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L S Hibbard

Publications and source records attributed to L S Hibbard.

26 records · Page 2Linked to original sources
PubMed1984

Regional cerebral glucose utilization during Althesin anesthesia.

The effect of Althesin, an anesthetic comprising two steroids, on regional cerebral function was determined by measurement of regional cerebral glucose utilization. Rats were anesthetized with an intravenous dose of 4, 8, or 20 mg total steroid/kg. These doses produced anesthesia for 12, 18, and 37 min, respectively. There were no physiologically significant effects of Althesin (20 mg/kg) on body temperature, blood pH, or blood gases. Blood pressure and heart rate decreased slightly after administration of Althesin. Althesin had a profound effect on glucose consumption in many, but not all, cerebral structures. The forebrain (especially cerebral cortex) was affected most, while the hindbrain was much less so or not at all. This pattern of functional depression is in accord with the minimal effects observed on physiologic variables. The effects of Althesin differ from those of other known anesthetics and suggest a unique mechanism. The possibility of action through naturally occurring steroid receptors is considered.

Alfaxalone Alfadolone Mixture↗
PubMed1984

Three-dimensional reconstruction of metabolic data from quantitative autoradiography of rat brain.

Quantitative autoradiography is a powerful method for studying brain function by the determination of blood flow, glucose utilization, or transport of essential nutrients. Autoradiographic images contain vast amounts of potentially useful information, but conventional analyses can practically sample the data at only a small number of points arbitrarily chosen by the experimenter to represent discrete brain structures. To use image data more fully, computer methods for its acquisition, storage, quantitative analysis, and display are required. We have developed a system of computer programs that performs these tasks and has the following features: 1) editing and analysis of single images using interactive graphics, 2) an automatic image alignment algorithm that places images in register with one another using only the mathematical properties of the images themselves, 3) the calculation of mean images from equivalent images in different experimental serial image sets, 4) the calculation of difference images (e.g., experiment-minus-control) with the option to display only differences estimated to be statistically significant, and 5) the display of serial image metabolic maps reconstructed in three dimensions using a high-speed computer graphics system.

Alfaxalone Alfadolone Mixture↗
PubMed1983

Glucose availability to individual cerebral structures is correlated to glucose metabolism.

Regional cerebral glucose influx was measured using quantitative autoradiography after the intravenous infusion of [2-14C]glucose for a period of 10 or 20 s. Glucose influx varied considerably among structures over an almost threefold range. When compared with rates of regional glucose utilization, a significant correlation by region was found between glucose influx and utilization, demonstrating that the glucose supply to individual cerebral structures is closely matched to their metabolic needs.

Animals↗
PubMed1982

Progressive development of a thrombin inhibitor binding site.

The studies reported here were undertaken to determine whether the thrombin precursors prothrombin, prethrombin 1, prethrombin 2, and Meizo thrombin interact with the fluorescent, reversible thrombin inhibitor dansylarginine N,N-(3-ethyl-1,5-pentanediyl)amide (DAPA) [Nesheim, M. E., Prendergast, F. G., & Mann, K. G. (1979) Biochemistry 18, 996--1003]. The results indicate that prothrombin and prethrombin 1, in which the cleavage sites at Arg274-Thr275 and Arg323-Ile324 both remain intact, do not bind DAPA, while prethrombin 2 or Meizo thrombin, which results respectively from a single cleavage of prothrombin at Arg274-Thr275 or Arg323-Ile324, do bind the inhibitor. Since prethrombin 2 is a precursor of thrombin without measurable enzymatic activity, a thorough characterization of its interaction with DAPA was undertaken. The interaction of DAPA with bovine thrombin similarly was studied for comparative purposes. The binding of DAPA to either protein is accompanied by changes in the fluorescence properties of the dansyl moiety including increases in emission intensity, excited-state lifetime, polarization, and a slight blue shift in the wavelength of maximum emission intensity. Corrected excitation spectra indicate energy transfer to DAPA from one or more aromatic side chains of both proteins. Values of P0 for both complexes were extrapolated from Perrin plots of polarization vs. temperature and suggest that the dansyl moiety is held more rigidly in thrombin than in prethrombin 2. With excitation at either 280 or 335 nm the emission intensity of DAPA-prethrombin 2 is substantially less than that of the DAPA-thrombin complex. In contrast, the intensity of the Meizo thrombin-DAPA complex is greater than that of the DAPA-thrombin complex. From measurements of intensity changes the dissociation constants and stoichiometry of DAPA binding to thrombin and prethrombin 2 were measured. Prethrombin 2 binds to DAPA with a Kd = 5.9 x 10(-7) M (n = 1) while thrombin binds about 30 times more tightly with a Kd = 2.0 x 10(-8) M (n = 1). The active site directed irreversible thrombin inhibitors diisopropyl phosphorofluoridate and D-phenylalanylprolylarginyl chloromethyl ketone displace DAPA from thrombin but not from prethrombin 2. The results of these studies indicate the binding of a presumed substrate analogue (DAPA) to an inactive zymogen, prethrombin 2. In addition, the lack of DAPA binding to prothrombin and prethrombin 1, under conditions in which it binds to prethrombin 2, implicates events that accompany cleavage at Arg274-Arg275 in the "progressive" formation of an active site, even though further cleavage at Arg323-Ile324 is required for expression of enzymatic activity.

