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Biomedical subjects

R Green

Publications and source records attributed to R Green.

At least 289 records · Page 16Linked to original sources
PubMed1990

Lithium clearance in healthy humans: effects of sodium intake and diuretics.

In summary, our experiments clearly demonstrate that lithium reabsorption occurs by frusemide- and bumetanide-sensitive reabsorption, but we have failed to identify the mechanism(s) responsible for the lower CLi and FELi in salt-depletion. It is possible that some, as yet unknown, factor increases the activity of the Na, K, 2Cl cotransporter and, hence, increases lithium reabsorption in the thick ascending limb in salt-depleted subjects. However, it is equally possible that a fraction of proximal tubular reabsorption is inhibited by frusemide and bumetanide. If this is correct, CLi in humans are reasonable markers of proximal tubular function even in conditions of avid salt retention and in salt depletion, when fractional reabsorption of salt and water in the proximal tubules is enhanced.

Amiloride↗
PubMed1989

The guanosine binding site of the Tetrahymena ribozyme.

The self-splicing Group I introns have a highly specific binding site for the substrate guanosine. Mutant versions of the Tetrahymena ribozyme have been used in combination with guanosine analogues to identify the nucleotide in the ribozyme that is primarily responsible for recognition of the guanine base.

Animals↗
PubMed1989

Misplacement of the amino-terminal positive charge in the prepro-alpha-factor signal peptide disrupts membrane translocation in vivo.

We have identified a series of mutations in the signal peptide of yeast prepro-alpha-factor which specifically attenuate translocation across the endoplasmic reticulum membrane in vivo. In prepro-alpha-factor-somatostatin hybrids, transposition of the amino-terminal tripeptide from wild-type NH2-Met-Arg-Phe to NH2-Met-Phe-Lys or NH2-Met-Phe-Arg causes a 45-75% reduction in the efficiency of membrane translocation. This is evidenced by the intracellular accumulation of unglycosylated, signal-containing precursors which are membrane-associated and are exposed to the cytosol. Surprisingly, abolition of the single positive charge by replacing arginine with phenylalanine has little effect on translocation into the endoplasmic reticulum. We conclude that the presence of an amino-terminal positive charge is not necessary for efficient targeting or translocation; however, misplacement by one position markedly disrupts translocation without affecting targeting. These mutations thus define an early stage of membrane interaction that is sensitive to local charge effects. Furthermore, our data suggest that post-translational translocation, signal cleavage, and core glycosylation of these polypeptides may occur to a significant extent in vivo.

Cell Membrane↗
PubMed1989

Prevalence of hazardous exposures in veterinary practice.

All female graduates of a major U.S. veterinary school were surveyed by mailed questionnaire to obtain details of work practice and hazard exposure during the most recent year worked and during all pregnancies. Exposure questions were based on previously implicated occupational hazards which included anesthetic gases, radiation, zoonoses, prostaglandins, vaccines, physical trauma, and pesticides. The response rate was 86% (462/537). We found that practice type and pregnancy status were major determinants of hazard exposure within the veterinary profession. Small-animal practitioners reported the highest rates of exposure to anesthetic gas (94%), X-ray (90%), and pesticides (57%). Large-animal practitioners reported greater rates of trauma (64%) and potential exposure to prostaglandins (92%), Brucella abortus vaccine (23%), and carbon monoxide (18%). Potentially hazardous workplace practices or equipment were common. Forty-one percent of respondents who reported taking X-rays did not wear film badges, and 76% reported physically restraining animals for X-ray procedures. Twenty-seven percent of the respondents exposed to anesthetic gases worked at facilities which did not have waste anesthetic gas scavenging systems. Women who worked as veterinarians during a pregnancy attempted to reduce exposures to X-rays, insecticides, and other potentially hazardous exposures. Some potentially hazardous workplace exposures are common in veterinary practice, and measures to educate workers and to reduce these exposures should not await demonstration of adverse health effects.

Anesthetics↗
PubMed1989

Determination of plasma homocysteine by high-performance liquid chromatography with fluorescence detection.

Severe homocystinemia is frequently associated with vascular disease while the pathological consequences of moderate or slightly elevated plasma homocysteine are unknown. Cobalamin and folate deficiencies may result in an elevation of plasma homocysteine. A sensitive and reproducible assay for total plasma homocysteine has been developed. The essential steps in the assay include (i) conversion of homocysteine disulfides to free homocysteine with borohydride reduction; (ii) conjugation of homocysteine with monobromobimane; (iii) separation of homocysteine-bimane from other plasma thiol-bimane adducts by reverse-phase high-performance liquid chromatography; and (iv) detection and quantitation of homocysteine-bimane by fluorometry. The method has a sensitivity of 4.4 pmol of homocysteine and is highly reproducible (intra- and interassay coefficients of variation = 4.97 and 4.53%, respectively). The mean concentration of total plasma homocysteine in nonfasting adult males (n = 12) and females (n = 12) was 15.8 (range, 7.0-23.7) and 16.5 nmol/ml (range, 8.6-20.7), respectively. Markedly elevated levels of homocysteine were found in patients with cobalamin and folate deficiency. Total plasma homocysteine represents approximately 4% of borohydride-generated thiol reactivity in the plasma of normal individuals.

