Transition from dynamically maintained to relaxed end-expiratory volume in human infants

Newborn infants, in contrast to adults, dynamically maintain end-expiratory lung volume (EEV) above relaxation volume. The purpose of this study was to determine at what age children develop a breathing strategy that is relaxed, i.e., determined by the mechanical characteristics of the lung and chest wall. Forty studies were performed in 27 healthy infants and children aged 1 mo to 8 yr during natural sleep. Volume changes were recorded with the use of respiratory inductance plethysmography (RIP). The volume signal was differentiated to yield flow. Flow-volume representations were generated for a random sample of the recorded breaths to determine the predominant breathing strategy utilized, i.e., relaxed, interrupted, or indeterminate. The respiratory pattern was predominantly interrupted below 6 mo of age and predominantly relaxed over 1 yr of age. Mixed patterns were observed in children 6-12 mo of age. The number of breaths that could not be classified (indeterminate) decreased with age. Respiratory frequency measured from the sample of breaths decreased with age and was accompanied by an increase in expiratory time. We conclude that a relaxed EEV develops at the end of the first year of life and may be related to changes in the mechanical properties of the chest wall associated with growth as well as changes in respiratory timing.     

Relation between Age of Onset of Obesity and Size and Number of Adipose Cells

The size and number of adipose cells in obese children and adults were compared with control data. An increase in adipose cell size was found in all the obese subjects. The total number of adipose cells was increased in those children who had become obese already by the age of 1 year and in those adults who dated their obesity to childhood.     

Cell proliferation and hormonal changes during postnatal development of the testis in the pig

Histometrical evaluation of the testis was performed in 36 Piau pigs from birth to 16 mo of age to investigate Sertoli cell, Leydig cell, and germ cell proliferation. In addition, blood samples were taken in seven animals from 1 wk of age to adulthood to measure plasma levels of FSH and testosterone. Sertoli cell proliferation in pigs shows two distinct phases. The first occurs between birth and 1 mo of age, when the number of Sertoli cells per testis increases approximately sixfold. The second occurs between 3 and 4 mo of age, or just before puberty, which occurs between 4 to 5 mo of age, when Sertoli cells almost double their numbers per testis. The periods of Sertoli cell proliferation were concomitant with high FSH plasma levels and prominent elongation in the length of seminiferous cord/tubule per testis. Leydig cell volume increased markedly from birth to 1 mo of age and just before puberty. In general, during the first 5 mo after birth, Leydig cell volume growth showed a similar pattern as that observed for testosterone plasma levels. Also, the proliferation of Leydig cells per testis before puberty showed a pattern similar to that observed for Sertoli cells. However, Leydig cell number per testis increased up to 16 mo of age. Substantial changes in Leydig cell size were also observed after the pubertal period. From birth to 4 mo of age, germ cells proliferated continuously, increasing their number approximately two- to fourfold at each monthly interval. A dramatic increase in germ cells per cross-section of seminiferous tubule was observed from 4 to 5 mo of age; their number per tubule cross-section stabilized after 8 mo. To our knowledge, this is the first longitudinal study reporting the pattern of Sertoli cell, germ cell, and Leydig cell proliferative activity in pigs from birth to adulthood and the first study to correlate these events with plasma levels of FSH and testosterone.     

Hypertrophy and/or Hyperplasia: Dynamics of Adipose Tissue Growth

Adipose tissue grows by two mechanisms: hyperplasia (cell number increase) and hypertrophy (cell size increase). Genetics and diet affect the relative contributions of these two mechanisms to the growth of adipose tissue in obesity. In this study, the size distributions of epididymal adipose cells from two mouse strains, obesity-resistant FVB/N and obesity-prone C57BL/6, were measured after 2, 4, and 12 weeks under regular and high-fat feeding conditions. The total cell number in the epididymal fat pad was estimated from the fat pad mass and the normalized cell-size distribution. The cell number and volume-weighted mean cell size increase as a function of fat pad mass. To address adipose tissue growth precisely, we developed a mathematical model describing the evolution of the adipose cell-size distributions as a function of the increasing fat pad mass, instead of the increasing chronological time. Our model describes the recruitment of new adipose cells and their subsequent development in different strains, and with different diet regimens, with common mechanisms, but with diet- and genetics-dependent model parameters. Compared to the FVB/N strain, the C57BL/6 strain has greater recruitment of small adipose cells. Hyperplasia is enhanced by high-fat diet in a strain-dependent way, suggesting a synergistic interaction between genetics and diet. Moreover, high-fat feeding increases the rate of adipose cell size growth, independent of strain, reflecting the increase in calories requiring storage. Additionally, high-fat diet leads to a dramatic spreading of the size distribution of adipose cells in both strains; this implies an increase in size fluctuations of adipose cells through lipid turnover.     

