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Biomedical subjects

R Kent

Publications and source records attributed to R Kent.

At least 55 records · Page 3Linked to original sources
PubMed1991

Mutans streptococci and non-mutans streptococci acidogenic at low pH, and in vitro acidogenic potential of dental plaque in two different areas of the human dentition.

Samples of human dental plaque were obtained from sound tooth surfaces in the lower anterior and upper posterior areas of each of 11 subjects with various degrees of caries experience. Both types of plaque were compared for: (1) their pH-lowering potential [pH at 10 and 60 min after sugar addition and the pH drop between 0 and 10 min (delta pH)] with an in vitro method involving dispersed plaque suspensions and excess glucose supply; (2) the proportions of mutans streptococci; and (3) the distribution of the predominant non-mutans streptococci according to their final pH in glucose broth. Compared with plaque from the lower anterior area, plaque from the upper posterior area exhibited a significantly higher pH-lowering potential, i.e., a lower pH at 10 and 60 min and a greater delta pH and significantly higher levels of mutans streptococci. The final pH values for the non-mutans streptococci exhibited a wide range from about 4.4 to over 5.0. The proportions of such organisms designated as capable of acidogenesis at low pH (final pH less than 4.6), whether expressed as a percentage of the total non-mutans streptococci or of the total plaque flora, were significantly increased in plaque from the upper posterior area. The proportions of non-mutans streptococci capable of acidogenesis at low pH in plaque from the upper posterior area were also significantly increased, with decreasing pH values at 10 and 60 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Acids↗
PubMed1990

Dental caries in congenitally athymic rats.

The importance of the immune response in dental infection was evaluated in heterozygous (rnu/+) normal and homozygous (rnu/rnu) congenitally athymic "nude" Rowett rats. Animals of both types were infected, or immunized and infected, with mutans streptococci (Streptococcus sobrinus strain 6715). The mean numbers of S. sobrinus cells recovered from the nude rats were higher than those from comparable (immune/nonimmune) normal rats in 10 of 12 possible comparisons. Also, S. sobrinus constituted a greater percentage of the total streptococci in the nude rats compared with normal animals (6 of 6 possible comparisons). Antibody to S. sobrinus whole cells or to S. sobrinus glucosyltransferase from nude rats in serum or in saliva was significantly lower (or absent) than that of comparable normal rats. This was seen after infection, but was most pronounced after immunization (and infection). Dental caries was also significantly elevated in the congenitally athymic animals. Immunologic deficiency of congenitally athymic rats can lead to a greater infection level with mutans streptococci and increased dental caries.

Analysis of Variance↗
PubMed1990

Association of the microbial flora of dental plaque and saliva with human root-surface caries.

Dental plaque was obtained from one or two sound root surfaces of subjects with different degrees of root-surface caries experience. From subjects with root-surface caries, plaque samples were also obtained from either one incipient or one more advanced lesion. Proportions of the total flora were determined for total streptococci and different streptococcal species, total and different Actinomyces species, and lactobacilli. A sample of saliva was obtained from about one-third of the subjects for determination of the concentrations of mutans streptococci and lactobacilli. The main observations were: (1) Subjects without root-surface caries or restorations (group I), as compared with subjects with root-surface caries with or without restorations (group II), were characterized by having a lower prevalence and proportion of mutans streptococci and a higher prevalence and proportion of A. naeslundii in plaque on sound root surfaces; (2) subjects in group I also tended to have a lower salivary concentration of mutans streptococci and lactobacilli than subjects in group II; (3) dental plaque on sound surfaces in group II subjects contained a lower proportion of mutans streptococci than plaque associated with incipient or advanced lesions; and (4) the prevalence and proportion of lactobacilli in plaque associated with sound as well as carious root surfaces were very low. The data reinforce findings from other studies and indicate that, as for coronal caries, the plaque and saliva populations of mutans streptococci specifically are correlated positively with the presence of root-surface caries.

Actinomyces↗
PubMed1990

Polymorphism of submandibular-sublingual salivary proteins which promote adhesion of Streptococcus mutans serotype-c strains to hydroxyapatite.

