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G Davidson

Publications and source records attributed to G Davidson.

At least 91 records · Page 5Linked to original sources
PubMed1991

Intracellular signalling in the ovine pars tuberalis: an investigation using aluminium fluoride and melatonin.

The effect of aluminium fluoride (AlF4-) has been studied on inositol phosphate accumulation, calcium mobilization, cyclic AMP production and [2-125I]iodomelatonin binding in ovine pars tuberalis cells. These cells have high-affinity receptors for, and respond to, melatonin through inhibition of forskolin-stimulated adenylate cyclase. In the presence of 10 mM LiCl, AlF4- stimulated the net accumulation of inositol monophosphate and inositol bisphosphate. Consistent with these findings, AlF4- increased intracellular calcium; although this response was attenuated in calcium-depleted medium, indicating that the calcium response comprises both intracellular and extracellular components. Melatonin was ineffective on either basal or AlF4(-)-stimulated turnover of inositol phosphates. In concordance with the inositol phosphate response, melatonin had no effect on either the AlF4(-)-stimulated or the basal calcium levels. AlF4- blocked the increase in cyclic AMP stimulation by 1 microM forskolin, being as effective as melatonin, achieving approximately 90% inhibition. AlF4- also attenuated the binding of [2-125I]iodomelatonin to ovine pars tuberalis membranes by 15%. At the concentration used, these results are consistent with the interpretation that AlF4- activates many G protein-mediated responses, and thus imply that the inhibitory pathway for cyclic AMP predominates over the stimulatory arm, whereas there can only be a stimulatory pathway linked to phosphoinositide metabolism in ovine pars tuberalis cells.

Aluminum↗
PubMed1990

The atriopeptidase inhibitor UK 69,578 increases atrial natriuretic factor and causes a natriuresis in normal humans.

The endopeptidase EC 3.4.24.11 (atriopeptidase) degrades atrial natriuretic factor (ANF). Intravenous administration of UK 69,578 (0.025 to 10.0 mg/kg), a new specific atriopeptidase inhibitor, in 16 normal volunteers produced a two- to three-fold rise in endogenous ANF. Peak levels were reached within 2 h declining to control values by 8 h. The rise in ANF was associated with an increase in urine volume and mean urinary sodium excretion rose from 64.9 mmoles/8 h after placebo to 116.1 mmoles/8 h after 10 mg/kg UK 69,578. Despite the natriuresis, plasma active renin concentration was suppressed for up to 8 h. We conclude that inhibition of the endopeptidase EC 3.4.24.11 in humans elevates endogenous ANF and causes a natriuresis and may offer a novel therapeutic approach to the treatment of hypertension and cardiac failure.

Adult↗
PubMed1990

A comparison of calcium pentagastrin and TRH tests in screening for medullary carcinoma of the thyroid in MEN IIA.

Intravenous injections of calcium gluconate and pentagastrin (CPG) or TRH were compared as secretagogues for calcitonin (CT) in screening for medullary thyroid carcinoma (MTC) in multiple endocrine neoplasia type IIA (MEN IIA). Administration of CPG resulted in a prompt increase in plasma CT in all five patients with MTC studied, one of whom had a normal baseline value (peak 412-371,000 ng/l, 636-4847% above basal). TRH produced a rise in plasma CT levels only in MTC patients with elevated basal values; the magnitude of increase was less than that observed with CPG (peak 168-17,200 ng/l, 113-180% above basal). CT levels did not rise above 300 ng/l with either test in four unaffected first-degree relatives of MEN IIA patients, three subjects with sporadic unilateral phaeochromocytomas and five controls with essential hypertension. CPG remains the CT secretagogue of choice in screening for MTC in MEN II A.

Adult↗
PubMed1990

Monte Carlo simulation of HIV infection in an intravenous drug user community.

Intravenous drug users are crucial to the understanding and control of human immunodeficiency virus (HIV) transmission. We have developed a population-based simulation of a community of intravenous drug users. This model was implemented using Monte Carlo techniques, which permit great flexibility in creating realistic social structures, to describe the needle-sharing network of drug users. We present the baseline behavior of this model in a generic community and demonstrate the model's utility for assessing public health interventions. Our early results demonstrate the powerful effects of social networks on HIV transmission and the importance of prevalence levels in assessing the effectiveness of interventions in the drug-injecting community.

