Nucleic acid content in intestine of rats after neutron radiation.

Male albino rats, approximately 200 gm. in weight, maintained on Fox Blox food (Allied Mills Co.) with water ad libitum were used. The rats were divided into 7 groups of 20 each; 10 of each group were irradiated and 10 were used as controls. Neutron irradiation was performed as described by Enns (3). Groups 1 to 5 were given 56 n and tissues were removed for examination at the following intervals after completion of irradiation: Group 1 immediately; Group 2, 4 hours; Group 3, 12 hours; Group 4, 24 hours; Group 5, 48 hours. Group 6 was given 100 n and tissues taken 24 hours later; Group 7 was given 200 n and tissues taken 24 hours later. The rats in each group were paired according to weight: one of each pair was irradiated, the other served as control. The tissue to be examined was taken from the duodenum one-half inch below the pylorus. Tissue was removed from the irradiated and control rats of each pair at the same time and was carried through the fixation and dehydration process together. The fixative was absolute ethyl alcohol 3 parts and glacial acetic acid 1 part. Specimens from control and irradiated animals were embedded in close proximity in the same block of embedding medium so that they were cut at the same time. Comparison was always made between control and irradiated sections that were cut with the same stroke of the knife. Sections for studies by ultraviolet light absorption were cut 3 microns in thickness and were mounted on quartz slides without the use of adhesive. After deparaffination in xylol, the sections were placed in 95 per cent ethyl alcohol, then mounted with glycerol. Sections for microincineration were cut 7 microns in thickness and were mounted on glass slides without the use of adhesive. Sections for Feulgen staining were cut 10 microns in thickness and those for methyl green-pyronin staining 6 microns and were mounted on glass slides with albumin as adhesive. A quartz optical system microscope in combination with a mercury-vapor lamp, monochromator, and 35 mm. camera were used to measure the ultraviolet light absorption by sections of tissues. The mercury light band 2654 A was used. Panatomic-X film was used and developed in Eastman Kodak D 19 developer. A 10 X ocular and a 2.5 mm. glycerine immersion objective were used. The magnification on the film was 195 X. A minimum of 5 microscopic fields of each irradiated and control section were photomicrographed on the same strip of film using the same exposure and light intensity for each exposure. One frame on each film was exposed through a clear space between sections as a "background" for densitometric measurements. Densities of the photomicrographic images on the film were measured by use of a microdensitometer. Thirty to fifty readings were made on each of 5 fields and each "background." These data were used for calculation of extinction coefficients. Feulgen stained sections were photomicrographed on microfile film and developed with Eastman Kodak developer D-9. Tungsten light and a green filter were used. Densitometric measurements on a scale comparable to that employed with the ultraviolet light absorption method were made and the data used for calculation of extinction coefficients. Methyl green-pyronin stained sections were examined microscopically for differences in intensity of pyronin staining as a measure of the comparative amounts of cytoplasmic ribonucleic acid. Brachet (1) showed that pyronin is highly specific as a stain for ribonucleic acid. Non-volatile inorganic ash was determined by densitometric measurements of intensities of darkfield photomicrographic images of microincinerated sections. The sections were incinerated at 600 to 625 o C. Photomicrographs of control and irradiated specimens to be compared were made with identical exposure and development times; thus differences in tone represent differences in absorption; the darker the tone, the greater the absorption.