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Biomedical subjects

R G Smith

Publications and source records attributed to R G Smith.

At least 253 records · Page 14Linked to original sources
PubMed1990

Copper status and urinary and salivary copper in young men at three levels of dietary copper.

Eleven young men were confined to a metabolic research unit for 90 d to determine the effect of the amount of dietary copper on copper nutriture. The study was divided into three metabolic periods (MP): 1) with an adequate-copper diet (1.68 mg/d) for 24 d, 2) with a low-copper diet (0.79 mg/d) for 42 d, and 3) with a high-copper diet (7.53 mg/d) for 24 d. Three indices of copper status, urinary copper, and salivary copper were determined at intervals throughout the study. Neither copper status, urinary copper, nor salivary copper differed among MPs. Sweat collections from three subjects suggested that losses of copper through sweat were very low and would not contribute significantly to copper balance. These results suggest that an amount of dietary copper slightly less than 0.8 mg/d is adequate to maintain copper status for greater than or equal to 42 d in normal, healthy men and that neither urinary nor salivary copper is affected by the amount of Cu in the diet.

Adult↗
PubMed1990

Milk's effect on the bioavailability of iron from cereal-based diets in young women by use of in vitro and in vivo methods.

A study was conducted in healthy young women to measure and compare the availability of iron from cereal-based diets with and without milk by use of in vivo and in vitro methods. In vitro iron-bioavailability tests demonstrated that the amounts of soluble and ionizable iron in cereal-based diets were increased two- and three-fold, respectively, when milk was added. 54Fe, a stable isotope of iron, and fecal monitoring were used to determine iron absorption in eight young women. Iron absorption was higher with milk than without milk in seven of the eight subjects but did not differ significantly between the two treatments. The results suggest that in vivo and in vitro effects differ and that the absorption of iron from cereal-based diets is neither enhanced nor inhibited by the addition of milk.

Absorption↗
PubMed1990

Large bowel problems.

Some large bowel disorders are common to all age groups, others are commoner in the elderly. Colonic function is complex and not fully understood. Diarrhoeal states tend to cause faecal incontinence in the elderly and constipation is commoner in immobile institutionalised elderly patients. Two types of constipation have been identified requiring different approaches in treatment. The management of constipation includes the treatment of the underlying cause and the clearing of the bowel using enemas and suppositories given rectally and laxatives given orally. The neurological causes of faecal incontinence may be local or more commonly cortical. Deliberate constipation and planned evacuation of the rectum may help to reduce the frequency of faecal incontinence. The management of diverticular disease centres around fibre and bulking agents. The treatment of ulcerative colitis and Crohn's disease is similar to that in younger patients.

Aged↗
PubMed1990

Regulation of Carbon Partitioning to Respiration during Dark Ammonium Assimilation by the Green Alga Selenastrum minutum.

The assimilation of NH(4) (+) causes a rapid increase in respiration to provided carbon skeletons for amino acid synthesis. In this study we propose a model for the regulation of carbon partitioning from starch to respiration and N assimilation in the green alga Selenastrum minutum. We provide evidence for both a cytosolic and plastidic fructose-1,6-bisphosphatase. The cytosolic form is inhibited by AMP and fructose-1,6-bisphosphate and the plastidic form is inhibited by phosphate. There is only one ATP dependent phosphofructokinase which, based on immunological cross reactivity, has been identified as being localized in the plastid. It is inhibited by phosphoenolpyruvate and activated by phosphate. No pyrophosphate dependent phosphofructokinase was found. The initiation of dark ammonium assimilation resulted in a transient increase in ADP which releases pyruvate kinase from adenylate control. This activation of pyruvate kinase causes a rapid 80% drop in phosphoenolpyruvate and a 2.7-fold increase in pyruvate. The pyruvate kinase mediated decrease in phosphoenolpyruvate correlates with the activation of the ATP dependent phosphofructokinase increasing carbon flow through the upper half of glycolysis. This increased the concentration of triosephosphate and provided substrate for pyruvate kinase. It is suggested that this increase in triosephosphate coupled with the glutamine synthetase mediated decline in glutamate, serves to maintain pyruvate kinase activation once ADP levels recover. The initiation of NH(4) (+) assimilation causes a transient 60% increase in fructose-2,6-bisphosphate. Given the sensitivity of the cytosolic fructose-1,6-bisphosphatase to this regulator, its increase would serve to inhibit cytosolic gluconeogenesis and direct the triosephosphate exported from the plastid down glycolysis to amino acid biosynthesis.

