Biomedical subjects
Publications and source records attributed to D M Barnett.
We derive here for the first time the equations that describe the combined motion and rotation of small prismatic dislocation loops in stress fields. When the applied torque is balanced by the self-torque of the loop, we show how the solution can be obtained for the loop orientation, and how this orientation affects the glide force on the loop.
The idea that the gene(s) that cause diabetes mellitus can be expressed in extrapancreatic cells has been examined by tissue culture techniques. Skin biopsies were obtained from 25 normal subjects (N), 26 overt diabetics (D), 16 of juvenile onset (JOD) and 9 of maturity onset (MOD), and 21 subjects genetically predisposed to diabetes (P) on the basis of maturity-onset diabetes in both parents. Each biopsy was subdivided, multiple skin fragments were explanted in vitro, and several parameters of cellular outgrowth were monitored in primary and secondary cultures until cell division ceased because of senescence. In general, the rank order of growth vigor was N greater than P greater than D although differences were often marginal and statistically significant between N and JOD and(or) MOD. Outgrowth of epithelial cells was more vigorous in N explants in early stages, but later, JOD and MOD cells grew better than those of N. Outgrowth of fibroblast cells from N explants was more vigorous both at early and later stages and required less time to achieve maximum percent outgrowth. In secondary cultures, N cells grew faster than the other three groups so that fewer days elapsed between subcultures but significant differences were only seen between N and one or two of the other groups over some of the first seven subcultures. The onset of cellular senescence occurred earlier in P and JOD cultures both in mean population doublings and calendar time. N cultures had a higher percent surviving clones after picking than MOD, and a shorter recloning time than clones of JOD. The replicative life-spans of cultures (mean population doublings +/- SE) were N = 52.54 +/- 2.24, P = 47.84 +/- 2.43, JOD = 47.12 +/- 2.99, and MOD = 46.40 +/- 4.04, but differences did not reach significance for N vs the other three groups. The data demonstrate that cellular growth is impaired in both JOD and MOD types of cultures and to a generally lesser extent in P cultures. This is consistent with intrinsic genetic defects but the possibility that persistent deleterious effects of in vivo pathophysiology contribute alone or in combination cannot be ruled out. Therefore, the diabetic defect(s) can be expressed in extrapancreatic cells of mesenchymal origin. This system should prove useful in exploring the interplay between genetic and environmental factors in diabetes, the mechanisms(s) of hyperglycemia and other metabolic derangements, and the propensity that affected individuals have to develop degenerative diseases.
Cultured skin fibroblasts from subjects with clinically apparent diabetes mellitus and from subjects genetically predisposed to diabetes have a replicative lifespan that is inversely related to donor age. Fibroblasts from carefully defined normal subjects not predisposed to diabetes fail to show this correlation. The data support the idea that physiologic status of the tissue donor is a more precise determinant of fibroblast replicative lifespan than chronologic age.
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Control of diabetes was studied during an 8-wk camp program in 18 insulin-dependent counselors with a mean age of 19.3 yr and a mean duration of diabetes of 11.4 yr. A composite score was obtained for each subject derived from three factors: percent sugar-free urine tests, 24-h glucose excretion as percent of carbohydrate intake, and mean preprandial blood glucose (MPBG). The mean hemoglobin A1c (HbA1c) at the end of the period was 8.3 +/- 1.6% (+/ SD) (normal range, 4-6%). Scores ranging from 24 (fair control) to 45 (excellent control) showed a significant inverse correlation with HbA1c (r = 0.807, P less than 0.001) and MPBG (r = -0.674, P less than 0.01). HbA1c showed a significant correlation with the MPBG (r = 0.693, P less than 0.01). The HbA1c level was predicted better by percent sugar-free urine tests than by the 24-h glucose excretion. Thus it appears that accurate quantification of control may be obtained by using a scoring system. Critical comparison of HbA1c levels to various glycemic indices may provide useful alternatives for estimating diabetes control.