Numerical simulation of thermal bone necrosis during cementation of femoral prostheses

The implant of a femoral prosthesis is a critical process because of the relatively high temperature values reached at the bone/cement interface during the cementation of the infibulum. In fact, the cement is actually a polymer that polymerizes in situ generating heat. Moreover, the conversion of monomer into polymer is never 100%; this is dangerous because of the toxicity of the monomer. In this paper, we present a 3-D axisymmetric mathematical model capable of taking into account both the geometry of the implant and the chemical/physical properties of the cement. This model, together with its numerical simulation, thus represents a useful tool to set up the optimal conditions for the new materials developed in this orthopaedic field. The real complex geometry is assumed to be a bone/cement/metallic system having cylindrical symmetry, thus allowing the model to be reduced to two space variables. The cementation process is described by the Fourier heat equation coupled with a suitable polymerization kinetics. The numerical approximation is accomplished by semi-implicit finite differences in time and finite elements in space with numerical quadrature. The full discrete scheme amounts to solve linear positive definite symmetric systems preceded by an elementwise algebraic computation. We present various numerical simulations which confirm some critical aspects of this orthopaedic fixing technique such as thermal bone necrosis and the presence of unreacted residual monomer.This work was partially supported by MURST (Fondi per la Ricerca Scientifica 40%) and CNR (IAN, Contract 880032601, and Progetto Finalizzato Sistemi Informatici e Calcolo Parallelo, Sottoprogetto Calcolo Scientifico per Grandi Sistemi) of Italy     

The effects of antibiotics on hemolytic behavior of red cells

Human blood was sheared between rotating polyethylene disks and plasma hemoglobin measured at intervals to produce kinetic hemolysis curves (KHC), plotted as free hemoglobin concentration vs time. The KHC produced by blood samples incubated in the presence of penicillin, streptomycin, gentamicin, and amikacin lie always below those for control samples, indicating a reduction in hemolysis; this reduction was greater as the drug concentration was increased. Explanations in terms of alterations in red cell structure were sought by several characterization tests of amikacin-loaded blood samples. Drug-localization studies demonstrated that significant fractions of the total dosage were associated with the red-cell membrane. Resistive pulse spectroscopy was used to show how amikacin affected cell size, deformability, and osmotic fragility; results were sensitive to storage age of the blood. In all cases, the effect of shearing was to reduce cell size, deformability, and osmotic fragility. Mechanisms for hemolytic protection by drugs are proposed.     

Carbonic acid as the host signal for the development of parasitic stages of nematodes

Petronijevic T., Rogers W. P. and Sommerville R. I. 1985. Carbonic acid as the host signal for the development of parasitic stages of nematodes. International Journal for Parasitology15: 661–667. This paper gives results on which may be based an identification of the component of the system CO₂ + H₂O ai H₂CO₃ ai H⁺ HCO₃^? which acts as the stimulus from the animal host for some nematodes. Using infective juveniles of Nematospiroides dubius and Haemonchus contortus, the effects on exsheathment of (1) low pCO₂ values, (2) the presence of carbonic anhydrase in the stimulating medium, and (3) the inhibition of carbonic anhydrase within the juveniles have been examined. The results lead to the suggestion that it is the “readily available” undissociated H₂CO₃, or H₂CO₃ + HCO₃^? which is the critical factor in the stimulus for development. The wide range of [H⁺]s over which “readily available” H₂CO₃ is present in physiological environments suggests that this host signal may be important for infection with many species.     

Various proteinase inhibitors decrease prolactin and growth hormone release by anterior pituitary cells

Proteinase inhibitors were tested for their ability to inhibit prolactin (PRL) and growth hormone (GH) release by cultured anterior pituitary cells of the rat. Inhibitors of microbial origin (chymostatin, elastatinal, leupeptin) had either no or a moderate effect on hormone release while some tripeptide aldehydes, especially those with lysine at their C terminus, inhibited markedly PRL and to a lesser extent GH release. Boc-DPhe-Phe-lysinal was the most effective on lactotrophs inhibiting PRL release more than 50% at 10(-4) M. The site(s) of action of tripeptide aldehydes remain to be elucidated.     

Deficiency of immunoreactive somatostatin in the median eminence of Snell dwarf mice

Snell dwarf mice (dw/dw) are characterized by a genetically determined, congenital lack of pituitary GH, TSH and prolactin. Given that hypothalamic somatostatin is involved in the regulation of pituitary GH and TSH release, it was decided to investigate the content of immunoreactive somatostatin (IRS) in the median eminence of dw/dw and phenotypically normal mice of the same strain. The content of IRS in the pyloric antrum and pineal gland of these animals was also examined. The effects of ovariectomy and of hyperprolactinemia (induced by a pituitary graft under the kidney capsule) on the median eminence content of IRS were also studied in both normal and dwarf mice. Median eminence IRS content was significantly lower in the dw/dw (23.6 +/- 1.8 ng) than in normal mice (57.4 +/- 7.1 ng); no difference was found in the pyloric IRS content of dw/dw (16.9 +/- 1.6 ng/mg of protein) and normal animals (13.8 +/- 1.9 ng/mg of protein), nor in the pineal content of IRS (639.4 +/- 64.4 pg/gland in the dw/dw; 732 +/- 265 pg/gland in normals). Neither ovariectomy nor hyperprolactinemia were found to affect the IRS content in the tissues studied in normal or dwarf mice. Treatment of an additional group of 9 dwarf mice with L-thyroxine (L-T4 2 micrograms/48 h. s.c. for 2 weeks) significantly increased the animals weight (10.2 +/- 0.4 g versus 7.4 +/- 0.3 g) and produced maturation of facial features; however, it did not change the IRS content in any of the tissues studied. It is concluded that the content of IRS in the median eminence of mice with a congenital lack of GH, TSH and prolactin is significantly reduced and that this is unlikely to be related to the deficiency of thyroid hormones in these animals.     

On the computation of the tertiary structure of globular proteins—IV. Use of secondary structure information

The distance geometry approach for computing the tertiary structure of globular proteins emphasized in this series of papers (Goelet al., J. theor. Biol. 99, 705–757, 1982) is developed further. This development includes incorporation of some secondary structure information—the location of alpha helices in the primary sequence—in the algorithm to compute the tertiary structure of alpha helical globular proteins. An algorithm is developed which estimates the interresidue distances between chain-proximate helices. These distances, in conjunction with the global statistical average distances obtainable from a database of real proteins and determined by the primary sequence of the protein under study, are used to determine the tertiary structure. Five proteins, parvalbumin, hemerythrin, human hemoglobin, lamprey hemoglobin, and sperm whale myoglobin, are investigated. The root mean square (RMS) errors between the calculated structures and those determined by X-ray diffraction range from 4.78 to 7.56 Å. These RMSs are 0.21–2.76 Å lower than those estimated without the secondary structure information. Contact maps and three-dimensional backbone representations also show considerable improvements with the introduction of secondary structure information.     

Restriction endonuclease EcoO109 from Escherichia coli H709c with heptanucleotide recognition site 5'-PuG/GNCCPy

A new restriction endonuclease, EcoO109, has been isolated from Escherichia coli H709c by polyethyleneimine (PEI) precipitation, DEAE-cellulose chromatography and heparin agarose chromatography. The yield was high, more than 3000 units/g of wet cells. The EcoO109 endonuclease recognizes and cleaves a nucleotide sequence of (formula: see text), in the presence of 10 mM Mg2+. The enzyme will be useful for structural analysis and molecular cloning of DNA because of the stability, high yield and easy handling of the producer strain.