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Biomedical subjects

C M Thomas

Publications and source records attributed to C M Thomas.

At least 289 records · Page 16Linked to original sources
PubMed1981

Nucleotide sequence of the region of the origin of replication of the broad host range plasmid RK2.

A DNA sequence consisting of 617 base pairs (bp) from the region of the origin of replication of the broad-host range plasmid RK2 has been determined. Included within this sequence is a 393 bp HpaII restriction fragment that provides a functional origin or replication when other essential RK2 specified functions are provided in trans. Also contained in this sequence is a region, distinguished functionally from the replication origin, which is involved in the expression of inc2 incompatibility, i.e., the ability of derivatives of RK2 to eliminate a resident RK2 plasmid. The 617 bp sequence includes eight 17 base pair direct repeats with 5 located within the region required for a functional replication origin and 3 within the region involved in inc2 incompatibility. In addition, a 40 bp region rich in A-T followed by a 60 bp stretch having a high G + C content is present. Deletion evidence indicates that the A-T rich and possibly the G + C regions are required for a functional replication origin. Based on the evidence contained in this and the preceding paper (Thomas et al. 1980 b) a model will be presented for the involvement of these specific sequences in the initiation of RK2 DNA replication, plasmid maintenance and plasmid incompatibility.

Base Sequence↗
PubMed1981

Ovulation, ovum transport and implantation in the adult golden hamster.

The time of ovulation in various hamster colonies and its relationship with the period of light as reported in the literature was compared with the observations made in this study. Ovulation and transport of ova to the oviduct was studied during days 4 and 1 of the estrous cycle. Microscopical examination of the various oviducal segments for the presence of ova resulted in a detailed description of physiological ovum transport for the adult golden hamster. Simultaneously the developmental stages of ova were checked together with the occurrence of unfertilized ova and the percentage of ova implanted in the uterus. Finally, the contractility of the oviduct in vitro was observed for groups of animals at different times in the pre- and postovulatory period. The presented data indicate that the golden hamster is useful for the study of ovum transport processes. This is due to the regularity of its estrous cycle including multiple ovulations, and because ovum transport can easily be monitored microscopically with a high degree of reliability.

Animals↗
PubMed1981

The value of intravesical prostaglandin E2 and F2 alpha in women with abnormalities of bladder emptying.

A clinical study of intravesical prostaglandin E2 (PGE2) and F2 alpha (PGF2 alpha) in the treatment of 13 female patients with difficulties in emptying their bladder is reported. Urodynamic investigations were performed before and after instillation of the drug. Although 3 patients had some reduction in residual urine volume, the remainder showed no obvious change and no patient experienced subjective improvement. In 6 patients, biopsies of the vesical mucosa were taken before and after instillation in order to measure the uptake of prostaglandin by the mucosa, but no conclusions could be drawn from these measurements. Although prostaglandins are known to have contractile effects on the detrusor muscle, the results of this study suggest that intravesical PGE2 and PGF2 alpha have no therapeutic value in the treatment of voiding dysfunction and residual urine.

Adolescent↗
PubMed1980

Effect of thymidine auxotrophy, thymidine starvation and nalidixic acid inhibition on the properties of DNA labelled by a pulse of [3H]thymidine in Staphylococcus aureus.

The labelling of DNA by pulse/chase experiments in Staphylococcus aureus has been investigated, analysing the products by alkaline sucrose velocity centrifugation. In S. aureus NCTC 8325 a short (60 s) pulse of [3H]thymidine labels both small (10 to 20 S) fragments and DNA that co-sediments with long-term label. In a thymidine-requiring derivative, 8325thy, most pulse label is incorporated into small fragments. In both bacterial strains small fragments can be chased into high molecular weight DNA. Thymidine starvation of 8325thy prior to pulse labelling results in smaller fragments (4 to 10S) being labelled. In a subsequent chase with unlabelled thymidine this label is incorporated into high molecular weight DNA, although more slowly than in the absence of thymidine starvation. The fact that nalidixic acid, an antibiotic which specifically inhibits DNA replication in S. aureus, does not inhibit the [3H]thymidine incorporation immediately after thymidine starvation and that nalidixic acid shows down the increase in size of pulse-labelled fragments through inhibition of DNA synthesis suggests that thymidine starvation results in changes at the replication fork. The possible nature of these changes is discussed. It is proposed that one of the results of thymidine starvation is to cause a long-lived gap between DNA synthesized before starvation and DNA synthesized after starvation.

