Synthesis of ppGpp and chloroplast ribosomal RNA in Chlamydomonas reinhardi.

A material identified as guanosine 5',3'-bis-diphosphate (ppGpp) has been detected in extracts of Chlamydomonas reinhardi ac-20 cells grown under mixotrophic conditions or in arg-2 cells deprived of arginine. The material was acid and base labile, susceptible to alkaline phosphatase, resistant to periodate oxidation, had spectral characteristics of a guanine derivative and comigrated on chromatograms with ppGpp from Escherichia coli. In ac-20 ppGpp may be involved in the control of chloroplast ribosomal RNA synthesis. When ac-20 cells were shifted from mixotrophic to autotrophic conditions, the 32Pi labeling of ppGpp, relative to that of GTP, was reduced, while the specific labeling of chloroplast ribosomal RNA was enhanced. Addition of low concentrations of cycloheximide had somewhat similar effects.

The chloroplast genome of bleached mutants of Euglena gracilis.

Bleached mutants of Euglena gracilis, traditionally thought to be completely deprived of chloroplast DNA, have been shown to contain a defective chloroplast genome, present at a very low copy number, and preferentially retaining ribosomal RNA genes. We propose to call these mutants phi-, because of their resemblance with the rho- mutants of yeast.

Pollen-Stigma Adhesion in Kale Is Not Dependent on the Self-(In)Compatibility Genotype.

The adhesion of pollen on the stigmas of flowering plants is a critical step for the success of reproduction in angiosperms, long considered to present some specificity in terms of self-incompatibility. We carried out quantitative measurements of the pollen-stigma adhesion (expressed in Newtons) in kale (Brassica oleracea), using the flotation force of Archimedes exerted by dense sucrose solutions (50%, w/v) to release pollen grains fixed on the surface of stigmas. We demonstrate that pollen adhesion varies with the genotypes of the plants used as partners, but increases with time in all cases for about 30 to 60 min after pollination. There is no correlation with the self- or cross-status of the pollinations, nor with the self-compatible or -incompatible genotypes of the parents. Only late events of pollination, after the germination or arrest of the pollen tube, depend on compatibility type. Biochemical and physiological dissection of pollen-stigma adhesion points to major components of this interaction: among male components, the pollen coating, eliminated by delipidation (or modified by mutation in the case of the cer mutants of the related species Arabidopsis thaliana), plays a major role in adhesion; the genetic background of the pollen parent is also of some importance. On the female side, the developmental stage of the stigma and the protein constituents of the stigmatic pellicle are critical for pollen capture. The SLG and SLR1 proteins are not involved in the initial stages of pollen adhesion on the stigma but one or both may be involved in the later stages.

Effect of liver impairment on the pharmacokinetics of tolcapone and its metabolites.

OBJECTIVE: To assess the effect of liver impairment on the pharmacokinetics of tolcapone and to derive appropriate dose recommendations for patients with this disease who are undergoing treatment for Parkinson's disease. STUDY DESIGN: In an open, two-way crossover study, 16 patients with moderate liver disease (eight with cirrhotic and eight with noncirrhotic liver disease) and eight healthy subjects received an oral dose of 200 mg tolcapone and an intravenous dose of 50 mg tolcapone on separate occasions. The concentrations of total and unbound tolcapone and its three major metabolites (tolcapone glucuronide, carboxylic acid, and 3-O-methyl metabolite) were assessed in plasma and urine. RESULTS: On the basis of total drug concentration, the differences in tolcapone pharmacokinetics between the groups were small. However, lower clearance and volume of distribution of unbound drug were found among patients with cirrhosis than among control subjects. Plasma concentration of the pharmacologically inactive glucuronide metabolite was increased among patients with cirrhosis. CONCLUSIONS: Half of the recommended dosage of tolcapone should be administered to patients with cirrhosis of the liver to maintain the target steady-state concentration of unbound drug and to avoid accumulation of tolcapone glucuronide. Our data did not indicate a requirement for dosage adjustment in the presence of moderate chronic hepatitis.

