Search PubMed⌕ Search

Biomedical subjects

A R Smith

Publications and source records attributed to A R Smith.

At least 181 records · Page 10Linked to original sources
PubMed1978

Complete versus selective dry cow therapy for mastitis control.

Two hundred and thirty-two cows were assigned alternately to complete dry cow therapy (infusion in all quarters on the day of drying off) or selective therapy (infusion in all quarters if a history of mastitis, California Mastitis Test score of +2 or +3 in any quarter, or if cell counts from bucket milk samples as determined by the membrane filter-deoxyribonucleic acid procedure were above 500,000 cells/ml). A dry cow product containing 10(6) units of procaine penicillin G and 1 g of dihydrostreptomycin in a slow release base was used. A 1% iodophor teat dip was used throughout the experiment. Infections of Staphylococcus aureus, Streptococcus agalactiae, other streptococci, and gram negative rods were eliminated from 85.4% of the infected quarters with complete therapy and 88.2% of the infected quarters with selective therapy. New infections occurred in 3.1% of quarters with complete therapy and in 6.5% of the quarters with selective therapy. Incidence of mastitis following the dry period was less with complete therapy compared to selective therapy (4.6% vs. 7.8% of the quarters). Selective therapy was as effective as complete therapy in eliminating existing infections. Complete therapy would be the choice in situations where new infections in dry period are of concern.

Animals↗
PubMed1978

Digit regeneration in the amphibian--Triturus cristatus.

Digit regeneration has been examined in Triturus cristatus. Because of their size, blastemas that form after digit amputation are relatively a lot more suitable for quantitative studies that involve for example the counting of cells in histological sections. They are also very useful for the study of some basic histological aspects of regeneration particularly cartilage formation. This has been looked at in regenerating digits, as there are only a maximum of three bones to regenerate and these lie in sequence, one after the other. It was seen that the cartilage is laid down as a solid rod by about 17 days post-amputation, and that by about 20 days, it starts to be split up into its three elements. An X-ray study of the growth of digit regeneration together with autoradiography experiments were also carried out as a comparison to studies already undertaken on larger more proximal blastemas. It was shown that in fact the behaviour of digit blastemas is very similar to those of a more proximal origin. This fact, together with the advantages of its size, make the digit a very strong candidate for the further study of regeneration.

Animals↗
PubMed1977

The mode of action of N-(n-Dodecyl)diethanolamine with particular reference to the effect of protonation on uptake by Escherichia coli.

In a homologous series of N-(n-alkyl)diethanolamines antimicrobial activity was related to surface activity and increasing octanol-water partition coefficient. Maximum activity was exhibited by the dodecyl-, tetradecyl- and hexadecyl-derivatives. Dodecyldiethanolamine (DDE) displayed a broad spectrum of activity. Towards Escherichia coli NCIB8277, its bacteriostatic and bactericidal activity increased as the degree of protonation lessened, and may have been influenced by the formation of micelles. Uptake of DDE by washed suspensions of E. coli was more rapid and more extensive at pH 7.0 than pH 4.0. Within this pH range, bacterial uptake, the octanol-water partition coefficient (lipid solubility) and the proportion of unprotonated DDE all increased. Uptake isotherms at pH values in the range 4.0 to 8.0 are interpreted as signifying different uptake mechanisms for the protonated and unprotonated forms.

Anti-Bacterial Agents↗
PubMed1977

The pattern of cell division during growth of the blastema of regenerating newt forelimbs.

Pulse and continuous labelling with tritiated thymidine are used for a quantitative study of cell division rates in regeneration blastemas. Proliferation is initially uniform; later a proximo-distal gradient develops in the mesenchyme, with the highest labelling index at the tip, where practically all cells are shown to be dividing. In the ectoderm there appear to be two growth bands, one close to the stump and the other close to the tip. The results are consistent with the progress zone theory, and agree well with the numerical estimates of growth rates used in our previously reported simulation.

Animals↗
PubMed1976

The pineal gland of the mole (Talpa europaea L.) III. A fluorescence histochemical study.

