Selective inhibition by chloramphenicol of ACTH‐induced reorganization of inner mitochondrial membranes in fetal adrenal cortical cells in tissue cultures

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Abstract
Tissue cultures of fetal rat adrenals were used to study effects of chloramphenicol on the ACTH‐induced synthesis of mitochondrial inner membranes in the cortical cells. Chloramphenicol alone added to the culture medium in concentrations of 0.003, 0.03, 0.3, and 0.6 μ mole/ml/6 days induced no changes in the ultrastructure of cortical cells. Chloramphenicol in concentrations of 0.3 and 0.6 μ mole/ml/6 days given together with 100 mu/ml/6 days of ACTH inhibited completely the ACTH induced changes of mitochondrial inner membranes (formation of 600 Å vesicles). Chloramphenicol in concentrations of 0.003 μ mole/ml/6 days caused no inhibition of the ACTH effects. In concentration of 0.03 μ mole/ml/6 days chloramphenicol resulted in incomplete inhibition of ACTH‐induced formation of mitochondrial vesicular cristae. None of these doses of chloramphenicol affected other ACTH‐induced changes in the fine structure of the cells such as increase of smooth surfaced endoplasmic reticulum, hypertrophy of Golgi apparatus, and development of microvillous processes of plasma membranes. Chloramphenicol also caused no inhibition of the ACTH‐induced accumulation of lipid in the cytoplasm. In cultivated cortical cells of Charles River strain albino rats small groups of annulated lamellae are commonly observed.The present observations suggest that: (1) the development of mitochondrial inner membranes is dependent, at least in part, on mitochondrial protein synthesis; (2) ACTH stimulation of mitochondrial protein synthesis in cortical cells is independent of ACTH‐induced stimulation of nuclear‐DNA‐dependent protein synthesis; (3) doses of chloramphenicol which inhibit specialization of mitochondrial inner membranes of fetal adrenal cortical cells are comparable to those which inhibit protein synthesis in bacteria.