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Biomedical subjects

D Davidson

Publications and source records attributed to D Davidson.

At least 235 records · Page 13Linked to original sources
PubMed1982

Differences in protein content of sister nuclei: evidence from binucleate and mononucleate cells.

DNA and protein contents of pairs of sister nuclei were determined using a combined Feulgen-dinitrofluorobenzene technique. Sister nuclei were studied in binucleate cells, induced by treatment with 0.1% caffeine, and in sister mononucleate cells of untreated roots. Excised pea roots, grown in culture, were treated with 5-aminouracil to induce mitotic synchrony and with caffeine at the time of peak mitotic index, to provide the maximum number of binucleate cells. The induced binucleate cells form a marked population which was followed through a cell cycle; sister nuclei showed a correlation of volume and protein content, r = 0.79. Protein contents of sister nuclei were rarely identical and at 1 + 2 and 1 + 6 h the difference in protein contents of sister nuclei was significant (p = 0.05). Mean nuclear protein content decreased from 1 + 2 to 1 + 6 h; then, as nuclei entered S phase, their protein content increased. From 1 + 2 to 1 + 14 h the increase in protein content, in absolute amount, was identical in both sister nuclei. This suggests that there was a biphasic pattern of protein uptake; it is differential, in sister nuclei, in the first part of G1 but is identical throughout the rest of interphase. Analysis of sister nuclei from sister mononucleate cells showed a similar pattern of change; this is further evidence, from untreated cells, of a biophasic pattern of protein uptake. Caffeine-treated nuclei had lower protein contents than untreated nuclei, yet they completed a cell cycle and entered mitosis; this suggests that nonessential proteins were no longer present. It is proposed that mitosis is asymmetrical for molecules that regulate rates of macromolecular synthesis, cell growth, and progress through a cell cycle and that once the initial asymmetry has been established, it is maintained throughout interphase, even in binucleate cells in which the two nuclei share a common cytoplasm.

Caffeine↗
PubMed1981

Angiotensin-converting enzyme activity and its modulation by oxygen tension in the guinea pig fetal-placental unit.

Angiotensin-converting enzyme (ACE) activity in the guinea pig fetal-placental unit was assessed at the different oxygen tensions found in utero, during labor, and at birth. To determine fetal-placental ACE activity, we separately perfused in situ term guinea pig fetuses and their placentas via the umbilical vessels under controlled conditions of flow, temperature, and pH. ACE activity was defined as the percent of angiotensin I (AO) or bradykinin (BK) in Krebs-Henseleit solution cleared by a single passage through the placenta or fetus. Peptide concentrations were measured by radioimmunoassay (RIA). Using BK as substrate, we found that placental and fetal ACE activities were reflected by 45% (SD = 10) and 24% (SD = 7) clearances, respectively, at a perfusate PO2 of 29 mm Hg. Maternal hypoxia (PaO2 = 28 mm Hg) decreased placental ACE activity to 16% (SD = 8) and maternal hyperoxia (PaO2 = 191 mm Hg) increased placental ACE activity to 56% (SD = 9). Using a perfusate PO2 of 95 mm Hg, fetal and placental ACE activity increased in less than 5 minutes to 75% (SD = 10) and 77% (SD = 9), respectively. Similar results were obtained using AI as substrate. We conclude that: fetal-placental ACE activity exhibits a chronically reduced level of activity appropriate to the low oxygen tension found in the fetal-placental unit; the placenta is the primary site of ACE activity in the fetus; maternal oxygenation modulates fetal-placental ACE activity; and fetal ACE activity acutely increases with increased fetal oxygenation and thus may play an important physiological role in the regulation of circulating levels of BK and AII and the circulatory adjustments at birth.

Animals↗
PubMed1980

Non-respiratory functions of the lung in the perinatal period.

Beginning with the hypothesis that interference with the metabolic function of the lung could lead to perinatal respiratory disease, we explored the role of one of these functions, angiotensin-converting enzyme activity, in the control of the fetal and newborn circulation. Converting enzyme regulates the concentration of two peptides, bradykinin and angiotensin, important in adapting the fetus to extrauterine life. Initial studies demonstrated decreasing amounts of converting enzyme activity and a parallel decrease in vascular surface with decreasing gestational age. Because we had demonstrated that there is little converting enzyme activity at the low PO2 values of the fetus we examined the fetal-placental unit and found that the placenta is the predominant site of converting enzyme activity in utero and this activity is modulated by maternal PO2. We also found that such pathophysiological accompaniments of premature birth as chilling and acidosis can stimulate the kallikrein-kinin system into overactivity. Because the kallikrein-kinin and renin-angiotensin systems are so closely interrelated with other vasoactive substances, an imbalance in production and degradation is likely to produce some of the pathophysiology seen with premature birth, including systemic hypotension, coagulopathy and oedema.

Angiotensin I↗
PubMed1980

"Popcorn" calcifications: a prognostic sign in osteogenesis imperfecta.

"Popcorn" calcifications appear roentgenographically as a collection of scalloped radiolucencies, each with a sclerotic margin and in some instances, with central densities. The radiographs of 46 children with osteogenesis imperfecta were reviewed retrospectively; 52% had "popcorn" calcifications at one or more sites. A study of these children indicated that these lesions are observed only during active skeletal growth, are not present at birth, occur predominantly around the knees and ankles, and are associated with irregularity or absence of the normal horizontal growth plate. Based on multiple roentgen observations, "popcorn" calcifications appear to result from fragmentation and disordered maturation of the physis, and their presence indicates a disturbance in enchondral ossification which may contribute to the severe growth retardation associated with osteogenesis imperfecta.

