Biomedical subjects
Publications and source records attributed to R Mack.
A sequential staining protocol for revealing first G- and then R-bands on early metaphase chromosomes is presented. Lymphocyte cultures are synchronized with methotrexate, and released from the S-phase block with bromodeoxyuridine. The resulting early metaphase cells are initially G-banded with Wright's stain and then R-banded by the fluorescence plus Giemsa (FPG) technique.
Acute hemilabyrinthectomized tadpoles of the Southern Clawed Toad (Xenopus laevis), younger than stage 47 (about 6 days old), perform no static vestibulo-ocular reflex (Fig. 1). Older acute lesioned animals respond with compensatory movements of both eyes during static roll. Their threshold roll angle, however, depends on the developmental stage. For lesioned stages 60 to 64, it is 75 degrees while stage 52 to 56 tadpoles respond even during a lateral roll of 15 degrees (Figs. 1 and 2). Selective destruction of single macula and crista organs revealed that the static vestibulo-ocular reflex is evoked by excitation of the macula utriculi (Figs. 3 and 4) even in young tadpoles. The results demonstrate that bilateral projections of the vestibular apparatus must have developed at the time of occurrence of the static VOR, that during the first week of life the excitation of a single labyrinth is subthreshold (Fig. 1). We discuss the possibility whether the loss of the static VOR during the prometamorphic period of life (Fig. 2) is caused by increasing formation of multimodal connections in the vestibular pathway.
A yellow chromophore has been isolated from Avena coleoptiles grown in the dark. It had previously been shown by Zenk [Zenk, M. H. (1967) Z. Pflanzenphysiol. 56, 122 - 140] to be a flavin of still unidentified structure, and had been suggested to be the 'blue light' photoreceptor in this organism. The structure of this flavin (F1-X) has been identified as 5'-malonylriboflavin by a combination of physicochemical techniques, and by its identity with a sample obtained synthetically. The 5'-malonylester linkage is relatively labile towards hydrolysis and photolysis, it isomerizes to an equilibrium mixture containing probably the 4' isomer. The electronic spectra of 5'-malonylriboflavin (absorption and fluorescence) are practically identical to those of normal riboflavin (vitamin B2).
We utilized ultrasonic-dimension crystals in approximately 50 patients during a three-year period to evaluate clinical sonomicrometry as a routine monitoring tool in patients undergoing cardiac operations. Standard research piezoelectric pulse transit ultrasonic transducers were modified with a hooked attachment in a tethered configuration to facilitate accurate alignment and quick insertion for the measurement of myocardial segment length changes. These segment crystals were used both intraoperatively and postoperatively to evaluate the left ventricular pressure-geometry relationships and to serve as a continuous monitor of myocardial function. The left ventricular pressure-volume relationship was varied by temporarily reapproximating the pericardium (pericardial closure resulted in a 12% reduction in fractional shortening, a 5% decrease in end-diastolic segment length, and an 8% increase in pulmonary artery diastolic pressure). During both the intraoperative and postoperative periods, we found good correlation between thermodilution, stroke volume, and myocardial dimensions; no correlation was noted between pulmonary artery diastolic pressure and stroke volume. No bleeding or major complications resulted from the use of these sonomicrometry transducers. Our initial clinical experience with sonomicrometry seems to support its use as a potentially valuable monitoring tool.
In 86 children with acute lymphocytic leukemia (ALL) and in 6 children with medulloblastoma 253 24-hour methotrexate (MTX) infusions with 150, 500, and 700 mg/m2 were performed. MTX concentrations in plasma and cerebrospinal fluid (CSF) were measured with a specific radioimmunoassay. In 131 infusions with 500 mg/m2 given to patients with ALL in remission, the MTX plasma concentration 24 h after the end of infusion did not exceed 7 X 10(-7) mol/1. Mild hematologic toxicity occurred in 22% of the treatment cycles. In contrast 8/45 infusions given to patients with ALL in relapse were associated with delayed MTX elimination followed by severe toxicity. The CSF: plasma ratio of MTX measured during 58 infusions did not exceed 11% in patients with ALL in remission, but was above this value in 13/34 infusions in patients with leukemia of the central nervous system (CNS). 24-hour MTX infusions with 500 mg/m2 were as hepatotoxic as 4- to 6-hour infusions with 3-8.5 g/m2. With MTX as single agent no remissions were achieved in 8 patients with ALL in relapse. The addition of asparaginase in 10 patients resulted in 3 complete and 2 partial remissions. In patients with ALL in first remission clinical results confirmed the value of intensive MTX therapy for disease-free survival.
Two chronic animal models and one acute animal model were used to evaluate exchange transfusion with stroma-free hemoglobin solutions. A direct comparison was made between stroma-free hemoglobin solutions having differing oxygen offloading characteristics as well as a colloid solution consisting of 7% bovine albumin. These studies involved a partial exchange involving approximately 50% of the animal's blood volume to simulate a clinically more appropriate partial blood replacement situation. We noted a consistent increase in the arterial oxygen content of animals exchanged with the stroma-free hemoglobin solutions and some modest improvement in oxygen dynamics. Our studies examining myocardial contractility, especially those carried out in the right heart bypass swine preparation failed to substantiate any difference between an exchange with albumin or stroma-free hemoglobin solutions. The conscious animal models examined both at rest and at exercise demonstrated marked differences in exercise response. Animals exchanged transfused with stroma-free hemoglobin solutions often had an almost normal exercise response while those animals exchanged with non-oxygen carrying albumin solution frequently failed to exercise on a treadmill. Blood flow measurements using radiolabeled microspheres were performed in chronically instrumented swine. These animals had a normal variation in organ blood flow during exercise which was noted both during the control period as well as following exchange with stroma-free hemoglobin solutions. Animals exchanged transfused with albumin had a marked derangement in organ blood flow apparently reflecting the decreased oxygen availability. Results from these three studies substantiate a significant benefit to animals undergoing a 50% exchange when that exchange is done with an oxygen carrying solution such as stroma-free hemoglobin solutions as opposed to a non-oxygen carrying but oncotically active solution such as albumin solution. These studies seem to offer encouragement to the continued investigation and ultimate clinical utilization of hemoglobin solutions as an appropriate blood substitute.
