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Biomedical subjects

D Davidson

Publications and source records attributed to D Davidson.

At least 217 records · Page 12Linked to original sources
PubMed1986

Systemic hemodynamics affecting cardiac output during hypocapnic and hypercapnic hypoxia.

Systemic hemodynamic adjustments involved in the control of cardiac output (CO) were examined in chronically instrumented unanesthetized sheep inhaling gas mixtures resulting in hypocapnic hypoxia (H) [arterial pH (pHa) = 7.53, arterial partial pressure of O2 (Pao2) = 30 Torr, arterial partial pressure of CO2 (Paco2) = 29 Torr] or hypercapnic hypoxia (HCH) (pHa = 7.14, Pao2 = 34 Torr, Paco2 = 72 Torr) for 1 h. H (n = 7) and HCH (n = 6) resulted in 26% and 61% increases in CO, respectively, and mean systemic arterial pressure rose to a greater extent during HCH. Both H and HCH resulted in increased blood flow (microsphere method) to the peripheral systemic circulation including the brain, heart, diaphragm, and nonrespiratory skeletal muscle (the latter blood flow increased 120% during H and 380% during HCH). Gastrointestinal and renal blood flow remained unchanged during H and HCH. Transit time of green dye from the pulmonary artery to regional veins in the hindlimb and intestine was 5.0 and 8.2 s, respectively, during base-line conditions and remained unchanged with HCH. During HCH, regional O2 consumption increased 274% for the hindlimb and decreased 39% for the intestine. Total catecholamines rose 250% during H and 3,700% during HCH. During hypocapnic and hypercapnic hypoxia, CO is augmented in part by systemic hemodynamic adjustments that include a redistribution of blood flow and a translocation of blood volume to the fast transit time peripheral systemic circuit. The sympathetic nervous system may play an important role in mediating these systemic hemodynamic adjustments.

Acid-Base Equilibrium↗
PubMed1986

Hormones, mood and sexuality in lactating women.

Of 25 primiparous women, investigated prospectively for six months post-partum, 19 persisted with breast feeding and six changed to artificial during the first six weeks. Sexual activity, mood, and feeding patterns were recorded in weekly diaries. Hormones were measured from weekly urine samples (oestrogen and pregnanediol) and fortnightly blood samples (prolactin, testosterone, androstenedione, and sex hormone binding globulin). In breast-feeding women, testosterone and androstenedione levels were significantly lower in those who reported severe reduction in sexual interest. Changes in sexuality or mood were not related to levels of prolactin or oestrogen, or to the return of follicular activity, which was delayed in persistent breast feeders. The relationships of mood, sexuality, and hormones are discussed.

Adult↗
PubMed1985

Do pregnancy complications contribute to neurodevelopmental disability?

In the Dundee Development Screening Programme all children born in Dundee in 1974 and 1975 were screened at intervals during infancy and childhood. The obstetric and neonatal antecedent factors in 300 of the 322 singleton children with neurodevelopmental disability (index group) were compared with those of the 600 children of normal development born immediately before and after each child with disability (control group). Low social class was associated with mental retardation, global delay, speech delay, and behavioural disorder, but not with cerebral palsy or motor delay. With the exception of cerebral palsy, strong associations were found between all categories of disability and severe hypertension, unclassified antepartum haemorrhage, and preterm uterine activity. Cerebral palsy was not associated with antepartum complications, but was with fetal tachycardia during labour. Our data suggest that neurodevelopmental disability may, in many cases, originate during pregnancy and delivery.

Birth Weight↗
PubMed1984

Systemic circulatory adjustments to acute hypoxia and reoxygenation in unanesthetized sheep. Role of renin, angiotensin II, and catecholamine interactions.

The hemodynamic consequences of the hypoxic inhibition of angiotensin-converting enzyme activity were studied in chronically instrumented unanesthetized sheep (n = 8) breathing a hypoxic gas mixture for 60 min (PaO2 = 31 mm Hg) followed by reoxygenation with room air. Changes in cardiac output, vascular pressures, blood flow distribution, arterial pH, PaCO2, PaO2, and arterial levels of plasma renin activity, angiotensin II, bradykinin, and catecholamines were measured at selected time points. Seven additional sheep underwent the same protocol but received saralasin, an angiotensin II receptor blocker beginning at 55 min of hypoxia and extending into the reoxygenation period. During hypoxia, both groups developed identical hemodynamic patterns including a rise in cardiac output (25%), blood pressure (15%), and preferential blood flow distribution to the heart, brain, adrenals, diaphragm, and skeletal muscle, as well as a decrease in the fraction of cardiac output to the kidneys and most of the gut. This was associated with a decrease in angiotensin II concentrations (from 35 to 17 pg/ml) in spite of a doubling in plasma renin activity and catecholamines. Bradykinin levels did not change. Upon reoxygenation, bolus production of angiotensin II (from 17 to 1,819 pg/ml) occurred in spite of a constant level of plasma renin activity. Concurrently, different hemodynamic patterns between control and saralasin groups emerged upon reoxygenation, including an elevation from base line in blood pressure and systemic vascular resistance in the control group. Cardiac work (heart-rate systolic pressure product) in the control group remained elevated upon reoxygenation while coronary blood flow returned to base-line values. Saralasin reduced cardiac work upon reoxygenation and restored the match between coronary blood flow and work. We conclude that plasma renin activity and oxygen tension together govern angiotensin II levels for an optimal level of systemic vasomotor tone during hypoxia. However, upon reoxygenation, bolus production of angiotensin II may result in pathophysiologic circulatory patterns, such as impairment in oxygen delivery to the myocardium proportional to persistently elevated cardiac work in the immediate postresuscitation period.

Angiotensin II↗
PubMed1984

Dermal cells form strong adhesions to the basement membrane during the development of feather primordia in chick skin.

Experiments are described which provide a direct measure of the adhesion between dermis and epidermis during the development of feather primordia in chick dorsal skin in culture. The epidermis was peeled from the dermis and the surfaces so exposed were examined under the scanning electron microscope: regions of strong adhesion between the tissues were revealed as areas where their separation was incomplete. The results show that soon after primorida become morphologically distinct, cells from the surface of dermal condensations form adhesions to the basement membrane which are stronger than those between dermis and epidermis interplumar skin. These adhesions may help to hold the epidermis and dermis together during the outgrowth of the primordium.

Animals↗
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↗