Biomedical subjects
K Carlson
Publications and source records attributed to K Carlson.
Criticism in perspective.
Explore the source record for details and available documents.
Peer review: part of the writing process.
Explore the source record for details and available documents.
Caring: a health paradigm for the 1990s.
Explore the source record for details and available documents.
Regionally selective alterations in enzymatic activities and metabolic fluxes during thiamin deficiency.
To further elucidate the molecular basis of the selective damage to various brain regions by thiamin deficiency, changes in enzymatic activities were compared to carbohydrate flux through various pathways from vulnerable (mammillary bodies and inferior colliculi) and nonvulnerable (cochlear nuclei) regions after 11 or 14 days of pyrithiamin-induced thiamin deficiency. After 11 days, large decreases (-43 to -59%) in transketolase (TK) occurred in all 3 regions; 2-ketoglutarate dehydrogenase (KGDHC) declined (-45%), but only in mammillary bodies; pyruvate dehydrogenase (PDHC) was unaffected. By day 14, TK remained reduced by 58%-66%; KGDHC was now reduced in all regions (-48 to -55%); PDHC was also reduced (-32%), but only in the mammillary bodies. Thus, the enzyme changes did not parallel the pathological vulnerability of these regions to thiamin deficiency. 14CO2 production from 14C-glucose labeled in various positions was utilized to assess metabolic flux. After 14 days, CO2 production in the vulnerable regions declined severely (-46 to 70%) and approximately twice as much as those in the cochlear nucleus. Also by day 14, the ratio of enzymatic activity to metabolic flux increased as much as 56% in the vulnerable regions, but decreased 18 to 30% in the cochlear nuclei. These differences reflect a greater decrease in flux than enzyme activities in the two vulnerable regions. Thus, selective cellular responses to thiamin deficiency can be demonstrated ex vivo, and these changes can be directly related to alterations in metabolic flux. Since they cannot be related to enzymatic alterations in the three regions, factors other than decreases in the activity of these TPP-dependent enzymes must underlie selective vulnerability in this model of thiamin deficiency.
Effect of gender on the response to a high fat diet in aging Fischer 344 rats.
The purpose of this study was to describe the effects of high fat (HF) and low fat (LF) diets in male and female Fischer 344 (F344) rats ages 5, 23 and 27 mo. Rats were fed the diet for 3 mo, and then resting metabolic rate, body composition and adipose tissue cellularity were evaluated. Although body mass was greater in rats fed the HF diet, this difference was due to a rapid increase in mass within the first 2 wk. There was no difference in the rate of body mass gain after this period. Resting mass-independent metabolic rate did not significantly differ due to age, diet or gender. In general, percentage fat mass was greater in rats fed the HF diet and in female than in male rats in both diet groups. However, lean body mass (%) was not altered due to diet or age. Cell number of the retroperitoneal depot increased with age and diet between 5 and 23 mo of age in both male and female rats. There was no effect of age, diet or gender on retroperitoneal cell size or gonadal cell number and size. These data suggest that age, gender and diet do not significantly alter the ability of F344 rats to regulate body composition or fat cell proliferation.
Separation of Protein Crystals from Spores of Bacillus thuringiensis by Ludox Gradient Centrifugation.
A method is described for the purification of Bacillus thuringiensis protein crystals by Ludox gradient centrifugation. This method is simple, inexpensive, fast, and efficient compared with other techniques. It has been successfully used to purify and characterize the protein crystals from several B. thuringiensis strains.
Effect of age and gender on thermoregulation.
Previous investigations have shown that during cold exposure 24-mo-old male Fischer 344 (F344) rats do not thermoregulate as well as do 12-mo-old animals. To determine if this deficiency also occurs in female rats, we measured oxygen consumption (thermogenesis) and colonic temperature of male and female rats 5, 23, and 27 mo of age at rest and during 6 h of exposure to 6 degrees C. In addition, nonshivering thermogenesis (NST) was evaluated from the capacity of brown adipose tissue (BAT) mitochondria isolated from cold-exposed rats to bind guanosine 5'-diphosphate (GDP). Neither age nor gender had a significant effect on resting or cold-exposed oxygen consumption expressed on a mass-independent basis (l/kg body mass0.67) or on a lean body mass independent basis (l/kg lean body mass0.67). The drop in colonic temperature in response to cold was greater in the male rats. However, females exhibited increased BAT mass and relatively constant GDP binding with advancing age, whereas males showed decreased mass and GDP binding. Although the data suggest greater NST capacity in the female rats, rates of cold-induced oxygen consumption were similar in older female vs. male rats. Taken together, our data indicate that gender has a significant impact on thermoregulation and that, under the cold exposure conditions of the study, this effect involves differential heat conservation rather than heat production.
