Biomedical subjects
G C Pitts
Publications and source records attributed to G C Pitts.
The response of skeletal muscle mass to changes in acceleration.
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Cellular aspects of growth and catch-up growth in the rat: a reevaluation.
The effect of nutritional perturbations upon growth and catch-up growth in mass in the rat have been reevaluated by interpretation of published data. The earlier described cellular mechanisms involved were prematurely reported to be invalid. Hypertrophy and hyperplasia have been separately assessed by employing studies providing DNA content of the body or organs permitting calculation of number of "DNA units" and mean size of the units. Changes in unit number and size accounted for reported changes in gross mass. Perturbation during the periods of gestation and/or nursing decreased or increased the number of units without changing the size of the units, and in these cases the change in body or organ mass persisted into maturity. Perturbation during adulthood changed size of the units without changing their number, and in these cases catch-up occurred. Post-weaning was a transitional period with perturbation sometimes changing unit number after which the change persisted and sometimes unit size after which catch-up occurred. Failure in most cases of DNA unit number and unit size to change simultaneously led to speculations about the mechanisms involved. Besides perturbations resulting from experimental interventions, the rat is influenced also by circumstances with unpredictable nutritional impact encountered during the ontogeny of free-living individuals, for example, interactions between pups and mother and between siblings. Presumably the generalizations arrived at above also apply in these cases.
History of physiology at the University of Virginia.
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Physiologic regulation of body energy storage.
Both new and published data (rats, mice, and human beings) on three parameters--fat mass, fat-free body mass (FFBM), and total body mass in some cases--are evaluated. Steady state values of the parameters are analyzed for changes in response to specific perturbing agents and for their frequency distributions. Temporal sequences of values on individuals are examined for evidence of regulatory responses. The results lead to the hypothesis that the FFBM is regulated, but probably not as a unit, and that mass of fat is regulated with a high priority near the range extremes but with a much lower priority in the mid-range. Properties and advantages of such a mechanism are discussed.
Exercise, dietary obesity, and growth in the rat.
Four regimens: high-fat diet, exercised (I); chow, exercised (II); high-fat sedentary (III); and chow, sedentary (IV) were initiated in 35-day-old male rats. Growth was exponential in I and II and exponential progressing to rectilinear in III and IV. The exponential model predicted the decreasing rank order in asymptotic weight to be: III, IV, I, II. Body composition data (9 components) showed rank order in masses of fat and the fat-free body mass compartment (FFBM) to be the same as for asymptotic live weight. The rectilinear growth mode probably reflected fat accretion. High-fat diet increased and treadmill exercise decreased FFBM, the latter being reversible. These effects depended on regimen initiations by the 5-7th wk of age. During growth, masses of H2O, muscle, and skin increased as functions of body size; bone as a function of age; and heart, liver, gut, testevity, and diet. Growth in body size was expressed more precisely with FFBM, instead of live weight, as the index of size.
Regulation of body mass in rats exposed to chronic acceleration.
Female rats approximately 6 mo old were chronically centrifuged for up to 30 days at 2.76 G or 3.18 G and sacrificed at intervals for body-composition study. Both fat and the fat-free body mass (FFBM) were reduced during the 1st wk of centrifugation, with the fat showing considerably more variation both within and between groups. The FFBM was reduced below control level to the same extent in rats fed commercial chow, a high-fat diet, or a high-protein diet or in rats prefasted to produce a body-mass deficit at the start of centrifugation. There were no centrifugation-associated changes in body water content. It was concluded that body fat showed no evidence of regulation, FFBM is regulated at any constant level of acceleration between 1 and 4.15 G, and the change in FFBM induced by a change in acceleration is probably not regulated.