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Biomedical subjects

A Dawson

Publications and source records attributed to A Dawson.

At least 145 records · Page 8Linked to original sources
PubMed1986

Endocrine changes associated with the termination of photorefractoriness by short daylengths and thyroidectomy in starlings (Sturnus vulgaris).

When starlings (Sturnus vulgaris) are transferred from short to long days, hypothalamic content of gonadotrophin-releasing hormone (GnRH) and pituitary gonadotrophin content eventually decrease, as birds become photorefractory, to values lower than they were on short days. This implies that both should increase as photorefractoriness is terminated some time after transfer from long to short days. Further, since thyroidectomy causes termination of photorefractoriness in birds held on long days, this should also result in an increase in hypothalamic GnRH and pituitary gonadotrophin contents. This study tests these hypotheses. Male starlings were transferred from short to long days for 10 weeks, by which time they should have become photorefractory. One group of birds was then killed; blood was collected, hypothalami and pituitaries were excised, and the stage of moult and testicular weights recorded. The remaining birds were then kept on long days, transferred to short days or thyroidectomized and kept on long days. Groups of birds in each treatment group were killed and sampled 2, 8 and 14 weeks later. Hypothalamic content of GnRH, and pituitary and plasma FSH and prolactin concentrations, were measured by radioimmunoassay. In birds sampled after 10 weeks of long days, hypothalamic content of GnRH was quite low, pituitary and plasma levels of FSH were very low, testes were small and pituitary and plasma prolactin levels were high. In intact birds kept on long days, hypothalamic GnRH content decreased further and remained low. Pituitary and plasma FSH levels remained low, testes remained small and pituitary and plasma prolactin levels decreased slowly.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

An obstetric microcomputer information system.

A systems analysis has been done to determine how computer technology can provide an information system to improve the care of the mother and her baby. A minimum data base was established complying with the recommendations of the Körner Committee and designed to meet the needs of the health personnel looking after the mother and baby. An ICL DRS 20/50 network of four microcomputers has been installed in the obstetric unit of a district teaching hospital with a link to the regional mainframe. There have been no significant software or hardware faults since the system became fully operational in January 1984. All women are registered on the system at their first visit allowing the pregnancy to be followed prospectively. Subsequently midwives enter data on line at delivery and at discharge. The on line validation and range checks improves the accuracy of the data allowing a reliable perinatal audit to be obtained routinely. The system has been accepted by the staff since much of the routine pregnancy documentation is produced automatically. This includes booking letters and summaries for general practitioners, admission slips, birth notification forms, registers and forms for the community midwives and health visitors. Immediate production of reports for community health staff allows better communication and improved patient care. No additional staff are needed in the obstetric unit and one job which was mainly of a clerical nature has been saved and the salary transferred to provide one more midwife for the postnatal wards.(ABSTRACT TRUNCATED AT 250 WORDS)

Computers↗
PubMed1985

Acute effects of oxygen treatment upon information processing in hypoxemic COPD patients.

The present study investigated the effects of oxygen therapy upon human information processing for hypoxemic COPD patients. Each of ten patients was admitted to a general clinical research center for a two-day period. In a randomly counter-balanced factorial design, patients breathed either room air or enriched oxygen for either six hours or 20 minutes prior to testing. The tests evaluated speed of information processing, ability to detect correct sequence of tones, and serial memory. In addition, patients were evaluated on critical flicker fusion and story recall. The results suggested that acute oxygen therapy does not reverse information processing deficits observed in hypoxemic COPD patients.

Aged↗
PubMed1985

Thyroidectomy results in termination of photorefractoriness in starlings (Sturnus vulgaris) kept in long daylengths.

