Decreased Cell Production Research Articles

A new and reliable way to detect frost tolerance in Pooideae plants

The morphological markers of plant-stress tolerance are often evaluated as having essential limitations: a continuous reaction to the environmental fluctuations and their excessive influence on each other. To avoid these limitations, the authors propose a new strategy for searching for markers, based on the identification of macro-traits related with adaptive growth bifurcation. The later manifests itself in roots as a sharp decline of meristem cell production at ~ 4 °C. It has been detected that under the hardening regime, the length of root growth zone of stress-tolerant Festuca pratensis is significantly shorter than that of less stress-tolerant Lolium multiflorum and Festulolium braunii. Using a quantitative approach, it was determined that this decrease in cell production results in the sharp decrease of growing cells number and also strongly reduces the growth zone length. Besides this, during the hardening regime, the length dynamics of F. pratensis root hairs was significantly higher than that of other species. This effect is caused by meristem bifurcation, which determines the rare release of cells from the growth zone, thus, the previous root hairs increase significantly. The proposed bifurcation-related markers seem to withstand these limitations and could be applied in plant breeding and the ecological evaluation of plants.

Tree Growth Under Climate Change: Evidence From Xylogenesis Timings and Kinetics.

Tree growth is one of the most studied aspects of tree biology, particularly secondary growth. In the Mediterranean region, cambial activity is mostly determined by water availability. Climatic projections for the Mediterranean region predict more frequent and intense droughts, and longer periods without precipitation. To investigate tree growth under the predicted scenarios of climate change, a water manipulation experiment was conducted in a maritime pine stand (Pinus pinaster Aiton). In 2017, fifteen trees were divided into three groups: control, rain exclusion, and irrigation. Drought conditions were simulated by installing a continuous plastic sheet on the forest floor from March to September. Trees under irrigation treatment were watered twice a week in September. Cambial activity and xylem formation was monitored every 10 days from February 2017 until March 2018. Cell production was maximal around the spring equinox in all treatments. Trees under rain exclusion decreased cell production rates, xylogenesis duration, and latewood cell wall thickness. The extra irrigation in September did not produce noticeable differences in xylogenesis compared to trees in the control treatment. The synchronization of maximum cambial division rates around the vernal equinox (spring) could allow Mediterranean trees to mitigate the impact of summer drought. With the predicted increase in drought intensity and frequency, lower tree productivity, carbon sequestration, and wood biomass are expected.

S-adenosylhomocysteine (AdoHcy)-dependent methyltransferase inhibitor DZNep overcomes breast cancer tamoxifen resistance via induction of NSD2 degradation and suppression of NSD2-driven redox homeostasis

Endocrine therapies (e.g. tamoxifen and aromatase inhibitors) targeting estrogen action are effective in decreasing mortality of breast cancer. However, their efficacy is limited by intrinsic and acquired resistance. Our previous study demonstrated that overexpression of a histone methyltransferase NSD2 drives tamoxifen resistance in breast cancer cells and that NSD2 is a potential biomarker of tamoxifen resistant breast cancer. Here, we found that DZNep, an indirect inhibitor of histone methyltransferases, potently induces the degradation of NSD2 protein and inhibits the expression of NSD2 target genes (HK2, G6PD, GLUT1 and TIGAR) involved in the pentose phosphate pathway (PPP). DZNep treatment of tamoxifen-resistant breast cancer cells and xenograft tumors also strongly inhibits tumor growth and the cancer cell survival through decreasing cell production of NADPH and glutathione (GSH) and invoking elevated ROS to cause apoptosis. These findings suggest that DZNep-like agents can be developed to target NSD2 histone methyltransferase for effective treatment of tamoxifen-resistant breast cancer.

Elucidating the regulatory roles of microRNAs in maize (Zea mays L.) leaf growth response to chilling stress.

