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Biomedical subjects

A Dawson

Publications and source records attributed to A Dawson.

At least 91 records · Page 5Linked to original sources
PubMed1997

Changes in gonadotrophin-releasing hormone (GnRH-I) in the pre-optic area and median eminence of starlings (Sturnus vulgaris) during the recovery of photosensitivity and during photostimulation.

Changes in GnRH-I in the pre-optic (POA) and medio-basal (MBH) areas of the hypothalamus and in pituitary and plasma LH were measured in starlings (Sturnus vulgaris) during the recovery of photosensitivity under short days, and following photostimulation at various times during the recovery of photosensitivity. During exposure to short days there was a significant increase in GnRH-I in the POA, with the first detectable increase after only 10 days. There was no increase in GnRH-I in the MBH or in pituitary or plasma LH. In birds photostimulated after 10 short days, there was an increase in GnRH-I in the POA, but this was no greater than that in birds remaining under short days. There was no increase in GnRH-I in the MBH or in plasma LH. Photostimulation after 20 short days caused an immediate increase in GnRH-I in the POA, delayed increase in GnRH-I in the MBH, but no increase in plasma LH. Photostimulation after 30 short days caused an immediate increase in GNRH-I in the POA and the MBH and in plasma LH. The results show that the recovery of photosensitivity is gradual; the first measurable change occurs in the POA, consistent with photosensitivity being due to renewed GnRH-I synthesis. The effects of photostimulation increase, both in magnitude and in terms of how far 'downstream' of the POA changes are apparent, as photosensitivity is gradually restored. The results support the hypothesis that daylength has a dual role, controlling both synthesis and secretion of GnRH.

Animals↗
PubMed1997

Effect of bedtime alcohol on inspiratory resistance and respiratory drive in snoring and nonsnoring men.

We measured inspiratory resistance (R1), inspiratory occlusion pressure (P0.1), and the ventilatory responses to hypercapnia and isocapnic hypoxia during waking and during stage 2 non-rapid eye movement sleep in nine young men who were habitual snorers. They were studied on 2 nights during the 3 hours after receiving a bedtime drink containing either a placebo or 100-proof vodka (1.5 ml/kg) in orange juice. We compared the results with those we reported previously in 10 nonsnoring but otherwise similar men. Waking R1 was the same in nonsnorers and snorers, and it was not affected by ethanol. During sleep on the control night, R1 increased by 70% in nonsnorers and by 280% in snorers. On the ethanol night, the increase from waking to sleeping was more than doubled in both nonsnorers and snorers. P0.1 and the responses to hypercapnia and hypoxia showed no differences between nonsnorers and snorers, therefore the results from the two groups were pooled. Minute ventilation and the hypercapnic response decreased from waking to sleeping and P0.1 was more negative during sleep, but there was no significant effect of ethanol. There was a significant correlation between the changes from waking to sleeping in R1 and P0.1 on the ethanol night suggesting that inspiratory effort increased in response to the increased resistance. The response to isocapnic hypoxia showed no effect of either sleep state or drink. Inspiratory time did not change but mean inspiratory flow (VT/T1) was significantly reduced during sleep on both control and ethanol nights. The duty cycle ratio (T1/Ttot) was significantly increased during sleep on the ethanol night. Despite its great effect on inspiratory resistance, especially in snorers, ethanol, in the dose used in our study, does not augment the depression of minute ventilation or of the hypercapnic response that occur normally in stage 2 non-rapid eye movement sleep. After ethanol, our subjects showed the decreased VT/T1 and the increased T1/Ttot that occur normally during sleep in response to an inspiratory resistive load. However, they also showed increased inspiratory effort. The combination of increased inspiratory resistance and greater inspiratory effort would increase the tendency of an unstable upper airway to collapse and could account for the aggravation of obstructive sleep apnea by ethanol.

Adult↗
PubMed1996

Image-guided core biopsy in patients with breast disease.

