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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
PubMed1983

Mood, sexuality, hormones, and the menstrual cycle. II. Hormone levels and their relationship to the premenstrual syndrome.

In women with premenstrual syndrome, negative changes start soon after ovulation gradually increasing as the corpus luteum develops, and reach a maximum during the last 5 days of the luteal phase. They decline rapidly once menstruation starts, disappearing within one or two days of ovarian steroids reaching baseline levels. Positive moods are at maximum when preovulatory estradiol reaches its peak. A comparison of hormone levels in women with high and low degrees of cyclical mood change showed no difference in progesterone, estradiol, testosterone, or androstenedione.

Adult↗
PubMed1983

Mood, sexuality, hormones, and the menstrual cycle. III. Sexuality and the role of androgens.

Sexual interest and activity at different stages of the menstrual cycle was recorded by 55 women with normal ovulatory cycles. In women with marked cyclical mood change, there was an associated cyclical pattern of sexual feelings. Subjective sexuality independent of mood change, was maximal in the mid-follicular (i.e., postmenstrual) and late luteal (i.e., premenstrual) phases. Sexual activity was maximal in the mid-follicular phase. There was no evidence of a periovulatory increase in sexual interest or activity. Mean testosterone levels were correlated with masturbation frequency but not with sexuality involving the partner. A weak association between testosterone and life style (i.e., in full-time work or a housewife) was also evident.

Adult↗
PubMed1983

Somitogenesis in amphibia. IV. The dynamics of tail development.

Following neurulation, the frog segments c.40 somites and concurrently undergoes a striking elongation along the anteroposterior axis. This elongation (excluding the head) is largely the result of a presegmental extension of posterior tissue with a lesser contribution from the extension of segmented tissue. Presegmental extension is entirely the result of activity within a narrow zone of extension that occupies the central region in the tail bud. Within the zone of extension, a minimum of six prospective somites undergo an eight- to ten-fold extension along the axis. The zone passes posteriorly across the tissue of the tail tip. The anterior of the tail bud contains three extended prospective somites in the course of segmentation. The anterior boundary of the zone of extension coincides in space exactly with the anterior boundary of the zone of abnormal segmentation that results from temperature shock. This means that extension ceases immediately before the sudden tissue change associated with segmentation.

Animals↗
PubMed1983

The mechanism of feather pattern development in the chick. 1. The time of determination of feather position.

A regular array of feather primordia covers chick dorsal skin in vivo. The pattern develops over a period of 2 days as a morphogenetic wave sweeps across either side of the back of the chick, forming successive anteroposterior rows of primordia. This paper describes a new method for the culture of chick skin which allows the development of large areas of the feather pattern to be investigated experimentally. Skin is cultured on a substratum of hydrated collagen; since the collagen is transparent, feather primordium development can be observed in detail. The new method has been used to investigate the problem of when the positions of feathers are determined. I show that during the time when the first few rows of primordia are forming, skin taken from just lateral to the most recently formed row can be caused to form an increased number of primordia per row by stretching it anteroposteriorly. This result indicates that the positions of feathers are determined sequentially along an invisible wave which moves just ahead of the visible wave of primordium morphogenesis.

Animals↗
PubMed1983

The mechanism of feather pattern development in the chick. II. Control of the sequence of pattern formation.

During the development of the dorsal feather pattern, a wave of morphogenesis sweeps across the skin forming successive anteroposterior rows of feather primordia. The preceding paper in this series showed that the morphogenetic wave is almost immediately preceded by a wave of determination at which feathers sites are established row by row, (Davidson, 1983). The present paper reports an in vitro experimental investigation of the movement of these waves across the skin. The waves pass undisturbed across a cut made before the pattern forms. Although cultured skin does not grow and consequently forms only a few rows of primordia, the morphogenetic wave takes the same time to cross the prospective feather tissue as in vivo, indicating that the passage of this wave through cultured skin reflects its traverse of the entire pattern in vivo. These results show that the movement of the waves of determination and morphogenesis does not depend on the propagation of any signal across the skin immediately ahead of primordium formation. Their movement derives from a gradient in the temporal differentiation of the skin, established before stage 29. In this respect, the temporal control of feather development in the chick skin resembles the control of somite development in the amphibian paraxial mesoderm (Pearson & Elsdale, 1979). The present results therefore suggest that a programmed gradient of temporal differentiation across the prospective patterned tissue is a common component of the mechanisms which form regular, repetitious patterns in vertebrate embryos.

Animals↗
PubMed1982

Endothelial cell functions in the hemodynamic responses to stress.

ACE is a function of the endothelial cell that appears vital to integrative homeostatic physiology in stress. The endothelial cell, both in the lung and in systemic tissues, is uniquely situated to detect changes in ambient oxygen tension; thereafter, as exemplified by the effects of altered oxygen tension on ACE, the cell is capable of initiating changes that modulate its functions to reflect the altered physiologic state. Based upon extensive studies of endothelial cells propagated in tissue culture, these altered functions are rapid in onset, rapidly reversible, and quite closely correlated to PO2. Integrity of the endothelial cell membrane is necessary for the modulating changes to occur, and indeed, ACE purified from the cell is insensitive to changes in oxygen tension: it is the cell, not the enzyme, that responds to changes in oxygen tension (FIGURE 5). It is important to emphasize the interdependent nature of the several vasoactive systems. The kallikrein-kinin system, in addition to its putative role in blood pressure regulation, is an intimate component of both the coagulation and fibrinolysis plasma protease cascades. The sympathetic nervous system has multiple points of interdigitation in both the kallikrein-kinin and the renin-angiotensin systems; high levels of epinephrine stimulate renin release and activate both plasma and tissue kallikrein. In turn, both of the vasoactive peptides of these systems, bradykinin and angiotensin II, stimulate epinephrine production from the adrenal medulla. Angiotensin II enhances the potency of norepinephrine released from postganglionic sympathetic nerve endings, increasing alpha-adrenergic tone. In addition, multiple interactions have been described between angiotensin II and bradykinin and the formation of prostaglandins by endothelial cells. Preliminary data indicate that the potency of these peptides in causing prostanoid release is, as might be expected, closely correlated to ACE activity, which itself is a function of ambient PO2. These multiple interactions are diagrammed in FIGURE 9. It is noteworthy that the two fundamental regulators of the circulation, pH and PO2, can be shown to interact at the most basic level with endothelial cell function.

Altitude↗
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↗