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Biomedical subjects

B Rasmussen

Publications and source records attributed to B Rasmussen.

At least 55 records · Page 3Linked to original sources
PubMed1991

Molecular basis of tetracycline action: identification of analogs whose primary target is not the bacterial ribosome.

Tetracycline analogs fell into two classes on the basis of their mode of action. Tetracycline, chlortetracycline, minocycline, doxycycline, and 6-demethyl-6-deoxytetracycline inhibited cell-free translation directed by either Escherichia coli or Bacillus subtilis extracts. A second class of analogs tested, including chelocardin, anhydrotetracycline, 6-thiatetracycline, anhydrochlortetracycline, and 4-epi-anhydrochlortetracycline, failed to inhibit protein synthesis in vitro or were very poor inhibitors. Tetracyclines of the second class, however, rapidly inhibited the in vivo incorporation of precursors into DNA and RNA as well as protein. The class 2 compounds therefore have a mode of action that is entirely distinct from the class 1 compounds, such as tetracycline that are used clinically. Although tetracyclines of the second class entered the cytoplasm, the ability of these analogs to inhibit macromolecular synthesis suggests that the cytoplasmic membrane is their primary site of action. The interaction of class 1 and class 2 tetracyclines with ribosomes was studied by examining their effects on the chemical reactivity of bases in 16S rRNA to dimethyl sulfate. Class 1 analogs affected the reactivity of bases to dimethyl sulfate. The response with class 2 tetracyclines varied, with some analogs affecting reactivity and others (chelocardin and 4-epi-anhydrotetracycline) not.

Bacteria↗
PubMed1990

Limb skeletal muscle adaptation in athletes after training at altitude.

Morphological and biochemical characteristics of biopsies obtained from gastrocnemius (GAS) and triceps brachii muscle (TRI), as well as maximal O2 uptake (VO2 max) and O2 deficit, were determined in 10 well-trained cross-country skiers before and after a 2-wk stay (2,100 m above sea level) and training (2,700 m above sea level) at altitude. On return to sea level, VO2 max was the same as the prealtitude value, whereas an increase in O2 deficit (29%) and in short-term running performance (17%) was observed (P less than 0.05). GAS showed maintained capillary supply but a 10% decrease in mitochondrial enzyme activities (P less than 0.05), whereas an increase in capillary supply (P less than 0.05) but unchanged mitochondrial enzyme activities were observed in TRI. Buffer capacity was increased by 6% in both GAS and TRI (P less than 0.05). A positive correlation was found between the relative increase in buffer capacity of GAS and short-term running time (P less than 0.05). Thus the present study indicates no effect of 2 wk of altitude training on VO2 max but provides evidence to suggest an improvement in short-term exercise performance, which may be the result of an increase in muscle buffer capacity.

Adaptation, Physiological↗
PubMed1988

Separate resistive loading of the respiratory phases during mild hypercapnia in man.

Eleven human subjects were studied during steady state, controlled mild hypercapnia with resistive loading of either inspiration (RI) or expiration (RE). Minute ventilation and frequency were significantly reduced by RI (P = less than 0.01) and even more so by RE (P = less than 0.001). Tidal volume was unchanged. Both RI and RE reduced mean flow in the loaded phase - an effect relatively greater with RE. Neither RI nor RE altered mean flow in the unloaded phase. Although mean inspiratory flow was unchanged with RE, mouth occlusion pressure (P0.1) was increased (P = less than 0.01). Functional residual capacity (seven subjects) was increased with RE, but not with RI (P = less than 0.05). Five additional subjects were similarly studied with and without RE in whom transdiaphragmatic pressure (PDi) and peak diaphragmatic EMG (EMGDi) were examined. Changes in ventilation, breathing pattern and P0.1 were similar to those described above. Neither PDi nor EMGDi were significantly altered by RE, but with RE, diaphragmatic EMG activity began 50-190 ms before inspiratory flow. In conclusion, ventilation is reduced more by RE than by RI due to greater respiratory phase time. Moderately heavy RE does not augment inspiratory drive as reflected by mean flow, PDi or EMGDi. With RE and increased FRC, P0.1 does not accurately reflect inspiratory drive because of dissociation between EMG and flow.

Adult↗
PubMed1987

Differential diagnosis of jaundice: junior staff experience with the Copenhagen pocket chart.

Originally published in 1984, the Copenhagen Pocket Chart for early differentiation between causes of jaundice has been tested with success in centres outside Denmark. Using a logistic discrimination model, it estimates probabilities of obstruction and non-obstruction in each case (and provides a further subdivision if desired). Here we evaluate its performance in the hands of young clinicians on a consecutive series of 173 jaundiced patients from two Danish hospitals. The chart performed as well as in the original series: confident diagnoses (probability greater than or equal to 0.80) were assigned to 124 patients; of these 115 proved correct (93%). In 46 patients diagnostic probabilities were less than 0.80, and 3 patients had an unknown cause of jaundice. There were 108 cases in which physician and chart were in agreement, both with a confident diagnosis, and only one of these cases was wrong. In one hospital, contributing 107 cases, each patient was independently examined by a medical student in addition to the physician's examination. Student performance was equally good, practically speaking, in particular when taking the scores on the chart into consideration. As to observer disagreement, the student and the physician typically differed on 0-2 of the chart's 21 items. In no case, however, did this lead to a confident obstructive diagnosis being changed into a confident diagnosis of non-obstruction, or vice versa.