A facility was established for long-duration ultraviolet (UV) radiation exposure of natural and synthetic materials in order to test hypotheses concerning Martian soil chemistry observed by the Viking Mars landers. The system utilized a 2500 watt xenon lamp as the radiation source, with the beam passing through a heat-dissipating water filter before impinging upon an exposure chamber containing the samples to be irradiated. The chamber was designed to allow for continuous tumbling of the samples, maintenance of temperatures below 0 degrees C during exposure, and monitoring of beam intensity. The facility also provided for sample preparation under a variety of atmospheric conditions, in addition to the Mars nominal. As many as 33 sealed sample ampules have been irradiated in a single exposure. Over 100 samples have been irradiated for approximately 100 to 700 h. The facility has performed well in providing continuous UV irradiation of multiple samples for long periods of time under simulated Mars atmospheric and thermal conditions.
The chemical reactivity of several minerals thought to be present in Martian fines is tested with respect to gases known in the Martian atmosphere. In these experiments, liquid water is excluded from the system, environmental temperatures are maintained below 0 degrees C, and the solar illumination spectrum is stimulated in the visible and UV using a Xenon arc lamp. Reactions are detected by mass spectrometric analysis of the gas phase over solid samples. No reactions were detected for Mars nominal gas over sulfates, nitrates, chloride, nontronite clay, or magnetitie. Oxidation was not observed for basaltic glass, nontronite, and magnetite. However, experiments incorporating SO2 gas--an expected product of volcanism and intrusive volatile release--gave positive results. Displacement of CO2 by SO2 occurred in all four carbonates tested. These reactions are catalyzed by irradiation with the solar simulator. A calcium nitrate hydrate released NO2 in the presence of SO2. These results have implications for cycling of atmospheric CO2, H2O, and N2 through the regolith.
A method for the quantitative determination of carbaryl insecticide by in situ densitometry was developed. After separation on silica gel thin layer plates, carbaryl residues were detected by using p-nitrobenzenediazonium fluoborate reagent and quantitated by scanning the resultant blue spots with a fiber optics densitometer and comparing them with standards. The method was applied to water fortified with carbaryl at 8 ppb and apples and lettuce fortified at 0.10 ppm; all recoveries were greater than 89%. The 2 crop extracts were cleaned up by using the AOAC thin layer chromatographic method for visual estimation of carbaryl. Related carbamate insecticides were detected by using the same reagent, and the potential for quantitation was demonstrated.
Untreated red cells of the Bombay variant Amh have traces of A. They are Le(b)-positive but H-negative. Following RDE-(Receptor destroying enzyme) treatment H is demonstrable by anti-HLa, -BHEe, and -HUe but not by anti-HLt. This type of reaction resembles that in O-newborns: H is present only in the form of a glycolipoid but not in the form of a mucoid. The barrier of neuraminic acid prevents recognition of H as his own. Anti-H is present. It has been shown that H as a precursor is necessary only for A1 but not for Am, A3, and A2.
A new type of self-retaining dry metal electrode for the electrocardiogram (ECG) is described which adheres to the skin by the application of negative pressure to an annulus surrounding the electrode, which is a bare silver. Data are presented for the factors which govern the adherence to the skin and the range of initial impedance and the values obtained at 2, 5, 10 and 20 minutes and with tap water under the electrodes. The initial impedance is usually high (0.18 to 10 megohms) and decreases progressively with time. Tap water placed under the electrodes dramatically reduces the initial range of impedance. Such electrodes, when used with an amplifier with an adequately high input impedance, can be used for recording electrocardiograms in a variety of situations.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
A crossover experimental design was used to examine the effects of saline (SAL) vs. taurocholate (TC) infusion on hepatic excretory function in isolated perfused livers from pregnant (19-21 days gestation) and nonpregnant female rats. Bile flow, bile acid concentration, bile acid secretory rate, dibromosulfophthalein (DBSP) concentration in bile, and DBSP secretory rates were determined in livers infused continuously with DBSP and initially with SAL (1 ml/hr, 45 min), followed by TC (60 mumol/hr, 1 ml/hr; 75 min) or initially with TC (45 min) followed by SAL (75 min). The order of infusion (SAL-TC vs. TC-SAL) had no significant effect. TC infusion significantly increased all measures in livers from both nonpregnant and pregnant rats. Two-way analysis of variance followed by the Tukey-Kramer test showed that bile flow (microliter/min/g liver) and DBSP concentration in bile (mumol/ml) were significantly decreased during SAL infusions in pregnancy. These two measures plus bile acid and DBSP secretory rates (nmol/min/g liver) were also significantly decreased during TC infusion in pregnancy. Pregnancy had no effect on bile acid concentration in the presence of SAL or TC infusions. When bile flow, bile acid, and DBSP secretory rates were calculated per whole liver, only the DBSP secretory rate was significantly decreased in pregnancy. These data indicate that bile flow and bile acid secretion do not increase in proportion to the increase in liver weight in pregnancy so that these measures are decreased when expressed per g liver. Pregnancy appears to have a real inhibitory effect on DBSP since its secretion is depressed when activity is expressed per g liver or per whole organ.