Ultrasonographically-guided core biopsy has been used as an adjunct to triple assessment when fine-needle aspiration cytology was inadequate or equivocal, if the overall assessment of the patient was uncertain, or if it was deemed the preferred diagnostic option. Some 143 of 2603 patients had a guided core biopsy, 125 to establish the diagnosis and 18 to obtain histology in cytologically proven malignancy. A diagnosis of malignancy was established in 43 of the 125 patients who had a diagnostic core biopsy. Some 45 patients with benign disease were either discharged or returned to follow-up on the basis of the core biopsy. The remaining 37 patients required surgical biopsy, of whom 13 had malignant and 24 benign disease. The overall positive predictive value for malignancy was 98 per cent. Experience with ultrasonographically-guided core biopsy shows that it can reduce the need for surgical biopsy in both benign and malignant conditions of the breast.

Biopsy, Needle↗
PubMed1996

Plasma thyroxine concentrations in farmed ostriches in relation to age, body weight, and growth hormone.

Thyroid hormones are of interest in ostriches because, in common with other ratites, ostriches are believed to have evolved through neoteny, a process which, in amphibia, is related to thyroid function. Farmed ostriches show marked differences in growth rates, a problem which also could be related to abnormal thyroid function. In adult farmed ostriches (more than 3 years old), mean plasma thyroxine concentration was 1.8 nmol middle dot liter-1 (range 0.2 to 6.5 nmol middle dot liter-1). This is a lower mean and a much greater range than those in adult starlings or Japanese quail measured at the same time. No sex differences were observed. In 5-month-old ostriches (approximately half grown) mean levels were again low (3.1 nmol x liter-1, range 0.2 to 9.9 nmol x liter-1). There was a correlation (P < 0.0005) between thyroxine and body weight, which ranged from 10.8 to 51.5 kg. Growth hormone in this group ranged from 0.7 to 45.6 microg x liter-1, but there was no correlation with body weight or with thyroxine. In the same group of birds at 10 months of age, plasma thyroxine concentrations were similar, but were not correlated with body weight. In young birds sampled between hatch and 13 weeks, mean thyroxine decreased from 7.6 nmol x liter-1 soon after hatching to less than 2 nmol x liter-1 at 2 weeks and remained less than 2 nmol x liter-1 for the following 3 months. Thyroxine was highly variable within and between individuals. There was no correlation with body weight or growth rate. There were no significant differences between values at 13 weeks, 5 months, 10 months, or in adults. The results do not suggest that slow growth is directly related to low thyroxine. However, the low means and wide range of values do suggest that thyroid function in the ostrich is abnormal compared to other birds.

Aging↗
PubMed1996

Effects of prochloraz and malathion on the red-legged partridge: a semi-natural field study.

A semi-natural field study was carried out to assess the likelihood of a potentiation of toxicity between the ergosterol biosynthesis inhibiting (EBI) fungicide, prochloraz, and the organophosphorus (OP) insecticide, malathion, in the red-legged partridge (Alectoris rufa). Groups of partridges kept in four large grassland enclosures were exposed to either prochloraz-treated or control wheat for 7 days after which two of the enclosures were sprayed with malathion whilst the remaining two were sham-sprayed. Cytochrome P-450, aldrin epoxidase and 7-ethoxyresorufin-O-deethylase (EROD) activities were found to be significantly higher in the group exposed to prochloraz alone compared to controls, suggesting that induction of the hepatic microsomal monooxygenase system had occurred by ingestion of prochloraz-treated wheat. However, the level of induction produced was not sufficient to cause a potentiation of malathion toxicity. There was evidence for induction of several forms of P-450 recognised by antibodies raised against 1A1, 2C6 and 4A1 in the prochloraz-exposed partridges.

Journal Article↗
PubMed1996

Neoteny and the thyroid in ratites.

The ratites (for example ostriches, emus) are neotenous descendants of flying birds. The best studied cases of neoteny among vertebrates are in the Amphibia. In this class, whether individuals metamorphose and breed as adults, or whether they become sexually mature as neotenous aquatic larvae, is controlled by the thyroid. In this review it is argued that the thyroid may have been important in the evolution of ratite neoteny. The evidence is based on characteristics of ratites that could indicate thyroid abnormality, similarities between ratites and thyroidectomized non-ratite birds, and preliminary results from a study of thyroid function in ostriches.

