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Biomedical subjects

R N Johnson

Publications and source records attributed to R N Johnson.

At least 127 records · Page 7Linked to original sources
PubMed1982

Serum myoglobin, creatine kinase and creatine kinase-MB as mutually supportive indices of myocardial infarction and infarct size.

A comparison was made between the appearance of serum myoglobin and creatine kinase in 22 patients with acute myocardial infarction who were admitted to a coronary-care unit within four hours of onset of chest pain. The MB isoenzyme of creatine kinase was measured in 12 patients. The more rapid appearance and disappearance of myoglobin relative to creatine kinase and creatine kinase-MB was confirmed, as was the correspondence between their respective peak values. A significant correlation was also obtained between the area under the myoglobin time-course and the respective peak levels. Whereas creatine kinase activity declined exponentially from a single peak, myoglobin appeared in multiple episodes inadequately represented by a single peak value and having no clear clinical correlation. The role of myoglobin as a diagnostic aid in myocardial infarction is probably limited to its ability to support creatine kinase and creatine kinase-MB as indices of infarct size.

Creatine Kinase↗
PubMed1981

Depletion of myocardial creatine kinase, lactate dehydrogenase, myoglobin and K+ after coronary artery ligation in dogs.

In order to compare the time-course of disappearance of macromolecules and electrolytes from ischaemic myocardium, measurements of creatine kinase and lactate dehydrogenase activity and myoglobin, K+ and Na+ concentration were made on myocardial extracts from dogs which had left anterior descending coronary artery ligation for 3, 6, 12 and 24 h (4 groups of 6 dogs each). Intensity of ischaemia was assessed by myocardial blood flow measured with 15+/- 5 micrometers microspheres at 15 min after ligation. Creatine kinase and lactate dehydrogenase activities and K+/Na+ concentration ratios were at all times correlated with the magnitude of collateral blood flow in the ischaemic myocardium, while myoglobin concentration was correlated with blood flow only at 12 and 24h. Comparisons of the intensity of depletion at the various times after ligation showed that K+, K+/Na+ and creatine kinase had all reached a steady state at 12 h after ligation while lactate dehydrogenase and myoglobin had still to reach a steady state at 24 h. We conclude that these indices are mutually supportive markers of the intensity of ischaemia of 24 h duration, but K+ or K+/Na+ may be the most reliable indices for shorter periods of ischaemia of 3 to 6 h duration.

Animals↗
PubMed1981

Gas-solid chromatographic determination of oxygen in various pharmaceutical products.

A method is described for the gas chromatographic determination of oxygen at the low part per million level in both aqueous systems and nonaqueous systems such as creams, oils, and waxes. This method offers advantages over other popular assay procedures such as the Winkler and polarographic methods. The purging technique developed can be applied to any liquid or solid with a melting point of 75 degrees C or less. Oxygen purged from the sample is passed through a molecular sieve 5A column where it is separated from nitrogen. Peaks obtained are compared to similarly prepared oxygen standards. The method is simple enough to be used routinely and up to 15 samples can be analyzed per day.

Chromatography, Gas↗
PubMed1980

Visual evoked potentials to stimulus trains: normative data and application to photosensitive seizures.

Visual evoked potentials (VEPs) to intermittent flash trains of various stimulus frequencies (VEP-T) were studied in 10 normal subjects and in 10 patients with photosensitive generalized seizures, 5 on medication and another 5 subjects without medication. In the normal group, early negative peaks were consistently demonstrated at 71 +/- 8 msec for monocular stimuli and 67 +/- 9 msec for binocular stimuli, regardless of different frequencies of stimuli. An oscillatory potential, poststimulus continuation of the oscillatory activity and damping out within 100 msec followed the initial peaks. The RMS values of the response epochs were stable and demonstrated consistent temporal changes at each stimulation frequency. In photoconvulsive seizures, the responses were facilitated with most marked changes over the second and third 125 msec epoch of the VEP-Ts with late slow negative deflections in some cases. These changes were pronounced in patients who were not taking anticonvulsant medication, but were not significantly different than controls in patients whose seizures were controlled with medication. It is suggested that the VEP-T is a more effective technique than single flash stimuli in consistently identifying early significant peaks and demonstrating neuronal excitability changes within the visual system.

Adolescent↗
PubMed1980

A multivariable evoked potential measure applied to human epilepsy.

Based upon a three-dimensional plot (response plane) representing a condensation of human sensory evoked potential data obtained from a paired stimulus protocol, a study was undertaken to investigate electrophysiological changes following sodium valproate administration in subjects with photosensitive epilepsy. Initial results in two patients and two normal subjects suggest that the measure is reproducible and sensitive to electrophysiological changes accompanying anticonvulsant administration.

Adult↗
PubMed1979

Conjugated estrogens bioinequivalence: comparison of four products in postmenopausal women.

The bioequivalence of four conjugated estrogens tablets USP was compared by measurement of seven estrogens or estrogen metabolites in the urine during steady-state dosing in postmenopausal women. Two studies compared three generic products with the innovator's product. The urinary excretion of 17 alpha-dihydroequilin, 17 alpha-dihydroequilenin, and 17 alpha-estradiol were significantly greater in all cases with the innovator's product than with the generic products. Statistically significant differences between products were observed occasionally for other components. The generic products thus were bioinequivalent to the innovator's product, although all products essentially met current compendial specifications. A third study observed no significant differences between three batches of the innovator's product for the seven components. Total conjugated estrogens excretion of all products at the steady state was essentially equal and correlated with neither disintegration time nor dissolution half-time. Bioinequivalence between products is discussed in relation to the need for an improved USP conjugated estrogens monograph. Evidence suggesting the metabolism of a fraction of dosed estrone, equilin, and 17 alpha-dihydroequilin to 17 beta-estradiol, 17 beta-dihydorequilim, and 17 alpha-dihydroequilenin, respectively, is presented.