Pharmacokinetics of retinoids in women after meal consumption or vitamin A supplementation.

These studies were conducted to evaluate the pharmacokinetics of several retinoids after meal consumption or vitamin A supplementation to establish a reference for future assessment of teratogenic risks of retinoid therapeutic agents. In the first study, 36 healthy young female volunteers consumed single meals containing vitamin A amounts ranging from 1,305 to 169,474 IU. In the second study, 24 other female volunteers took vitamin A supplements at a dose level of 5,000, 10,000, or 25,000 IU/day for 60 days. Plasma concentrations of tretinoin, isotretinoin, 4-oxo-tretinoin, and 4-oxo-isotretinoin in samples collected during the studies were analyzed using a high-performance liquid chromatography method with ultraviolet detection. Pharmacokinetic parameters for the retinoids were calculated using model-independent methods. Plasma concentrations of tretinoin were not altered by meal consumption or vitamin A supplementation. Plasma levels of 4-oxo-tretinoin were below the assay detection limit (0.3 ng/mL) in the majority of samples collected throughout the studies. Linear relationships between dose and maximum concentration (Cmax) and dose and area under the concentration-time curve (AUC) for isotretinoin and 4-oxo-isotretinoin were derived from data from the meal study. For the most bioavailable formulation used in the supplement study, daily ingestion of 5,000 IU of vitamin A caused increases of 141 +/- 53% and 171 +/- 77% from baseline in the 24-hour AUCs of isotretinoin and 4-oxo-isotretinoin, respectively. Dose-related increases in systemic exposure to retinoids were observed after ingestion of vitamin A by means of a meal or a supplement. Findings from these studies can be used as a basis for future safety evaluations of retinoid compounds.

Serial M-mode echocardiography in evaluation of the cardiovascular effects of tiapamil and their relationship to plasma levels in patients with coronary heart disease.

Tiapamil (Ro 11-1781) is a new calcium antagonist. Several investigators have reported about its efficacy against cardiac arrhythmias and angina pectoris. However, there was no study that assessed a possible relationship between hemodynamic effects and plasma concentration. Our study was aimed to investigate any possible relationship between cardiovascular effects of tiapamil and its plasma concentration. We selected 8 coronary; patients (6 males and 2 females) with a mean age of 61.9 yr and a mean weight of 70.9 kg. Tiapamil was administered per os at the dose of 250 mg t.i.d. for 4 consecutive days. Hemodynamic data were obtained by means of echocardiography, ECG and sphygmomanometry. Plasma concentrations of Ro 11-1781 and its major metabolites were measured by means of high pressure liquid chromatography. With tiapamil, the morning systolic BP fell from 130.6 +/- 19.5 (mean +/- SD, pretreatment) to 114.4 +/- 18.2 mm Hg on day 4, the change being clinically and statistically significant (P less than 0.02 by paired t-tests). Diastolic BP and HR remained unchanged. LVEDD and LVESD were not affected to any relevant extent, but VCF was significantly (P less than 0.05) and persistently increased. Tiapamil was well absorbed, but large interindividual variations were observed. As a general rule, no direct relationship between plasma concentrations and hemodynamic effects could be demonstrated. However, the number of patients is too small to allow general conclusions. At the above dose, tiapamil did not elicit any clinically detectable negative inotropic or negative chronotropic effect, probably because of its lowering effect on systolic BP.

Animal pharmacokinetics and interspecies scaling of Ro 25-6833 and related (lactamylvinyl)cephalosporins.

