Search PubMed⌕ Search

Biomedical subjects

A Barnes

Publications and source records attributed to A Barnes.

At least 109 records · Page 6Linked to original sources
PubMed1985

Calcitonin cell population and distribution in the thyroid gland of the rat.

Calcitonin-containing cells (C cells) were identified in male Wistar white rats using an immunoperoxidase technique. They occupied a central position within the thyroid; very few were found peripherally, inferiorly, and superiorly; and none were present in the isthmus. The number of calcitonin-containing cells present per gram of body weight increased with age up to 70 days and had declined by 100 days. Determining the true total C-cell count through the entire thyroid is a very laborious procedure. However, a simple estimate of this total count can be made; the total number of C cells in every tenth section (6 microns) of thyroid was found to be highly correlated with the weight of the animal expressed as an allometric function. A better estimate can be derived from counts of just three sections: the tenth, twentieth, and thirtieth after the section of greatest cross sectional area.

Age Factors↗
PubMed1985

Seasonal variations in plasma testosterone concentrations in the male marsupial bandicoot Isoodon macrourus in captivity.

Although bandicoots in Queensland mate throughout the year, the majority of births occur in late winter and spring. To ascertain whether this seasonality in mating is manifest in the male reproductive system; body weight, testes size, and plasma testosterone concentration were examined in eight bandicoots throughout the year. The size of the testes increased with age in all bandicoots and there was no evidence of seasonal variation. Plasma testosterone concentrations fluctuated from 0.1 to 70.0 ng/ml and a seasonal cycle was observed, with a nadir in concentrations in March and a peak in September. The peak in testosterone concentration coincided with the period of the year when the majority of births occurred. Subsequent statistical analysis suggested that the annual plasma testosterone profile correlated well with the rate of change of day length.

Acclimatization↗
PubMed1984

Norms for hand grip strength.

Norms for hand grip strength of healthy children are presented. Sex and age specific centiles for age 5 to 18 years have been determined using a portable strain gauge dynamometer with an accuracy of 0.5 N. The test group comprised 1417 healthy, urban school children from a middle class suburb of Brisbane. Mean maximum grip strength (of four tests, two with each hand) and mean peak grip strength (best of four tests) were recorded. Mean values of peak grip strength were 10 to 15% higher than the average maximum grip in all age groups. At all ages girls had a reduced grip strength compared with boys and although boys manifested a continual, approximately linear increase in grip strength through all age groups, girls manifested an approximately linear increase up to 13 years after which mean hand grip usually remained constant. By the age of 18 years boys had a mean grip strength some 60% higher than girls. Correlations with height and weight are also presented. "Handedness' influenced grip strength and was most noticeable in children aged over 10 years. The clinical use of hand grip strength centiles for the early indication of neurological and muscular disorders and for following the natural history of neuromuscular disease is discussed.

Adolescent↗
PubMed1984

The uniformity of growth within the litter of the marsupial, Isoodon macrourus.

The amount of information concerning reproduction in eutherian mammals differs markedly with that available for marsupials. There is at present a good understanding of growth in the eutherian litter after birth but the respective information for litter bearing marsupials has still to be obtained. In this study the growth of the young bandicoot after leaving the pouch was examined. Each of the monitored young, 38 females and 12 males, was weighed weekly and a growth rate estimated for the ages 65 to 105 days. Although these growth rates varied from 3.80 to 9.50 g/days and large variations in growth rate were observed between litters, the findings suggest that development within a pouch, in contrast to uterine development, gives rise to a litter which is more uniform in size.

Animals↗
PubMed1983

Theoretical analysis of a method for determining the pattern of macromolecular synthesis during the cell cycle.