Previously, we showed that human submandibular-sublingual (SMSL) salivas contain one or more proteins, Mr circa 300,000 daltons, which specifically promote adhesion of Streptococcus mutans serotype-c strains to hydroxyapatite. Also, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that the adhesion-promoting proteins (APPs) exhibit heterogeneity. The aims of the present study were to determine whether APPs are generally present in human SMSL salivary secretions and to characterize the noted heterogeneity. Acid-stimulated SMSL saliva samples were obtained from 54 Japanese subjects, and Mr values were obtained by SDS-PAGE. APPs were present in all saliva samples examined, though at significantly different concentrations. The APPs occurred as either single (20 subjects) or double bands (34 subjects), with a mean Mr (88 bands) of 297 kD and a range of 248-338 kD. A plot of the frequency distribution of the APPs according to Mr showed a trimodal distribution, with mean Mr values, standard deviations, and ranges for the three groups being 265 (S.D., 6.9; range, 248-278), 293 (S.D., 6.7; range, 280-305), and 320 (S.D., 7.0; range, 310-338) kD. Variations of Mr within groups may be attributed to experimental variation, although microheterogeneity cannot be excluded. Differences between groups can best be explained in terms of three polymorphic proteins, with low (L), intermediate (I), and high (H) Mr values. Six phenotypes were detected with L, I, H, LI, LH, and IH Mr bands. A Hardy-Weinberg analysis showed that the phenotype data fit a single-gene, three-alleles model.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Adhesion↗
PubMed1989

Transcription in vaccinia virus.

Transcription of poxvirus genes is temporally regulated and takes place in the cytoplasm of the infected cell. Virus-encoded enzymes produce capped, methylated and polyadenylated mRNA. The virus transcriptional apparatus recognises promoter sequences within the virus genome which bear little resemblance to either eukaryotic or prokaryotic promoter regions. mRNA's produced late in infection possess 5'poly (A) sequences which are not encoded in the genome. The process of transcription in poxviruses is reviewed using vaccinia virus as the prototype.

Base Sequence↗
PubMed1988

Localization of a human Na+,K+-ATPase alpha subunit gene to chromosome 19q12----q13.2 and linkage to the myotonic dystrophy locus.

The gene coding for a Na+,K+-ATPase alpha subunit (ATP1A3) has been localized to the q12----q13.2 region of human chromosome 19, potentially close to the myotonic dystrophy (DM) gene. In view of previous studies implicating a Na+,K+-ATPase in the pathology of DM, we have examined the possibility that ATP1A3 is a candidate for the DM locus. Although linked, several clear instances of recombination between ATP1A3 and DM rule out the possibility that mutations in ATP1A3 cause the disease. Examination of multiply informative pedigrees indicates the gene order DM-APOC2-ATP1A3.

Animals↗
PubMed1988

Analysis of the time distribution and time sequence of behavioral acts.

A technique for analyzing the temporal structure between various initiations of a particular behavioral act has been developed using a parameter known as the K-function, the cornerstone of recent statistical research on spatial point processes and patterns. The technique has been extended to the study of the joint relationship of separate acts. Bootstrap methods are used to estimate the uncertainty in these measures. The usefulness of these techniques is demonstrated using data from studies of rats exposed to phenytoin and nitrous oxide.

Animals↗
PubMed1987

Enhanced caries inhibition by certain NaF-surfactant combinations in animal models.

The purpose of this animal investigation was to determine whether the cariostatic effect of sodium fluoride can be enhanced by combining it with certain surfactants. The surfactants, Zonyl FSC and Lodyne S-110, were selected because they had been found to accelerate the rate of deposition of firmly-bound fluoride in vitro in enamel during enamel-fluoride interaction. Sixty male hamsters and 60 female rats, 21 days old, were placed on the high-sucrose diet 2000 and inoculated with Streptococcus mutans (strain #6715). Each set of animals was divided into six groups of 10 each. The groups received either distilled water, NaF, NaF with Lodyne S-110, NaF with Zonyl FSC, Lodyne S-110, or Zonyl FSC. The animals were scored for caries at the termination of the study. The caries findings in the hamster and the rat series closely paralleled each other. Animals receiving NaF with Zonyl FSC experienced the least decay (about 90% inhibition compared with about 65% for the NaF-alone group). A statistical evaluation showed significant interaction between Zonyl FSC and NaF. No effect on caries experience was seen from administration of Lodyne S-110.

Animals↗
PubMed1986

A longitudinal study of the growth of the New Zealand white rabbit: cumulative and biweekly incremental growth rates for body length, body weight, femoral length, and tibial length.