MAIN CONCLUSION: miRNAs control leaf size of maize crop during chilling stress tolerance by regulating developmentally important transcriptional factors and sustaining redox homeostasis of cells. Chilling temperature (0-15°C) is a major constraint for the cultivation of maize (Zea mays) which inhibits the early growth of maize leading to reduction in leaf size. Growth and development take place in meristem, elongation, and mature zones that are linearly located along the leaf base to tip. To prevent shortening of leaf caused by chilling, this study aims to elucidate the regulatory roles of microRNA (miRNA) genes in the controlling process switching between growth and developmental stages. In this respect, hybrid maize ADA313 seedlings were treated to the chilling temperature which caused 26% and 29% reduction in the final leaf length and a decline in cell production of the fourth leaf. The flow cytometry data integrated with the expression analysis of cell cycle genes indicated that the reason for the decline was a failure proceeding from G2/M rather than G1/S. Through an miRNome analysis of 321 known maize miRNAs, 24, 6, and 20 miRNAs were assigned to putative meristem, elongation, and mature zones, respectively according to their chilling response. To gain deeper insight into decreased cell production, in silico, target prediction analysis was performed for meristem specific miRNAs. Among the miRNAs, miR160, miR319, miR395, miR396, miR408, miR528, and miR1432 were selected for confirming the potential of negative regulation with their predicted targets by qRT-PCR. These findings indicated evidence for improvement of growth and yield under chilling stress of the maize.

The MADS transcription factor XAL2/AGL14 modulates auxin transport during Arabidopsis root development by regulating PIN expression

Elucidating molecular links between cell-fate regulatory networks and dynamic patterning modules is a key for understanding development. Auxin is important for plant patterning, particularly in roots, where it establishes positional information for cell-fate decisions. PIN genes encode plasma membrane proteins that serve as auxin efflux transporters; mutations in members of this gene family exhibit smaller roots with altered root meristems and stem-cell patterning. Direct regulators of PIN transcription have remained elusive. Here, we establish that a MADS-box gene (XAANTAL2, XAL2/AGL14) controls auxin transport via PIN transcriptional regulation during Arabidopsis root development; mutations in this gene exhibit altered stem-cell patterning, root meristem size, and root growth. XAL2 is necessary for normal shootward and rootward auxin transport, as well as for maintaining normal auxin distribution within the root. Furthermore, this MADS-domain transcription factor upregulates PIN1 and PIN4 by direct binding to regulatory regions and it is required for PIN4-dependent auxin response. In turn, XAL2 expression is regulated by auxin levels thus establishing a positive feedback loop between auxin levels and PIN regulation that is likely to be important for robust root patterning.

Severe Shading Reduces Early Fruit Growth in Apple by Decreasing Cell Production and Expansion

Shading during early fruit development reduces fruit growth and initiates fruit abscission in apple (Malus ×domestica). The mechanisms mediating the decline in fruit growth in response to shading are not well understood. In this study, the effects of shading during early fruit development on cell production and expansion were investigated. Additionally, the effects of shading on the expression of genes associated with carbohydrate metabolism, fruit growth, and cell production and expansion were investigated to develop a better understanding of the molecular mechanisms and to identify genes that mediate the reduction in fruit growth. Shading of isolated branches or entire trees ≈15 to 18 days after full bloom resulted in a sharp decline in fruit growth by 3 days after treatment. Reduction in fruit growth was consistently mediated by a decline in cell production within 3 days after treatment. Reduced fruit growth was also associated with lower cell size by 3 to 7 days after shading in two different years. These data indicate that the reduction in fruit growth as a result of shading is mediated by a reduction in cell production and expansion. The expression of two sorbitol dehydrogenase (SDH) genes, MdSDH1 and MdSDH2, was higher in the shaded fruit by up to 10-fold, suggesting an increase in SDH activity to meet the immediate respiratory demands of the developing fruit. The auxin response factor (ARF), MdARF106, displayed ≈3-fold higher expression in the shaded fruit, suggesting its involvement in regulating mechanisms that mediate the reduction in fruit growth. Two A2-type cyclins, MdCYCA2;2 and MdCYCA2;3, which are positively associated with cell production, displayed lower expression in the shaded fruit by up to 4.6-fold. Conversely, MdKRP4 and MdKRP5, cell cycle genes negatively associated with cell production, displayed 3.9- and 5.3-fold higher expression in the shaded fruit, respectively. Additionally, two genes associated with cell expansion, MdCOB1 (cobra1) and MdEXPA10;1 (expansin), displayed lower expression in the shaded fruit. Together, these data indicate that shading results in coordinated changes in the expression of carbohydrate metabolism-related genes, key transcription factors related to fruit growth, and genes associated with cell production and expansion. These changes may subsequently decrease the progression of the primary processes that mediate fruit growth.

