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Biomedical subjects

R C Thompson

Publications and source records attributed to R C Thompson.

At least 415 records · Page 23Linked to original sources
PubMed1977

Fat-cell changes as a mechanism of avascular necrosis of the femoral head in cortisone-treated rabbits.

Large doses of cortisone were given to growing and adult rabbits over a five-month period to produce avascular necrosis of the femoral head. The cortisone caused an increase in the serum cholesterol, fatty metamorphosis of the liver, and fat emboli visible in sections of the femur and humerus. These emboli partially obliterated the microcirculation of the subchondral vessels of both femoral and humeral heads. The average diameter of the marrow fat cells also increased more than ten micrometers. This increase in cell volume might be significant because in the closed chamber of the femoral head it could increase tissue pressure, diminish perfusion, and be the mechanism for avascular necrosis induced by cortisone.

Animals↗
PubMed1976

The development of brood capsules and protoscolices in secondary hydatid cysts of Echinococcus granulosus. A histological study.

Using the Mongolian jird (Meriones unguiculatus) as a laboratory host for the cystic stage of the British horse strain of Echinococcus granulosus, the mode of development of brood capsules and protoscolices was studied histologically. The successive stages in development in secondary hydatid cysts are described and shown to correspond closely with previous observations on primary hydatid cysts. The usefulness of this experimental model for future ultrastructural studies is emphasized.

Animals↗
PubMed1976

The active centers of Streptomyces griseus protease 3 and alpha-chymotrypsin: enzyme-substrate interactions remote from the scissile bond.

Kinetic constants are reported for alpha-chymotrypsin- and Streptomyces griseus protease 3 (SGP3)-catalyzed amide hydrolysis of a number of peptide amides of varying substrate chain length. alpha-Chymotrypsin, but not SGP3, will hydrolyze rapidly specific acetyl amino acid amides. SGP3-catalyzed, but not alpha-chymotrypsin-catalyzed, hydrolysis is greatly stimulated by the presence of up to four amino acid residues N-terminal to the scissile bond of the substrate. The enzyme-substrate interactions utilized to promote hydrolysis, therefore, differ in these two enzymes, which, in other respects, show marked similarities. alpha-Chymotrypsin depends mainly on primary enzyme-substrate contacts, those with the amino acid residue (P1) whose carbonyl group forms part of the scissile bond, whereas SGP3 depends mainly on "secondary" enzyme-substrate contacts with amino acid residues (P2-P4) more remote from the scissile bond. A comparison with porcine elastase, a related serine protease, indicates that there is an inverse relation between the importance of primary and secondary enzyme substrate interactions in this family of enzymes. A rationale is proposed for this effect based on the observation that both types of enzyme-substrate interaction predominantly affect the rate constant for the acylation step of substrate hydrolysis.

Amides↗
PubMed1976

The active centers of Streptomyces griseus protease 3, alpha-chymotrypsin, and elastase: enzyme-substrate interactions close to the scissile bond.

Kinetic constants are reported for alpha-chymotrypsin-, Streptomyces griseus protease 3 (SGP3)-, and elastase-catalyzed hydrolysis of a number of peptides. SGP3, like alpha-chymotrypsine, hydrolyzes most readily amide bonds whose immediate acyl group (P1) is a large, hydrophobic, amino acid residue. SGP3, however, has a broader specificity for P1 residues than does alpha-chymotrypsin, primarily because the most important interactions between SGP3 and residue P1 of the substrate involve the Cbeta and Cgamma groups of the P1 side chain. For substrates of all three proteases, the amino acid residue contributing the amino group of the scissile bond (P1') is less important than P1 in determining kcat/Km for the hydrolysis reaction. Each enzyme interacts favorably with a hydrophobic P1' side chain. A substate with a large P1' side chain is bound more strongly, but is hydrolyzed less rapidly, than that with P1' Ala. The observation that strong binding of P1' is not necessarily conducive to rapid hydrolysis is consistent with the idea that parts of P1' must undergo a considerable displacement during substrate hydrolysis.