Biological Availability↗
PubMed1979

Cerebellar stimulation: regional effects on a thalamocortical system.

Regional effects of electrical stimulation of the cerebellar surface were quantitatively analyzed. Computer controlled stimulus sequences were delivered to ventrolateral thalamus and evoked responses recorded from ipsilateral sensorimotor cortex in the cat. Threshold and excitability profiles were produced with an on-line computer, and their modification by cerebellar stimulation was determined. The results of electrical stimulation of the cerebellar surface were: (1) depressed excitability from paramedian lobule and lobulus simplex; (2) uniquely elevated thresholds from paramedian lobule; and (3) a profound and long-lasting depression of excitability following termination of lobulus simplex stimulation. In comparison with our anticonvulsant drug studies, these data suggest that cerebellar surface stimulation has a far greater capacity to control excitability and threshold responsiveness of thalamocortical systems. Cerebellar electrode placement and temporal pattern of stimulation appear to be important factors in the production of antiepileptic effects.

Animals↗
PubMed1979

Effects of valproate and ethosuximide on thalamocortical excitability.

Sodium valproate and ethosuximide are anticonvulsants employed in the treatment of petit mal epilepsy; both drugs are considered to be thalamically active. Valproate and ethosuximide both decreased the average evoked response following the second of two stimuli delivered to the ventrolateral thalamus at stimulus frequencies in the region of 3 Hz. Ethosuximide, but not valproate, enhanced the average evoked response at high stimulus frequencies an action shared with several convulsant treatments having different modes of action. The clinical effects of valproate and ethosuximide can be related to this differential modulation of thalamocortical excitability.

Animals↗
PubMed1979

Clearance of macromolecular and particulate substances from the cerebrospinal fluid system of the rat.

Arachnoid villi in the intracranial dural sinuses constitute the principal sites for absorption of proteins and particulates from the cerebrospinal fluid (CSF) system. Although arachnoid villi in the rat are morphologically less complex than those found in other mammals, their resistance to CSF outflow, as assessed by a graded series of contstant flow manometric infusions, is similar to that found in other species. Moreover, inulin and polystyrene beads, when infused into the spinal subarachnoid space of rats, are rapidly cleared from the CSF system into intracranial dural sinuses. Inulin appeared in sinus blood 3 minutes after onset of infusion and reached concentrations 26 times greater than those found in the systemic circulation; particulate matter in the form of 0.5 micrometer polystyrene beads showed similar efflux characteristics. Hence, the CSF system of the rat is functionally similar to that found in other mammalian species, with arachnoid villi constituting a major efflux route for clearance of macromolecular and particulate substances.

Absorption↗
PubMed1979

Gas-solid chromatographic determination of moisture in lyophilized pharmaceutical products.

A gas-solid chromatographic procedure is described for the analysis of low levels of moisture in individual lyophilized vials of pharmaceutical products. Dry ethanol, which contains methanol as the internal standard, is injected through the septum of the vial to dissolve the lyophilized contents. An aliquot of this solution is then withdrawn and injected onto a Porapak QS column at 110 degrees C where the components are separated and detected using thermal conductivity detection. A solvent blank correction allows quantitation of the water in the individual vial. The method is conveniently applied to samples containing as little as 50 microgram water/vial, and as many as 25 vials can be assayed/day. A simple technique is also described for removing water from the ethanol solvent to less than 100 ppm, using a molecular sieve.

Chromatography, Gas↗
PubMed1978

The uptake of silicic acid by rat liver mitochondria.

1. To gain insight into a putative role for mitochondria in silicon metabolism, mitochondrial uptake (by which it is meant the removal from the medium) of silicic acid [Si(OH)4] was studied under conditions minimizing SI(OH)4 polymerization. 2. Measurements of mitochondrial respiration and swelling indicated indirectly a significant uptake of Si(OH)4 as a weak acid, but this was not confirmed when 31Si(OH)4 was used as a tracer. 31Si(OH)4 occupied a mitochondrial volume similar to that of 3H2O and was relatively unaffected by mitochondrial energy status and by the pH gradient across the mitochondrial inner membrane. 3. Uptake was directly proportional to Si(OH)4 concentration in the range 0-3 mM. 4. The uptake consisted of two components: under all conditions examined, the greater quantity, amounting to 1-2nmol of Si(OH)4/mg of mitochondrial protein, was bound, a major portion of it external to the inner membrane, with the lesser quantity free within the matrix space. 5. Equilibration of 31Si(OH)4 between medium and matrix was a slow process, having a half-time of approx. 10 min at 22 degrees C. 6. Mersalyl and N-ethylmaleimide inhibited the uptake by preferentially lowering the amount of Si(OH)4 bound. Their action was somewhat variable, depending on the precise nature of the suspending medium, and suggesting that the bound material may represent polymerized forms of Si(OH)4. 7. It is concluded that Si(OH)4 may penetrate the mitochondrial inner membrane by a simple diffusion mechanism.

Animals↗