Journal Article↗
PubMed1990

Relationship between NH(4) Assimilation Rate and in Vivo Phosphoenolpyruvate Carboxylase Activity : Regulation of Anaplerotic Carbon Flow in the Green Alga Selenastrum minutum.

The rate of NH(4) (+) assimilation by N-limited Selenastrum minutum (Naeg.) Collins cells in the dark was set as an independent variable and the relationship between NH(4) (+) assimilation rate and in vivo activity of phosphoenolpyruvate carboxylase (PEPC) was determined. In vivo activity of PEPC was measured by following the incorporation of H(14)CO(-) (3) into acid stable products. A linear relationship of 0.3 moles C fixed via PEPC per mole N assimilated was observed. This value agrees extremely well with the PEPC requirement for the synthesis of the amino acids found in total cellular protein. Determinations of metabolite levels in vivo at different rates of N assimilation indicated that the known metabolite effectors of S. minutum PEPC in vitro (KA Schuller, WC Plaxton, DH Turpin, [1990] Plant Physiol 93: 1303-1311) are important regulators of this enzyme during N assimilation. As PEPC activity increased in response to increasing rates of N assimilation, there was a corresponding decline in the level of PEPC inhibitors (2-oxoglutarate, malate), an increase in the level of PEPC activators (glutamine, dihydroxyacetone phosphate), and an increase in the Gln/Glu ratio. Treatment of N-limited cells with azaserine caused an increase in the Gln/Glu ratio resulting in increased PEPC activity in the absence of N assimilation. We suggest glutamate and glutamine play a key role in regulating the anaplerotic function of PEPC in this C(3) organism.

Journal Article↗
PubMed1990

Phenytoin dosage individualization--five methods compared in the elderly.

Five methods to predict phenytoin dosage have been compared in nine continuous care elderly patients. For each patient three steady-state plasma concentrations were obtained at three different doses. The data were used to estimate the 'optimum' dose for each patient by direct linear plot. The optimum dose for each patient was predicted from each plasma concentration using five dosage prediction methods based on the Michaelis-Menten equation using: (i) the population mean Vmax, (ii) the population mean KM, (iii) the linearized Bayesian method, (iv) the Rambeck nomogram, and (v) two plasma concentration-dose data pairs to estimate both Vmax and KM. The predictive precision was similar for each of methods (i-iv). Ninety-six out of 126 dosage predictions with the five methods were within 25 mg of the optimum dose. Methods (ii) and (iv) tended to overpredict dosage, particularly when used to interpret low plasma phenytoin concentrations.

Aged↗
PubMed1990

A bird zinc-finger protein closely related to ZFY.

The ZFY gene is thought to reside in the "sex-determining" region of the mammalian Y chromosome and encodes a zinc-finger protein that may function in determining the sex of embryos. Although birds have a ZZ(male)/ZW(female) sex-determination system, they possess a gene, Zfb, that is highly homologous to ZFY. We used ZFY as a hybridization probe to clone the zinc-finger domain of the chicken Zfb gene. Chicken Zfb is widely transcribed in male and female tissues and encodes a protein with a zinc-finger domain that is 93% identical in amino acid sequence to the zinc-finger domain of ZFY. Thus, the putative DNA-binding domains of the Zfb and ZFY proteins diverged little from a common ancestral protein that existed prior to birds and mammals, suggesting that the DNA binding site has been similarly conserved. The absence of sex differences in the hybridization patterns of Zfb raises the question of whether this gene is present on the Z/W sex chromosomes in birds.

Age Factors↗
PubMed1990

Vectors, promoters, and expression of genes in chick embryos.