Changes of time constants during infancy and early childhood

We used respiratory inductance plethysmography to record tidal respiration in 27 healthy unsedated infants and children 1 mo to 8 yr of age during sleep. Rib cage and abdominal outputs were present at approximately equal gains and summed to obtain an estimate of volume. Flow-volume curves were generated from the uncalibrated volume signal and its flow derivative. Expiratory time constants (tau) were obtained by visually drawing a line through the linear portion of the expiratory flow-volume relationship. tau increased significantly during the first 10 mo of life. After 10 mo, the estimated rate of increase of tau for older children was less than 5% of the estimated initial rate and not significantly different from zero. Prolongation of tau was paralleled by an increase in expiratory time (Te), and no changes in Te/tau were observed in the first 2 yr of life. These changes in tau likely reflect the increase in lung compliance induced by rapid alveolar growth during infancy. After the first year, expiratory time constants appear to remain relatively constant and may be consistent with balanced changes in compliance and resistance beyond infancy.     

Cell size, cell cycle and transition probability in mouse fibroblasts

This paper describes the relationship between cell size and cell division in two situations. In the first, quiescent cells were sorted on the basis of cell size using a fluorescence-activated cell sorter and returned to culture. The results of this type of experiment are compatible with the idea that once cells have completed a size-dependent lag, the rate of entry of cells into S phase is controlled by a rate-limiting random event (or transition).The second kind of experiment follows the kinetics of complete cell cycles in rapidly proliferating cells whose mothers had been sorted on the basis of cell size. The cells born of small mother cells have longer cycle times than cells derived from large mothers. The difference in the cycle time of these two classes was due to differences in the B phase of the cell cycle [containing S, G2, M and part of G1 (G1B)], transition probability being the same in both size classes. Our results show that S, G2 and M are unaffected by size, thus confining the effect of size to G1B. It seems probable that the variability of B phase in cloned cell populations is partly due to variations of cell size at division, and correlations between the cycle times of sister cells result because sibling cells are more similar in size than unrelated cells. The major factor controlling cell division in mouse fibroblasts is shown, however, to be the transition probability; size has a more minor role.     

Effects of dietary cholesterol on adipose tissue lipoprotein lipase in the baboon

The effects of infant diet (breast milk or formula containing 2, 30 or 60 mg/dl cholesterol) and subsequent dietary cholesterol (0.02, 1.0 or 1.7 mg/kcal) and fat (saturated or unsaturated) on heparin-releasable lipolytic activity from omental adipose tissue was estimated from 99 baboons of 5-8 years of age. This lipase activity was characterized as lipoprotein lipase based on salt inhibition and apolipoprotein C-II activation. Lipoprotein lipase activity released from adipose tissue by heparin was significantly (P less than 0.002) lower in high cholesterol-fed baboons than in those fed low cholesterol. Most of this difference was due to impaired long-term heparin release of lipoprotein lipase. Adipose tissue lipoprotein lipase increased with increasing fat cell size regardless of diet, but there was no effect of diet on adipocyte size. There were no significant effects of infant cholesterol intake nor adult saturated or unsaturated fat on lipoprotein lipase activity. Adult baboons breast fed as infants had lower adipose tissue lipoprotein lipase activity (P less than 0.07) than adults fed formula as infants.     