Centrifugation, Density Gradient↗
PubMed1980

Regions of broad-host-range plasmid RK2 which are essential for replication and maintenance.

The sites of cleavage on the map of the broad-host-range plasmid RK2 (56 kilobases) were determined for the BglII, PstI, and SmaI restriction enzymes, and the determinants for tetracycline and ampicillin resistance were localized. The cleavage sites were clustered at or near the drug resistance genes. To localize regions required for plasmid replication and maintenance in Escherichia coli, we deleted nonessential regions of RK2 by partial digestion with the restriction endonuclease HaeII to produce small derivatives. The smallest stable replicon obtained contained five HaeII fragments of RK2 which total 5.4 kilobases. These fragments were derived from three regions of RK2 that are separated from each other by antibiotic resistance genes. One of these HaeII fragments (0.75 kilobases) has the properties expected of the origin of replication. The outer four fragments, located in two separate regions of RK2, were found to provide, in trans, functions that permit the replication of the HaeII fragment carrying the origin of the replication. These results indicate that at least two plasmid-encoded genes, capable of acting in trans, and a replication origin are required for RK2 replication and maintenance.

Anti-Bacterial Agents↗
PubMed1978

Radioimmunoassays for prostaglandins. I. Technical validation of prostaglandin F2alpha measurements in human plasma using sephadex G-25 gelfiltration.

Human plasma samples of 1 ml were processed according to three different procedures prior to Radioimmunoassay (RIA) of Prostaglandin F2alpha (PGF2alpha). Serial dilutions of ethyl acetate extracts as such, or combined with either silicic acid or Sephadex G-25 chromatography were assessed for linearity, homogeneity and parallelism with the corresponding standard dose response line. For plasma extracts used as such, non-parallelism is observed. Subsequent chromatography on silicic acid of such extracts gave only a limited linear and parallel portion upon serial dilution. However, purification of the extracts by gelfiltration on Sephadex G-25 results in linear and parallel lines over the full range of the standard dose response line (B/BO 0.9-0.2). Upon comparison of separation by Polyethylene glycol (PEG) and Dextran coated charcoal (DCC) in these systems, PEG proved to give the best results. It was found that in the Sephadex G-25 procedure, separation by PEG is essential. The method of gelfiltration on Sephadex G-25 is simple and reliable. Intra- and inter-assay coefficients of variation are 6% and 12%, respectively. Accuracy, as measured by recovery of added known amounts of PGF2alpha is 97.6%.

Chromatography, Gel↗
PubMed1978

Isolation and transduction analysis of temperature-sensitive mutants of Staphylococcus aureus defective in DNA replication.

Four temperature-sensitive mutants of Staphylococcus aureus with defects affecting DNA synthesis have been isolated and partially characterized. They fall into two groups: three have defects either in elongation of DNA or synthesis of its precursors; the fourth has properties inconsistent with a defect in either elongation or initiation. Transduction analysis indicated that the mutation in this fourth mutant is unlinked to the mutations in the other three, which are all clustered on one side of a gene conferrring resistance to novobiocin.

DNA Replication↗
PubMed1978

Properties of a temperature-sensitive mutant of Staphylococcus aureus defective in DNA replication and cell division and replication of plasmids in the mutant.

The properties of a temperature-sensitive mutant (ts39) of Staphylococcus aureus NCTC 8235 are described. After transfer to the restrictive temperature (42 degrees C), absorbance increased 10-to 20-fold but DNA content did not increase beyond 150 to 200% and cell division continued at a greatly reduced rate. On transfer back to the permissive temperature, both cell division and DNA synthesis resumed if the transfer occurred after less than 120 min at 42 degrees C. Resumption of DNA replication was blocked by chloramphenicol (100 microgram ml-1). The results are discussed with reference to possible defects in DNA replication. Replication of the plasmids pI258 and pT10501 and the chromosome were affected to a similar extent in ts39. Growth at 42 degrees C resulted in the appearance of an increased amount of pI258 DNA in a form that sedimented slowly in a sucrose gradient.

Chromosomes, Bacterial↗
PubMedDate not supplied

Deletions in the tetracycline resistance determinant reduce the thermosensitivity of a trfA(Ts) derivative of plasmid RP1 in Pseudomonas aeruginosa.