Transgenic chickens were produced by injecting the Day-1 egg with 10(5) infectious particles of a replication-competent virus based on the Schmidt-Ruppin A strain of Rous sarcoma virus. The chickens were resistant to transforming subgroup A virus containing the src gene but not the corresponding subgroup B virus. Transgenic chickens producing bovine growth hormone (bGH) were generated using a modified virus containing the Bryan high titre polymerase gene. The virus was constructed with the bGH gene and the mouse metallothionein promoter in the reverse orientation relative to the viral structural genes. Two male chickens produced serum concentrations of approximately 100 ng bGH/ml; the birds were larger than controls and matured more rapidly. Transgenic mice required for the analysis of skeletal muscle-specific expression in vivo were produced using 5'-flanking regions of the chicken alpha-skeletal actin promoter linked to a luciferase reporter gene to determine the region essential for tissue-specific expression. The defined promoter sequences are to be used in experiments designed to direct expression of growth-promoting genes in skeletal muscle of chickens.

Animals↗
PubMed1990

Production of plasmid DNA in a simple, inexpensive and reusable fermentor.

Performance data for the production of plasmid DNA in bacterial cultures have been obtained using a new concept of simplified fermentor, the Lofstrand Bactolift. The unique design of this fermentor incorporates a standard 500-ml or 1-liter centrifuge bottle as the bacterial growth vessel, thus eliminating the necessity to transfer the cultures for subsequent processing. Bacterial and plasmid yields have been shown to be equal to or greater than those obtained using conventional shake flasks. Twelve 1-liter Bactolift fermentors can be operated in a standard laboratory water bath that occupies less than two square feet of bench space, as compared to a limit of six 2.8-liter Fernbach flasks containing one liter of culture held in an incubator shaker cabinet that occupies nine square feet of laboratory floor space.

Bacteriological Techniques↗
PubMed1989

Amplification, rearrangement, and elevated expression of c-myc in the human prostatic carcinoma cell line LNCaP.

We have investigated the structure and expression of the c-myc proto-oncogene in DNA isolated from the immortal cell line LNCaP. This cell line was derived from a lymph node metastasis of human prostate cancer. Msp I digest of LNCaP DNA when hybridized to a human c-myc probe showed a 1.45 kb band of intensity about two-fold greater than that observed in normal lymphocytes. In addition, the LNCaP cells contain rearranged and amplified c-myc structures which are not present in normal lymphocytes. Quantitation of these bands by scanning densitometry is consistent with an approximately 10-fold amplification of c-myc. To determine whether this amplification was accompanied by increased expression, RNA was isolated from these cells and compared to RNA isolated from a control cell line in which c-myc was not amplified. Northern blot analysis showed that the RNA transcripts from LNCaP cells were approximately 50-fold higher. Although androgens modulate the cell growth of LNCaP, there was no change in the level of c-myc RNA transcripts in serum-free medium in the presence or absence of androgens. Further investigation to determine whether altered structure, amplification, and overexpression of c-myc constitute a common characteristic of metastatic human prostate cancer might prove profitable in understanding this disease.

DNA, Neoplasm↗
PubMed1989

Extracorporeal pulsatile biventricular support after cardiac transplantation.

A donor heart failed to adequately sustain hemodynamic function after cardiac transplantation. The cause of the donor heart dysfunction was unknown, and there were no definite risk factors identified to suggest the heart would not recover. A Symbion Acute Ventricular Assist Device System was used to support both ventricles. The heart gradually recovered and the system was explanted after 1 week of support. The patient recuperated and has been discharged from the hospital.

Assisted Circulation↗
PubMed1989

The prevalence and aetiology of long-term L-dopa side-effects in elderly parkinsonian patients.

Fifty-one elderly parkinsonian patients (mean age 80 years) on long-term (greater than 5 years) L-dopa therapy were identified from the patients within the three geriatric units in Edinburgh. Side-effects were identified in 57% of patients and tended to be mild in severity. Mean duration of disease was 10.2 years in those with side-effects and 6.7 years in those without (p less than 0.01). Past and present L-dopa side-effects are more likely to be caused by disease progression than by L-dopa therapy. It is therefore recommended that L-dopa should be prescribed at disease onset to elderly Parkinsonian patients.

Age Factors↗
PubMed1989

Mechanism of Photosynthetic Carbon Dioxide Uptake by the Red Macroalga, Chondrus crispus.

