Hypermutability of mouse chromosome 2 during the development of x-ray-induced murine myeloid leukemia

In an effort to identify the precise role of a deletion at regions D-E of mouse chromosome 2 [del2(D-E)] during the development of radiation-induced myeloid leukemia, we conducted a serial sacrifice study in which metaphase chromosomes were examined by the G-banding technique. Such metaphase cells were collected from x-irradiated mice during the period of transformation of some of the normal hematopoietic cells to the fully developed leukemic phenotype. A group of 250 CBA/Ca male mice (10-12 weeks old) were exposed to a single dose of 2 Gy of 250-kilovolt-peak x-rays; 42 age-matched male mice served as controls. Groups of randomly selected mice were sacrificed at 20 hr, 1 week, and then at intervals of 3 months up to 24 months after x-irradiation. Slides for cytogenetic, hematological, and histological examination were prepared for each animal at each sacrifice time. An expansion of cells with lesions on one copy of chromosome 2 was evident in 20-25% of treated mice at each sacrifice time. The majority of such lesions were translocations at 2F or 2H, strongly suggesting hypermutability of these sites on mouse chromosome 2. No lesions were found in control mice. The finding leads to the possibility that genomic lesions close to 2D and 2E are aberrants associated with radiation leukemogenesis, whereas a single clone of cells with a del2(D-E) may lead directly to overt leukemia. The data also indicate that leukemic transformation arises from the cumulative effects of multiple genetic events on chromosome 2, reinforcing the thesis that multiple steps of mutation occur in the pathogenesis of cancer.     

The effect of the special instruction of bronchial asthma patients on the efficacy of their treatment

As the data collected in a survey we conducted show, a major part of the modern general practitioner's work continues to be in the field of family medicine. This fact is also confirmed by the results of other surveys of general practice today. Patients still appreciate their GPs as a source of good medical care and counseling for the whole family. Our own study has shown that most patients would even like to see an expansion of the GP's counseling activities. The duration of the doctor-family relationship extends over many years, and is frequently longer than a decade.     

Quantitative aspects of the formation of a half chromatid chiasma as an intermediate product of genetic recombination in bacteriophages

Formal genetic consequences of generation and break-up of a half chromatid chiasma have been studied on the basis of a model with the symmetric exchange of two strands between parental DNA molecules. In recombination analysis, generation and break-up of this structure gives rise to a critical frequency R (zeta), which corresponds to recombination between two markers separated by a distance equal to the mean genetic length zeta of the hybrid region at the time of scission of the cross connection. The use of the distance zata as a natural unit of a genetic map is suggested. In the case of bacteriophage T4 under conditions of standard crosses the half chromatid chiasma is characterized by the value R (zata) equal to 3.0-10(-2), the structure acquiring with equal probability either of the two alternative isomeric configurations at the time of scission of the cross connection. About four per cent of the total number of mismatches as a result of break-up to the half chromatid chiasm were repaired.     

Effect of hypoxemia on the erythropoietic activity of organs during perfusion

Hypoxemia (45-minute) influence in vivo on erythropoietic activity of the kidney, liver, spleen, and sternum was studied by normoxemic perfusion of the isolated organs. The erythropoietic activity proved to increase after 6-hour perfusion of the liver; this confirmed the participation of this organ in the extrarenal secretion of the erythropoietic factor.     

Gigantic pseudomucinous cyst simulating inoperable malignant ovarian tumor

A new operation has been done on 11 patients with post-traumatic impassible prostatomembranous urethral strictures. Complications have been minimal. The disadvantages and difficulties with 2 other procedures are discussed.     

Growth rate of malignant tumors of the large intestine

The rates of colonic tumor growth were studied on the basis of evaluation of the case histories of 19 cancer patients in whom dynamic endocolonoscopy had been carried out. In some cases, malignant tumors appeared in the colon within 12 months after previous colonoscopy. Tumors were under 2.0 cm in size and were not accompanied by any clinical symptoms. Repeated endoscopic examinations performed within a period of 1-3 years detected large tumors which caused the constriction of colonic lumen. Clinical symptoms developed in such patients approximately 1-4 months prior to tumor detection. It is concluded that although the rates of growth of colonic malignancies are rather high, tumorigenesis is preceded by a long-term stage of preclinical disease.