Animals↗
PubMed1995

Farm visits and zoonoses.

Recent reports of outbreaks of gastrointestinal illness, such as cryptosporidiosis, associated with visits to farms have drawn attention to the possible risks of acquiring zoonotic infections through contact with farm animals. These risks seem to be small, but it is important that people who work in urban and rural farms, and such establishments as animal sanctuaries where the general public can come into close contact with farm livestock and other animals, should be alerted to the simple precautions needed to prevent transmission of infections.

Adult↗
PubMed1995

A comparison of the responses to gonadotrophin-releasing hormone of adult and juvenile, and photosensitive and photorefractory European starlings, Sturnus vulgaris.

The reproductive system of juvenile European starlings appears to be similar to that of photorefractory adults, yet the increase in plasma luteinizing hormone (LH) in juveniles in response to gonadotrophin-releasing hormone (GnRH) is much less than that of photorefractory adults. To investigate this apparent anomaly, the effects of age, reproductive state, and sex on the increase in plasma LH concentration in response to im injections of GnRH were investigated. The results show that photorefractory juveniles needed 10 times the dose of GnRH to elicit the same increase in LH as photorefractory adults, and the response of photosensitive juveniles to 10 micrograms GnRH was at least 15 times as great as that of photorefractory juveniles (e.g., 6.14 micrograms/liter compared to 0.35 microgram/liter 2 min after injection). However, the response of photosensitive adults was not greater than that of photorefractory adults. These differences were not due to differences in the amount of LH stored in the pituitary: this was 298 +/- 34 and 306 +/- 51 ng/gland in photorefractory juveniles and adults, respectively, and 367 +/- 47 in photosensitive juveniles. Repeated weekly treatment with GnRH enhanced LH responses: LH levels 3 min after GnRH treatment increased in birds on short days from 7.7 micrograms/liter after the first treatment to 24.6 micrograms/liter after the sixth treatment and in birds on long days it increased from 0.54 to 1.8 micrograms/liter. The greater response of photorefractory adults compared to photorefractory juveniles may therefore be due to the self-priming effect of GnRH during a preceding period of photosensitivity and/or photostimulation. The response to exogenous GnRH depends more on age and history than on prevailing physiological state. There was also a marked sex difference: females showed a sevenfold greater response to GnRH.

Aging↗
PubMed1995

Flow cytometric determination of pre-transfusion red cell volume in fetuses and neonates requiring transfusion based on RhD+ dilution by transfused D- red cells.

We report a case of feto-maternal haemorrhage and describe a new flow-cytometric method of determining a fetus's or infant's pre-transfusion red cell volume (RCV). We validate this method against an established technique, employing fetal haemoglobin (HbF) dilution, for determining the RCV in fetuses and neonates requiring intravascular transfusion. We discuss advantages and other potential applications of this new method.

Blood Transfusion, Intrauterine↗
PubMed1994

Seasonal plasma levels of luteinizing and steroid hormones in male and female domestic ostriches (Struthio camelus).

Ostriches are low-latitude birds and can be considered to be seasonal breeders. However, they are also opportunistic in that they can breed all year round. Monthly hormonal plasma concentrations were measured in six female and six male domestic ostriches kept at a latitude of 31 degrees 20'N. Measurements were made over a year, during which time each female laid an average of 28.7 eggs. Egg laying occurred between March and September, with peak numbers in May-June. Concentrations of plasma luteinizing hormone (LH) increased in February in both sexes and started declining before termination of egg laying. Plasma testosterone concentrations in males increased in April, about 2 months after the increase in LH. In females, plasma estradiol concentrations peaked in May but were elevated from March to August, basically all of the egg-laying period. Plasma hormonal changes in the ostriches were gradual and not abrupt, as seen in many wild seasonal breeders of higher latitude.