Four groups of 10 male starlings were transferred from short daylengths (8 h light/day) to long daylengths (18 h light/day), which caused the tests to develop rapidly to maximum size and then to decrease to minimal size as birds became photorefractory. Birds were surgically thyroidectomized at 8, 16 or 28 weeks. A fourth group was left intact. Testicular volume and plasma FSH and prolactin concentrations were measured. After 42 weeks all birds were castrated and plasma FSH was measured during the next 6 weeks. Testicular growth began in all thyroidectomized birds between 4 and 8 weeks after thyroidectomy. By 42 weeks, the testes of all thyroidectomized birds were large, whereas those of intact birds were still of minimal size. Plasma FSH concentrations remained low in all birds and plasma prolactin values, originally elevated by long daylengths, decreased at a similar rate in thyroidectomized and intact birds. After castration at 42 weeks, plasma FSH values increased rapidly in all thyroidectomized birds but remained low in non-thyroidectomized birds. The results demonstrate that thyroidectomy of photorefractory starlings does not induce immediate testicular growth but may initiate a process which eventually terminates photorefractoriness in a way similar to that caused by return to short daylengths.

Animals↗
PubMed1985

Hypothalamic gonadotrophin-releasing hormone and pituitary and plasma FSH and prolactin during photostimulation and photorefractoriness in intact and thyroidectomized starlings (Sturnus vulgaris).

Changes in concentrations of hypothalamic gonadotrophin-releasing hormone (GnRH) and pituitary and plasma FSH and prolactin were measured in intact and thyroidectomized female starlings (Sturnus vulgaris) after transfer from short to long photoperiods. In intact birds, hypothalamic GnRH did not increase significantly during the first 6 weeks of photo-stimulation, but by 12 weeks, as birds became photorefractory, it had decreased to levels significantly lower than those before photostimulation. In thyroidectomized birds, which did not become photorefractory, hypothalamic GnRH remained high after 12 weeks of photostimulation. Pituitary FSH increased in both intact and thyroidectomized birds; it then decreased to low levels in intact photorefractory birds, but remained high in thyroidectomized birds. Plasma FSH increased to a peak after 2 weeks, but by 6 weeks it had decreased to low levels in both groups. In intact birds there was a 70-fold increase in pituitary prolactin during the first 6 weeks, and levels were still high after 12 weeks of photostimulation. In thyroidectomized birds, pituitary prolactin remained low. The results suggest that while the initial effect of long daylengths is to cause gonadal maturation, the ultimate effect is to switch off the reproductive system.

Animals↗
PubMed1985

Recombinant interferon-gamma (immuneron): results of a phase I trial in patients with cancer.

Recombinant DNA-produced interferon-gamma (rIFN-gamma) was administered intravenously to patients with solid tumors in a Phase I study. The rIFN gamma was prepared from Escherichia coli and purified to greater than 95% with a specific activity of greater than or equal to 30 X 10(6) units/mg protein. Twenty patients received intravenous bolus injections once weekly for 4 consecutive weeks. They were assigned to one of six dose groups ranging from 1 to 81 X 10(6) units/m2 body surface area; intrapatient dose escalation was not allowed. Patients were monitored intensively for toxicity, but no dose-limiting toxicity was demonstrated. Fever was the predominant side effect, occurring in all patients treated, and usually reached 38-40 degrees C. Short-term somnolence and fatigue were also observed, but no chronic fatigue was seen. Decreases in white blood cell and platelet counts, generally within the normal range, were observed; however, the counts rose again after intervals of 2-5 days. There was no firm evidence of a relationship between adverse effects and dose. No life-threatening side effects were noted and no antibodies developed to either rIFN gamma or E. coli proteins. The pharmacokinetics of rIFN gamma did not appear to alter from week 1 to week 4. Calculated half-lives were from 0.8 to 3.5 h. Doses greater than 9 X 10(6) units/m2 gave measurable serum levels for at least 12 h. A partial response of 8 weeks' duration was observed in a patient with hepatoma.

Adult↗
PubMed1984

Photorefractoriness in European starlings: associated hypothalamic changes and the involvement of thyroid hormones and prolactin.