Adipose tissue extract shows potential for wound healing: in vitro proliferation and migration of cell types contributing to wound healing in the presence of adipose tissue preparation and platelet rich plasma

Growth factors are the key elements in wound healing signaling for cell migration, differentiation and proliferation. Platelet-rich plasma (PRP), one of the most studied sources of growth factors, has demonstrated to promote wound healing in vitro and in vivo. Adipose tissue is an alternative source of growth factors. Through a simple lipoaspirate method, adipose derived growth factor-rich preparation (adipose tissue extract; ATE) can be obtained. The authors set out to compare the effects of these two growth factor sources in cell proliferation and migration (scratch) assays of keratinocyte, fibroblast, endothelial and adipose derived stem cells. Growth factors involved in wound healing were measured: keratinocyte growth factor, epidermal growth factor, insulin-like growth factor, interleukin 6, platelet-derived growth factor beta, tumor necrosis factor alfa, transforming growth factor beta and vascular endothelial growth factor. PRP showed higher growth factor concentrations, except for keratinocyte growth factor, that was present in adipose tissue in greater quantities. This was reflected in vitro, where ATE significantly induced proliferation of keratinocytes at day 6 (p < 0.001), compared to plasma and control. Similarly, ATE-treated fibroblast and adipose stem cell cultures showed accelerated migration in scratch assays. Moreover, both sources showed accelerated keratinocyte migration. Adipose tissue preparation has an inductive effect in wound healing by proliferation and migration of cells involved in wound closure. Adipose tissue preparation appears to offer the distinct advantage of containing the adequate quantities of growth factors that induce cell activation, proliferation and migration, particularly in the early phase of wound healing.     

The Expression of Peroxisome Proliferator‐Activated Receptor γ in Pig Fetal Tissue and Primary Stromal‐Vascular Cultures

Objective: This study was designed to determine when peroxisome proliferator‐activated receptor γ (PPARγ) is expressed in developing fetal adipose tissue and stromal‐vascular adipose precursor cells derived from adipose tissue. In addition we examined developing tissue for CCAAT/enhancer‐binding protein β (C/EBPβ) expression to see if it was correlated with PPARγ expression. Pituitary function and hormones involved with differentiation (dexamethasone and retinoic acid) were also tested for their effects on PPARγ expression to determine if hormones known to affect differentiation also effect PPARγ expression in vivo and in cell culture. Research Methods and Procedures: Developing subcutaneous adipose tissues from the dorsal region of the fetal pig were collected at different gestation times and assayed using Western blot analysis to determine levels of PPARγ and C/EBPβ. Hypophysectomy was performed on 75‐day pig fetuses and tissue samples were then taken at 105 days for Western blot analysis. Adipose tissue was also taken from postnatal pigs to isolate stromal‐vascular (S‐V) cells. These adipose precursor cells were grown in culture and samples were taken for Western blot analysis to determine expression levels of PPARγ. Results: Our results indicate that PPARγ is expressed as early as 50 days of fetal development in adipose tissue and continues through 105 days. Expression of PPARγ was found to be significantly enhanced in adipose tissue from hypophysectomized fetuses at 105 days of fetal development (p < 0.05). C/EBPβ was not found in 50‐ or 75‐day fetal tissues and was found only at low levels in 105‐day tissues. C/EBPβ was not found in hypophysectomized (hypoxed) 105‐day tissue where PPARγ was elevated. S‐V cells freshly isolated from adipose tissue of 5‐ to 7‐day postnatal pigs showed the expression of PPARγ1. When S‐V cells were cultured, both PPARγ1 and 2 were expressed after the first day and continued as cells differentiated. High concentrations of retinoic acid decreased PPARγ expression in early S‐V cultures (p < 0.05). Discussion: Our data indicate that PPARγ is expressed in fetal adipose tissue very early before distinct fat cells are observed and can be expressed without the expression of C/EBPβ. The increase in PPARγ expression after hypophysectomy may explain the increase in fat cell size under these conditions. Adipose precursor cells (S‐V cells) from 5‐ to 7‐day postnatal pigs also express PPARγ in the tissue before being induced to differentiate in culture. Thus S‐V cells from newborn pig adipose tissue are probably more advanced in development than the 3T3‐L1 cell model. S‐V cells may be in a state where PPARγ and C/EBPα are expressed but new signals or vascularization are needed before cells are fully committed and lipid filling begins.     

Differential Effects of Thiazolidinediones on Adipocyte Growth and Recruitment in Zucker Fatty Rats

Background

Adipose tissue grows by two mechanisms: hyperplasia (cell number increase) and hypertrophy (cell size increase). Thiazolidinediones are insulin-sensitizing peroxisome proliferator-activated receptor gamma agonists that are known to affect the morphology of adipose tissue.