The dual-labelling centrifugal-elutriation method has been extensively used to study patterns of macromolecular synthesis and accumulation in the yeast cell cycle. Cells are long-term labelled with a radioactive precursor for about 1.5 cycles (a measure of macromolecular mass), then pulse-labelled with a precursor containing a different radioactive isotope for the final 0.1 cycle (a measure of rate of synthesis). Harvested cells are fractionated into cell cycle stages by centrifugal elutriation, and changes in pulse : long-term labelling during the cycle determined. This pattern of change is compared with theoretical changes in rate : mass calculated for various patterns of synthesis. Using this method, it has been suggested that rates of synthesis and accumulation of several types of RNA and protein all increase exponentially through the cycle. In contrast, experiments using synchronous cultures or zonal centrifugation for cell cycle analysis have suggested other synthetic patterns, including periodic doubling in rate in each cycle. In this paper we analyse whether the dual-labelling, centrifugal-elutriation method is capable of discriminating between exponential and periodic rate-doubling patterns. Three possible sources of imprecision in the method and its application are examined. (1) Theoretical rate : mass curves have been simulated for macromolecules with a wider range of properties than previously considered. It is shown that for some important classes, such as messenger RNAs, with turnover rates in the range measured experimentally, and proteins, differences between rate : mass curves for exponential and periodic rate-doubling models are considerably smaller than previously suggested. (2) Long-term labelling is shown to be an accurate measure of macromolecular mass, but pulse-labelling can be inadequate as a measure of rate of synthesis. The error is greater with RNAs with faster turnover, and again reduces the ability of the method to discriminate exponential and periodic rate-doubling models of synthesis. The error is greater with RNAs with faster turnover, and again reduces the ability of the method to discriminate exponential and periodic rate-doubling models of synthesis. (3) Imperfections in cell cycle fractionation by centrifugal elutriation are examined, and by computer simulation it is shown that these also reduce the ability of the method to distinguish between the two models of synthesis. The three sources of imprecision are cumulative. It is concluded from simulation analyses that the differences between exponential and periodic rate-doubling patterns analysed by the method would be so small as to be almost impossible to establish against the background of error in experimental measurement. We therefore suggest that in practice, the dual-labelling centrifugal-elutriation method is unable to discriminate between the exponentially increasing and periodic rate-doubling models. The mathematical treatment developed in this paper should be applicable to analysis of other methods and cell cycle events.

Cell Cycle↗
PubMed1979

Potassium: aldosterone relationships in pregnant ewes and chronically cannulated ovine fetuses.

UNLABELLED: As maternal hyperkalemia quickly induces fetal hyperkalemia, it was decided to investigate the effect of small elevations of plasma [K+] on the peripheral blood aldosterone concentration in chronically catheterized ovine fetuses and to compare this response to that obtained in the adult ewe both pregnant and nonpregnant. Fol elevations of plasma [K+] of 0.1 to 0.3 mmole/liter blood aldosterone concentrations were elevated by 6.7 +/- 4.9 (9) ng/dl in nonpregnant sheep, 6.3 +/- 5.0 (6) in pregnant ewes, but only 0.3 +/- 1.7 (4) in fetal sheep. For increments in plasma [K+] of 0.4--1.0 mmole/liter aldosterone increments in nonpregnant ewes were 9.5 +/- 4.5 (4) ng/dl compared with 10.1 +/- 4.7 (5) in pregnant ewes and 1.5 +/- 2.6 (7) in fetuses. There was no obvious correlation between the age of the fetus and the response to increased plasma [K+]. In effect, the blood aldosterone concentration of the fetus was not elevated by increasing plasma plasma [K+]. SPECULATION: The ovine fetus is not able to cope with hyperkalemia by increasing blood aldosterone concentration. Until the fetus is close to term, hyperkalemia may jeopardize the pregnancy by causing placental hemorrhages.

Aldosterone↗
PubMed1979

Analysis of the significance of a periodic, cell size-controlled doubling in rates of macromolecular synthesis for the control of balanced exponential growth of fission yeast cells.

Mutant strains of the fission yeast Schizosaccharomyces pombe are available which divide at smaller mean sizes than wild type. Earlier work by the present authors has shown that all these strains double their rates of polyadenylated messenger RNA synthesis as a step once in each cell cycle. The smaller the cell, the later in the cycle is the doubling in rate of synthesis. Strains of all sizes, however, double their synthetic rate when at the same threshold size. We show here that the differences in cell cycle stage of doubling in rate of polyadenylated messenger RNA synthesis are enough to explain the reduced mean steady state polyadenylated messenger RNA contents of the smaller strains. The cell size-related control over doubling in rate of synthesis is also shown to maintain the mean polyadenylated messenger RNA content as a constant proportion of cell mass, irrespective of cell size. This control thus allows cells to maintain balanced exponential growth, even when absolute growth rate per cell is altered by mutation. It is also shown that the concentration of polyadenylated messenger RNA itself could act as a monitor of the threshold size triggering the doubling in rate of synthesis in each cell cycle.

