EFFECT OF TOTAL-BODY X-RADIATION FROM NEAR THRESHOLD TO TISSUE-LETHAL DOSES ON THE SMALL BOWEL EPITHELIUM OF THE RAT. II. CHANGES IN NUCLEIC ACID AND PROTEIN SYNTHESIS IN RELATION TO CELL DIVISION

Technical Report · Fri Jan 24 04:00:00 EST 1958

OSTI ID:4276296

Toal, J N; Reid, J C; Williams, Jr, R B; White, J

The initial blockage of mitosis produced b x radiation in the rat small bowel epithelium is not accompa nied by a proportionate reduction in the rate of DNA synthesis. After very low doses of x rays there is little or no immediate effect on DNA synthesis. The drop encountered from 1 to 5 hours after higher doses is believed to be due to acute destruction of the cells involved in active synthesis. At doses of 2000 r the initial fall is much greater than 50 percent. Depending upon the dose of x rays administered DNA synthesis falls to a low level during or before the transient recovery of mitotic activity noted in the proximal postirradiation period. DNA synthesis resumes before final mitotic recovery from radiation injury begins. The length of the interval is dose- dependent. Final recovery is accompanied by an overshoot in the synthetic rate or DNA, PNA, and protein direcitly related to the time and extent of the overshoot in mitotic rate. Five hours after administration of glycine-N/sup 15/ to rats intraperitoneally the concentration of isotope in quanine of PNA and DNA in the small intestine exceeds that of adenine in both normal animals and in those dosed at various times following whole-body x radiation. After irradiation the concentration of isotope in DNA purines is reduced relatively more than in those of PNA during periods of mitotic inhibition and is increased relatively more during final recovery. Within each type of nucleic acid the purine pairs exhibit essentially parallel changes in isotope concentration. The PNA pyrimidines acquire equal isotope concentrations in normal animals, and rise in parallel fashion during periods of accelerated synthesis during recovery from x radiation. Very little if any inhibition of incorporation into PNA pyrimidines occurs at any stage after irradiation. A transient stimulation in protein synthesis occurs shortly after irradiation followed by a stimulationn of greater magnitude during the period of final recovery which is relatively smaller than the enhancement of uptake in the nucleic acids during this period. Depression below normal levels does not occur even with tissue-lethal doses which sterilize epithelial cells lining the crypts. The different classes of radiation effects observed are thought to have their origin in different classes of stem cells distinguishable by the position they occupy in the mitotic cycle. (auth)

• Research Organization: Naval Medical Research Inst., Bethesda, Md.; National Cancer Inst., Bethesda, Md.
• NSA Number: NSA-13-005227
• OSTI ID: 4276296
• Report Number(s): NM-62-02-00.02.02
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ADENINE
AMINES
AMINO ACIDS
BIOLOGY AND MEDICINE
BODY
DNA
GLYCINE
GUANINE
HETEROCYCLICS
INTESTINE
ISOTOPES
LETHAL DOSE
METABOLISM
MITOSIS
NITROGEN 15
NUCLEIC ACIDS
ORGANIC NITROGEN COMPOUNDS
PROTEINS
PURINES
PYRIMIDINES
QUANTITY RATIO
RADIATION DOSES
RADIATION EFFECTS
RADIATION INJURIES
RATS
RECOVERY
X RADIATION