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.