Biomedical subjects

T Meehan

Publications and source records attributed to T Meehan.

58 records · Page 4Linked to original sources

PubMedDate not supplied

Functional analysis of the cooled rat testis.

Direct cooling of the testis results in the depletion of most germ cells in vivo. Germ cell-depleted testes are now commonly used to investigate spermatogenic regeneration and can serve as recipients for germ cell transplantation. The present study explored the effects of cooling rat testes on the depletion of endogenous germ cells, spermatogenic regeneration, and Sertoli cell function. Adult rat testes were cooled with iced Ringer's solution for 60 minutes, which results in the initiation of apoptotic germ cell loss within 8 hours. Pachytene spermatocytes at stages XII-I were the cells most sensitive to cooling. In 46%-67% of seminiferous tubule cross-sections, only Sertoli cells remained in the cooled testes 3-10 weeks after treatment. Germ cell loss was accompanied by a significant decrease in circulating inhibin B and an increase in follicle-stimulating hormone concentrations, which indicated a change in Sertoli cell function. Quantitative analysis of mRNA expression associated with apoptotic signals showed no significant uniform changes among the cooled testes, although some individuals had a distinct up-regulation of FAS mRNA at 24 hours. Attempts to use the cooled testes as recipient testes for mouse-to-rat germ cell transplantation were undertaken, but none of the mouse germ cells transplanted into the testes 15-34 days after cooling appeared to have undergone spermatogenesis 64-92 days after transplantation. These data suggest that modifications to Sertoli cell function resulting from testicular cooling create an environment that is unable to support spermatogenesis by donor germ cells.

Animals↗

PubMedDate not supplied

Synthesis and properties of an oligodeoxynucleotide modified with a pyrene derivative at the 5'-phosphate.

The synthesis of an oligonucleotide (ODN) modified with pyrene (pyr) on the 5'-phosphate is described. The ODN and pyrene are joined through a linker composed of four methylene groups. Modification of the oligonucleotide was effected via condensation of the 2-cyanoethyl N,N-diisopropylphosphoramidite of 4-(1-pyrenyl)butanol (pyr-m4OPAm, 2) with the 5'-OH of an ODN. This derivative is suitable for incorporation into automated solid-phase DNA synthesis and was attached to the 5' terminus of the DNA chain through a phosphodiester linkage. The properties of the 5'-(pyr-m4)d(T)15 (3) and the duplex it formed with d(A)15 were investigated by fluorescence and absorbance spectroscopy. The pyrene fluorescence in the modified duplex was quenched 96.3% relative to an identical concentration of free 4-(1-pyrenyl)butanol. The ultraviolet spectrum of the 5'-(pyr-m4)-d(T)15 and 5'-(pyr-m4)-d(T)15-d-(A)15 modified duplex, in the 320-360-nm region, was red-shifted 6 nm relative to the free 4-(1-pyrenyl)-butanol. The Tm values of the unmodified and modified duplexes at 0.1 M NaCl were 34.9 and 41.9 degrees C, respectively. The pyrene-induced stabilization corresponds to a free energy change (delta delta G degrees) of -2.6 kcal/mol.

Oligonucleotides↗

PubMedDate not supplied

Halide-catalyzed cis product formation in the hydrolysis of anti-benzo[a]pyrene diol epoxide and its alkylation of poly(A).

The carcinogen 7-r,8-t-dihydroxy-9-t,10-t-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (anti-BPDE) forms diastereomeric cis and trans products in its reactions with nucleic acids and water (adducts and tetrols, respectively). The effects of salts, buffers, and DNA on the hydrolysis product ratio were tested. Halide ions increase the cis-tetrol/trans-tetrol ratio, with the order of effectiveness being I > Br > Cl >> F. No cation effect was apparent. Non-halide salts of strong acids increase the ratio to a small degree. Buffers decrease the ratio, with phosphate being more effective than cacodylate. DNA also reduces the ratio, with denatured DNA being more potent than native DNA. Halide ions appear to catalyze cis-tetrol formation via trans halohydrin intermediates. At the lowest halide concentrations which significantly raise the product ratio, and at all levels of chloride ion, the rate of anti-BPDE hydrolysis is not greatly increased, indicating that the halide ions are reacting primarily with the BPDE carbocation formed in the rate-determining step. At higher concentrations, iodide ion and, to a lesser degree, bromide ion significantly accelerate hydrolysis, indicating that BPDE undergoes SN2 attack by these ions. Chloride ion was also found to increase the proportion of cis adducts formed between anti-BPDE and poly(A). The cis adduct/trans adduct ratio was quadrupled by 0.5 M NaCl. This suggests that chlorohydrins can be intermediates in the alkylation of nucleic acids by epoxides of polycyclic aromatic hydrocarbons.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMedDate not supplied

Immobilization of cesium-137 and uranium in contaminated sediments using soil amendments.

Batch and dynamic leaching methods were used to evaluate the effectiveness of hydroxyapatite (HA), illite, and zeolite, alone and in combination, as soil additives for reducing the migration of cesium-137 (137Cs+) and uranium (U) from contaminated sediments. Amendment treatments ranging from 0 to 50 g kg(-1) were added to the sediment and equilibrated in 0.001 M CaCl2. After equilibration, the treatment supernatants were analyzed for 137Cs+, U, PO4, and other metals. The residual sediments were then extracted overnight using one of the following: 1.0 M NH4Cl, 0.5 M CaCl2, or the Toxicity Characteristic Leaching Procedure (TCLP) extractant. Cesium was strongly sorbed to the contaminated sediments, presumably due to interlayer fixation within native illitic clays. In fact, 137Cs+ was below detection limits in the initial equilibration solutions, the CaCl2 extract, and the TCLP solution, regardless of amendment. Extractants selective for interlayer cations (1.0 M NH4Cl) were necessary to extract measurable levels of 137Cs+. Addition of illitic clays further reduced Cs+ extractability, even when subjected to the aggressive extractants. Zeolite, however, was ineffective in reducing Cs+ mobility when subjected to the aggressive extractants. Hydroxyapatite was less effective than illite at reducing NH4+-extractable Cs+. Hydroxyapatite, and mixtures of HA with illite or zeolite, were highly effective in reducing U extractability in both batch and leaching tests. Uranium immobilization by HA was rapid with similar final U concentrations observed for equilibration times ranging from 1 h to 30 d. The current results demonstrate the effectiveness of soil amendments in reducing the mobility of U and Cs+, which makes in-place immobilization an effective remediation alternative.

Cesium Radioisotopes↗