From a series of six (lactamylvinyl)cephalosporins, candidates for clinical evaluation were selected on the basis of their kinetic profile in animals and predicted pharmacokinetics in man. Exploratory pharmacokinetic studies with Ro 25-6833 and five related cephalosporins were performed following intravenous administration to rats, dogs, and cynomolgus monkeys. All compounds were characterized by a high protein binding in rat, monkey, and human plasma (unbound fraction < or = 5%), whereas in dog plasma, protein binding was markedly lower. Accordingly, for most compounds, clearance was highest in dogs, and lowest in monkeys. Comparison of the renal clearance of unbound drug with creatinine clearance suggests a renal elimination of Ro 25-6833 by glomerular filtration in both rats and dogs (urinary excretion in monkey was not determined due to drug instability in monkey urine). All other compounds showed different renal excretion mechanisms in rats and dogs, thus making the validity of allometric scaling questionable. Unbound clearances in man were predicted by allometric scaling (Ro 25-6833 only) and by a correlation analysis of cephalosporin pharmacokinetics in monkey and man. Limitations of both methods are discussed. When Ro 25-6833 was later studied in man, the predicted pharmacokinetic data in man from both approaches were found to be in good agreement with the observed values.

Influence of liver cirrhosis upon the pharmacokinetics of tenoxicam.

The effects of impaired hepatic function upon the pharmacokinetics of tenoxicam were studied in six patients with cirrhotic liver disease who ingested a single, oral 20 mg dose of the drug. Data from these patients were compared with those obtained from 14 healthy subjects who received the same regimen. Virtually all of the pharmacokinetic parameters computed for the two groups were similar. Cmax in the cirrhotic patients was 2.63 micrograms/ml (s.d. = 0.92) and tmax was 2.5 h (s.d. = 0.8). The corresponding values for the control subjects were 2.77 micrograms/ml (s.d. = 0.72) and 3.2 h (s.d. = 1.6), respectively. The elimination half-life (t1/2) was 53.0 h (s.d. = 19.0) in the cirrhotic patients and 69.2 h (s.d. = 19.3) in the controls. There were no significant (p greater than 0.05) differences between groups with respect to any of these values. Area under curve was significantly (p less than 0.05) smaller in the cirrhotic patients (159 micrograms.h/ml; s.d. = 65) than in the controls (254 micrograms.h/ml; s.d. = 92). The urinary excretion of the 5'-hydroxy metabolite of tenoxicam averaged 21.6% (s.d. = 3.8) of the administered dose in the cirrhotic patients and 22.1% (s.d. = 3.1) in the control subjects. The plasma protein binding of tenoxicam was also very similar in the two groups. The unbound drug fraction averaged 0.8% (s.d. = 0.3) in the cirrhotic patients and 0.8% (s.d. = 0.1) in the 12 control subjects who contributed data to this portion of the study. The single-dose data presented in this report demonstrated substantially unaltered kinetics with no evidence of impaired elimination and drug retention.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma tenoxicam concentrations after single and multiple oral doses.

The pharmacokinetics of single- and multiple-dose administration of tenoxicam 20 mg were evaluated in 8 healthy males. Maximum plasma concentration (Cmax) after the first dose was 2.76 +/- 0.48 micrograms/ml (mean +/- s.d.) and the time to reach Cmax (Tmax) was 5.0 +/- 3.0 h. The area under the plasma concentration-time curve (AUC0-infinity) after a single administration of tenoxicam was 242.5 +/- 73.5 micrograms x h/ml. The elimination half-life (t1/2) was 66.3 +/- 15.8 h and the plasma concentration at 24 hours after dosing (Cmin) was 1.84 +/- 0.33 micrograms/ml. Steady-state plasma concentrations of tenoxicam were virtually reached after 10 consecutive daily doses. At steady-state, Cmax averaged 13.63 +/- 3.33 micrograms/ml and Tmax remained 5.0 +/- 3.0 hours. AUC within a dosing interval at steady-state was 262.2 +/- 67.0 micrograms x h/ml, Cminss was 9.67 +/- 3.25 micrograms/ml, and t1/2 averaged 74.2 +/- 13.3 h. The average fluctuation during multiple-dose administration was 26.8 +/- 8.0% and the accumulation ratio was 5.82 +/- 0.60. Steady-state pharmacokinetic parameters predicted from the first-dose data slightly underestimated observed values, but the results supported the assumption of linear pharmacokinetics during multiple-dose tenoxicam administration.