Maternal Tobacco Smoking and Decreased Leukocytes, Including Dendritic Cells, in Neonates

Maternal smoking in pregnancy is associated with respiratory diseases in the offspring, possibly due to prenatal influences on the developing immune system. We investigated whether maternal smoking in pregnancy was associated with cord blood leukocyte numbers, including precursor dendritic cells, adjusting for concomitant factors. In a prospective healthy birth cohort study, total leukocyte counts were reduced in neonates of smoking mothers [10.7 (8.4-13.0), n=14] compared with nonexposed infants [14.7 (13.7-15.7), n=74, p=0.002] [geometric mean cells x 10(3)/microL (95% confidence interval)]. All leukocyte subsets were decreased, most prominently segmented neutrophils [4.3 (2.8-5.7) versus 6.2 (5.5-6.8), p=0.021], lymphocytes [3.8 (2.9-4.8) versus 5.0 (4.5-5.6), p=0.036], and myeloid precursor dendritic cells [12.7 cells/microL (9.1-17.8) versus 18.3 (15.8-21.2), p=0.055]. These differences persisted after adjustment for possible confounders. Predictors of myeloid precursor dendritic cell numbers in multivariable models were maternal smoking (-5.1 cells/microL, p=0.042), age (-0.5 cells/microL/y, p=0.035), and, marginally, asthma (+8.1 cells/microL, p=0.075). The decrease of all leukocytes in neonates of smoking mothers could be clinically significant and suggests a decreased cell production, increased peripheral recruitment, or retention in bone marrow. Given the importance of dendritic cells in early immune responses, their decrease might reflect an impact of maternal smoking on the developing fetal immune system.

Long-Term Coculture of Adult Human Healthy Donor CD34+ Cells Shows Elevation of Telomeres in a Subgroup of Donors Independent of Age, Stem Cell Function and Telomerase Activity.

Long-term cytokine-supplemented or stromal cocultures of human CD34+ cells, particularly from cord blood (CB), show expansion of hematopoietic progenitors and stem cells. Ultimately, however cultures decline and terminally differentiate. Despite upregulation of telomerase activity in proliferating primitive hematopoietic cells, telomere shortening has generally been reported in long-term cultures of CB, bone marrow or G-CSF mobilized peripheral blood CD34+ cells. In earlier reports, we described a long-term culture of hematopoietic stem cells on a murine OP9 bone marrow stroma cell line transfected with an adenovector expressing thrombopoietin, which allowed an extensive proliferation and self-renewal of CB CD34+ cells for 4–5 months with sustained elevation of telomerase activity and without concomitant significant telomere shortening (Blood, 2004). Here, we evaluated adult healthy donor peripheral blood (PB) CD34+ cells in the same OP9/Tpo coculture system. To determine progenitor and stem cell production, standard CFC and 2ndry cobblestone area-forming cell assays (CAFC assayed at 5 weeks on MS5 stroma) were undertaken weekly with suspension cells. In addition telomere length was measured by telomere restriction fragment (TRF) assay, and telomerase activity by TRAP assay on input CD34+ cells, and weekly on culture suspension cells. Maximum total cell, CFC and CAFC production was seen in the first 4 weeks with up to 80-fold expansion in cell count, up to 4-fold expansion in CFC and up to 13-fold expansion in CAFC. Thereafter a continuous decrease in production of cells, CFC 2ndry CAFC was observed and cultures terminated at week 8. Mean telomere length of input PB CD34+ cells was 9,5 ± 0,5 kbp. After 4 weeks in culture, telomere length remained stable (9,6 ± 0,5 kbp). In 3/6 cultures terminated, cultures showed only a slightly decrease of telomere length compared to the input population (0,55 ± 0,1 kbp loss). However, in 2/6 cultures we could demonstrate an elevation of telomeres (+ 0,3 kbp) independent of a rapid loss of telomerase activity in all cultures during the culture period. Furthermore, the elevation of telomeres did not correlate with an enhanced stem/progenitor cell activity. These data confirm earlier results of granulocyte telomere change in myeloma patients following chemotherapy and tandem transplantation, where 154/193 patients showed an expected loss of telomeres during the treatment period, whereas 39/193 patients had an unexpected elevation of telomeres. We could now show in healthy donors that this phenomenon is independent of bone marrow stress due to chemotherapeutic treatment. In conclusion, we could show that the stromal coculture system with OP9/Tpo is highly effective in stem/progenitor cell expansion not only in CB but also in PB CD34+ cells. It is the first culture system, which allows expansion of hematpoietic cells without significant telomere erosion. We furthermore describe for the first time an age-independent healthy donor population which shows telomerase-independent, significant telomere elevation. Further studies have to demonstrate, if this phenomenon is potentially linked to a higher susceptibility for cancer disease.