Animals↗
PubMed1994

Measurement by ELISA of equine alpha-1-proteinase inhibitor in uterine flushings from mares.

An enzyme linked immunosorbent assay (ELISA) was developed and used to estimate the concentrations of the serine proteinase inhibitor, alpha-1 proteinase inhibitor (API), in uterine flushings recovered from mares at different stages of the oestrous cycle and before and after the induction of experimental endometritis. There was a significant increase in the concentrations of API and albumin relative to total protein in flushings recovered during oestrus compared with dioestrus but no difference was observed in the concentrations of these proteins relative to total protein before and after the induction of endometritis. A regression analysis revealed a significant correlation between the concentrations of albumin and API in the flushings examined, suggesting that the API was derived entirely from serum and was not produced locally in the uterus.

Animals↗
PubMed1994

The extent of parental compliance with timing of administration of their children's antibiotics.

Antibiotics are widely prescribed to children, and the responsibility for ensuring adequate administration typically rests with parents. However, compliance with antibiotic medication is generally low, and previous studies often fail to specify the criteria for compliance adequately. In particular, little attention has been paid to accuracy of timing of antibiotic administration outside hospital, even though timing is important in maintaining therapeutic drug levels. The current study examined the self-reports of 75 mothers of their behaviours in administration of antibiotics to their children, with particular attention being paid to the frequency and timing of administration. The study found that, when timing of doses was considered, only seven parents could be considered as fully compliant with dosage instructions, a much lower proportion than indicated in previous studies which applied a more lenient definition of compliance. The implications of this finding are discussed, with particular reference to the role of the nurse and to the comparative usefulness of different definitions of compliance.

Adult↗
PubMed1994

Observer variation in the histopathological classification of thymoma: correlation with prognosis.

AIMS: To assess the ability of three histopathologists, experienced in thoracic surgical reporting, consistently to classify thymomas as cortical, medullary, or mixed pattern tumours. METHODS: Three histopathologists classified 74 thymomas (none frank carcinomas) as of either cortical, medullary, or mixed pattern, on two separate occasions. Kappa statistics were used to assess inter- and intra-observer agreement. Tumour type was compared with surgical stage as a predictor of biological behaviour. RESULTS: Inter- and intra-observer agreement were only moderate (kappa 0.48 and 0.52, respectively). For only 26 of 74 tumours could a categorisation be consistently agreed on. Follow up information was obtained for 73 cases, with a mean follow up period of five years. The prognoses for those 26 of 74 cases appeared to be at variance from previously reported studies, and showed internal inconsistency, with the mixed pattern category showing a worse survival than the cortical category. For the group as a whole, however, stage at presentation was related to survival, with an overall five year survival of 78% (100% for stage I, 84% for stage II, 27% for stage III and 0% for stage IV). CONCLUSIONS: The classification of thymomas into cortical, medullary, or mixed pattern tumours is difficult to apply. Surgical stage remains a better guide to prognosis.

Adolescent↗
PubMed1994

Thyroidectomy does not affect the daily or free-running rhythms of plasma melatonin in European starlings.

Thyroidectomy results in the suppression of reproductive photoperiodic responses in starlings. Could this be a consequence of an effect on perception of daylength or on circadian pacemakers? Daily changes in plasma melatonin concentrations were monitored in intact and thyroidectomized starlings held in long days (LD 16:8) and short days (LD 8:16), and in intact and thyroidectomized starlings allowed to free-run in constant darkness from long days or short days. In long days and short days, melatonin was low during the light period and high during darkness. There was no difference between intact and thyroidectomized birds. In free-running birds, the melatonin profile of the preceding long day or short day was retained during the first day of constant darkness, with peak levels occurring at the same time they did during the light-dark cycles. Again there was no difference between intact and thyroidectomized birds. These data demonstrate that either the photoreceptive and circadian mechanisms driving melatonin secretion are independent of those concerned with reproductive photoperiodic responses, or that thyroidectomy affects reproduction "downstream" from the photoreceptive-circadian apparatus.

Animals↗