Equipment Contamination↗
PubMed1989

Guanine nucleotides regulate the affinity of melatonin receptors on the ovine pars tuberalis.

The effect of guanine nucleotides and related analogues on the binding of 2-[125I]-melatonin to membranes prepared from ovine pars tuberalis was studied. Dose-dependent inhibition of 2-[125I]-melatonin binding was observed, with an order of potency of GTP gamma S much greater than Gpp(NH)p greater than GTP = GDP. GMP, cyclic GMP and ATP had negligible effects. Analysis of saturable binding revealed that GTP gamma S (1 microM) promoted an apparent reduction in receptor density of about 50%, without a concomitant change in receptor affinity. These results are consistent with a melatonin receptor existing in an equilibrium between high- and low-affinity states, with GTP and related analogues able to cause a shift in the equilibrium in favour of the lower-affinity form. The sensitivity of 2-[125I]-melatonin binding to guanine nucleotides implies the presence of a melatonin receptor on the ovine pars tuberalis, the action of which is mediated via a G protein.

Animals↗
PubMed1989

Health insurance and welfare reentry.

This study presents a theoretical model of welfare reentry that examines the importance of private health insurance in determining whether working recipients terminated from Aid to Families with Dependent Children (AFDC) as a result of the Omnibus Budget Reconciliation Act returned to welfare over a two-year period. Our empirical results suggest that the lack of private health insurance is a statistically significant and quantitatively important determinant of welfare reentry. Since the vast majority of the terminated families remained off welfare, however, these results suggest the difficulty of meeting the health needs of the employed uninsured.

Adolescent↗
PubMed1989

Allocative efficiency of case managers for the elderly.

This study presents an analysis of the allocative efficiency of case managers for the community-based elderly in an environment in which case management and a range of home and community-based services were available and directly linked to a mandatory preadmission screening program for nursing home applicants. We collected data for a one-year follow-up period on client placement, health and functional status, informal support, and use of health and social services for clients in two urban and two rural counties that participated in the Minnesota Pre-Admission Screening/Alternative Care Grants Program (PAS/ACG). We found that among those receiving ACG-supported services, the relationship between variation in the level of support for home and community-based services and the length of time elderly clients remained in the community suggested that case managers were allocating home and community-based services in a reasonably efficient manner. This finding offers support for using case managers to target services to the elderly.

Activities of Daily Living↗
PubMed1989

Anti-gliadin antibody specificity for gluten-derived peptides toxic to coeliac patients.

The specificities of serum and intestinal antibodies from coeliac and normal individuals towards gluten-derived peptides, known to be toxic in coeliac disease, has been investigated. Though untreated coeliacs had high serum antibody levels towards gliadin and some gluten-derived peptides, antibody specificities to various toxic gluten-derived peptides were similar to normal patients. Further, no significant binding in any patient group was found to the alpha-gliadin-derived peptides B1342 (Wieser, Belitz & Ashkenazi, 1984) or the 12 amino-acid A-gliadin peptide (Kagnoff, 1985). There appears to be no direct relationship between the toxicities and the antigenic reactivity of gluten-derived peptides. Thus, the intestinal damage in coeliac disease is probably not primarily caused by antibody-dependent mechanisms. The specificities of several monoclonal antibodies which bound to wheat prolamins as well as prolamins from other coeliac-toxic cereals have also been investigated with these toxic gluten-derived peptides, in order to identify possible common epitopes. No monoclonal antibody tested bound the B1342 and 12-amino-acid A-gliadin peptide. However the monoclonal antibodies which were specific for the coeliac-toxic cereal prolamins did show the strongest binding to other coeliac-toxic gluten-derived peptides.

Adult↗
PubMed1988

Substitution of formal and informal care for the community-based elderly.