Responsivity to photostimulation in previously photorefractory European starlings is caused by subjection to short daylengths and is characterized by a marked activation of the hypothalamus in terms of synthesis of gonadotropin releasing hormone. This active hypothalamic state is amplified for a time by a subsequent exposure to long days but is soon completely reversed as the birds become photorefractory again. This latter effect of long photoperiods and the concurrent secretion of prolactin are dependent on the presence of thyroid hormones. Conceivably, prolactin causes photorefractoriness by inhibition at a hypothalamic level.

Animals↗
PubMed1984

Changes in plasma thyroxine concentrations in male and female starlings (Sturnus vulgaris) during a photo-induced gonadal cycle.

Previous studies have shown that the thyroid must be important during the onset of photorefractoriness because thyroidectomised starlings (Sturnus vulgaris) do not become photorefractory. Therefore, to determine changes in plasma thyroxine during the onset of photorefractoriness, starlings were kept on photoperiods which induce photorefractoriness at different rates. Four groups of males and females were transferred from 8 hr light:16 hr darkness (8L:16D) to either 18L:6D, 13L:11D, 11L:13D, or 8L:16D and weekly blood samples were taken and assayed for thyroxine. In males and females on the two longer photoperiods, plasma thyroxine increased to a peak after 2-3 weeks. In those on 18L:6D, this was followed by a second peak after 9 weeks. Both 18L:6D and 13L:11D induced photorefractoriness. In birds held on 11L:13D, which became sexually mature but did not become photorefractory, there was no change in thyroxine. The results demonstrate that an increase in thyroxine concentration is associated with the onset of photorefractoriness.

Animals↗
PubMed1984

Growth-inhibitory activity of lymphoid cell plasma membranes. I. Inhibition of lymphocyte and lymphoid tumor cell growth.

Membranes isolated from normal spleen cells or lymphoid tumor cells were found to inhibit in vitro growth of several murine tumor cell lines including a B cell hybridoma, a thymoma, and a mastocytoma. 50% inhibition occurred at membrane protein concentrations of 60-100 micrograms/ml. A similar concentration dependence was found for inhibition of [3H]-thymidine incorporation by tumor cells and for the lipopolysaccharide-induced mitogenic response of normal spleen cells. The inhibitory activity co-purified with the plasma membrane upon fractionation of crude membranes. Membrane solubilization with deoxycholate followed by dialysis to remove the detergent gave good recovery of inhibitory activity in the resulting reconstituted membranes. Membrane-mediated growth inhibition resulted from a decreased rate of proliferation and not from increased cell death. A toxic effect of the membranes was further ruled out by the finding that increasing the fetal calf serum content of the medium could substantially reverse the growth inhibition. Thus, the plasma membrane of lymphoid cells contains a component that can slow or stop the growth of cells in culture. This membrane component may have a role in cell contact-mediated regulation of growth.

Animals↗
PubMed1984

Effects of gonadectomy on seasonal changes in plasma LH and prolactin concentrations in male and female starlings (Sturnus vulgaris).

Intact and gonadectomized male and female starlings (Sturnus vulgaris) were held in outdoor aviaries for 1 year. Blood samples were taken frequently and assayed for LH and prolactin, and intact males were laparotomized to determine testis size. Changes in testis size in intact males were similar to those in wild starlings with maximum size during April. Hormone levels in intact males and females also followed a similar pattern to those in wild birds although absolute levels were somewhat lower. Levels of LH increased during spring, were highest in early May and then declined rapidly as birds became photorefractory. Prolactin levels did not begin to increase until April, reached a peak in late May and then declined. In gonadectomized males and females, high levels of LH were maintained throughout the early part of the year when birds were photosensitive, but declined rapidly as they became photorefractory. This occurred at the same time as in intact birds. During photorefractoriness, LH levels in gonadectomized birds were similar to those in intact birds. Prolactin showed the same seasonal pattern in gonadectomized birds as that in intact birds. These results demonstrate that gonadal steroid feedback is unimportant in initiating and maintaining photorefractoriness and confirm that increased prolactin secretion coincides with the onset of photorefractoriness.

