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R A Hawkins

Publications and source records attributed to R A Hawkins.

At least 19 recordsLinked to original sources
PubMed1992

Neutral amino acid transport by the blood-brain barrier. Membrane vesicle studies.

Endothelial cell membranes, the site of the blood-brain barrier, were obtained from the capillaries of cow brain. The luminal and abluminal membranes were separated by centrifugation on a discontinuous Ficoll gradient. Electron microscopy revealed that the membrane preparations consisted almost entirely of sealed vesicles. The release of latent enzyme activity showed that both membrane preparations were primarily right side out. Radiolabeled L-phenylalanine uptake by luminal vesicles was proportional to membrane protein concentration, with less than 10% binding. Transport was by a high affinity carrier (Km 11.8 +/- 0.1 microM, asymptotic standard error) that showed little or no stereospecificity, and was independent of Na+ or H+ gradients. Transport was inhibited by L-tryptophan, L-leucine, 2-aminobicyclo[2,2,1]heptane-2-carboxylate and D-phenylalanine, but not by N-(methylamino)-isobutyrate. Abluminal membranes showed an additional component in which a Na+ gradient accelerated the transport of both phenylalanine and N-(methylamino)-isobutyrate. These studies demonstrate the utility of membrane vesicles as a model to characterize the transport properties of the distinct membranes of the polar endothelial cells that form the blood-brain barrier.

Amino Acids↗
PubMed1992

Indications for primary tamoxifen therapy in elderly women with breast cancer.

A group of 66 elderly women with primary breast cancer were treated with tamoxifen and followed for a minimum of 2 years. Of these, 32 whose disease remained controlled for the 2-year period were considered to have had a 'worthwhile' response, 27 in whom disease progressed were considered to have had an unsatisfactory result and seven opted for alternative treatment. By Union Internacional Contra la Cancrum (UICC) criteria, 14 women had a complete response, 20 a partial response, in five disease remained static and in 20 it progressed without response. Prediction of outcome after assessment according to UICC criteria at 3 and 6 months was unsatisfactory (19 and 34 of 59 correctly predicted respectively). Analysis of multiple tumour measurements over 12 weeks was no better (33 of 59 correctly predicted). Immunocytochemical assay of fine-needle aspirates for oestrogen receptor (ER) provided a better predictor (38 of 47 correct) and the difference in survival between patients with and without ER activity was significant (P < 0.001). Conventional assessments of response at 3 and 6 months are unsatisfactory for judging the long-term benefit to the patient. ER status is the best predictor of response and outcome.

Aged↗
PubMed1992

Expression of interferon-gamma receptors on bladder cancer cells: does it correlate with biological response?

Previously we have shown a differential biological response of three human bladder cancer cell lines (RT4, RT112 and MGH-U1) to gamma interferon (IFN-gamma). The present study examines the relationship between the biological response and the expression of the interferon-gamma receptor on the tumour cell surface. Using a competitive radioligand binding assay and Scatchard analysis, we measured the number and affinity of the IFN-gamma receptors on each of the above cell lines. Individual cells from each line expressed large numbers (29,100-41,800) of high-affinity receptors (kd = 2.4-3.9 x 10(10) M). There was no statistically significant difference in either of these parameters between the three lines. We therefore conclude that the biological response of these bladder lines to IFN-gamma does not relate to the number or affinity of its receptor on the plasma membrane of these tumour cells.

Carcinoma, Transitional Cell↗
PubMed1992

Computer simulation of the blood-brain barrier: a model including two membranes, blood flow, facilitated and non-facilitated diffusion.

A mathematical model of blood-brain barrier (BBB) transport was developed to assist in experimental design and data analysis. The model includes the luminal and antiluminal endothelial cell membranes, each with separate transport systems. Substrate movement between 3 compartments can be calculated: the capillary lumen, the endothelial cell cytoplasm, and the brain parenchyma. Blood flow, substrate concentration and competition in each compartment, concentration gradients along the capillary, and non-steady-state conditions are considered. The utility of the model is demonstrated by predicting: (1) complex concentration profiles along the length of the capillary lumen under different circumstances, (2) the permeability-surface area products along the capillary lumen, (3) the time course of events during brain-uptake index (BUI) experiments, (4) the accuracy of the BUI in measuring glucose transport over a range of endogenous glucose concentrations, (5) the influence of 2 membranes in series with different kinetic constants, and (6) a comparison of kinetic constants expected from high-flow infusion and BUI experiments.

Blood-Brain Barrier↗
PubMed1992

The role of positron emission tomography in oncology and other whole-body applications.