Cell cycle modulation in the response of the primary root of Arabidopsis to salt stress.

Salt stress inhibits plant growth and development. We investigated the importance of cell cycle regulation in mediating the primary root growth response of Arabidopsis to salt stress. When seedlings were transferred to media with increasing concentrations of NaCl, root growth rate was progressively reduced. At day 3 after transfer of seedlings to growth medium containing 0.5% NaCl the primary roots grew at a constant rate well below that prior to the transfer, whereas those transferred to control medium kept accelerating. Kinematic analysis revealed that the growth reduction of the stressed roots was due to a decrease in cell production and a smaller mature cell length. Surprisingly, average cell cycle duration was not affected. Hence, the reduced cell production was due to a smaller number of dividing cells, i.e. a meristem size reduction. To analyze the mechanism of meristem size adaptation prior to day 3, we investigated the short-term cell cycle events following transfer to saline medium. Directly after transfer cyclin-dependent kinase (CDK) activity and CYCB1;2 promoter activity were transiently reduced. Because protein levels of both CDKA;1 and CDKB1;1 were not affected, the temporary inhibition of mitotic activity that allows adaptation to the stress condition is most likely mediated by posttranslational control of CDK activity. Thus, the adaptation to salt stress involves two phases: first, a rapid transient inhibition of the cell cycle that results in fewer cells remaining in the meristem. When the meristem reaches the appropriate size for the given conditions, cell cycle duration returns to its default.

The decrease in growth of phosphorus‐deficient maize leaves is related to a lower cell production

ABSTRACTThe spatial distribution of leaf elongation and adaxial epidermal cell production in leaf 6 of maize (Zea mays L. cv. Cecilia) plants grown in a growth chamber under two contrasting availabilities of P in the soil was investigated. Lower displacement velocities from 32.5 mm from leaf base and a shorter growth zone were found in low P (LP) leaves compared with control leaves. P deficiency significantly diminished maximum relative elemental growth rate and shifted its location closer to the leaf base. Cells were significantly longer in LP than in control leaves for all positions from the leaf base except at the end of the growth zone. For both treatments it took a similar time for a cell situated at the leaf base to reach the limit of the growth zone. The average length of the cell division zone was decreased by 21% in LP leaves. Significant differences were found in cell production and cell division rates from 12.5 mm from the leaf base although maximum values were similar between P treatments. A shorter zone of cell division with lower cell production rates along most of its length was the regulatory event that decreased cell production, and ultimately leaf elongation rates, in P‐deficient maize plants.

Target organ toxicity and leukopenia in Fischer 344 rats given intravenous doses of vinblastine and desacetyl vinblastine

The toxicity and leukopenia produced by vinblastine or desacetyl vinblastine were established in 1-month studies in rats. Groups of male Fischer 344 rats were given weekly intravenous doses of vinblastine or desacetyl vinblastine at doses of 0.08, 0.16, 0.32, 0.64, or 1.28 mg/kg. The target organ toxicity was similar for both compounds. Decreased cell production in the thymus, testes, and bone marrow was produced in the animals of the two highest dose groups for both compounds with the degree of severity greater in the highest dose group. All high dose rats (1.28 mg/kg) given desacetyl vinblastine and three rats given vinblastine died prior to study termination. Body weight loss was more pronounced in high dose rats given desacetyl vinblastine, but at lower doses there were no significant differences in body weight reduction for rats receiving either compound. Leukopenia occurred at all dose levels of 0.32 mg/kg and higher. During the first 2 weeks of the study, rats given 1.28 mg/kg of desacetyl vinblastine had a greater leukopenic response than rats given 1.28 mg/kg of vinblastine. It is concluded that both compounds produced similar target organ toxicity and leukopenia without deaths at doses of 0.32 and 0.64 mg/kg given once a week for 4 weeks. At the high dose (1.28 mg/kg) desacetyl vinblastine was more toxic than vinblastine resulting in greater mortality and body weight reduction.

