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Biomedical subjects

W Hoffman

Publications and source records attributed to W Hoffman.

At least 55 records · Page 3Linked to original sources
PubMed1984

Structure of Limulus and other invertebrate thick filaments.

We have demonstrated remarkable similarity among the skeletal muscles of chelicerate arthropods with respect to the cross-bridge arrangement on the surface of their thick filaments. The latter, gently isolated from the muscles of three representative species (Limulus telson , tarantula leg and scorpion leg and tail) have been examined by electron microscopy and optical diffraction using both negatively stained and unidirectionally metal shadowed preparations. The filaments are highly periodic and produce clear and detailed diffraction patterns. The cross-bridge projections form integral surface helices, with an axial spacing of 14.5 nm between adjacent crowns and a major axial repeat every 43.5 nm. We have demonstrated previously that Limulus filaments are four-stranded and analysis of both electron micrographs and their transforms, as well as optical reconstructions of the arachnid filaments is consistent with their also having a four-start surface helix, which is right-handed in all cases. Of all those examined, thus far, only Limulus thick filaments have been demonstrated to change length under various conditions. Shortened Limulus filaments isolated from K+-stimulated fibers retain the 43.5 nm axial repeat periodicity and 14.5 nm axial spacing between crowns. In preliminary analysis of negatively stained and metal shadowed preparations, we see no systematic change with respect to screw or rotational symmetry in short as compared with long filaments. A few of the former have a very slightly increased diameter (3-4 nm) in the middle of each filament arm. This region often shows disorder on optical transforms. From our results we cannot rule out the possibility that disaggregation and reaggregation of thick filament proteins accompany the changes in length of Limulus thick filaments.

Animals↗
PubMed1984

Hyperglycemia and hypoinsulinemia during xylazine-ketamine anesthesia in Thoroughbred horses.

Plasma glucose and serum insulin concentrations in Thoroughbreds administered xylazine hydrochloride (1.1 mg/kg; IV) and ketamine hydrochloride (2.2 mg/kg; IV) at dosages sufficient to induce short periods of recumbency and anesthesia were measured. Samples of blood were collected from 6 adult horses before, during, and after the anesthetic period. Plasma glucose (mg/dl) was significantly increased above control (-30 minute concentration) from 15 to 150 minutes after xylazine administration with the peak value occurring at 30 minutes. Serum insulin (microU/ml) was significantly decreased from control from 5 to 90 minutes after xylazine administration, with the nadir occurring at 15 minutes. The alterations in plasma glucose and serum insulin concentrations in xylazine-ketamine-anesthetized horses were similar to the changes in xylazine-sedated horses.

Anesthesia↗
PubMed1983

Proteinase inhibitory assays of serum using high-performance size exclusion chromatography.

A size exclusion column (Spherogel TSK-2000 SW) was utilized in a high-performance size exclusion chromatographic assay to determine the proteinase inhibitory capacity of human sera. Values from assays using this technique agreed well with the standard spectrophotometric inhibitory assays. Nanogram to milligram amounts of protein, namely, alpha 1-proteinase inhibitor, elastase, trypsin, chymotrypsin and their corresponding complexes with the inhibitor, were fractionated in less than 15 min. The nitrated or oxidized alpha 1-proteinase inhibitor was shown to retain its ability to form stable complexes with trypsin or chymotrypsin; however, they lost the inhibitory activity against elastase and instead they behaved as common protein substrates for this enzyme. The present chromatographic procedure was unable to detect any peptide released when the native inhibitor and any of the proteinases reacted to form a complex. Moreover, dissociation of the alpha 1-proteinase inhibitor--elastase complex in an alkaline pH did not result in the formation or release of any peptide.

Chromatography, Gel↗
PubMed1982

Large edentulous ridges--are they better for dentures than small ridges?

A method was described for measuring not only the area of the basal seat of an edentulous ridge but also the bearing area, stabilizing area, and the areas shared. A definition for small, medium, and large edentulous ridges was provided. Correlations between the basal seat, stabilizing area, and the shared areas were computed. A high positive correlation was found between the area of the basal seat and that of the stabilizing areas. Contrary to what was expected, no correlation was found between the area of the basal seat and that of the bearing areas of the small to large categories.

Denture Bases↗
PubMed1978

Subjective Lorentz transformations and the perception of motion.

It has been known for some 40 years that the perceived velocity of a moving object does not correspond to its physical velocity. It is also known that the perceived length and temporal duration of a moving objects is affected by its physical velocity. In this paper it is argued that such phenomenal distortions can be embedded in a model for motion perception that involves the concepts of moving frames, Lorentz transformations, perceived length contractions, and time dilations. Experimental results support this model and indicate that c, the maximum perceivable velocity of movement, plays a crucial role in determining motion effects.

Humans↗
PubMed1978

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PubMed1978

Pharmacokinetics of BCNU in man: a preliminary study of 20 patients.

Using the technique of direct sample insertion selected ion monitoring chemical ionization mass spectroscopy, BCNU levels were measured in vivo in patients and in vitro in serum, sera ultrafiltrates, and buffered Ringer's solution. The disappearance of BCNU in vitro was found to be first-order with a half-time of 11.6 minutes (+/- 0.5 SD) in volunteers and 15.6 minutes (+/- 2.3 SD) in patients. The disappearance from serum was catalyzed by a macromolecular component of the serum and was slowed by serum lipids. Analysis of the pharmacokinetics of BCNU in 20 patients using a two-compartment open model demonstrated a volume of distribution of 3.25 liters/kg (+/- 1.69 SD), a clearance of 56 ml/minute/kg (+/- 56 SD), and a transfer constant from the central compartment to the outside (K10) OF 0.0324 MINUTE-1 (+/- 41% SD), which was close to the decomposition rate observed for BCNU in serum in vitro. The pharmacokinetics of BCNU in patients may be affected by the percent of body fat and the lipid content of the serum.

Body Composition↗