Ascomycota↗
PubMed1978

Cure of intractable watery diarrhoea by excision of a vipoma.

A 56-year-old man suffered unexplained watery diarrhoea for 5 years which ultimately produced quadraparesis due to serve potassium depletion. All investigations were negative until demonstration of elevated plasma vasoactive intestinal peptide (VIP) indicated the presence of a vipoma. Removal of the VIP-producing tumour tissue--an adrenal ganglioneuroma--resulted in complete cure. Plasma VIP measurement is thus a valuable diagnostic screen in such cases and can be used to predict prognosis and to guide further therapy.

Adrenal Gland Neoplasms↗
PubMed1978

Magnitude, dose-requirement and mode of development of tachyphylaxis to suxamethonium in man.

Tachyphylaxis to suxamethonium infused at a constant rate was studied in 15 surgical patients under enflurane-nitrous oxide-oxygen anaesthesia. The compound electromyographic response of the adductor pollicis muscle to stimulation of the ulnar nerve was monitored. A short-lasting and a long-lasting nearly steady state were observed in Phase I and in Phase II, respectively, during both of which a constant infusion resulted in a constant block. Tachyphylaxis occurred during the transition of phases, beginning after infusion of 1.4 +/- 0.6 (SD) mg kg-1 of suxamethonium, and 36 +/- 14 (SD) minutes of exposure. Tachyphylaxis peaked after 2.6 +/- 1.3 (SD) mg kg-1, and 72 +/- 38 (SD) minutes of exposure. The maximum gain in neuromuscular transmission from the initial maintenance level of block as the result of tachyphylaxis was 53 +/- 24 (SD) % of the control. The results are thought to reconcile previously reported conflicting clinical observations on tachyphylaxis.

Adult↗
PubMed1978

Regulation of amniotic fluid volume and composition in the ovine fetus.

To determine the role of fetal swallowing in the control of amniotic fluid volume and composition and fetomaternal sodium transport, 4 ovine fetuses of 101--129 days' gestation had their esophagi surgically occluded. Amniotic and fetal vascular cannulas were implanted at the same time in these fetuses and in four intact controls. There was no difference between the amniotic sodium or potassium of these two groups over the next 3 weeks, at which time cesarean section was performed and the volume of amniotic fluid measured. Hydramnios did not result from esophageal atresia. Twenty-four hours after injection of 24Na into the amniotic fluid, the percentages of the dose in the fetal/maternal compartment were similar in intact and esophagus-ligated fetuses.

Amniotic Fluid↗
PubMed1977

Absence of "recurarization" in patients with demonstrated prolonged neuromuscular block.

The possibility of "recurarization" after antagonism of the competitive neuromuscular block with anticholinesterases was studied. Observations were made on the time-course of the block in five patients at risk from recurarization because of multiple organ failure and who demonstrated unusually prolonged blockade. In none of these patients did the block recur. We conclude that, provided spontaneous recovery of neuromuscular transmission has made progress before the antagonism, and that the patient does not deteriorate or become exhausted afterwards, recurarization is unlikely.

Adult↗
PubMed1977

Neuromuscular facilitation during train-of-four and tetanic stimulation in healthy volunteers: observations with half-refractory paired responses.

The compound electromyographic response of the thenar musculature was elicited by supramaximal stimulation of the ulnar nerve in 12 awake healthy volunteers. The half-refractory period of the neuromuscular transmission was determined. Twin stimuli separated by the half-refractory interval were repeated as a unit at 2 Hz and at 50 Hz. Thus two trains of responses, one beginning with a maximal response, the other with a half-maximal response, were obtained with each frequently of stimulation. Marked facilitation of the electromyographic response began with the train of stimulation, especially with tetanic stimulation. A secondary fade occurred occasionally. These changes were more remarkable in the train of half-refractory responses. We conclude that nerve stimulation facilitates neuromuscular transmission and deduce that the characteristic fade observed with a curariform block, rather than being an uncovered physiological phenomenon, is caused by tubocurarine and related drugs.

Action Potentials↗