This longitudinal study documents cumulative and incremental growth in the New Zealand white rabbit from 2 to 34 weeks of age at biweekly intervals. Body weight, body length, femoral length, and tibial length have been assessed in 17 male and 12 female rabbits, with the data tabulated separately. A specially designed restrainer was used that allowed the sequential clinical measurements and femoral and tibial radiographs to be performed without the use of anesthesia. Skeletal growth was complete at 28 weeks, with the 34-week values thus representing mature adult lengths. The mean body weight at 2 weeks of age was 6% that at 34 weeks, and by 16 weeks, 72% of the weight at 34 weeks was achieved. Weight continued to increase in the adult. The mean body length at 2 weeks was 40% that at 34 weeks, and by 16 weeks, 91% of mature adult length was achieved. The mean femoral length at 2 weeks was 38% of the adult length, and at 16 weeks, it reached 95% of adult length. The mean tibial length at 2 weeks was 38% of the adult length, and 94% of the adult value was achieved by 16 weeks. The longitudinal data document the rate and extent of growth of the New Zealand white rabbit, and allow for more accurate timing and quantitation of physical and systemic interventions on the developing skeleton of the commonly investigated New Zealand white rabbit.

Animals↗
PubMed1986

Hemodynamic predictors of outcome in patients undergoing valve replacement.

The afterload-corrected end-systolic volume index (ratio of end-systolic stress to end-systolic volume index [ESS/ESVI]) was previously useful in predicting outcome in patients with mitral regurgitation undergoing valve replacement. Therefore we tested ESS/ESVI together with standard hemodynamic variables as possible predictors of outcome in 39 patients with various valvular lesions who underwent valve replacement. Thirteen patients had preoperative mitral regurgitation, 16 had aortic stenosis, nine had aortic regurgitation, and one had mitral stenosis. Twenty-seven patients (group S) had a satisfactory outcome as defined by a return to NYHA class I or II together with a normal postoperative ejection fraction. Twelve patients who died, remained in class III or IV, or had a subnormal postoperative ejection fraction were deemed to have an unsatisfactory result (group U). Mean right atrial pressure, pulmonary arterial pressure, pulmonary capillary wedge pressure, end-diastolic volume index, end-systolic volume index (ESVI), and end-systolic wall stress were all greater in group U, whereas ESS/ESVI and ejection fraction were lower in group U. When these and other factors were submitted to stepwise discriminant multivariate analysis, ESS/ESVI and ESVI were the only independent predictors of outcome. However, when patients with mitral regurgitation (who might have biased the study) were excluded, discriminant analysis showed ESVI as the only independent predictive variable. We conclude that end-systolic indicators of ventricular function are superior to other standard hemodynamic variables in predicting outcome of valve replacement.

Aortic Valve↗
PubMed1985

The effect of peripheral chemodenervation on the ventilatory response to potassium.

The present experiments were designed to test the hypothesis that the increase in plasma potassium which occurs during exercise acts as a stimulus to respiration via the peripheral chemoreceptors. The effect of intravenous infusion of KCl on ventilation was measured in anaesthetised cats while they were loaded with CO2 intravenously via a bubble gas exchanger. Ventilation during K+ infusion was compared with that immediately before in 'intact' and peripherally chemodenervated cats. In the 'intact' group there was a highly significant increase in ventilation of approximately 25% (+253 +/- 22 ml/min, P less than 0.001), whereas in the chemodenervated group there was no significant change (+ 17 +/- 11 ml/min) in spite of similar increases in arterial K+ concentration. The results of these experiments indicate that K+ infusions stimulate ventilation and that this effect is abolished by peripheral chemodenervation.

Animals↗
PubMed1983

Longitudinal trends in subcutaneous fat thickness during adolescence.

Longitudinal principal components (LPC) analysis is used to summarize adolescent trends in subcutaneous fat thickness at three sites (biceps, suprailiac, and abdominal). For each site, component 1 (C1) represents fatness level, and component 2 (C2) represents an increase followed by a decrease (fat wave) in fatness. Components 3-5 (retained for girls only) represent more complicated patterns of change (multiple increases and decreases). Correlations among scores for C1 for each site and among scores for C2 for each site indicate a high correspondence of fatness level and the magnitude of the fat wave. Associations between components and other indicators of maturity are apparent, indicating that serial fat patterns are controlled to some degree by influences affecting other pubescent events. Continuity between childhood fatness levels and adolescent patterns of fatness are relatively weak. Continuity between adolescent and adulthood fatness is somewhat greater.

Adipose Tissue↗