Imaging and quantifying biochemical and physiological processes with PET clearly has major potential significance for all organ systems and many disease states. Although the full utility and potential of emerging new applications of PET in organs other than the heart and brain must be demonstrated in basic and clinical research studies, the rapidly accumulating aggregate experience in oncology in particular, and in other organ systems and disease states as well, indicates that PET is now truly becoming a modality of both clinical and investigative use for the body as a whole as well as for specific organ systems. Whole-body PET FDG imaging (Fig 9) illustrates the potential of biochemical imaging to map the distribution of cancer throughout the body. With the growing list of radiopharmaceutical and quantitative techniques applicable to cancer studies with PET, this field will continue to realize significant growth.

Humans↗
PubMed1992

Change in the oestrogen receptor status of breast cancer with age--comparison of two types of assay.

The oestrogen receptor (ER) is considered to be an essential component of the mechanism of response of a breast tumour to endocrine therapy, but ER measurements have proved to have only modest predictive value. In the present study, we have examined ER status by both immunocytochemical assay (ER-ICA) on a fine needle aspirate and by radioligand-binding assay (DCC) on an excised portion of tumour. There was a correlation between the ER level detected by the two assays (Spearman's r = 0.77 for DCC versus ER-ICA staining intensity, r = 0.70 for DCC versus ER-ICA percentage of cells stained, P < 0.0001, n = 137 in each case). Each assay showed an increasing proportion of ER+ve results with increasing patient age. In the case of ER+ve tissues only, while ER concentration by DCC assay increased steadily with age (r = 0.39, P < 0.0001, n = 108), the ER-ICA assay revealed that, staining intensity increased with age (r = 0.26, P = 0.001, n = 149) but the percentage of cells stained did not (r = 0.08, P = NS, n = 149). It is concluded that increasing endocrine responsiveness with advancing age could reflect the increasing proportion of ER+ve tumours with increased levels of ER per cell (as indicated by staining intensity) rather than increasing proportion of ER+ve cells.

Adult↗
PubMed1992

The application of positron emission tomographic imaging with fluorodeoxyglucose to the evaluation of breast disease.

Positron emission tomography (PET) is a computer-aided tomographic imaging technique that uses positron-emitting compounds to trace biochemical processes of tissue, and construct images based on them. The authors applied a whole-body PET imaging technique to patients with breast masses or mammographic abnormalities using the isotope 2-[F-18]-fluoro-2-deoxy-D-glucose (FDG), in a clinical trial to evaluate the feasibility of using PET to identify primary breast cancer, axillary lymph node involvement, and systemic metastases, before surgical resection. Fourteen patients have been entered on this study, 10 of whom proved to have breast cancer. Positron emission tomography correctly predicted the nature of 12 of the 14 primary breast lesions, and correctly determined the lymph node status of 11 of the 14 patients. The authors conclude that PET with FDG has potential as a diagnostic modality for detection of primary breast cancer, particularly in the patient with radiodense breasts by conventional mammography, and that it has potential for the preoperative identification of axillary lymph node metastases.

Adolescent↗
PubMed1992

The differing predictive values of oestrogen receptor assays for large breast cancers.

Thirty elderly patients with T3 or T4 breast cancer underwent a wedge biopsy for radioligand-binding assay (RLA) of oestrogen receptor (ER) activity. A second, separate group of 21 elderly patients with T3 and T4 breast cancers underwent fine needle aspiration biopsy (FNA) for immunocytochemical assay of ER (ER-ICA). All the women received tamoxifen as primary treatment and response was assessed by UICC criteria. Tumour ER concentration by RLA was correlated with both response (Spearman's R = + 0.52) and time to progression (R = + 0.76). Nine patients with receptor-rich tumours (> 100 fmol/mg protein) failed to show a response. However, the percentage of cells staining for ER by ER-ICA assay was much more strongly related to the likelihood of response (R = + 0.89); no patient with < 20% cells staining responded. Wedge biopsy and the biochemical determination of ER activity is of limited value in predicting the likely response to tamoxifen; ER-ICA assays on such tumours may be more informative.

Aged↗
PubMed1992

Positron emission tomography detects metabolic viability in myocardium with persistent 24-hour single-photon emission computed tomography 201Tl defects.