Antibodies to granulocyte precursors in selective myeloid hypoplasia and other suspected autoimmune neutropenias: use of HL-60 cells as targets

Patients with syndromes of autoantibody-mediated hematocytopenias may manifest signs of increased cell destruction and/or decreased cell production, depending on the maturity of the target cell and the effects of antibody binding. The purpose of this study was to use a cultured human cell line of hematopoietic origin for in vitro assays of antibody binding to overcome the relative inaccessibility of natural human marrow progenitor cells. This report describes the detection, using radioiodinated staphylococcal protein A (SPA), of antibodies binding to a human promyelocytic cell line (HL-60) in sera from three patients with chronic idiopathic granulocytic hypoplasia ("pure white cell aplasia," PWCA) and 22 patients with other syndromes of suspected immune neutropenia. Bone marrow from patients with increased IgG binding to HL-60 cells showed less than 15% granulocytic lineage cellularity in 11 of 17 cases. In vitro differentiation of HL-60 cells by retinoic acid resulted in increased IgG binding for sera that had shown increased IgG binding to mature granulocytes but not undifferentiated HL-60 cells; in contrast, for sera with antibodies to untreated HL-60 cells and for normal serum, in vitro differentiation had little effect on IgG binding. Antibodies eluted from mature granulocytes were similar to the parent serum regarding the ratio of IgG binding to mature cells v HL-60 cells. No sera from 19 patients with febrile transfusion reactions showed increased IgG binding to HL-60 cells in the absence of increased IgG binding to mature granulocytes, although two sera had antibodies to both cell types. The use of HL-60 cells as targets may permit measurement of serum antibodies associated with granulocytic hypoplasia. In combination with assays to detect antibody binding to mature granulocytes, these techniques may discriminate among autoantibody specificities for antigens that are gained, conserved, or lost during myeloid maturation.

Antibodies to Granulocyte Precursors in Selective Myeloid Hypoplasia and Other Suspected Autoimmune Neutropenias: Use of HL-60 Cells as Targets

Abstract Patients with syndromes of autoantibody-mediated hematocytopenias may manifest signs of increased cell destruction and/or decreased cell production, depending on the maturity of the target cell and the effects of antibody binding. The purpose of this study was to use a cultured human cell line of hematopoietic origin for in vitro assays of antibody binding to overcome the relative inaccessibility of natural human marrow progenitor cells. This report describes the detection, using radioiodinated staphylococcal protein A (SPA), of antibodies binding to a human promyelocytic cell line (HL-60) in sera from three patients with chronic idiopathic granulocytic hypoplasia (“pure white cell aplasia,” PWCA) and 22 patients with other syndromes of suspected immune neutropenia. Bone marrow from patients with increased IgG binding to HL-60 cells showed less than 15% granulocytic lineage cellularity in 11 of 17 cases. In vitro differentiation of HL-60 cells by retinoic acid resulted in increased IgG binding for sera that had shown increased IgG binding to mature granulocytes but not undifferentiated HL-60 cells; in contrast, for sera with antibodies to untreated HL-60 cells and for normal serum, in vitro differentiation had little effect on IgG binding. Antibodies eluted from mature granulocytes were similar to the parent serum regarding the ratio of IgG binding to mature cells v HL-60 cells. No sera from 19 patients with febrile transfusion reactions showed increased IgG binding to HL- 60 cells in the absence of increased IgG binding to mature granulocytes, although two sera had antibodies to both cell types. The use of HL-60 cells as targets may permit measurement of serum antibodies associated with granulocytic hypoplasia. In combination with assays to detect antibody binding to mature granulocytes, these techniques may discriminate among autoantibody specificities for antigens that are gained, conserved, or lost during myeloid maturation.

Inhibition of cell proliferation by cytosine-arabinoside and its interference with spatial and temporal differentiation patterns in the chick retina.