Algorithms↗
PubMed1987

Pituitary-thyroid axis in critical illness.

Severe nonthyroidal illness has been claimed to cause secondary hypothyroidism. We reevaluated this concept measuring serum free T4 and free T3 by an ultrafiltration method and serum TSH by an ultrasensitive technique (detection limit, and serum TSH by an ultrasensitive technique (detection limit, 0.05 mU/L). Forty-five critically ill patients suffering from hepatic coma (n = 10), terminal cancer (n = 9), stroke (n = 8), and respiratory insufficiency not treated (n = 7) and treated (n = 11) with dopamine were studied. The mortality rate was 80%. No patients received glucocorticoids, and only patients in the last group received dopamine. Serum total as well as free thyroid hormone index values were grossly reduced in the majority of the patients. The 34 patients not receiving dopamine in general had normal values of serum free T4 (32 of 34) and free T3 (31 of 34), measurable TSH (33 of 34), and detectable TSH responses to iv TRH (33 of 34). In contrast, the dopamine-treated patients had reduced serum free T4 and TSH levels compared to normal subjects (P less than 0.05), as well as reduced TSH responses to TRH (P less than 0.01). Serum free T4 and free T3 were below the normal range in 3 patients and 1 patient, respectively, and serum TSH was below the detection limit in 2 patients. We conclude that critically ill patients with nonthyroidal illness not receiving dopamine have normal pituitary-thyroid function, whereas dopamine induces some degree of secondary hypothyroidism.

Adult↗
PubMed1987

Effect of concomitant administration of cimetidine and phenobarbital on antipyrine elimination and metabolite formation.

Cimetidine 1000 mg/day and phenobarbital 100 mg/day were given to five healthy volunteers for 13 days in order to investigate the combined effect and time course of inhibition and induction on hepatic drug metabolism. The one-sample antipyrine saliva clearance (APC) and urinary metabolite profile were measured weekly, once before, two times during and four times after drug administration. On the second day of drug treatment APC was 0.7 fold and the formation clearance of the 3 oxidized metabolites 0.6 fold decreased owing to an early inhibition by cimetidine (p less than 0.05). After 8 days of concomitant drug administration, i.e. when the drug mediated inhibition and induction are supposed to be at maximum, mean APC was 0.85 times the initial value (p greater than 0.05), whereas the formation clearances of nor- and 3-hydroxymethylantipyrine were still significantly depressed. Four and 11 days after drug withdrawal, when phenobarbital, but not cimetidine could be demonstrated in plasma, APC was 1.2 times the initial value (p less than 0.05). The results suggest, that the respective effects of cimetidine and phenobarbital on antipyrine elimination are additive, when given concomitantly, but that cimetidine exerts a relatively greater inhibition in the phenobarbital induced state.

Adult↗
PubMed1985

Increased hepatic microsomal enzyme activity after surgery under halothane or spinal anesthesia.

Thirty-two fit patients scheduled for explorative arthrotomy of the knee were allocated randomly to either halothane/oxygen anesthesia or spinal anesthesia with bupivacaine 0.25 mg X kg-1. The day before and 1, 10, and 21 days after surgery, the aminopyrine breath test (ABT) was performed. The day before and 5, 10, and 21 days after surgery, the antipyrine clearance (APcl) was measured by the single sample saliva technique. The ABT as well as the APcl were increased significantly postoperatively (P less than 0.01). The day after surgery the ABT was increased by 13 +/- 21% in the spinal anesthesia group only, whereas a late increase by 14 +/- 31% was found in the halothane group. Five days after surgery, the APcl was increased by 36 +/- 45% in the spinal anesthesia group and by 21 +/- 28% in the halothane group. Both tests returned to base line values within 3 weeks postoperatively. In five volunteers following the same sampling scheme but receiving bupivacaine 0.25 mg X kg-1 im without surgery, no change in the ABT or the APcl was observed. The authors conclude that surgery may cause microsomal enzyme induction regardless of the anesthetic agent or technique used. The mechanism of this induction remains to be elucidated.

Adolescent↗
PubMed1985

Carnitine and left ventricular function in haemodialysis patients.

Left ventricular function was non-invasively studied in 28 randomly selected haemodialysis patients before and after administration of L-carnitine, 2 g i.v. three times per week or saline in a double blind designed study over a six-week period. Cardiac function variables showed no relationship to muscle (vastus lateralis) and plasma carnitine concentrations. No apparent deficiency in muscle carnitine was found, whereas total plasma carnitine was lower in female patients than in female controls, p less than 0.002. The echocardiographic left ventricular end-diastolic diameter was initially increased in about one third and the ejection fraction was depressed in about one fifth of the patients. An increased A:H ratio was found in 15%. Systolic time intervals were deranged in 30% of the patients. After carnitine administration, marked increases of muscle and plasma carnitine levels were found, p less than 0.01, but no effects were recorded in any of the cardiac tests. Muscle carnitine increased from 14.6 mmol/kg dry weight to a median of 23.7 mmol/kg. We found no support for the hypothesis that carnitine depletion is responsible for cardiac dysfunction in haemodialysis patients.

Adult↗