A Radioautographic Study With H3-Thymidine on Adrenal Medulla Nuclei of Rats Intermittently Exposed to Cold

Abstract

A considerable decrease (24 to 40%) of DNA content per nucleus previously observed in the adrenal medulla of rats exposed intermittently to cold is followed by restoration to normal and supranormal values. This phenomenon has now been studied by use of H3-thymidine, which was given to normal rats, to rats exposed to cold, and to animals brought to room temperature after cold exposure. In the first two conditions, no significant labeling of nuclei was observed. In the third, labeling took place clearly in the 1st 3 days. The grain counts showed that the early labeled nuclei had more grains than those labeled later, indicating differences in the rate of DNA synthesis. A statistically significant correlation was found, on the same nuclei, between amount of Feulgen dye and number of grains. It is concluded that net synthesis of DNA takes place in the phase of recovery from cold. This fact is not related to cell division, as no mitoses could ever be detected, but rather to the cold-induced loss of DNA. Clear demonstration is thus given of a marked variation in the amount of DNA per nucleus in relation to the functional conditions of adrenal medulla cells.

Iii. Decrease of Labeled Dna in Cells of the Adrenal Medulla After Intermittent Exposure to Cold

“…1 A) . These findings are in agreement with previous results, which showed that the nuclei appear weakly labeled also after multiple injections (13) .…”

“…Sections treated with DNase do not show any radioautograph. Thymidine-3H (Tables II, III, IV) In agreement with the results of Viola-Magni (13), an incorporation of thymidine 3H has been found in the nuclei of adrenal medullary cells of rats intermittently exposed to cold . Five per cent of the nuclei appear labeled after 14 days of film exposure .…”

“…labeled nuclei is 7 .3% . In a previous study (13) performed with the same technique and exposure period (30 days), a labeling index of 28 .86% was found after 4 injections of thymidine 3H ad- Cold for 300 hr and Injected with Thymidine-3 H After 6 hr at Room Temperature Some of the rats were subsequently re-exposed to cold ; others were kept at room temperature as controls.…”

“…This loss was compensated for a few clays after returning the animals to room temperature . Concurrently, incorporation of thymidine-1 11 started immediately after the end of the cold exposure and continued for 3 days (13) . Since the adrenal medullary cells are considered either as nondividing cells (14) or as having a very low TABLE I Plan of the Experiment 33 Albino Italico Rats were exposed intermittently to cold for a total of 300 hr (20 days) .…”

“…Three animals were sacrificed at that time . The rest were divided into 2 groups and subsequently treated as set out in this (10,15,16), these observations cannot be accounted for by pre-mitotic synthesis, and have been tentatively explained in terms of a metabolic turnover of DNA (12,13), produced, or in some way accelerated, by cold treatment . In order to test this hypothesis, the behaviour of the label incorporated in nuclei of cells of the adrenal medulla of rats has been studied in detail .…”