The neurotropic action of ACTH: effects of ACTH-like peptides on the incorporation of leucine into protein of brain stem slices from hypophysectomized rats

Biphasic modulation by ACTH-like peptides of protein synthesis in a cell-free system from rat brain

Brain protein synthesis in a cell-free system was stimulated by 10(-8) M-ACTH1-24. This stimulatory effect was completely inhibited by aurintricarboxylic acid (ATA), an inhibitor of reinitiation of new peptide chains. The N-terminal peptide sequence 4-10 exerted a biphasic modulation of cell-free protein synthesis, i.e., a stimulation at low concentrations (10(-8) and 10(-10) M) and an inhibition at a high concentration (10(-4) M). The D-isomer, ACTH4-10-7-D-phe, also showed a biphasic modulation that, however, was in a direction opposite to that shown by ACTH4-10-7-L-phe at 10(-8) M and 10(-4) M.

Pineal protein synthesis highly sensitive to ACTH-like neuropeptides

Pineal protein synthesis was studied in vitro over a period of 6-8 h after dissection. The level of protein synthetic activity of the pineal gland was greatly dependent on the time of dissection showing a maximum at midnight and a minimum at 10.00 h, 2 h after onset of light. Low concentrations of ACTH1-24 (down to 10(-11) M) could stimulate protein synthesis in vitro. The sensitivity to hormonal stimulation showed a circadian variation similar to that observed in the basal protein synthetic activity. Furthermore, overall synthetic activity appeared to be under neural influence. These neural and hormonal influences seemed to be mediated by beta-receptor stimulation and cyclic AMP. Structure-activity studies of the ACTH-effect on pineal protein synthesis gave results similar to those previously observed for excessive grooming behaviour, synaptic plasma membrane phosphorylation, adenylcyclase-activity and cell-free protein synthesis in brain. It was concluded, that overall pineal protein synthesis is both under neural and hormonal control. The action of ACTH on protein synthesis rate might be mediated by a calcium-dependent release of norepinephrine followed postsynaptically by beta-receptor activation, cAMP production, and stimulation of translation.

Effects of stressful procedures as ether anesthesia and intracranial injections on amino acid incorporation into brain protein

Ether anesthesia elevates plasma corticosterone levels considerably and interferes severely with the incorporation of centrally applied [3 H] leucine into brain protein. Only minor changes in leucine incorporation are observed in conscious rats with an implanted cannula in the third brain ventricle as compared to noncannulated controls. Injection through this cannula can be regarded as a minor stressful procedure comparable to subcutaneous injection both causing moderate elevations in plasma corticosterone levels. Injection through the cannula per se did not affect the leucine incorporation. In studies which require local application of the radioactive precursor, it is therefore recommended to avoid ether anesthesia and to use a preimplanted cannula in the brain ventricular system.