Incubation of chick embryos with 200 nmoles/egg of cytosine arabinoside (AraC) completely inhibits cell proliferation in the embryo. At an age older than embryonic day 4 (E4) more than 90% of the embryos survive this treatment. The drug induces various malformations; in particular the retina is heavily affected. This simple method offers the possibility to study the effect of a more or less decreased cell production on processes of further differentiation and histogenesis of retinal tissue. The following results are obtained: In spite of the inhibition of cell proliferation in the retina by AraC an abnormally thick basal lamina is found and the expansion of the eye still proceeds, indicating that eye growth is not only dependent on retinal cell numbers. Stereotyped malformations of retinal histogenesis are induced and categorized into three groups: in addition to areas of normal structure cells are found arranged in rosettes and in half-rosettes sometimes linked by areas of undefined transient cell arrangements. The results point to a strong tendency of a severely diminished cell population to form regularly laminated retinal-like structures as long as a minimal ratio of cell types is given. The spatio-temporal appearance of the type of retinal malformation in a given retinal area is dependent on the time of AraC exposure and thus on the degree of differentiation reached at a "spatio-temporal spot": Full rosettes develop at earlier, and half-rosettes at later stages of AraC interference. Furthermore, deformities first appear on temporal and ventral sides. Thus, the establishment of these malformations follows and reflects the normal sequence of differentiation within the retina. Cells within rosettes organize in specific layers and start to differentiate normally. This shows that earlier formed cells are not dependent on the influence of factors derived from cells that are formed later for their proper differentiation.

Morphological and cell proliferative study on the growth of visceral organs in monosodium L-glutamate-treated obese mice.

The growth pattern of visceral organs was investigated in monosodium L-glutamate (MSG)-treated obese mice with hypothalamic lesions. Male Jcl-ICR strain mice were subcutaneously injected with MSG, 2 mg/g of body weight daily, for five days after birth. The MSG-treated mice became obese after 4 weeks of age. According to patterns of weight gain compared with those in the control mice, the visceral organs in the MSG-treated mice were classified into three groups as follows: The first group of organs (heart, lungs, spleen, pancreas, kidneys, testes, brain and submandibular glands) remained absolutely lower in weight throughout their growth. The second group of organs (liver and stomach) was low in weight until 12 weeks of age, but became identical to that of the control mice after 16 weeks of age. The third group of organs (epididymal fat, small intestine and colon) showed lower weight until 4 weeks of age and were significantly heavier than those in the control mice after 8 weeks of age. The heart in the first group of organs apparently had hypertrophic muscle cells after 8 weeks of age and became significantly hypoplastic due to decreased cell production as was revealed by the continuous suppression of mitotic activity and DNA synthesis by [3H]thymidine autoradiography. The liver in the second group of organs became significantly hypoplastic due to decreased cell production and showed the same weight with the control mice due to the development of fatty liver. The small intestine in the third group of organs became hypoplastic due to decreased cell production in the crypts until 4 weeks of age, and became hypertrophic and hyperplastic by the acceleration of cell production in the crypts from 4 to 8 weeks of age. From these findings, in the MSG-treated mice with specific growth patterns of visceral organs, it is suggested that low energy expenditure results in a relatively excessive energy supply and leads to obesity, because most of the important organs with major physiological functions became hypoplastic. Moreover, it seems that hypertrophy and hyperplasia of the intestine suggest a possible acceleration of the absorptive function.

5,5'-Diphenylhydantoin (phenytoin) attenuates the action of 3,5,3'-triiodo-L-thyronine in cultured GC cells.

We have previously reported that 5,5'-diphenylhydantoin (DPH) inhibits total cellular and specific nuclear T3 binding by cultured GC cells, a rat pituitary tumor cell line that produces GH. DPH decreased competitively the rate of T3 accumulation by GC cells and noncompetitively inhibited specific nuclear T3 binding as well. To determine the biological consequences of these DPH effects on cellular and nuclear T3 binding, we studied the effect of DPH on the growth rate and GH production of GC cells cultured in Dulbecco's Modified Eagle's Medium with 10% serum. Incubation with T3 stimulated the GC cell growth rate in a dose-dependent manner. The half-maximal growth rate was achieved at a T3 concentration of 0.18 nM, and the maximal effect was observed at 0.4 nM T3. Addition of DPH to GC cells cultured with 0.15 nM T3 resulted in a dose-dependent decrease in the GC cell growth rate. The half-maximal depression of the rate of GC cell growth occurred at 185 microM DPH, a concentration that results in an approximately 50% decrease in cellular and nuclear T3. The DPH-induced decrease in GC cell growth was abolished by the addition of increasing concentrations of T3 (maximal concentration, 1.0 nM). Similarly, DPH effected a dose-dependent decrease in GH production in cells cultured with physiological concentrations of T3 (0.15 nM). The decrease in GH production of cells incubated with 200 microM DPH was associated with a decrease of similar magnitude in GH mRNA. These findings suggested that the DPH effect on GH production was mediated at a pretranslational level. Addition of increasing concentrations of T3 up to 5 nM completely abolished the DPH-associated decrease in GH production. Finally, studies of the effects of DPH on cell growth and GH production in cultures maintained with T3-depleted conditions were carried out to detect putative agonist activity of DPH. In the present investigation, we were unable to detect agonist activity of DPH that was more than 10-15% of the effect of maximal doses of T3. The data suggest that DPH attenuates the action of T3 in GC cells, probably because of a decrease in the steady state concentrations of cellular and nuclear T3. These attributes of DPH suggest that the drug or related analogs may serve as prototypes of agents that may decrease thyroid hormone activity at target tissues.