Animals↗
PubMed1983

Equilibrium and kinetic studies of oxygen binding to fragments of Lymnaea stagnalis (freshwater snail) haemocyanin obtained by proteolytic digestion.

Functional fragments of the haemocyanin from the gastropod mollusc Lymnaea stagnalis (freshwater snail) were obtained by partial digestion with trypsin and plasmin. The fragments were purified by ion-exchange chromatography and characterized by detergent/polyacrylamide-gel electrophoresis and crossed immunoelectrophoresis. Three types of single-functional unit fragment were isolated from the trypsin digest, and two immunologically distinct three-functional unit fragments and a single-functional unit fragment were isolated from the plasmin digest. The O2-binding behaviour of the fragments was investigated by equilibrium and kinetic methods. Over the pH range 7.0-8.2, in the presence of 10-20 mM-CaCl2, all of the single-functional unit fragments displayed non-co-operative O2 binding and showed no evidence of a Bohr or a salt effect. A Hill coefficient of less than 1.0 was obtained with one of the two three-functional unit fragments studied, whereas both of these fragments displayed a Bohr effect. Functional heterogeneity of the fragments was indicated by the variation in the O2 affinity, the P50 (partial pressure of O2 at half saturation) ranging between 0.26 and 0.77 kPa (approx. 2-6 mmHg). Stopped-flow data reflected the O2 equilibrium behaviour. Thus there was a fall in the value of the O2 dissociation rate constant from approx. 15 to 1s-1 in parallel with the increase in O2 affinity.

Animals↗
PubMed1983

Plasma corticosterone in wild starlings (Sturnus vulgaris) immediately following capture and in relation to body weight during the annual cycle.

Free-living starlings (Sturnus vulgaris) were caught by mist netting. Blood samples were taken from them between 20 sec and 4 min after capture and assayed for corticosterone. Before 1 min corticosterone levels were constant (10.3 nmol litre-1) but after 1 min they increased rapidly (27.0 +/- 3.6 nmol litre-1 min-1). Male and female free-living starlings were caught throughout the year with mist nets, and traps placed in nest boxes. Blood samples were taken within 1 min of capture and body weights recorded. Plasma corticosterone varied between 3 and 13 nmol litre-1. In both sexes the level was high during winter and through the breeding season. It fell to low levels during late summer and increased again during autumn. Body weight in both sexes was highest in midwinter and lowest in midsummer but there was no correlation between body weight and plasma corticosterone concentration.

Animal Population Groups↗
PubMed1983

Plasma gonadal steroid levels in wild starlings (Sturnus vulgaris) during the annual cycle and in relation to the stages of breeding.

Blood samples were collected from male and female free-living starlings in every month during the year and at all stages of the breeding cycle. The samples from females were assayed for oestradiol-17 beta, oestrone, and progesterone, and the samples from males were assayed for testosterone and 5 alpha-dihydrotestosterone. The testicular weights were recorded. All hormones other than oestrone showed a pronounced unimodal cycle. In females, oestradiol was highest in April, corresponding to the period of greatest nest-building activity. It decreased during the later stages of the breeding cycle and maintained low levels until the autumn when levels began to increase. Progesterone was highest in laying birds and reached a peak in May. During the rest of the year it remained at a lower but fairly constant level. Oestrone was normally only detectable in laying birds. In males, testicular weight and plasma concentrations of testosterone and 5 alpha-dihydrotestosterone were all highest during April. Plasma testosterone and 5 alpha-dihydrotestosterone were highest in nest-builders. They decreased during the later stages of breeding, remained low during the summer and increased slightly in the autumn. Testicular weight was high in nest-builders, but peaked during laying, by which time testosterone and 5 alpha-dihydrotestosterone had decreased significantly. Testicular weight decreased during incubation and feeding the young and remained low until the following year.

