A simple mathematical model of the interaction between intracranial pressure and cerebral hemodynamics

Ursino, Mauro, and Carlo Alberto Lodi. A simplemathematical model of the interaction between intracranial pressure andcerebral hemodynamics. J. Appl.Physiol. 82(4): 1256-1269, 1997.A simplemathematical model of intracranial pressure (ICP) dynamics oriented toclinical practice is presented. It includes the hemodynamics of thearterial-arteriolar cerebrovascular bed, cerebrospinal fluid (CSF)production and reabsorption processes, the nonlinear pressure-volumerelationship of the craniospinal compartment, and a Starling resistormechanism for the cerebral veins. Moreover, arterioles are controlledby cerebral autoregulation mechanisms, which are simulated by means ofa time constant and a sigmoidal static characteristic. The model isused to simulate interactions between ICP, cerebral blood volume, andautoregulation. Three different related phenomena are analyzed: thegeneration of plateau waves, the effect of acute arterial hypotensionon ICP, and the role of cerebral hemodynamics during pressure-volume index (PVI) tests. Simulation results suggest the following:1) ICP dynamics may become unstablein patients with elevated CSF outflow resistance and decreasedintracranial compliance, provided cerebral autoregulation is efficient.Instability manifests itself with the occurrence of self-sustainedplateau waves. 2) Moderate acutearterial hypotension may have completely different effects on ICP,depending on the value of model parameters. If physiological compensatory mechanisms (CSF circulation and intracranial storage capacity) are efficient, acute hypotension has only negligible effectson ICP and cerebral blood flow (CBF). If these compensatory mechanismsare poor, even modest hypotension may induce a large transient increasein ICP and a significant transient reduction in CBF, with risks ofsecondary brain damage. 3) The ICPresponse to a bolus injection (PVI test) is sharply affected, viacerebral blood volume changes, by cerebral hemodynamics andautoregulation. We suggest that PVI tests may be used to extractinformation not only on intracranial compliance and CSF circulation,but also on the status of mechanisms controlling CBF.

     

Production of neosolaniol byFusarium tumidum

Extracts from autoclaved maize culture ofFusarium tumidum strain R-5823 were toxic towardsArtemia salina. Bioassay-guided fractionation of the organic extract led to the isolation of the toxic compound that was identified as the trichothecene toxin neosolaniol (NEOS) by¹H,¹³C nuclear magnetic resonance spectroscopy and low-resolution electronic impact mass spectrometry. The amount of NEOS produced by the strain R-5823 was 300 mg/kg maize culture. NEOS was also detected by HPLC in cultures of four out of seven additional strains ofF. tumidum andGibberella tumida with different origin, in amounts ranging from 1 to 311 mg/kg. This is the first report on the production of a trichothecene toxin byF. tumidum.     

Crystallization,characterization, and preliminary crystallographic studies of mitochondrial carbamoyl phosphate synthetase I of Rana catesbeiana

Carbamoyl phosphate synthetase I (ammonia; E C 6.3.4.16) was purified from the liver of Rana catesbeiana (bullfrog). Crystals of the protein have been obtained at 22°C by the hanging drop vapor diffusion technique, with polyethylene glycol as precipitant. Tetragonal crystals of about 0.3 × 0.3 × 0.7 mm diffract at room temperature to at least 3.5 Å using a conventional source and are stable to X-radiation for about 12 h. Therefore, these crystals are suitablefor high resolution studies. The space group is P4₁2₁2 (or its enantiomorph P4₃2₁2), with unit cell dimensions a = b = 291.6 Å and c = 189.4 Å. Density packing considerations areconsistent with the presence of 4-6 monomers (M_r of the monomer, 160,000) in the asymmetric unit. Amino-terminal sequence of the enzyme and of a chymotryptic fragment of 73.7 kDa containing the COOH-terminus has been obtained. The extensive sequence identity with rat and human carbamoyl phosphate synthetase I indicates the relevance for mammals of structural data obtained with the frog enzyme. © 1995 Wiley-Liss, Inc.     

Improved method for extraction of hydroperoxide lyase from Chorella

Summary Hydroperoxide lyase converts fatty acid hydroperoxides to oxo-fatty acids which, after further oxidation, are suitable for the synthesis of higher polyamides. An improved method utilizing an acetone powder step for isolation of this enzyme from the unicellular alga Chlorella was developed. Using this procedure a five fold increase in hydroperoxide lyase activity from Chlorella pyrenoidosa was obtained compared to previously used extraction methods. Other Chlorella species were assayed, and it was found that C. fusca also contained significant hydroperoxide lyase activity.     

