Biosynthesis of mitochondrial DNA. Is 8 S DNA an artifact?

Sucrose density gradient fractionation of isolated rat liver mitochondrial DNA ordinarily yields two peaks, one at 39 S, the other at 27 S. However, when these mitochondria are first incubated with a labeled DNA precursor, a labeled peak at about 8 S is also observed. Is this low molecular weight 8 S DNA merely an artifact of contamination or breakdown, or is it a functioning part of the mitochondrial genome? That it is not a nuclear contaminant is shown by: (a) the absence of nuclei or nuclear fragments in active mitochondrial preparations; (b) the insensitivity of 8 S DNA synthesis to treatment of mitochondria with DNase and RNase; (c) the ability of inner membrane preparations to synthesize this DNA; (d) the ability of atractyloside to inhibit incorporation of [3H]dATP into 8 S and 39 S or 27 S DNA equally; (e) the labeling of 8 S DNA (as well as 39 S and 27 S DNA) but not of nuclear DNA after the administration in vivo of [3H]thymidine. The evidence that 8 S DNA is not an artifact resulting from DNA breakdown during mitochondrial incubation or DNA isolation is as follows: (a) 8 S DNA can be isolated from unincubated mitochondrial; (b) 8 S DNA becomes labeled when labeled DNA precursors are administered in vivo; (c) 8 S DNA biosynthesis continues in the complete absence of labeled 39 S or 27 S DNA (whose synthesis is repressed by ethidium bromide), making it unlikely that 8 S DNA is formed from the breakdown of 39 S or 27 S DNA; (d) substitution of milder methods of DNA extraction does not decrease 8 S DNA labeling; moreover, the usual conditions of extraction, when applied to purified 39 S and 27 S DNA, do not generate 8 S DNA, nor does an additional mitochondrial washing cycle; (e) the specific radioactivity of 8 S DNA is higher than that of 39 S or 27 S DNA, making it improbable that the latter forms are precursors of 8 S DNA. Since 8 S DNA is double-stranded, it is not identical to the 7 S fragment of D loop DNA. The hypothesis that the artifactual nicking of those DNA molecules which contain opposing D loops leads to the release of double-stranded fragments was tested. The DNA which was released was predominantly (and probably completely) single-stranded. We conclude that 8 S DNA is probably not an artifact and studies are in progress on its function.     

Passive and active exercises increase cerebral blood flow velocity in young, healthy individuals

Zinc levels in seminal plasma were measured. The study was done on 122, random selected males from infertile couples. The atomic absorption spectrophotometer was used. Sperm density of ejaculate was also determined. These parameters were compared in subgroups: normospermic and oligospermic and in classes of variable oligospermic severity. Semen serum zinc levels in normospermic men was significantly increased as compared to oligospermic men. There were no significant differences in zinc levels between the different classes of oligospermia.     

Electrolytic acetoxylation of methyl oleate

The electrolysis of methyl oleate in acetic acid solution with LiClO₄ as the supporting electrolyte was studied. Both stirred and pumped undivided cells were used with Pt electrodes. Constant current at 6, 8, 16 and 24 ma/cm² current densities was used. The amount of acetoxyl substitution appeared to be independent of the current density. With 4 Faradays of charge, about 1.1 acetoxy groups were introduced/mole at a current efficiency (i.e., net chemical reaction/net charge) of 50 to 60%. The acetoxylated octadecenoates exhibit thermal instability upon molecular distillation with the formation of conjugated unsaturation by loss of acetic acid. Catalytic hydrogenation of the acetoxylated product yielded distillable acetoxylated methyl octadecanoates. The unsaturated acetoxylated products gave 25–47% undistillable material upon molecular distillation, while the saturated acetoxy derivatives had as little as 1%. From the corresponding alcohols of the unsaturated acetoxy products,t-butyldimethylsilyl ethers were prepared and analyzed by mass spectrometry. This analysis supported the hypothesis that the principal points of acetoxyl substitution in the mono-acetoxylated esters were at C-8,9,10 and 11, while the acetoxylation in the poly-acetoxylated esters was more widely dispersed.     

A fatal drug interaction between clozapine and fluoxetine

A case is presented of a fatal drug interaction caused by ingestion of clozapine (Clozaril) and fluoxetine (Prozac). Clozapine is a tricyclic dibenzodiazepine derivative used as an "atypical antipsychotic" in the treatment of severe paranoid schizophrenia. Fluoxetine is a selective serotonin reuptake inhibitor used for the treatment of major depression. Clinical studies have proven that concomitant administration of fluoxetine and clozapine produces increased plasma concentrations of clozapine and enhances clozapine's pharmacological effects due to suspected inhibition of clozapine metabolism by fluoxetine. Blood, gastric, and urine specimens were analyzed for fluoxetine by gas chromatography/mass spectrometry (GC/MS) and for clozapine by gas-liquid chromatography (GLC). Clozapine concentrations were: plasma, 4.9 micrograms/mL; gastric contents, 265 mg; and urine, 51.5 micrograms/mL. Fluoxetine concentrations were: blood, 0.7 microgram/mL; gastric contents, 3.7 mg; and urine 1.6 micrograms/mL. Norfluoxetine concentrations were: blood, 0.6 microgram/mL, and none detected in the gastric contents or urine. Analysis of the biological specimens for other drugs revealed the presence of ethanol (blood, 35 mg/dL; vitreous, 56 mg/dL; and urine 153 mg/dL) and caffeine (present in all specimens). The combination of these drugs produced lethal concentrations of clozapine and high therapeutic to toxic concentrations of fluoxetine. The deceased had pulmonary edema, visceral vascular congestion, paralytic ileus, gastroenteritis and eosinophilia. These conditions are associated with clozapine toxicity. The combined central nervous system, respiratory and cardiovascular depression of these drugs was sufficient to cause death. The death was determined to be a clozapine overdose due to a fatal drug interaction.     

Maintenance treatment of ulcerative proctitis with mesalazine suppositories: a double-blind placebo-controlled trial. The Italian IBD Study Group

OBJECTIVE: To examine the outcome of trial second labor after a first cesarean performed because of cephalopelvic disproportion, defined according to strict diagnostic criteria. METHODS: Obstetric details of nulliparous women delivering at 37 or more weeks' gestation by cesarean for cephalopelvic disproportion, between 1975 and 1990, were recorded prospectively. The diagnostic criteria for cephalopelvic disproportion were cervical dilation arrested after 5 cm, unresponsive to oxytocin augmentation, after active dilatation of 2 cm or more in 2 hours. Fetal malpresentations and malpositions were excluded. The outcome of next delivery in our hospital by each woman enrolled was then examined. RESULTS: Eighty-four of 42,793 women met the criteria for disproportion, and 40 with cephalic presentations delivered their next baby in our hospital. All 40 underwent a trial of labor and 27 (68%) delivered vaginally, comprising seven (47%) women with larger second and 20 (80%) with smaller second babies. Of 15 women previously delivered by cesarean at full dilatation, 11 (73%) delivered vaginally with no serious maternal or neonatal morbidity. CONCLUSION: The strictly defined diagnosis of nulliparous cephalopelvic disproportion should not constitute an automatic "recurrent" indication for elective cesarean delivery, because 68% of patients in our series had successful vaginal deliveries in their next pregnancies. This rate is similar to those reported after all nulliparous cesareans for dystocia.