Methodology

In this study, adipose cell-size probability distributions were measured in six Zucker fa/fa rats over a period of 24 days, from four weeks of age, using micro-biopsies to obtain subcutaneous (inguinal) fat tissue from the animals. Three of the rats were gavaged daily with rosiglitazone, a thiazolidinedione, and three served as controls. These longitudinal probability distributions were analyzed to obtain the rate of increase in cell-size diameter in rosiglitazone-treated animals, and the hyperplasia induced by treatment quantitatively.

Conclusions

We found that treatment leads to hypertrophy that leads to an approximately linear rate of cell diameter increase (2 m/day), and that the hyperplasia evident in treated animals occurs largely within the first eight days of treatment. The availability of additional lipid storage due to treatment may alleviate lipotoxicity and thereby promote insulin sensitivity. The hypothesis that a TZD regimen involving repeated treatments of limited duration may suffice for improvements in insulin sensitivity merits further investigation.     

Regulation of cholesterol storage in adipose tissue

Adipose tissue is a major site of cholesterol storage. In an attempt to define mechanisms controlling this process, a variety of nutritional and metabolic alterations were employed and their effects on adipose tissue cholesterol levels were determined by direct chemical analysis. When rats were raised on Purina chow, a linear increase in the cholesterol/DNA ratio in relation to animal weight (from 120 g [5-6 wk] to 700 g [2 yr]) occurred. The rate of cholesterol accumulation was related to the dietary cholesterol load. Cholesterol accumulation by adipose tissue also occurred in rats raised on a cholesterol-free diet and reached levels exceeding those observed in animals fed on a diet containing 0.05 or 0.1% (w/w) cholesterol. In rats maintained on semisynthetic diets containing 0 to 5% (w/w) cholesterol, the serum cholesterol concentration was inversely related to the dietary concentration, suggesting that feedback inhibition of cholesterol formation may be an important determinant of serum cholesterol levels in this species. Early dietary alterations affected adipose tissue levels later in life. Net cholesterol mobilization from adipose tissue also occurred after acute starvation. Comparison of obese mice with nonobese littermate controls showed that the size of the adipose cholesterol pool was proportional to the degree of adipocity because the amount of cholesterol stored per unit glyceride mass was identical. Adipose tissue cholesterol was not affected by animal sex. Thus, adipose tissue cholesterol levels were dependent on animal age, dietary cholesterol load, early nutritional deprivations, and the size of the adipose organ itself.     

Demography,female life history,and reproductive profiles among the chimpanzees of Mahale

Demography provides critical data to increase our understanding of the evolution, ecology, and conservation of primate populations. The chimpanzees of the Mahale Mountains National Park, Tanzania, have been studied for more than 34 yr on the basis of individual identification and standardized attendance records. From this long-term study, we derived the following demographic data: The major cause of death was disease (48%), followed by senescence (24%) and within-species aggression (16%). Fifty percent of Mahale chimpanzees died before weaning. The median ages of female life history variables were: first maximal swelling, 10.0 yr (n = 5); emigration, 11.0 yr (n = 11); and first birth, 13.1 yr (n = 5). The median period of adolescent infertility was 2.8 yr (n = 4) when calculated from the age at immigration to that at first birth. Female fecundity was highest between 20 and 35 yr of age, with an annual birth rate of 0.2. Twenty-six females that were observed from a young age (10-13 yr) to death at various ages (15-40 yr) gave birth to an average of 3.9 and weaned an average of 1.4 offspring. Twenty-five females that were observed from middle age (18-33 yr) to death in older age (31-48) gave birth to an average of 2.7 and weaned an average of 2.0 offspring. The post-reproductive lifespan for female chimpanzees was defined as the number of years that passed from the year when the last offspring was born to the year when the female died, minus 5. Twenty-five percent of old females had a post-reproductive lifespan. The interbirth interval after the birth of a son (x = 72 mo) tended to be longer than that after the birth of a daughter (x = 66 mo). The extent of female transfer, which is a rule in chimpanzees, is influenced by the size and composition of the unit group and size of the overall local community.     