Animals↗
PubMed1983

An effect of nerve growth factor on parasympathetic neurite outgrowth.

Addition of nerve growth factor (NGF) to dissociated parasympathetic ciliary ganglion neurons resulted, within 60 min of its addition, in a 2-fold increase in average neurite length and an accompanying enlargement and spreading of neuronal growth cones. These effects occurred over a concentration range of NGF of 0.1-10 ng/ml and were blocked by affinity-purified antibody to NGF. Epidermal growth factor, fibroblast growth factor, and angiotensin did not have these effects, although insulin at high concentrations was able to induce a response similar to that of NGF. Dissociated sympathetic chain neurons also responded to NGF with increased neurite lengths, and, in addition, NGF considerably extended the survival time of these neurons in culture. However, the effect of NGF on ciliary ganglion neurons was limited to neurite outgrowth, and NGF did not promote the survival of these parasympathetic neurons.

Animals↗
PubMed1983

Plasma prolactin and gonadotrophins during gonadal development and the onset of photorefractoriness in male and female starlings (Sturnus vulgaris) on artificial photoperiods.

Previous studies have shown that an increase in prolactin secretion coincides with the beginning of the photorefractory phase in starlings (Sturnus vulgaris). To determine how closely this increase is associated with the onset of refractoriness, we kept starlings on photoperiods which would induce refractoriness at different rates. Four groups of males and females were transferred from 8h light:16h darkness (8L:16D) to either 18L:6D, 13L:11D, 11L:13D or 8L:16D. Weekly blood samples were assayed for LH, FSH and prolactin and the males were frequently laparotomized to determine testis volume. In males, both 18L and 13L induced marked increases in plasma gonadotrophin levels and rapid gonadal maturation. A photoperiod of 18L induced an earlier onset of refractoriness (2-4 weeks) than 13L (6 weeks). In both cases prolactin levels began to increase immediately before the onset of refractoriness. Males on 11L showed a slight increase in gonadotrophin levels and slow gonadal maturation. There was no increase in prolactin levels and these birds did not become refractory. Hormonal data from the females were similar to those from males. These results confirm that increased prolactin secretion is associated, in some way, with the onset of photorefractoriness in this species, although whether it is a cause or consequence of photorefractoriness, or simply of gonadal regression, remains unclear.

Animals↗
PubMed1982

Equilibrium and kinetic studies of oxygen binding to the haemocyanin from the freshwater snail Lymnaea stagnalis.

The binding of oxygen by the haemocyanin of the gastropod Lymnaea stagnalis was studied by equilibrium and kinetic methods. The studies were performed under conditions in which the haemocyanin molecule was in the native state. Over the pH range 6.8-7.6, in the presence of 10mM-CaCl2 the haemocyanin bound O2 cooperatively. Over this pH range the haemocyanin molecule displayed a normal Bohr effect whereby the O2 affinity of the molecule decreased with a fall in the pH of the solution. The maximum slope of the Hill plot (hmax.) was 3.5, obtained at pH 7.5. An increase in the CaCl2 concentration from 5 to 20 mM at pH 6.8 resulted in a slight increase in the oxygen affinity, with hmax. remaining virtually unchanged. At constant pH and CaCl2 concentration, an increase in NaCl concentration from 0 to 50 mM resulted in a small decrease in O2 affinity, but a significant increase in the value of hmax. from 3.5 to 8.6. Temperature-jump relaxation experiments over a range of O2 concentrations produced single relaxation times. The dependence of the relaxation time on the reactant concentrations indicated a simple bimolecular binding process. The calculated association and dissociation rate constants for this process at pH 7.5 are 29.5 X 10(6) M-1 X S-1 and 49 S-1 respectively. The association rate constant kon was found to be essentially independent of pH and CaCl2 concentration. The dissociation rate constant, koff, however, increased with a decrease in the pH, but was also independent of CaCl2 concentration. These results indicate that the stability of the haemocyanin-O2 complex is determined by the dissociation rate constant.

Animals↗