The effect of single and of multiple doses of prednisolone tertiary butyl acetate on cell population kinetics in the small bowel mucosa of the rat.

The effect of single and of multiple doses of prednisolone upon cell population kinetics in the rat jejunal crypt was investigated, using autoradiography and stathmokinetic techniques with vincristine. Single injections of prednisolone (2.5 mg/kg body weight) induced a depression both flash thymidine labelling and mitotic indices; this change was shown to be due to a decreased cell production rate. Recovery of these proliferative indices occurred over seven days after injection; measurement of crypt size parameters showed a transient decrease in crypt population. Multiple daily injections of prednisolone (1 mg/kg body weight) produced a more sustained decrease in labelling and mitotic indices, which lasted as long as injections were continued (7 days); stathmokinetic techniques showed decreases in cell production rates, and the crypt population was also depressed throughout this period. It is concluded that prednisolone depresses cell proliferative rates in rat jejunal mucosa.

Cell turnover and loss and the gastric mucosal barrier.

Decreased turnover and increased loss of gastric epithelial cells cause disruption of the gastric mucosal barrier. Stress, cortisone, ACTH, and uremia reduce the production rate of gastric epithelial cells. Aspirin, alcohol, phenylbutazone, chili powder, and tobacco powder cause acute loss of epithelial cells. In atrophic gastritis there is a high turnover which may be partly responsible for its resistance to the effect of aspirin. Any situation where there is increased cell loss and/or decreased cell production will lead to disequilibrium, disruption of the gastric mucosal barrier, and clinically significant gastric lesions such as gastric erosions and hemorrhagic erosive gastritis.

Intestinal cell proliferation during fractionated abdominal irradiation.

In the mouse, at normal steady state of cell proliferation, the compensatory proliferative response to intestinal irradiation is such that when radiation exposures totalling 1,000 R are concentrated over the first few days of the week, summated proliferative activity for the entire week is near control levels. Symmetrically distributed exposures over a five-day treatment week (200 R daily, and especially 333 R on Monday, Wednesday and Friday) result in depressed levels of overall weekly proliferation. In these instances, the weekend break is particularly crucial. Similar results were obtained when the one-week measurement period was inserted between the third and fifth week of abdominal therapy, except in this instance, 200 R per day did not result in sub-control levels of proliferation, whereas 333 R on M, W and F, continued to do so. The intestine seems able to maintain its barrier epithelium for extended periods of diminished cell input, provided such is not too severe and that it seems from decreased cell production rate per crypt rather than from crypt attrition. A partial explanation for this relative tolerance is given by the finding that the vast majority of proliferative cells, even those irradiated and rendered permanently incapable of further division, succeed in migrating up the villus and hence help to maintain a barrier epithelium. In that sense, nearly all cell divisions become useful, even in the face of repeated exposures.

Amprolium poisoning of preruminant lambs: an investigation of the encephalopathy and the haemorrhagic and diarrhoeic syndromes.

An experiment was conducted to investigate the mechanisms responsible for the brain lesions, diarrhoea and haemorrhages produced by amprolium poisoning of preruminant lambs. The encephalopathy was preceded by a reduction of cerebrocortical transketolase activity. Diarrhoea was not associated with histological evidence of pathological change in the small intestine, and in lambs with severe diarrhoea the small intestinal levels of alkaline phosphatase and lactase were unaffected. Haemorrhages were associated with a thrombocytopenia which was attributed to degeneration of bone marrow megakaryocytes. The bone marrow of the majority of the lambs which had received amprolium for 3 wk or more was severely depopulated, erythrocyte precursors being the most severely affected. The marrow depopulation was atrributed to decreased cell production, as the majority of the remaining cells showed little evidence of degeneration and the number of mitotic figures in the marrow of amprolium-treated lambs was considerably reduced as compared with the controls.