The aim of this study was to determine how Chondrus crispus, a marine red macroalga, acquires the inorganic carbon (C(i)) it utilizes for photosynthetic carbon fixation. Analyses of C(i) uptake were done using silicone oil centrifugation (using multicellular fragments of thallus), infrared gas analysis, and gas chromatography. Inhibitors of carbonic anhydrase (CA), the band 3 anion exchange protein and Na(+)/K(+) exchange were used in the study. It was found that: (a) C. crispus does not accumulate C(i) internally above the concentration attainable by diffusion; (b) the initial C(i) fixtion rate of C. crispus fragments saturates at approximately 3 to 4 millimolar C(i); (c) CA is involved in carbon uptake; its involvement is greatest at high HCO(3) (-) and low CO(2) concentration, suggesting its participation in the dehydration of HCO(3) (-) to CO(2); (d) C. crispus has an intermediate C(i) compensation point; and (e) no evidence of any active or facilitated mechanism for the transport of HCO(3) (-) was detected. These data support the view that photosynthetic C(i) uptake does not involve active transport. Rather, CO(2), derived from HCO(3) (-) catalyzed by external CA, passively diffuses across the plasma membrane of C. crispus. Intracellular CA also enhances the fixation of carbon in C. crispus.

Journal Article↗
PubMed1989

Short-Term Metabolite Changes during Transient Ammonium Assimilation by the N-Limited Green Alga Selenastrum minutum.

In this study, we measured the total pool sizes of key cellular metabolites from nitrogen-limited cells of Selenastrum minutum before and during ammonium assimilation in the light. This was carried out to identify the sites at which N assimilation is acting to regulate carbon metabolism. Over 120 seconds following NH(4) (+) addition we found that: (a) N accumulated in glutamine while glutamate and alpha-ketoglutarate levels fell; (b) ATP levels declined within 5 seconds and recovered within 30 seconds of NH(4) (+) addition; (c) ratios of pyruvate/phosphoenolpyruvate, malate/phosphoenolpyruvate, Glc-1-P/Glc-6-P and Fru-1,6-bisphosphate/Fru-6-P increased; and (d) as previously seen, photosynthetic carbon fixation was inhibited. Further, we monitored starch degradation during N assimilation over a longer time course and found that starch breakdown occurred at a rate of about 110 micromoles glucose per milligram chlorophyll per hour. The results are consistent with N assimilation occurring through glutamine synthetase/glutamate synthase at the expense of carbon previously stored as starch. They also indicate that regulation of several enzymes is involved in the shift in metabolism from photosynthetic carbon assimilation to carbohydrate oxidation during N assimilation. It seems likely that pyruvate kinase, phosphoenolpyruvate carboxylase, and starch degradation are all activated, whereas key Calvin cycle enzyme(s) are inactivated within seconds of NH(4) (+) addition to N-limited S. minutum cells. The rapid changes in glutamate and triose phosphate, recently shown to be regulators of cytosolic pyruvate kinase, are consistent with them contributing to the short-term activation of this enzyme.

Journal Article↗
PubMed1989

Thromboembolic complications of the Symbion AVAD System.

The Symbion Acute Ventricular Assist Device (AVAD) System is an experimental paracorporeal pulsatile ventricular assist device (VAD) for single or biventricular assist. Eleven patients were implanted but 2 died within 24 h and were excluded from the study. Nine patients, four with left ventricular assist devices (LVADs) and five with biventricular assist devices (BIVADs), with a mean implant time of 24 days, were studied to determine the incidence and site of thrombus formation within the device and the incidence of thromboembolic complications. Anticoagulation consisted of heparin titrated to keep the partial thromboplastin time (PTT) twice control and dipyridamole 50 to 200 mg q6h p.o. Seven of nine patients (78%) developed thrombus; five had thrombus visible within the clear housing of the device during the implant period, and two patients had thrombus discovered only after VAD explantation. Common sites of formation were the diaphragm-housing junction, the housing near the outflow orifice, and the de-airing port. Three patients with thrombus developed thromboembolic complications; two suffered strokes and one had multiorgan emboli. The Symbion AVAD System has significant thrombogenic properties that may limit its clinical application.

Cerebrovascular Disorders↗