Adenylate cyclase activity of membrane fractions isolated from sea urchin sperm

The adenylate cyclase activity of sperm membrane fragments isolated from Lytechinus pictus sperm according to Cross [20] has been studied. Two distinct fractions preferentially coming from the flagellar plasma membrane are obtained. Surface I¹²⁵-labeling experiments performed by Cross [20] indicate that these membranes are representative of the entire sperm plasma membrane. Both fractions are enriched in their adenylate cyclase activity: the specific activity of the top membranes is eightfold higher than in whole sperm, whereas that of the middle membranes is 15-fold higher. The cyclase seems to be associated with the membranes. Lytechinus pictus egg jelly has no effect or slightly inhibits the adenylate cyclase activity of the isolated sperm plasma membrane fragments. Mg⁺⁺ and Na⁺ stimulated their cyclase activity about sevenfold at 2.5 mM Mn⁺⁺ and 3.2 mM ATP. At this ATP to Mn⁺⁺ ratio, high concentrations of Ca⁺⁺ have a small stimulatory effect.     

An investigation on the effect of oligomycin on state-4 respiration in isolated rat-liver mitochondria

The inhibitory action of oligomycin on State-4 respiration in rat-liver mitochondria has been investigated in detail with regard to the extent, mode and characteristics of the inhibition. The possibility that this effect may be due either to some damage of the mitochondrial preparation used or to the presence of heavy contaminations by microsomes has been excluded. It has been found that the concentration of specific binding sites is the same in State 4 as in State 3. The extent of the inhibition appears to be related to the ADP concentration, rather than to $\text{ATP}\text{ADP}$ ratios. The inhibition of this antibiotic on State-4 respiration does not depend on the experimental conditions used (i.e., choice of substrates or composition of the reaction medium). In agreement with these observations, it has been found that the membrane potential of State 4 is significantly increased when oligomycin is added. All these results provide further evidence to the conclusion that a large portion of State-4 respiration is linked to phosphorylation.     

Structural and functional properties of rat liver mitochondria in hexachlorobenzene induced experimental porphyria

A possible link between changes in iron and porphyrin content in liver mitochondria, from rats treated with either hexachlorobenzene, iron, or hexachlorobenzene plus iron, as a function of treatment time and their structural-functional properties, has been investigated. Normal oxidative phosphorylation in mitochondria from rats treated with iron has been shown. By contrast a significant and constant uncoupling of the phosphorylative process, fully reversed by albumin, in mitochondria from rats treated with hexachlorobenzene and hexachlorobenzene plus iron has been presented. A possible involvement of pentachlorophenol in causing these abnormalities has been proposed.     

Involvement of thiol groups in the activity of phosphoenolpyruvate carboxylase from maize leaves

Purified maize leaf phosphoenolpyruvate carboxylase (EC 4.1.1.31) was completely inactivated by several thiol-modifying reagents, including, CuCl₂, CdCl₂ and N-ethylmaleimide. The inactivation by CuCl₂ could be reversed by dithiothreitol, suggesting the involvement of vicinal dithiols in the inactivation process.Complete inactivation of phosphoenolpyruvate carboxylase was correlated with the incorporation of two mol (³H)N-ethylmaleimide per 100-kilodalton subunit. The total protection of the enzyme against N-ethylmaleimide inactivation afforded by the substrate, phosphoenolpyruvate, was correlated with the protection of one mol (³H)N-ethylmaleimide reactive residue per mol subunit.The complete inactivation of phosphoenolpyruvate carboxylase by N-ethylmaleimide and the protection afforded by phosphoenolpyruvate against modification suggest the presence of an essential cysteine residue in the catalytic site of the C₄ leaf enzyme.Abbreviations PEP, phosphoenolpyruvate - Mops, 4-morpholinepropanesulphonic acid (Consejo Nacional de Investigaciones Científicas y Técnicas, Fundación M. Lillo y U.N. de Rosario).     

Microscopic anatomy of the ovary ofAlouatta caraya

The microscopic structure of theAlouatta caraya ovary is studied in different ages and reproductive stages. The most significant feature seems to be the presence in adult ovaries of abundant glandular interstitial tissue which occupies both the cortex and medulla. It seems to be derived from the theca interna of atretic follicles. Discrete luteinized masses are present in the medulla in all the ovaries observed. Invaginations of the surface epithelium are seen only in infant and juvenile ovaries. The development of cystic follicles seems to be a common pathway of atresia.     

The larval midgut of the cassava hornworm (Erinnyis ello)

Summary Columnar cells of the larval midgut of the cassava hornworm, Erinnyis ello, display microvilli with vesicles pinching off from their tips (anterior and middle midgut) or with a large number of double membrane spheres budding along their length (posterior midgut). Basal infoldings in columnar cells occur in a parallel array with many openings to the underlying space (posterior midgut) or are less organized with few openings (anterior and middle midgut). Goblet cells have a cavity, which is formed by invagination of the apical membrane and which occupies most of the cell (anterior and middle midgut) or only its upper part (posterior midgut). The infolded apical membrane shows modified microvilli, which sometimes (posterior midgut) or always (anterior and middle midgut) contain mitochondria. The cytoplasmic side of the membrane of the microvilli that contain mitochondria are studded with small particles. The results suggest that the anterior and middle region of the midgut absorbs water, whereas the posterior region secretes it. This results in a countercurrent flux of fluid, which is responsible for the enzyme recovery from undigested food before it is expelled. Intermediary and final digestion of food probably occur in the columnar cells under the action of plasma membrane-bound and glycocalix-associated enzymes.