BACKGROUND: Four-hour 201Tl redistribution images underestimate myocardial viability in patients with coronary artery disease (CAD). Because 4-hour defects often redistribute late, delayed imaging may enhance assessment of tissue viability. Myocardial metabolic activity was therefore assessed with positron emission tomography (PET) in 26 CAD patients with impaired ventricular function (ejection fraction, 32.1 +/- 13.9%) and 24-hour single-photon emission computed tomography (SPECT) 201Tl defects. METHODS AND RESULTS: On circumferential profile analysis, PET ischemia was defined by preserved glucose metabolism in hypoperfused myocardium, and PET infarction was defined by concordant reductions in perfusion and metabolism. On 19 stress-redistribution and seven rest-redistribution SPECT studies, four observers visually scored 201Tl activity in eight segments on a scale from 0 (normal) to 3 (complete defect). Using an improvement in visual score > or = 0.75 to define redistribution, there were 100 fixed, 17 partially reversible, and 12 completely reversible defects. PET identified tissue metabolic activity in 51 (51%) segments with fixed defects (21 PET ischemia, 30 PET normal) and nine (53%) segments with partially reversible defects (five PET ischemia, four PET normal). When grouped by 24-hour score, the proportion of fixed defects with metabolic activity varied from 84% (scores < or = 1.4) to 15% (scores > 2.6). For partially reversible defects, only 53% with scores < 2.0 and one of two with scores > or = 2.0 were considered metabolically viable on PET. Of 12 completely reversible defects, six (50%) were normal, five (42%) had PET ischemia, and one (8%) had PET infarction. The proportion of fixed defects with metabolic activity did not depend on whether a rest or stress study was performed or on the change in visual score used to define 201Tl redistribution (0.25, 0.50, 0.75, and 1.00). CONCLUSIONS: In CAD patients, PET identifies glucose metabolic activity in the majority of fixed 24-hour 201Tl defects. However, very severe (near-complete) 24-hour 201Tl defects are less likely to exhibit metabolic activity on PET imaging than are defects with less-pronounced reductions in segmental 201Tl activity.

Coronary Angiography↗
PubMed1992

Alfentanil-induced hypermetabolism, seizure, and histopathology in rat brain.

We evaluated the effect of alfentanil on hippocampal glucose utilization and histopathology associated with alfentanil-induced seizures. Three separate experiments were performed. First, anesthetized, paralyzed Long-Evans rats (n = 15; 5 rats per group) were mechanically ventilated and randomly assigned to three groups: (a) control, 70% N2O and 30% O2 continued for 1 h; (b) low-dose alfentanil (150 micrograms/kg i.v. bolus), followed by infusion at 15 micrograms.kg-1 x min-1 for 1 h without N2O; or (c) high-dose alfentanil (1000 micrograms/kg i.v. bolus), followed by infusion at 100 micrograms.kg-1 x min-1 for 1 h without N2O. After 1 h, [6-14C]glucose was injected intravenously for autoradiography. With high-dose alfentanil, there was increased glucose utilization in the ventral hippocampus and the lateral septal nucleus. In the second experiment, anesthetized, paralyzed Sprague-Dawley rats (n = 12; 4 rats per group) were mechanically ventilated, underwent insertion of hippocampal depth electrodes, and were randomly assigned to three groups: (a) control, 70% N2O and 30% O2; (b) low-dose alfentanil (150 micrograms/kg i.v. bolus), with 70% N2O and 30% O2; or (c) high-dose alfentanil (1000 micrograms/kg i.v. bolus), with 70% N2O and 30% O2. An epileptiform pattern was observed on hippocampal and subdermal electroencephalographic recordings in both alfentanil groups. In the third experiment, anesthetized, paralyzed Sprague-Dawley rats (n = 20) were mechanically ventilated and assigned to two groups: (a) control, 70% N2O and 30% O2 (n = 5) or 100% O2 (n = 5) continued for 1 h; or (b) alfentanil (2000 micrograms/kg i.v. bolus), followed by infusion at 33.3 micrograms.kg-1 x min-1 for 1 h with 100% O2. After tracheal extubation, the rats recovered overnight. Light-microscopic evaluation revealed hippocampal or amygdaloid damage in 6 of the 10 alfentanil-treated rats. High doses of alfentanil administered to rats can produce limbic system seizure activity with hypermetabolism associated with neuropathologic lesions.

Alfentanil↗
PubMed1992

Positron emission tomography: a new, precise imaging modality for detection of primary head and neck tumors and assessment of cervical adenopathy.

Positron emission tomography (PET) has been shown to be effective in detecting intracranial malignancies based on cerebral glucose metabolism. To evaluate the ability of PET to detect extracranial head and neck neoplasms and cervical metastases, 16 patients with primary squamous cell carcinomas were examined. All patients received preoperative computerized tomography (CT) and magnetic resonance imaging (MRI) scans and underwent PET evaluation using intravenous 18F-2-fluoro-2-deoxy-D-glucose (FDG). Histopathologic analysis compared tumor invasion and positive lymph nodes with findings on MRI, CT, and PET images. All primary tumors were delineated by PET, while MRI and CT failed to detect one superficial tumor involving the anterior tongue. Ten nodes were detected by CT and MRI versus 12 nodes demonstrated by PET. PET is highly effective in detecting head and neck carcinomas as well as metastatic cervical lymph nodes. In addition, PET may be useful in evaluating postsurgery and postradiotherapy patients for recurrent and new primary tumors.