Age Factors↗
PubMed1978

Analysis of growth of tetraploid nuclei in roots of Vicia faba.

Growth of nuclei of a marked population of cells was determined from G1 to prophase in roots of Vicia faba. The cells were marked by inducing them to become tetraploid by treatment with 0.002% colchicine for 1 hr. Variation in nuclear volume is large; it is established in early G1 and maintained through interphase and into prophase. One consequence of this variation is that there is considerable overlap between volumes of nuclei of different ages in the cell cycle; nuclear volume, we suggest, cannot be used as an accurate indicator of the age of the cell in its growth cycle. Nuclei exhibit considerable variation in their growth rate through the cell cycle. Of the marked population of cells, about 65% had completed a cell cycle 14--15 hr after they were formed. These tetraploid nuclei have a cell cycle duration similar to that of fast cycling diploid cells of the same roots. Since they do complete a cell cycle, at least 65% of the nuclei studied must come from rapidly proliferating cells, showing that variability in nuclear volumes must be present in growing cells and cannot be attributed solely to the presence, in our samples, of non-cycling cells.

Cell Cycle↗
PubMed1978

Differential growth of sister nuclei in binucleate microspores of Tradescantia paludosa.

Binucleate microspores were induced in Tradescantia paludosa with heat shocks. Nuclear and cell volumes were determined from early G1 to G2. Volumes of sister nuceli, present in a single cell, were rarely the same. It is suggested that, at least in part, nuclear volume is controlled by factors that are 1) present in nuclei, 2) not distributed equally at anaphase, and 3) not rapidly exchanged.

Cell Count↗
PubMed1977

Monoamine metabolites in cerebrospinal fluid in multiple sclerosis.

The concentrations of homovanillic acid (HVA), 5-hydroxyindolylacetic acid (5-HIAA), and 4-hydroxy, 3-methoxyphenylethylene glycol (MHPG) were estimated in the lumbar cerebrospinal fluid (CSF) of control subjects and in some patients who probably, and others who definitely, suffered from multiple sclerosis (MS). In the control group, the concentration of HVA was lower in people who underwent lumbar puncture having fasted and been recumbent for 12 hours before the procedure than in those from whom CSF was obtained under non-standardised conditions. These studies demonstrate that a standardised procedure for lumbar puncture is required in order to obtain meaningful results. In patients suffering from MS the CSF 5-HIAA concentrations were significantly lower than in comparable controls but the HVA concentrations did not differ. There was no relationship between metabolite concentrations, site of lesion, the duration of the disease, gamma-globulin levels nor the occurrence of relapse within the previous month.

Female↗
PubMed1977

Relationship between nuclear morphology and the phases of the cell cycle during cercarial development of the digenetic trematode Trichobilharzia ocellata.

During the proliferative phase of cercarial development in the digenetic trematode Trichobilharzia ocellata, nuclei varied in size, appearance of the chromatin, and intensity of Feulgen staining. On the basis of interphase nuclear morphology six nuclear classes were identified. Data from microspectrophotometric determinations and 3H-TdR labeling experiments were used to correlate each kind of interphase nucleus with a phase of the cell cycle. Marked variability in nuclear area developed between cells by time they reached late G1. Increases in nuclear area could not be correlated with the onset of DNA synthesis. Throughout all stages of development of T. ocellata cercariae, proliferating cells divide mitotically; meiotic divisions were never seen. Thus, the mode of reproduction appears to be asexual. No evidence was found to support previous suggestions of diploid parthenogenesis.

Animals↗
PubMed1977

Cell cycle analysis in developing cercariae of Trichobilharzia ocellata (Trematoda: Schistosomatidae).

Cellular proliferation has been analyzed during cercarial development of the digenetic trematode Trichobilharzia ocellata. Prior to the tail-bud stage (about 1,000 cells), cells were actively involved in cellular proliferation. The mean cell cycle was 15.2 hr. The time for mitosis was 1.6 hr; for G1, 5.6 hr; for G2, 3.2 hr, and for the S phase, 4.8 hr. Beginning with the tail-bud stage, an increasing proportion of cells accumulate in the G1 phase. Cytological evidence of changes in the amount of cytoplasm per cell revealed that these noncycling cells were differentiating. During organ development and differentiation, the proportion of proliferating cells decreases and by the 2,000-celled stage proliferation ceases. Our results do not support a germinal lineage theory of cercarial development since none of the observed nuclear types could be unequivocally identified as belonging to the germ line.

Animals↗
PubMed1976

Lysosomal enzymes in cerebral atrophy.

In seven patients with cerebral atrophy due to pre-senile dementia and/or cerebrovascular disease, the activity of acid phosphatase in lumbar cerebrospinal fluid (CSF) was higher (p less than 0.05) than in six controls. The activity of arylsulphatase and beta-galactosidase in CSF was the same in the two groups. In the serum, the activities of acid phosphatase and arylsulphatase were the same in the two groups but the activity of beta-galactosidase was lower (p less than 0.02) in patients with cerebral atrophy.

Acid Phosphatase↗