[Relation between the clinical effect and plasma concentration of midazolam in volunteers]. / Relation entre l'effet clinique et la concentration plasmatique du midazolam chez des sujets volontaires.

In 12 healthy volunteers, the pharmacological effects of midazolam were investigated following intravenous (0.15 mg X kg-1 and 12.5 mg in 6 subjects each), intramuscular (12.5 mg in 6 subjects) and oral administration (20 mg in 6 subjects and 10 mg in 4 subjects). The findings were correlated with the plasma concentrations of midazolam and its alpha-hydroxy metabolite. The effects were assessed using objective and subjective methods (reaction time, memory test and subjects' self-assessment with an analog scale covering the degree of sedation). Plasma samples were assayed for midazolam and its alpha-hydroxy metabolite by gas chromatography. The results of the memory test showed that mnemonic retention and recall of a number remained intact for the period preceding intravenous or intramuscular administration. The maximum impairment occurred at 30 min after injection for recall of a number presented at the 15th min. The impairment was no longer detectable 4 h after injection. The plasma concentration time course was similar to that of the reaction time after administration of an identical intravenous or intramuscular dose. The maximum effect was attained within 15 min and 30 min after intravenous and intramuscular administration respectively. Within 2 to 4 h after parenteral administration, the reaction time had returned to normal. At identical plasma concentrations of midazolam, the reaction time was slightly longer in the period immediately following oral administration than after parenteral administration. This result suggested that the alpha-hydroxy metabolite contributed actively to the effect of midazolam. After its intravenous injection, this metabolite's sedative effects attained their maximum with 15 min, having disappeared 4 h later.

[Is monotherapy with ß-lactam antibiotics still up to date? New aspects for treatment of severe infections]. / Sind Monotherapien mit ß-Laktamantibiotika noch zeitgemäss?

Mortality of sepsis is still high. Crucial for therapeutic response are the early start of treatment as well as the choice of antibiotics or antibiotic combinations. ß-lactam antibiotics with bactericidal mode of action are often recommended in guidelines. But this antibiotic class can trigger the immune system to a maximum by releasing cell wall components or exotoxins. This may lead to a worsening of the patient's clinical situation. In contrast, antibiotics with bacteriostatic action often inhibit bacterial protein synthesis with decrease of production of virulence factors and minimize release of cell wall components. The purpose of this review is to summarise the significance of some bacteriostatic antibiotics and to discuss whether a combination of bactericidal and bacteriostatic agents may improve the course of the illness.

Structure and variability of nuclear ribosomal genes in the genus Helianthus.

The restriction map of the rDNA unit of Helianthus annuus was constructed using EcoRI, BamHI, HindIII, KpnI and SacI restriction enzymes. Variations in this map among 61 ecotypes representing 39 species of the genus Helianthus were analyzed. The sizes of the rDNA unit ranged from 9.8 to 11.0 kbp, due to a length-repeat heterogeneity of the external non-transcribed spacer by increments of 200 base pair segments. Lengthrepeat heterogeneity and restriction polymorphism were found to be characteristic of populations or species of Helianthus. Restriction patterns and thermal melting with probes of a cloned H. annuus ENTS segment allowed us to differentiate species from each other. However, most lines of the cultivated sunflower were found to be identical on the basis of the physical properties of their ribosomal DNA.

Determination of tenoxicam in human plasma by high-performance liquid chromatography.

A high-performance liquid chromatographic method for the determination of tenoxicam in plasma has been developed. Tenoxicam was extracted from buffered plasma (pH 3 or 4, respectively) with dichloromethane and the evaporated extracts were analysed on a C18 reversed-phase column using a methanol-phosphate buffer mobile phase and with UV detection at 371 nm. The detection limit was 20 ng/ml using a 0.5-ml sample. The method is selective with respect to the 5'-hydroxy metabolite, which is present in plasma after multiple administration of tenoxicam; this metabolite may also be determined using this procedure.