Chromatography, High Pressure Liquid↗
PubMed1989

The role of folate and vitamin B-12 in neurotransmitter metabolism and degenerative neurological changes associated with aging: proceedings of a workshop.

Under the sponsorship of the National Institute on Aging and the National Institute of Diabetes and Digestive and Kidney Diseases, the Life Sciences Research Office of the Federation of American Societies for Experimental Biology held a workshop entitled, "The Role of Folate and Vitamin B-12 in Neurotransmitter Metabolism and Degenerative Neurological Changes Associated with Aging." The purpose of the May 1988 workshop was to bring together scientists from various disciplines to identify opportunities for research on an important topic relating to neuroscience, nutrition and aging.

Aging↗
PubMed1989

Melatonin profile in marmots: the influence of catecholamines, hibernation, and light.

The aim of this study was to determine the effects of circulating catecholamines and light on the daily melatonin rhythm in the marmot. Endogenous levels of circulating catecholamines and plasma melatonin were measured during arousal from hibernation in light and studies were performed on the circadian melatonin rhythm in two photoperiods (LD 4:20 and LD 8:16). In addition, studies were done on the capacity of broad-band white light at normal room intensities (32 muW/cm2 or 108 Ix) and of low-intensity monochromatic green light (500 nm; 1.4muW/cm2 or 3.1 Ix) to suppress high nocturnal melatonin levels. We conclude that high levels of plasma catecholamines that occur during arousal from hibernation do not influence the production and secretion of pineal melatonin. During the nocturnal portion of its light/dark cycle, the marmot plasma melatonin rhythm is suppressed by both white light and low-intensity green light.

Animals↗
PubMed1989

Effect of magnesium infusion on calcium handling in the rat kidney.

Anaesthesized rats were infused with 100 microliters min-1 of 0.9% saline or saline containing 2 or 4 mmol l-1 of magnesium chloride and renal function was studied. Magnesium had no effect on urine flow rate, excretion of sodium or potassium, or glomerular filtration rate (GFR). Infusion of either dose of magnesium increased calcium excretion and calcium concentration in the urine. The increased urinary calcium excretion is due to a decrease in tubular reabsorption of calcium.

Animals↗
PubMed1989

Reflection coefficients and water permeability in rat proximal tubule.

Simultaneous microperfusion of proximal tubules and peritubular capillaries in kidneys of rats anesthetized with Inactin was used to measure reflection coefficients. All perfusates contained cyanide to inhibit active transport; the tubular perfusate was isotonic and the peritubular capillaries were perfused with solutions made hypertonic with NaCl, NaHCO3, L-glucose, or sodium ferrocyanide. Measurements of recollected fluid enabled a precise mean gradient and ionic fluxes to be calculated; net water flux was measured with inulin. Imposed gradients always partly dissipated. Reflection coefficients were 0.59 +/- 0.01 for NaCl, 0.87 +/- 0.04 for NaHCO3-, and 0.96 +/- 0.07 for ferrocyanide, assuming that L-glucose was 1. Water permeability of the proximal tubule was 1,030 microns/s. Ionic permeability of Cl- (21.6 +/- 1.3 X 10(-5) cm/s) was greater than that for Na+ (13.3 +/- 2.7 X 10(-5) cm/s); permeability for L-glucose was 5.4 +/- 1.3 X 10(-5), and for ferrocyanide ions 2.7 +/- 0.9 X 10(-5) cm/s. It is concluded that in rat proximal tubule both NaCl and NaHCO3 have reflection coefficients less than 1.0 and solute asymmetry across the epithelium is a significant driving force for fluid reabsorption. Furthermore the data suggest that there is a significant contribution of solvent drag to solute movement.

Animals↗
PubMed1989

Osmotic forces driving water reabsorption in the proximal tubule of the rat kidney.

Simultaneous microperfusion of proximal tubules and peritubular capillaries in kidneys of rats anesthetized with Inactin was used to measure reabsorption of fluid in response to an imposed osmotic gradient. The tubular fluid was isotonic and the peritubular capillaries were made hypertonic with NaCl or NaHCO3. Mean gradients and ionic fluxes were measured. When no gradient was imposed tubular fluid became hypotonic and rate of fluid reabsorption was 0.700 nl.mm-1.min-1. Imposition of a 25 mM NaCl gradient increased fluid flux to 3.887 nl.mm-1.min-1, whereas 25 mM NaHCO3 stimulated 5.226 ml/mm fluid reabsorption. This gave a relative reflection coefficient of NaCl:NaHCO3 of 0.73. Apparent water permeability varied with highest values for the smallest gradients. This suggests the possibility of a compartment in the epithelium that is hypertonic to the peritubular capillaries. The hypertonicity required to account for fluid movement was 6-16 mosmol/kg.