Life History of Cercopithecus mitis stuhlmanni in the Kakamega Forest, Kenya

Comparative data from wild populations are necessary to understand the evolution of primate life history strategies. We present demographic data from a 29-yr longitudinal study of 8 groups of individually recognized wild blue monkeys (Cercopithecus mitis stuhlmanni). We provide estimates of life history variables and a life table for females. Most females had their first infant at 7 yr. The mean interbirth interval was 28 mo, and decreased from 31 to 18 mo if the first infant died within a year. Interbirth intervals did not differ according to infant sex, but females had longer intervals after their first vs. subsequent births. Infant mortality was 23% and did not differ strongly by sex or mother’s parity. Maximal female lifespan was 32.5–34.5 yr. Across the lifespan, both survivorship and fecundity showed typical primate patterns. Survivorship was lowest in infants, leveled off among juveniles, and then decreased gradually with increasing age in later life. Fecundity was highest among young females and decreased among older females. Births were seasonal, with 64% occurring within 3 mo at the end of the dry season and beginning of the wet season. Survival to 12 mo was higher for infants born during drier months. Birth season timing is plausibly related to thermoregulation of infants, weanling foods, or maternal energy demand. Blue monkeys are a forest-dependent species with a very slow life history and relatively low immature and adult mortality rates compared to closely related guenons living in open habitats. Even among cercopithecines as a whole, they appear to have an exceptionally slow life history relative to body size. Differences in life history “speed” between blue monkeys and their close relatives seem to be related to lower juvenile and adult mortality in forests relative to more open habitats.     

Spermatogenesis in Bclw-deficient mice.

Bclw is a death-protecting member of the Bcl2 family of apoptosis-regulating proteins. Mice that are mutant for Bclw display progressive and nearly complete testicular degeneration. We performed a morphometric evaluation of testicular histopathology in Bclw-deficient male mice between 9 days postnatal (p9) through 1 yr of age. Germ cell loss began by p22, with only few germ cells remaining beyond 7 mo of age. A complete block to elongated spermatid development at step 13 occurred during the first wave of spermatogenesis, whereas other types of germ cells were lost sporadically. Depletion of Sertoli cells commenced between p20 and p23 and continued until 1 yr of age, when few, if any, Sertoli cells remained. Mitochondria appeared to be swollen and the cytoplasm dense by electron microscopy, but degenerating Bclw-deficient Sertoli cells failed to display classical features of apoptosis, such as chromatin condensation and nuclear fragmentation. Macrophages entered seminiferous tubules and formed foreign-body giant cells that engulfed and phagocytosed the degenerated Sertoli cells. Leydig cell hyperplasia was evident between 3 and 5 mo of age. However, beginning at 7 mo of age, Leydig cells underwent apoptosis, with dead cells being phagocytosed by macrophages. The aforementioned cell losses culminated in a testis-containing vasculature, intertubular phagocytic cells, and peritubular cell "ghosts." An RNA in situ hybridization study indicates that Bclw is expressed in Sertoli cells in the adult mouse testis. Consequently, the diploid germ cell death may be an indirect effect of defective Sertoli cell function. Western analysis was used to confirm that Bclw is not expressed in spermatids; thus, loss of this cell type most likely results from defective Sertoli cell function. Because Bclw does not appear to be expressed in Leydig cells, loss of Leydig cells in Bclw-deficient mice may result from depletion of Sertoli cells. Bclw-deficient mice serve as a unique model to study homeostasis of cell populations in the testis.     

Division Cycle of Myxococcus xanthus III. Kinetics of Cell Growth and Protein Synthesis

