Investigations on the turnover of adrenocortical mitochondria. VI. An autoradiographic study of the effect of ACTH on the radioactivity decay in the mitochondrial compartment from the zona fasciculata of 3H-thymidine injected rats.

The radioactivity decay of the mitochondrial compartment from the zona fasciculata of the adrenal cortex of 3H-thymidine-injected rats was followed by high resolution autoradiography. The number of days in which the radioactivity of the mitochondrial compartment was reduced to a half was calculated from the semilogarithmic plots of radioactivity versus time. Since DNA is a very stable molecule, it was assumed that this parameter can be an estimate of the half-life of adrenocortical mitochondria. The half-life of mitochondria from the zona fasciculata of the normal rat averaged 11.17 days, and ACTH was found to increase significantly this figure to about 15 days. It is hypothesized that the ACTH-elicited stimulation of the growth of rat adrenal zona fasciculata mitochondria involves not only hypertrophy and proliferation of the organelles (Nussdorfer et al., '74b), but also the slowing down of the degeneration rate of mitochondria.