Absorption↗
PubMed1989

A comparative evaluation of four hearing aid selection procedures. I--Speech discrimination measures of benefit.

Speech discrimination measures of the benefit provided by four different hearing-aid selection procedures were determined on a group of experienced hearing-aid users. The results revealed that the advantages of prescriptive methods of selection (specifically the procedures of Berger et al., and of Byrne and Tonisson) over intuitive fitting (using an experience clinician) or 'fixed' selection (+ 6 dB/octave frequency response slope) are substantial in some circumstances. The effect of selection procedure on benefit was little influenced by degree of hearing loss but considerably influenced by configuration of loss (flat, sloping or irregular). For patients with gently to steeply sloping losses, the prescriptive methods of selection were shown to provide more benefit than the other methods studied.

Aged↗
PubMed1989

A comparative evaluation of four hearing-aid selection procedures. II--Quality judgements as measures of benefit.

Quality judgements by hearing-aid wearers were used to compare hearing-aid frequency responses selected by four different aid selection procedures: the methods of Berger et al. and Byrne and Tonisson, 'intuitive' fitting by an experienced clinician, and a fixed frequency response of + 6 dB/octave. A previous study had demonstrated that the two 'prescription' methods (of Berger et al. and Byrne and Tonisson) showed greater benefit as measured by speech discrimination tests, particularly for patients with sloping audiograms. The results of this study indicated that quality judgements did not appear to be significantly influenced by the fitting procedure used. The only significant factor was the order in which the patients listened to the hearing aids. The second aid was always preferred. This finding was confirmed by a second study in which the only experimental variable was order. Again the second aid was preferred. The implications of this finding for clinical hearing-aid evaluation are discussed.

Aged↗
PubMed1989

A new red cell discriminant incorporating volume dispersion for differentiating iron deficiency anemia from thalassemia minor.

A novel red cell discriminant function [MCV2 x RDW/(Hgb x 100)] was compared to six other discriminants in 102 patients with established mild iron deficiency anemia and 33 patients with beta-thalassemia minor. The discriminant incorporates the two key measurements of erythrocyte cell volume distribution, namely the mean (MCV) and standard deviation (RDW), which are known to be helpful for distinguishing between these two frequent causes of microcytic hypochromic anemia. Data used for the learning set to develop the new discriminant were obtained using an electrical impedance automated whole blood analyzer (Coulter S + IV) and were applied as a validation set for six other discriminants. The discriminant was also tested on smaller subsets of the patients groups using data obtained on either an alternate electrical impedance instrument (Sysmex E-5000) or a laser light scattering based system (Technicon H*1). From the comparison it was concluded that use of a discriminant function that incorporates a measurement of red cell volume dispersion results in enhanced accuracy for distinguishing iron deficiency anemia from thalassemia minor.

Anemia, Hypochromic↗
PubMed1989

Kidney transplantation in insulin dependent diabetic patients: improved survival and rehabilitation.

Between 1977 and 1986, 50 insulin-dependent diabetic patients received a kidney transplant, 19 from living related donors and 31 from cadaveric donors. Cumulative patient survival was 81% and graft survival was 64% and 33% for living related and cadaveric donor kidneys, respectively, at five years. These results are comparable to that of nondiabetic patients. While physical performance and visual acuity significantly improved after a successful kidney transplantation, neuropathies and angiopathies might not improve. Physical performance improved even in those patients whose nerve conduction time had deteriorated. These findings suggest that kidney transplantation is an effective means of improving survival and rehabilitation of diabetic patients with end-stage renal disease.

Adult↗
PubMed1989

Acute torticollis secondary to rupture of the sternocleidomastoid.

Trauma to the neck musculature and cervical spine is frequently caused by hyperextension injuries which may result in muscular spasm or rupture. Partial rupture of the sternocleidomastoid muscle with subsequent formation of a fibrotic band is an unusual cause of acute torticollis. The case of a 21-year-old man who developed an acute torticollis and cervical pain after a motor vehicle accident is presented. Computed tomography scan demonstrated 75% rupture of the left sternocleidomastoid muscle with fibrotic band replacing the absent muscle tissue. Neck range of motion was markedly decreased. The patient underwent a trial of muscle relaxants and intensive physical therapy with no significant improvement. Surgical release of the residual fibrotic band was performed, and the left deviation of the neck was reduced from 25 degrees preoperatively to 5 degrees postoperatively. With surgical release and intensive postoperative physical therapy, the patient regained full motion and strength of the cervical spine musculature.

Adult↗