The kinetics of cell growth and protein synthesis during the division cycle of Myxococcus xanthus was determined. The distribution of cell size for both septated and nonseptated bacteria was obtained by direct measurement of the lengths of 8,000 cells. The Collins-Richmond equation was modified to consider bacterial growth in two phases: growth and division. From the derived equation, the growth rate of individual cells was computed as a function of size. Nondividing cells (growth phase) comprised 91% of the population and took up 87% of the time of the division cycle. The absolute and specific growth rates of nondividing cells were observed to increase continually throughout the growth phase; the growth rate of dividing cells could not be determined accurately by this technique because of changes in the geometry of cells between the time of septation and physical separation. The rate of protein synthesis during the division cycle was measured by pulselabeling an exponential-phase culture with radio-active valine or arginine and then preparing the cells for quantitative autoradiography. By measuring the size of individual cells as well as the number of grains, the rate of protein synthesis as a function of cell size was obtained. Nondividing cells showed an increase in both the absolute and specific rates of protein synthesis throughout the growth phase; the specific rate of protein synthesis for dividing cells was low when compared to growthphase cells. Cell growth and protein synthesis are compared to the previously reported kinetics of deoxyribonucleic acid and ribonucleic acid synthesis during the division cycle.     

REPRODUCTION IN THE FEMALE SUBANTARCTIC FUR SEAL, ARCTOCEPHALUS TROPICALIS

The reproductive tracts of 89 female subantarctic fur seals, taken at Gough Island between November 1977 and October 1978, were examined. Females started ovulating at age 4 yr and all 6-yr-old females were sexually mature. They are mono-ovulatory, alternating between ovaries, and only single embryos were found. Females older than 13 yr ( n = 11) showed poor follicular development and some failed to ovulate. The gestation period (first recorded ovulation to first recorded birth) was 360 d, while delayed implantation (first recorded ovulation to first recorded implantation) lasted for 139 days. Follicle numbers in the functional ovary declined sharply after ovulation while the corpus luteum increased in size until at least 1 mo prior to parturition. The number of follicles in the contralateral ovary increased after midwinter (June/July), and the mean size of the largest follicles peaked prior to ovulation in December. The mean size of the largest follicles increased in both ovaries near implantation time, after reaching a low subsequent to, ovulation. The regressing corpus albicans, conspicuous for approximately 3 mo after parturition, could not be detected macroscopically within one year postpartum. Subantarctic fur seals at Gough Island have a distinct postreproductive class of older females. The pregnancy rate for all females ≥4 yr of age was 79%, and it was 84.5% for the sexually mature group of ≥6 yr of age, while the mean age at puberty was 4.80 yr.     

In Vitro Evaluation of Endothelial Progenitor Cells from Adipose Tissue as Potential Angiogenic Cell Sources for Bladder Angiogenesis

Autologous endothelial progenitor cells (EPCs) might be alternative angiogenic cell sources for vascularization of tissue-engineered bladder, while isolation and culture of EPCs from peripheral blood in adult are usually time-consuming and highly inefficient. Recent evidence has shown that EPCs also exist in the adipose tissue. As adipose tissue is plentiful in the human body and can be easily harvested through a minimally invasive method, the aim of this study was to culture and characterize EPCs from adipose tissue (ADEPCs) and investigate their potential for the neovascularization of tissue-engineered bladder. Adipose stromal vascular fraction (SVF) was isolated and used for the culture of ADEPCs and adipose derived stem cells (ADSCs). After SVF was cultured for one week, ADEPCs with typical cobblestone morphology emerged and could be isolated from ADSCs according to their different responses to trypsinization. Rat bladder smooth muscle cells (RBSMCs) were isolated and cultured from rat bladder. RBSMCs exhibited typical spindle-shaped morphology. ADEPCs had higher proliferative potential than ADSCs and RBSMCs. ADEPCs stained positive for CD34, Stro-1, VEGFR-2, eNOS and CD31 but negative for α-SMA, CD14 and CD45. ADSCs stained positive for CD34, Stro-1 and α-SMA but negative for VEGFR-2, eNOS, CD31, CD14 and CD45. RBSMCs stained only positive for α-SMA. ADEPCs could be expanded from a single cell at an early passage to a cell cluster containing more than 10,000 cells. ADEPCs were able to uptake DiI-Ac-LDL, bind UEA-1 and form capillary-like structures in three-dimensional scaffolds (Matrigel and bladder acellular matrix). ADEPCs were also able to enhance the human umbilical vein endothelial cells’ capability of capillary-like tube formation on Matrigel. Additionally, significantly higher levels of mRNA and protein of vascular endothelial growth factor were found in ADEPCs than in RBSMCs. These results suggest the potential use of ADEPCs as angiogenic cell sources for engineering bladder tissue.     