The pineal gland of the mole, a mammal which lives in permanent darkness, has been studied using fluorescence histochemistry. An extensive catecholaminergic innervation is demonstrated. A yellow formaldehyde-induced fluorescence, characteristic of indoleamines, was not observed. If formaldehyde vapour treatment was omitted in the procedure, numerous cells containing yellow-orange autofluorescent material could be shown. The nature and possible function of this material is discussed.

Animals↗
PubMed1976

Antimicrobial action of dodecyldiethanolamine: induced membrane damage in Escherichia coli.

Studies on the uptake of the antimicrobial agent N-dodecyldiethanolamine by Escherichia coli show that it rapidly penetrates the cell wall and damages the cytoplasmic membrane. Membrane damage is evident from the induced release of potassium ions and other cytoplasmic components from whole cells and from the lytic effect upon isolated spheroplasts. Concentrations of 0.4 mM and below lyse spheroplasts whereas higher concentrations cause coagulation of the cytoplasm which prevents lysis. The effect of membrane damage upon glucose oxidation in whole cells is also dependent upon the concentration of dodecyldiethanolamine. Concentrations of 0.4 mM and below stimulate oxygen uptake and higher concentrations inhibit it.

Anti-Bacterial Agents↗
PubMed1976

Antimicrobial action of dodecyldiethanolamine: activation of ribonuclease I in Escherichia coli.

Treatment of Escherichia coli with the antimicrobial agent N-dodecyldiethanolamine results in damage to the cytoplasmic membrane and rapid release of components of the metabolic pool. A slower secondary release then takes place. The material in the secondary release contains mainly low molecular compounds, nucleotides and nucleosides derived from the breakdown of ribosomal RNA. Some transfer RNA is also released. Breakdown of RNA occurs as a result of activation of the 'latent' ribonuclease I. Breakdown is inhibited by the ribonuclease inhibitors Ca2+ and Mg2+ and does not occur in a ribonuclease I-deficient strain of E. coli.

Anti-Bacterial Agents↗
PubMed1975

Effect of pinealectomy, gonadectomy, pCPA and pineal extracts on the rat parvocellular neurosecretory hypothalamic system; a fluorescence histochemical investigation.

Using the fluorescence histochemical technique, yellow autofluorescent granules were observed in neurones of the arcuate and ventromedial hypothalamic nuclei of the rat (type I cells). In the same nuclei, neurones could be demonstrated showing a formaldehyde-induced yellow fluorescence (type II cells). Microelectrophoresis and special staining methods applied to the pineal gland revealed the autofluorescent compound to be a protein containing a relatively high content of tryptophan. It is probable that the formaldehyde-induced yellow fluorescence is due to the presence of serotonin. In view of investigating a possible functional relationship between the pineal gland and the parvocellular hypothalamic nuclei mentioned, hypothalamic type I and type II cells, as well as autofluorescent and serotonin-containing pinealocytes, if present, were quantified under the following experimental conditions: (1) p-chlorophenylalanine (pCPA) administration, (2) castration, (3) pinealectomy, and (4) pinealectomy followed by substitution using rat and sheep pineal extract. Administration of pCPA caused a decrease in the number of type II and an increase in the number of type I cells, both in the pineal gland and the hypothalamic nuclei. Castration, in contrast, was followed by an increase in the number of autofluorescent pinealocytes, but a decrease of autofluorescent neurones in the hypothalamic nuclei (type I cells) while the number of serotonin-containing pinealocytes increased; decreasing in both hypothalamic nuclei. After pinealectomy the hypothalamic nuclei showed an increase of type I neurones, but a decrease of type II nerve cells. Pinealectomy followed by substitution using pineal extracts restored the number of type I and type II neurones to that normally found in the arcuate and ventromedial hypothalamic nuclei of control animals. The present investigation brings histological evidence of an influence exerted by the rat pineal gland on nuclei forming part of the hypothalamic hypophyseotropic area. The data obtained and some of the literature strongly suggest that the type II neurones, which probably contain serotonin, inhibit, in the same hypothalamic nuclei, the production of luteinizing hormone-releasing factor (LH-RF). As yet, the function of the autofluorescent compound present in the type I neurones is not known.

Animals↗