *a(n); this observation serves as evidence for the mechanism proposed earlier by Liao et al. for fragmentation of such charged derivatives. The results also help elucidate the structure of the *a(n) ions, *b(n) ions, and others formed during cleavage at the proline residue, as well as the ions formed during loss of the C-terminal residue from these charged derivatives.

Selective detection of the tolyl cation among other [C7H 7] (+) isomers by ion/molecule reaction with dimethyl ether.

The ion/molecule reaction of the tolyl cation with dimethyl ether has been investigated using triple quadrupole mass spectrometry. Three isomers with [C7H7](+) composition, the 3-tolyl, benzyl, and tropylium cations, were individually selected and reacted with dimethyl ether at a pressure of 1 mtorr in the second quadrupole (Q2) collision cell. Only the tolyl ion reacted to yield a methoxylated product ion peak at m/z 122. This reaction product having m/z 122 is postulated to be identical in structure with the molecular ion of 3-methyl anisole, as supported by thermochemical data and the similarity of the collision induced dissociation (CID) daughter ion mass spectra of the product ion and the molecular ion of authentic 3-methyl anisole. The daughter ion mass spectra of the three [C7H7](+) isomers during CID, by using a triple quadrupole mass spectrometer, are nearly identical; on the other hand, the analytical approach based on the ion/molecule reaction with dimethyl ether clearly exhibits distinct gas-phase chemistry reflecting structural differences among the isomers. Sot.

Comparison of tandem and conventional mass spectrometry using electron capture negative ionization in the detection of chemically oxidized dexamethasone in human plasma.

Chemistry and Biochemistry, Michigan State University, East Lansing, Michigan, USA Dexamethasone, a synthetic steroid, can be oxidized chemically to a ketonic steroid structure that is readily detected by electron capture negative ionization mass spectrometry (ECNI/MS). Previous work from this laboratory has demonstrated that the chemical oxidation procedure provides advantages of low detection limits and high selectivity for detection of oxidized dexamethasone against chemical background that would otherwise interfere with detection of this steroidal drug in biological samples using more conventional methodology. This report describes the extent to which tandem mass spectrometry (MS/MS) can further enhance the selectivity of the oxidation/ECNI methodology for the detection of dexamethasone during the analysis of human plasma and presents evidence that sample introduction by direct inlet probe (DIP) can be used successfully under ECNI conditions. For purposes of comparing the methodologies, the same human plasma samples are analyzed by ECNI, first with detection by conventional mass spectrometry using selected ion monitoring (SIM) and then by MSIMS using selected reaction monitoring (SRM) with sample introduction by the gas chromatographic (GC) inlet and by the DIP. The results indicate that use of the DIP is a viable means of sample introduction for ECNI when sample processing involves the specialized oxidation procedure described herein because the sample matrix does not compete significantly for the thermal electrons in the ion source. Whereas SIM and SRM provide comparable results when sample introduction is achieved by the GC inlet, the MS/MS approach offers the possibility for sample introduction using the DIP, which significantly simplifies and shortens the analysis.

Quantitative assessment of cysteine and cystine in peptides and proteins following organomercurial derivatization and analysis by matrix-assisted laser desorption ionization mass spectrometry.

Protocols for the analysis of the sulfhydryl content in peptides and proteins using chemical derivatization by organomercurial reagents and analysis by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) have been developed. The number of reactive cysteine residues in peptides and proteins can be determined by exploiting the affinity and selectivity of organomercurial reagents for macromolecular thiols. Mass shifts observed in MALDI mass spectra obtained before and after cysteine derivatization with p-hydroxy-mercuribenzoate (pHMB) permit the number of free sulfhydryl groups to be determined. The pHMB derivative of each free cysteine residue provides a mass shift of 321 u, overcoming limitations in the mass resolution of MALDI time-of-flight mass spectrometry. Reactive cysteine residues in a macromolecule can be selectively derivatized by using a fivefold molar excess of pHMB reagent. Total sulfhydryl content (i.e., cysteine and cystine) can be determined after disulfide reduction. However, analyses for total cysteine content are more complex, requiring protein denaturation, cystine reduction, and sample purification before derivatization and analysis by MALDI-MS. Conditions for sample denaturation, alkyl-phosphine reduction, pHMB derivatization, and sample purification by analyte adsorption and desalting on protein transfer membranes, are described for cysteine/cystine analysis performed on microgram (10-200 pmol) quantities of somatostatin, insulin, hemoglobin, and ß-lactoglobulin.

A study of the gas-phase reaction between protonated acetaldehyde and methanol.

Protonated acetaldehyde is methylated on the oxygen during interaction with methanol in the gas phase. The ionic product of the iomnolecule reaction between methanol and protonated acetaldehyde is identical with C-protonated methylvinyl ether (high-pressure ionization), and with the (M - C2H5)(+) fragment ion of sec-butyl methyl ether (following electron ionization), and also with the (M - OCH3)(+) fragment ion of acetaldehyde dimethylacetal (following electron ionization). The structures of these ions and the mechanism of their formation were established by isotope-labeling experiments and collision-induced dissociation mass spectra of model compounds obtained with three different types of tandem mass spectrometers (BEQQ, triple-quadrupole, and a penta-quadrupole instrument). Gas phase synthesis of the product ion from [(2)H3]-methanol or [(2)H 4]-acetaldehyde provided insight into its mode of formation and collision-induced dissociation. (J Am Soc Mass Spectrom 1990, 1, 481-488).

Clinical temporary ventricular assist. Pathologic findings and their implications in a multi-institutional study of 41 patients.

Forty-one patients, distributed among four centers, had left (33 patients), right (five), or bilateral (three) temporary ventricular assistance with textured (24) or smooth (17) surfaced diaphragm pumps, during an evaluation supported by the National Institutes of Health. Cardiac failure had occurred in 39 postoperative patients (after aorta-coronary bypass [23], valve replacement [four], both [nine], or other [three]), with total cardiopulmonary bypass time mean 306 minutes (range 69 to 600). Two patients had cardiomyopathy. Death of 35 nonsurvivors was due to myocardial necrosis (14), hemorrhage (nine), cerebrovascular accidents (three), infection (three), and other (six). Mean duration of support in all patients was 62 hours. In 16 patients (40%) whose condition improved, cardiac assist duration was mean 127 hours (range 48 to 264), compared with mean 19 hours (range 1 to 120) in 25 who did not. Of 17 patients in whom duration of support exceeded 72 hours, 15 (88%) improved, 11 were weaned, and six survived long term. Tissue examination (in 33 patients) by biopsy at pump implantation or autopsy revealed coagulation or contraction band myocyte necrosis, with or without hemorrhage, in 26 patients; of these, 10 improved and six were long-term survivors. Pump-related complications (two) included pulmonary embolism, most likely related to a cannulation site thrombus, and an aortic cannulation site infection in one patient each. This study suggests that mechanical cardiac assist may be accomplished with a low complication rate; should not necessarily be denied to patients with existing necrosis, because myocardial necrosis does not preclude improvement or survival; and frequently leads to functional myocardial recovery if patients survive early noncardiac complications, often the result of long duration of cardiopulmonary bypass.