A derivative of the broad-host-range plasmid RP1, pME301, was temperature-sensitive (Ts) at 43 degrees C for maintenance in Pseudomonas aeruginosa, P. mendocina, Klebsiella aerogenes and Escherichia coli. In E. coli, the Ts defect of pME301 could be complemented in trans by the cloned trfA gene, which is known to be essential for RP1 replication in E. coli and P. aeruginosa. Because pME301 expressed a Ts phenotype in P. mendocina and K. aerogenes, we assume that the trfA function is also vital in these organisms. When plasmid-encoded carbenicillin resistance (on transposon Tn801) was selected at non-permissive temperatures in P. aeruginosa strain PAO carrying pME301, we obtained either Tn801 insertions into the chromosome or pME301 derivatives having a deletion (or point mutation) in their tet genes, which determine resistance to tetracycline and are not transposable. From cloning experiments, we infer that the tet gene product(s) destabilize the pME301 replicon in P. aeruginosa at 40-43 degrees C.

Chromosome Deletion↗
PubMedDate not supplied

The impact of calcium, magnesium, zinc, and copper in blood and seminal plasma on semen parameters in men.

To investigate the impact of calcium, magnesium, zinc, and copper in blood and seminal plasma on semen parameters, 107 fertile and 103 subfertile males provided a standardized blood and semen specimen. Total calcium and magnesium concentrations were determined with colorimetric end point assay procedures. Zinc and copper were determined by flame atomic absorption spectrophotometer (AAS). Semen analysis was performed according to World Health Organization guidelines (1992). The concentrations of calcium, magnesium, zinc, and copper in blood and seminal plasma were not different between the subfertile and fertile group. Weak correlations were demonstrated between blood plasma zinc concentrations and sperm count (rs = 0.18), sperm motility (rs = 0.15), and abnormal sperm morphology (rs = 0.13). Zinc and magnesium concentrations in seminal plasma correlated weakly with sperm count (rs = 0.17 and rs = 0.16, respectively), and copper concentrations in blood plasma with motility (rs = 0.25). Strong correlations were found between calcium, magnesium, and zinc in seminal plasma. Although calcium, magnesium, zinc, and copper play an essential role in spermatogenesis and fertility, the determination of these elements in blood and seminal plasma does not discriminate on the basis of fertility in this group of men.

Adult↗
PubMedDate not supplied

Short- and long-term hormonal effects of a single dose of 50 mg tamoxifen administered to normal males.

To five potentially fertile males, a single dose of 50 mg tamoxifen was administered orally to explore the short- and long-term hormonal effects on the hypothalamic-pituitary-gonadal axis. Blood specimens were obtained through an integrated sampling technique for the first two hours after the intake of the drug. Then, samples were taken daily throughout one week, and twice weekly for the next two weeks. Hormone measurements of luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone and oestradiol were obtained by specific RIA. All the subjects showed different response patterns. No general characteristic of the hormonal changes in the investigated group could be given. A consistent correlation between the within-individual levels of gonadotrophin and sex steroid changes could not be observed. It is concluded, within the limits of the used experimental design, that in healthy males a single administration of tamoxifen does not result in consistent changes in serum levels of either gonadotrophins or sex steroid hormones.

Adult↗
PubMedDate not supplied

Effect of lower versus higher doses of tamoxifen on pituitary-gonadal function and sperm indices in oligozoospermic men.

Administration of the antiestrogen tamoxifen for one month to 12 patients with idiopathic oligozoospermia significantly increased the mean basal testosterone (T) level and the responses of luteinizing hormone (LH) and follicle stimulating hormone (FSH) to constant luteinizing hormone releasing hormone (LHRH) infusion but did not significantly influence the mean oestradiol (E2) levels or the E2 over testosterone ratio. Mean sperm concentration and total sperm output increased by about 70% after a mean treatment period of 5.5 +/- 0.4 months. No statistically significant difference was found between the two subgroups of patients treated with either the lower (5 or 10 mg once daily) or higher dose of tamoxifen (10 mg twice daily) with respect to basal or LHRH stimulated gonadotropin and testosterone response or the E2/T ratio and the effect on sperm density and total sperm output. In both subgroups the sperm motility and morphology remained unchanged. In conclusion higher doses of tamoxifen in this study prove not to be superior to lower doses in improving mean sperm density and total sperm output. The relative small percentage of patients achieving normalisation of only these sperm parameters pleads for further search for more effective selection of patients and other more effective treatment modalities in patients with idiopathic oligozoospermia.

Dose-Response Relationship, Drug↗