[Biopsy of the temporal arteries--is it an adequate examination?].
Explore the source record for details and available documents.
Medical ethics and personal dilemmas.
Explore the source record for details and available documents.
Pertussis toxin modifies the characteristics of both the inhibitory GTP binding proteins and the somatostatin receptor in anterior pituitary tumor cells.
The effects of pertussis toxin treatment on the characteristics of somatostatin receptors in the anterior pituitary tumor cell line AtT-20 were examined. Pertussis toxin selectively catalyzed the ADP ribosylation of the alpha subunits of the inhibitory GTP binding proteins in AtT-20 cells. Toxin treatment abolished somatostatin inhibition of forskolin-stimulated adenylyl cyclase activity and somatostatin stimulation of GTPase activity. To examine the effects of pertussis toxin treatment on the characteristics of the somatostatin receptor, the receptor was labeled by the somatostatin analog [125I]CGP 23996. [125I]CGP 23996 binding to AtT-20 cell membranes was saturable and within a limited concentration range was to a single high affinity site. Pertussis toxin treatment reduced the apparent density of the high affinity [125I]CGP 23996 binding sites in AtT-20 cell membranes. Inhibition of [125I]CGP 23996 binding by a wide concentration range of CGP 23996 revealed the presence of two binding sites. GTP predominantly reduced the level of high affinity sites in control membranes. Pertussis toxin treatment also diminished the amount of high affinity sites. GTP did not affect [125I]CGP 23996 binding in the pertussis toxin-treated membranes. The high affinity somatostatin receptors were covalently labeled with [125I] CGP 23996 and the photoactivated crosslinking agent n-hydroxysuccinimidyl-4-azidobenzoate. No high affinity somatostatin receptors, covalently bound to [125I]CGP 23996, were detected in the pertussis toxin-treated membranes. These results are most consistent with pertussis toxin uncoupling the inhibitory G proteins from the somatostatin receptor thereby converting the receptor from a mixed population of high and low affinity sites to only low affinity receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Mind out of focus: the altered self.
Explore the source record for details and available documents.
Distribution patterns of ventricular premature complexes at different heart rates.
The relation between distribution patterns of ventricular premature complexes (VPCs) and heart rate in Holter recordings abundant in VPCs was analyzed using computer-assisted determination of the number of interectopic sinus beats at different heart rates. Within the complete 24-hour heart rate spectrum, zones were demonstrated that were characterized by manifest or concealed bigeminy or manifest or concealed trigeminy. Bigeminy zones were found in 26 and trigeminy zones in 21 of 42 patients. Bigeminy zones were found at a significantly lower heart rate, on the average, then trigeminy zones. In 10 patients both bigeminy and trigeminy zones were observed. Bigeminy and trigeminy zones probably correspond to the distribution patterns of VPCs predicted from modulation of a pacemaker and reflected reentry, both of which can be induced by electrotonically mediated impulses across a zone of impaired conduction in isolated bundles of Purkinje fibers. The bigeminy and trigeminy zones will correspond at least partly to the entrainment zones found during electrotonic modulation of parasystolic foci. The bigeminy zones will correspond to 2:1 entrainment and the trigeminy zones mainly to 3:1 entrainment.
Bacteriophage T4 endonucleases II and IV, oppositely affected by dCMP hydroxymethylase activity, have different roles in the degradation and in the RNA polymerase-dependent replication of T4 cytosine-containing DNA.
Bacteriophage T4 mutants defective in gene 56 (dCTPase) synthesize DNA where cytosine (Cyt) partially or completely replaces hydroxymethylcytosine (HmCyt). This Cyt-DNA is degraded in vivo by T4 endonucleases II and IV, and by the exonuclease coded or controlled by genes 46 and 47.-Our results demonstrate that T4 endonuclease II is the principal enzyme initiating degradation of T4 Cyt-DNA. The activity of endonuclease IV, but not that of endonuclease II, was stimulated in the presence of a wild-type dCMP hydroxymethylase, also when no HmCyt was incorporated into phage DNA, suggesting the possibility of direct endonuclease IV-dCMP hydroxymethylase interactions. Endonuclease II activity, on the other hand, was almost completely inhibited in the presence of very small amounts of HmCyt (3-9% of total Cyt + HmCyt) in the DNA. Possible mechanisms for this inhibition are discussed.-The E. coli RNA polymerase modified by the products of T4 genes 33 and 55 was capable of initiating DNA synthesis on a Cyt-DNA template, although it probably cannot do so on an HmCyt template. In the presence of an active endonuclease IV, Cyt-DNA synthesis was arrested 10-30 min after infection, probably due to damage to the template. Cyt-DNA synthesis dependent on the unmodified (33-55-) RNA polymerase was less sensitive to endonuclease IV action.