Adult↗
PubMed1992

A new noninvasive quantification of renal blood flow with N-13 ammonia, dynamic positron emission tomography, and a two-compartment model.

In order to determine if dynamic positron emission tomography (PET) and N-13 ammonia can be used to quantitate regional RBF (rRBF) noninvasively, six anesthetized dogs were examined with PET imaging after an iv bolus administration of 5 mCi of N-13 ammonia. Renal time activity curves and the arterial input function were derived from regions of interest drawn over the renal cortex and abdominal aorta, respectively. For calculation of rRBF, less than 120 s of the initial data were used to minimize contamination by plasma metabolites of N-13 radioactivity. rRBF was quantitated with a two-compartment model, and the results were compared with simultaneously acquired microsphere blood flow measurement. Fourteen experiments were performed in six dogs, and four regions of interest on renal cortex were selected on each PET image. RBF derived from dynamic PET imaging with N-13 ammonia was linearly related to microsphere (MS) values (rRBF = 1.06 x MS - 0.17; r = 0.91). Mean rRBF in the canine experiments was 4.0 mL/min/g. The results indicate that dynamic N-13 ammonia renal PET can provide noninvasively quantitative rRBF.

Ammonia↗
PubMed1992

Pentobarbital-enhanced [3H]flunitrazepam binding throughout the rat brain: an autoradiographic study.

The gamma-aminobutyric acidA/benzodiazepine receptor contains distinct ligand binding sites for hypnotic barbiturates and benzodiazepines. It is thought that barbiturate-induced sedation is produced, in part, by enhancing agonist binding to this receptor. The present study tested the hypothesis that pentobarbital would enhance benzodiazepine binding in a site-specific manner across the rat brain. In vitro receptor autoradiography was used to localize and quantitatively map [3H]flunitrazepam ([3H]FLU) binding in the absence and presence of pentobarbital in 133 brain areas. Each area demonstrated a statistically significant increase in [3H]FLU binding in the presence of in vitro pentobarbital (P < or = 0.05). Hindbrain nuclei dominated the top 20% of brain areas demonstrating the greatest pentobarbital-induced increases in [3H]FLU binding. The greatest mean percent increase in [3H]FLU binding occurred in the medulla, including areas known to be important for cardiovascular control, breathing, motor tone and regulating levels of arousal. These findings show that differential enhancement of benzodiazepine binding in the presence of pentobarbital occurred in brain areas controlling physiological functions known to be impaired by systemically administered pentobarbital.

Animals↗
PubMed1992

Evaluation of the skeletal kinetics of fluorine-18-fluoride ion with PET.

To evaluate the feasibility of quantitatively assessing regional skeletal fluoride uptake in humans in focal and generalized bone disease, we investigated the skeletal kinetics of [18F]fluoride ion with dynamic PET imaging. Dynamic image sets were acquired over a 60-min interval in a multiplane PET device, and input functions (plasma 18F time-activity curves) were measured directly from arterialized blood and, in some cases, determined from image-derived left ventricular cavity activity measurements. Our results indicate: 1. A steady-state ratio of [18F]fluoride ion concentration in plasma to whole blood greater than unity (1.23 for plasma to directly assayed whole blood and 1.44 for plasma to left ventricular cavity imaged concentrations. This concentration difference produces a scaling factor that must be considered when using image derived or directly measured input functions. 2. The preferred tracer kinetic model configuration for [18F]fluoride ion skeletal kinetics is a three compartment model that includes a "bound" and "unbound" bone [18F]fluoride ion compartment. 3. The rate constant for forward transport of [18F]fluoride ion from plasma to the extravascular space of bone (K1) and the regional blood volume parameter generate estimates of bone blood flow and vascular volume, respectively, that are in the physiologic range of reported for mammals. Estimates of the uptake constant for fluoride in bone, using nonlinear regression (KNLR = 0.0360 +/- 0.0064 ml/min/ml), are in very good agreement with an estimate of the same parameter obtained with Patlak graphical analysis (KPAT = 0.0355 +/- 0.0061 ml/min/ml). 4. Generating parametric images of KPAT facilitates quantification of regional bone [18F]fluoride ion kinetics. The method is computationally practical, and, with either the parametric imaging approach or with standard region of interest analysis, can be used to generate quantitative estimates of fluoride uptake (a "bone metabolic index") in focal skeletal regions or in more generalized distributions.

