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Biomedical subjects

W Anderson

Publications and source records attributed to W Anderson.

At least 127 records · Page 7Linked to original sources
PubMed1980

Tetracycline labeling of bone in vivo.

We have analyzed various aspects of tetracycline labeling technique for the measurement of bone apposition rate in vivo. Our efforts were restricted to those aspects that are frequently questioned when data obtained using this technique are interpreted as representing the rate of bone apposition. Rat bone was labeled in vivo by sequential injections of oxytetracycline at a dose range of 3 to 24 mg/kg body weight and at intervals ranging from 24 to 72 h. The bone apposition rate was calculated by measuring the distance from the first dose of label to the subsequent ones. As these distances are by far too small to be determined accurately by any available micrometer eyepiece, we have used a scanning microscope photometer which allows measurements on slow-forming sites that otherwise would have been considered nongrowing sites. Using these techniques, we have demonstrated that oxytetracycline has no effect on the bone apposition rate when used in the concentrations indicated. In addition, we found that at labeling intervals of 96 h or more, periods of osteoblastic inactivity are likely to be included in measurements at individual sites. The instantaneous apposition rate is thus underestimated at these long time intervals.

Animals↗
PubMed1980

The influence of molecular size and pH on the macrocationic inhibition of pepsin by polylysine.

Polylysines of 7-371 lysine residues inhibited pepsin over the pH range 3.6-5.0 in a system using azocoll as substrate. Tetralysine was inactive. An almost 1:1 molar ratio with pepsin gave maximum inhibition for a polylysine containing 59 lysine residues but increase in polylysine molecular size beyond this size was not accompanied by increase in activity on a weight basis although the polylysine:pepsin molar ratio for maximum inhibition decreased and inhibition mechanism varied. Polylysines of 59 and 158 lysine residues which were intermediate in the series were non-competitive inhibitors, whilst polylysines of greater and smaller molecular size were competitive inhibitors, although only the smallest inhibitory polylysine, containing 7 lysine residues, was a pure competitive inhibitor. Polylysine inhibition of pepsin was found to be strongest at pH 5.0 and the pH dependence appeared to be associated with the relative concentrations of the enzyme and inhibitors in ionized form. For each polylysine it was possible to detect a polylysine:pepsin concentration ratio for which inhibition was pH-independent over the range 3.6-5.0.

Binding, Competitive↗
PubMed1980

Barium sulphate preparations for use in double contrast examination of the upper gastrointestinal tract.

Physical properties relevant to upper gastrointestinal radiology have been compared for five barium sulphate preparations and related to radiographic results. Evaluation of particles (size and stability) and whole suspension (dispersibility and fluidity) resulted in ranking of the preparations generally in accord with that based on radiological experience in double contrast examinations of the stomach. Experiments with extirpated pig stomach revealed a tendency for large particles in a low viscosity barium sulphate suspension to settle in mucosal grooves. This is believed to contribute to good radiographic definition of both the areae gastricae and small lesions. Particle size is therefore important and susceptibility to flocculation, a possible cause of random change in size during use, was assessed by measuring particle electrophoretic mobility under varying conditions; quantitative differences in suspension flow and dispersibility were also demonstrated. Fluidity and dispersibility together with rapid sedimentation of suitably sized particles resistant to flocculation underlie the successful use of low viscosity high density barium sulphate suspensions.

Animals↗
PubMed1980

Areae gastricae.

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Animals↗
PubMed1979

The response of bone apposition rate to some nonphysiologic conditions.

The response of bone apposition to some nonphysiologic conditions was investigated. In rabbits, the normal osteogenic rhythm was totally abolished shortly following treatment of hydrocortisone at a dose of 2 mg/kg body weight daily. A new rhythm developed after the treatment was continued for 20 1/2--34 days. The rate of bone apposition was significantly depressed compared to normal data reported previously. In rats receiving one U.S.P. unit of parathyroid extract daily for 14 days, the rate of bone apposition was significantly higher than that in control rats. In both sepcies, the response to an exogenous hormone was identified for all skeletal locations. It was concluded that new bone apposition was a function of activated osteoblasts, and that this function responded only to general body control mechanisms.

Animals↗
PubMed1979

Energy-conformation studies of frequency of beta-turns in tetrapeptide sequences.

The optimized energies of seven beta-bends, repeating C5 and C7, and right- and left-handed alpha-helical conformations for each of eight tetrapeptides have been computed using empirical methods. Eight tetramers were selected: four helix-forming sequences with hydrophobic residues such as Val, Leu, Ile and Trp, and four helix-breaking sequences with hydrophilic residues such as Asp, Asn and Ser, as determined by their frequency of occurrence in beta turns in proteins. Analysis of the optimized conformations with energies less than or equal to 2.1 kcal/mol from the absolute minimum energy conformer for each tetramer reveals a correlation between low-energy conformations and those predicted from observed protein structures. These results show that energy calculations on small peptide fragments may be usefulin predicting protein structure.

Amino Acid Sequence↗
PubMed1978

Activation of adenylate cyclase in cultured fibroblasts by trypsin.

Adenylate cyclase activity measured in membranes of cultured normal rat kidney (NRK) fibroblasts was markedly increased by prior treatment of the intact cells with trypsin. Cell population density influenced the extent of activation observed. Trypsin treatment of sparse cells significantly enhanced adenylate cyclase activity, whereas similar treatment of confluent cells caused only a slight increase in adenylate cyclase activity. The degree of activation noted after trypsin treatment also varied depending on the adenylate cyclase function measured. Activity determined in the presence of GTP alone showed the greatest increase after trypsin treatment. Similar enhancement of adenylate cyclase activity of a washed cell membrane preparation was achieved by the addition of low concentrations of trypsin directly to the adenylate cyclase reaction mixture. The membranes of confluent NRK fibroblasts initially exhibited higher adenylate cyclase activity than did membranes of sparse cells. The present results suggest that this change in adenylate cyclase activity at cell confluence is not due to an increase in the amount of adenylate cyclase in the cell membrane but rather to a change in membrane components that regulate its activity. Proteolytic activation of adenylate cyclase appears to result from degradation of cell membrane proteins that modulate the activity of this enzyme.

Adenylyl Cyclases↗