Effects of plating density and age in culture on growth and cell division of neonatal rat heart primary cultures

Summary The cell-type composition of the initial cell population from protease-dispersed neonatal rat heart tissue has been evaluated using time lapse photography and identification of cell type-specific functions. The effects of two commonly employed plating densities on growth and cell division of the two major cell types were examined. Total protein synthesis rates were not affected by plating density but did change with age in culture. Maximum protein synthesis rates were observed during the period of maximum cell division and cell growth (increase in total cell protein), which was from 24 h in culture to the 4th d in culture. After 6 d in culture, synthesis rates for total proteins remained constant for at least 2 wk. Sizing of cells by Coulter counter analysis indicated that essentially all the cells were increasing in size with age in culture. Measurements of cell numbers and rate of DNA synthesis indicated that the extent of cell division was dependent on plating density. Cells disaggregated from neonatal rat hearts consisted of approximately 75% muslce cells and 25% nonmuscle cells. This composition approximates the cell-type composition of the intact neonatal rat heart. In high density cultures there is little cell division and the relative proportionsof the cell types are preserved with time in culture. In low density cultures, proliferation of nonmuscle cells is a significant process and the composition of the cell population changes drastically during the first 2 to 3 d in culture. These results suggest that the low plating density used by many researchers may limit correlation of data derived from such cultures with the physiological state. It also indicates that plating densities should be given in published accounts for comparisons to be made with results from other laboratories. This work was supported in part by U.S. Public Health Service Grant HL10018 and The Pennsylvania State University Agricultural Experiment Station and was authorized for publication as Paper 5490 in the journal series of the Pennsylvania Agricultural Experiment Station.     

Differences in the mean fat cell diameter of males between 1 and 48 months of age

The mean fat cell diameter was determined from measurements of abdominal adipose cells, obtained during inguinal hernia repair, of 126 white and 95 black males ranging in age from 1 through 48 months of age. The mean diameters of black and white subjects did not differ significantly, suggesting that differences in fatness among adults of these two ethnic groups have their origin beyond the age range of this study. The mean fat cell diameter increased through the 6-8 month age group, decreased until the end of the first year, and then levelled off through 48 months of age. Comparison of this curve with those for the triceps, subscapular, abdominal, and suprailiac skinfolds of the same subjects showed generally parallel courses except for the triceps, which continued to increase in size after the means of fat cell diameters and the other skinfolds had levelled off. Our data indicate that changes in body fatness on the trunk at least in the first 4 years of life may be accounted for by changes in fat cell size.     

Synchronous Cell Division in Cultured Explants of Jerusalem Artichoke Tubers: the Effects of 5-Fluorouracil on Messenger RNA Synthesis and the Induction of Cell Division

Explants of secondary xylern parenchyma tissue from Jerusalemartichoke tubers were induced to undergo cell division and de-differentiateby culture in nutrient medium. The first division was inherentlysynchronous. The system was used to study the involvement ofmessenger RNA synthesis in the induction and continuance ofcell division in previously non-dividing cells. The base analogue 5-fluorouracil (5-FU) inhibited ribosomalRNA synthesis and the processing of ribosomal RNA precursorto mature 25 S and 18 S RNAs. The synthesis of messenger-likeRNAs (heterogeneous in size, labelled to a high specific activityin a pulse incubation, and containing a polyadenylic acid sequence)was less inhibited by 5-FU. Explants grown in 5-FU did not synthesize DNA and did not divide.A direct inhibition of DNA synthesis by 5-FU added late in culturewas reversed by thymidine. An indirect inhibition of DNA synthesisoccurred when 5-FU was present from the start of culture andwas not reversed by thymidine. Because ribosomal RNA synthesisis not necessary for the induction of cell division (Fraser,1975) and because 5-FU was incorporated into mENA, probablyinterfering with its function, these results suggest that 5-FUinhibited the metabolism of mRNA which was required for DNAsynthesis and cell division. The timing of mRNA synthesis required for DNA synthesis andcell division was investigated by adding 5-FU plus thymidineto cultures at various times. By the beginning of DNA synthesisfor the first division, explants were competent, in terms ofmRNA synthesized, to complete the first division. MessengerRNA synthesis occurring before the end of the first divisionallowed explants to undergo at least three more divisions.