Adult↗
PubMed1992

Whole-body positron emission tomography: Part I. Methods and performance characteristics.

Methods for whole-body PET imaging have been developed to provide a clinical tool for the detection and evaluation of primary and metastatic cancers. The axial FOV of the PET system is extended by imaging at multiple bed positions to cover the whole body. In typical rectilinear PET scans, only a small fraction of the data is collected to form two-dimensional projection images. In this work, 100% of the projection data was collected to form the two-dimensional projection images. These projection images were generated for continuous angles over 180 degrees by resorting sinogram data. In addition, tomographic images were formed by using filtered backprojection reconstruction without attenuation correction. Coronal and sagittal cuts were then extracted from the three-dimensional data set. The tomographic images were reconstructed to a resolution of 10.8 mm in all dimensions because of statistical limitations of the data. Both methods of image formation resulted in images of high quality with the tomographic reconstruction providing the highest contrast and resolution. An acquisition time of 1-2 min/bed position after a 10-mCi injection of [18F]fluoride ion or [18F]FDG was found to give a sufficient number of counts for producing images of good resolution and contrast, from a total scanning time of 32-64 min.

Deoxyglucose↗
PubMed1991

Hyperammonaemia depresses glucose consumption throughout the brain.

Recent studies showed that hyperammonaemia caused many of the metabolic changes in portacaval-shunted rats, a model of hepatic encephalopathy. These changes included a depression in the cerebral metabolic rate of glucose (CMRGlc), an indication of decreased brain function. 2. The purpose of the present experiments was to determine whether the depression of CMRGlc caused by ammonia is confined to certain brain structures, or whether the depression is an overall decrease in all structures, such as occurs in portacaval-shunted rats. To accomplish this objective, rats were made hyperammonaemic by giving them intraperitoneal injections of 40 units of urease/kg body wt. every 12 h; control rats received 0.154 m-NaCl. CMRGlc was measured 48 h after the first injection, by using quantitative autoradiography with [6-14C]glucose as a tracer. 3. The experimental rats had high plasma ammonia concentrations (control 70 nmol/ml, experimental 610 nmol/ml) and brain glutamine levels (control 5.4 mumol/ml). Hyperammonaemia decreased CMRGlc throughout the brain by an average of 19%. CMRGlc showed an inverse correlation with plasma ammonia, but a stronger correlation with the brain glutamine content. 4. Hyperammonaemia led to a decrease in CMRGlc throughout the brain that was indistinguishable from the pattern seen in portacaval-shunted rats. This is taken as further evidence that the cerebral depression found in portacaval-shunted rats is a consequence of hyperammonaemia. The observation that depression of CMRGlc correlated more closely with brain glutamine content than with plasma ammonia suggests that metabolism of ammonia is an important step in the pathological sequence.

Ammonia↗
PubMed1991

Hyperammonaemia does not impair brain function in the absence of net glutamine synthesis.

1. It has been established that chronic hyperammonaemia, whether caused by portacaval shunting or other means, leads to a variety of metabolic changes, including a depression in the cerebral metabolic rate of glucose (CMRGlc) increased permeability of the blood-brain barrier to neutral amino acids, and an increase in the brain content of aromatic amino acids. The preceding paper [Jessy, DeJoseph & Hawkins (1991) Biochem. J. 277, 693-696] showed that the depression in CMRGlc caused by hyperammonaemia correlated more closely with glutamine, a metabolite of ammonia, than with ammonia itself. This suggested that ammonia (NH3 and NH4+) was without effect. The present experiments address the question whether ammonia, in the absence of net glutamine synthesis, induces any of the metabolic symptoms of cerebral dysfunction associated with hyperammonaemia. 2. Small doses of methionine sulphoximine, an inhibitor of glutamine synthetase, were used to raise the plasma ammonia levels of normal rats without increasing the brain glutamine content. These hyperammonaemic rats, with plasma and brain ammonia levels equivalent to those known to depress brain function, behaved normally over 48 h. There was no depression of cerebral energy metabolism (i.e. the rate of glucose consumption). Contents of key intermediary metabolites and high-energy phosphates were normal. Neutral amino acid transport (tryptophan and leucine) and the brain contents of aromatic amino acids were unchanged. 3. The data suggest that ammonia is without effect at concentrations less than 1 mumol/ml if it is not converted into glutamine. The deleterious effect of chronic hyperammonaemia seems to begin with the synthesis of glutamine.

Amino Acids↗