Animals↗
PubMed1981

Isolation of functional human coagulation factor V by using a hybridoma antibody.

Spleen cells obtained from mice immunized with partially purified human coagulation Factor V were fused with NS-1 mouse myeloma cells, and hybrids were selected. Culture media were screened for anti-Factor V activity, and an antibody-positive clone was obtained and passaged as an ascites tumor in mice. The ascitic fluid from the hybridoma-bearing mouse could be diluted 1:10(6) before losing reactivity in an anti-Factor V radioimmunoassay. When immobilized on agarose, the monoclonal antibody quantitatively removed Factor V activity from human plasma. Factor V activity could be eluted with 1.2 M NaCl at pH 6.5. Homogeneous Factor V was isolated by chromatography of barium citrate-adsorbed, polyethylene glycol 6000 precipitated plasma on the antibody column followed by chromatography on phenyl-Sepharose. The isolated Factor V exhibited a single band upon gel electrophoresis in sodium dodecyl sulfate with an apparent Mr comparable to that of bovine Factor V (330,000). Upon exposure to thrombin, the activity of Factor V increased 53-fold when measured in Factor V-deficient plasma. This increased activity was associated with discrete proteolytic cleavages of the parent molecule.

Animals↗
PubMed1980

The calcium-binding properties of bovine factor V.

The calcium-binding properties of the coagulation cofactor, Factor V, have been investigated using atomic absorption spectrophotometry, equilibrium dialysis, and chemical exchange experiments. Two classes of binding sites have been observed: one site containing a single Ca2+ ion bound with an unusually high affinity (Kd less than 10(-8) M), and a second site in which 2 mol of calcium are bound/mol of Factor V with an association constant Ka = 1.7 +/- 0.52 x 10(4) M-1 (Kd = 5.9 +/- 1.9 x 10(-5) M). The binding of the dissociable Ca2+ ions is apparently noncooperative. The single high affinity Ca2+ ion may be removed readily by EDTA under native conditions with an immediate loss of Factor V activity, and the activity of the Factor V can be restored by the addition of a molar excess of calcium. The high affinity Ca2+ ion will exchange with radiolabeled calcium in solution, and Factor V labeled in this way was used to provide an independent measure of the stoichiometry of this high affinity binding site, and to observe directly the interaction of calcium in this site with EDTA. In addition, elemental analyses of solid lyophilized samples of Factor V revealed that no transition metals are present and that no phosphorus (or phospholipid) is retained by the Factor V after purification.

Animals↗
PubMed1978

Expression of functionality of alpha-chymotrypsin. Effects of guanidine hydrochloride and urea in the onset of denaturation.

Crystals of alpha-chymotrypsin (CHT) at equilibrium in solutions of 2.0 M guanidine hydrochloride and 3.0 M urea at pH 3.6 were prepared, three-dimensional X-ray intensities were measured, and difference electron-density maps were calculated and examined. The guanidine hydrochloride derivative displayed changes occurring exclusively on the surface of the protein. The difference peaks represented mostly small changes in various protein surface groups and in the adjacent solvent regions, and some displayed convincing evidence of binding of the guanidinium ion to the protein. The urea difference map likewise showed that changes had occurred on the surface of the protein, but also that numerous changes in the structure occurred in the hydrophobic interior of the CHT molecule. Further, the urea difference map contained evidence for two kinds of interactions of urea with protein groups. There are examples of bound urea either causing or accompanying structural changes and examples of urea binding with no accompanying changes to the protein. Examples of both kinds of binding were observed in both the surface regions and in the hydrophobic interior of the molecule. From an examination of these two derivatives, it is clear that guanidine hydrochloride and urea unfold proteins by different mechanisms.

Chymotrypsin↗