Dna Turnover in Adrenal Medullary Cells of Different Strains of Rats and Its Enhancement After Intermittent Exposure to Cold

Abstract

In Italico and Wistar rats maintained at room temperature 1% of nuclei of cells in the adrenal medulla incorporate 3H‐thymidine. Following intermittent exposure to cold, the numbers incorporating increase to 10% and 7% in Italico and Wistar strains respectively. Only in the Wistar strain does the increase occur during actual exposure. Assuming S to be 6–8 hr the labelling indices actually determined indicate a turnover time of DNA of 21–29 days. Since mitotic indices in experimental and control animals were found to be 0.004% without colchicine treatment and 0.009% after 3 hr of colchicine treatment, the turnover times of cells were calculated to be 1388–3125 days. To correlate mitotic indices and labelling indices, an S period of 400 hr would have to be assumed. It is concluded therefore that: (i) most of the observed labelling of DNA is due to metabolic turnover of DNA and only a small proportion represents pre‐mitotic synthesis, (ii) differences in the rates of DNA synthesis found during exposure to cold in Italico and Wistar rats respectively are sufficient to account for the differences in reduction of DNA previously found between the two strains under these experimental conditions.

Insulin-like growth factors act synergistically withbasic fibroblast growth factor and nerve growth factor to promote chromaffincell proliferation.

“…The scarcity of mitotic figures in adult rat chromaffin cells in vivo has led to the dogma that adult chromaffin cells are postmitotic (2) and more recent work has confirmed that adult rat chromaffin cells rarely divide in situ (3)(4)(5). However, adult rat chromaffin cells are not irreversibly postmitotic as they reveal a growth potential comparable to that of neonatal chromaffin cells when exposed to the synergistic action of IGF-I or IGF-II and bFGF or NGF in culture.…”

“…In the rat, chromaffin-cell precursors invade the primordial adrenocortical structure about embryonic day 14 where they differentiate into mature chromaffin cells (1). Chromaffin-cell division in the rat occurs mainly during fetal and neonatal development, whereas proliferation of adult chromaffmi cells is very low (2)(3)(4)(5). Little is known about the factors that regulate the growth of chromaffin cells.…”

Regulation of bFGF gene expression and subcellular distribution of bFGF protein in adrenal medullary cells.

“…Even the adult adrenal medulla may undergo hyperplasia, increased vascularization and, in some instances, neoplastic transformation (Tischler and DeLeUis, 1988;. Stimuli that trigger these changes increase the activity of the nerves innervating the adrenal medulla or directly stimulate acetylcholine receptors on adrenal medullary cells (Malvaldi and Viola-Magni, 1972; for review see Tischler and DeLellis, 1988;.…”

DNA Turnover in Adrenal Medullary Cells of Long Evans Rats

“…2 It has also been demonstrated that the decrease of DNA per nucleus in the adrenal medulla of Italico rats fed with the Randoin and Causeret3 diet is the result of two opposing processes of loss and synthesis, which take place during the periods of exposure to cold and room temperature respectively. 5 The processes of synthesis are therefore more active and lead to a smaller loss than that found in Italico rats fed with Randoin and Causeret's diet. 4 In Wistar rats fed with the commercial diet, DNA synthesis takes place during the period of cold Differentiation 1, 1973 exposure during the first 20 days of the experiment.…”

“…4 In Wistar rats fed with the commercial diet, DNA synthesis takes place during the period of cold Differentiation 1, 1973 exposure during the first 20 days of the experiment. 5 The processes of synthesis are therefore more active and lead to a smaller loss than that found in Italico rats fed with Randoin and Causeret's diet. 3 The changes in rates of DNA synthesis and turnover in these two strains caused by reversing the diet suggest that DNA synthesis may be controlled by some dietary factors in a manner which is still unknown.…”