The Minnesota Pre-Admission Screening/Alternative Care Grants Program screens those at risk of nursing home placement and funds services that will allow the elderly to be cared for at home. Information was collected for a 1-year period on client placement, health and functional status, informal support, use of health and formal services, and care-giver characteristics for 214 clients screened during the last quarter of 1984. A two-equation model was hypothesized to examine the formal service decisions of case managers and the amount of informal care provided for elderly clients at risk of institutionalization. A system of two simultaneous equations was estimated using a two-stage least-squares approach. The findings suggest that case managers allocate formal services based primarily on client need. The amount of informal care provided to clients did not affect significantly the decisions of case managers and is not determined significantly by the amount of formal services received by the elderly in the community. The lack of substitution between formal services and informal care reinforces the findings of previous research.

Aged↗
PubMed1987

Health care and insurance loss of working AFDC recipients.

The federal Omnibus Budget Reconciliation Act of 1981 (OBRA) produced substantial changes in the Aid to Families With Dependent Children (AFDC) program. The main effect of the changes has been the denial of assistance and hence Medicaid coverage to many AFDC recipients with jobs. Our analysis of the health care and insurance loss of working AFDC recipients in Hennepin County, Minnesota, found that the vast majority (87%) of families that were terminated from AFDC due to OBRA were able to remain off welfare and the majority (70% adults, 60% children) had private health insurance coverage 2 years later. These results highlight the dilemma facing state policymakers who want to develop successful programs to meet the health needs of the working poor, yet at the same time must cope with tight, short-term fiscal constraints.

Adolescent↗
PubMed1987

Effect of sodium depletion on pressor responsiveness in ACTH-induced hypertension in man.

1. Pressor responsiveness to angiotensin II (AII) and phenylephrine (PHE) was measured before and after 5 days of ACTH (1 mg i.m. daily) in six normal men maintained on low sodium diet (15 mmol daily). 2. ACTH caused a significant increase in systolic blood pressure of 9 mmHg. 3. There was no change in pressor responsiveness to AII with ACTH. 4. ACTH increased pressor responsiveness to PHE for both systolic and diastolic blood pressure, with a fall in the threshold for response from 0.9 to 0.6 micrograms/kg per min. 5. Increased pressor sensitivity to catecholamines during ACTH administration in man is not sodium-dependent.

Adrenocorticotropic Hormone↗
PubMed1987

Transependymal benign dorsally exophytic brain stem gliomas in childhood: diagnosis and treatment recommendations.

Sixteen children with dorsally exophytic transependymal benign brain stem gliomas were treated at the Hospital for Sick Children, Toronto, between 1949 and 1985. The diagnosis of these benign brain stem gliomas was based on neuroradiographic and operative observations. Five children were diagnosed in the pre-computed tomography (CT) era using ventriculography and pneumoencephalography, and 11 children were diagnosed using CT with and without contrast enhancement. Histological diagnosis was obtained in all 16 cases. In 1980, we first described this distinct group of benign brain stem gliomas, which accounted for 8% (total, 121 cases) of all brain stem gliomas diagnosed at our institution. However, with the use of high resolution CT in recent years, earlier and better definition of this particular type of brain stem tumor can be made. During the 10 years (1976 to 1985) in which CT has been used for preoperative evaluation in our institution, we have treated 49 patients with primary brain stem tumors. Eleven of these cases (22%) fell into the category of dorsally exophytic transependymal benign brain stem tumors. These tumors characteristically protrude into and largely fill the 4th ventricle, breaking through the overlying ependyma and frequently extending into the cisterna magna. On CT, they are isodense and enhance brightly with contrast agent. Clinically, these patients have a longer history of symptoms in comparison with patients with the more malignant, intrinsic types of brain stem tumor. All of our patients were treated by subtotal resection. Radiotherapy was utilized in 7 of the 16 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Neoplasms↗
PubMed1984

Australian aboriginal spatial cognition and dyslexia: a criticism of Pontius (1982).

Pontius ' neuropsychological explanation of some Aboriginal Australians' poor reading performance is not supported by an examination of the socio-cultural and educational considerations surrounding their performance or by research into the neurophysiological bases of reading retardation. Classification of children as "ecologically" dyslexic was based on hear-say general impressions of Aborigines' school performance and not on children's reading errors.

Art↗