Amides↗
PubMed1976

Developing protoscoleces of Echinococcus granulosus on the outer surface of the brood capsule, detected by scanning electron microscopy.

By means of scanning electron microscopy, stalked protrusions were observed arising from the outer surface of intact brood capsules of Echinococcus granulosus. Histological studies showed these protrusions to be developing protoscoleces. However, complete development is not attained and the protoscoleces eventually die. It is suggested that external development is a result of overcrowding within the brood capsule.

Animals↗
PubMed1976

Treatment of aseptic necrosis of the femoral head with Phemister-type bone grafts.

This study was performed in order to assess the success and failure of bone grafting in early aseptic necrosis of the hip. Ten patients (11 hips) with a minimum of two years follow-up were evaluated by radiographic and clinical parameters. Seven of the 11 hips had good or excellent results. The criteria for a successful result were proper patient selection and exact placement of the bone grafts. The Phemister bone grafts appear to be the treatment of choice in early aseptic necrosis of the femoral head.

Adolescent↗
PubMed1976

The effect of environmental pH on glycosaminoglycan metabolism by normal human chondrocytes.

The synthesis and release of sulfated glycosaminoglycans by normal human chondrocytes in culture are markedly affected by environmental pH. The biosynthetic rate is increased threefold as the pH of the growth medium is raised from 7.0 to 8.0. This coincides with a corresponding elevation in total protein and cell growth. The rate of release of newly synthesized sulfated glycosaminoglycans from the cell layer as well as their distribution between intra- and extracellular localization in the cell layer is also modulated by environmental pH. At pH 8, 35 per cent is found within the cells, this value is reduced to 13 per cent at pH 7. Pulse-chase experiments showed that previously incorporated sulfated proteoglycans were released at a faster rate at pH 7 than at pH 8. The data suggest that proton concentrations affect the biosynthesis and the mode of distribution of newly synthesized sulfated glycosaminoglycans.

Adolescent↗
PubMed1975

Mechanism of dissociation of ribosomes of Escherichia coli by initiation factor IF-3.

Initiation factor IF-3 clearly can cause dissociation of ribosomes by binding to 30S subunits and thus shifting the spontaneous equilibrium, but it theoretically may also do so by binding to 70S ribosomes. Previously reported experiments with differentially labeled ribosomes and subunits seemed to eliminate the latter mechanism, but these experiments neglected a substantial decrease in the specific activity of the added subunits resulting from net dissociation of the ribosomes by IF-3. The present experiments eliminate or correct this effect. The results exclude direct action on 70S ribosomes as a significant mechanism of dissociation by IF-3.

Escherichia coli↗
PubMed1975

An experimental study of surface injury to articular cartilage and enzyme responses within the joint.

An experimental model of degenerative joint disease on chondromalacia consists of a surgically-scarified articular surface of the adult dog knee joint. In 52 dogs, evaluated by histologic and enzymatic assays over a period of 1 to 110 weeks post-surgery, the levels of acid hydrolase activity varied on various areas of articular cartilage within the same joint. There was a transient rise in most of the acid hydrolases in the synovium as a response to arthrotomy of the knee joint. All of the acid hydrolases studied did not respond uniformly to surgically created trauma. There was evidence of repair of the cartilage lacerations even when the subchondral zone was not breached. Lacerations in the central portion of the patella rarely showed healing in contrast to those placed more to the periphery of the articular surface. There was no gross or histologic evidence of progressive degenerative joint disease up to 2 years post-surgery. Thus an injury inflicted to the surface of the articular cartilage may be in itself insufficient in severity to produce destructive changes in the joint. This should not be too surprising, since, clinically, all joint surface injury does not lead to degenerative arthritis. The joint seems to have an injury threshold whereby chondrocytes are capable of repairing surface injury if the damage is not massive or repetitive. Insofar as lacerations in the center of the patella rarely healed, while the peripheral ones showed consistent signs of healing, the site of injury, as well as the magnitude of injury, may be critical.

Acetylglucosaminidase↗