[Correlation between the circadian rhythms of plasma ACTH and corticosterone, and of motor activity, evolving freely after ocular enucleation in the rat].

21, 35 and 60 days after bilateral ocular enucleation a similar phase-shift vs an environmental 12 L-12 D photoperiod was observed in the circadian rhythms of plasma ACTH and corticosterone (B) and of motor activity. This phase-shift is indicative of free-running endogenous circadian rhythms whose period was estimated at 2492-24.3 h. The rhythms' amplitude (C) appeared decreased at 21 d for both hormones, and subsequently for ACTH only, whereas the rhythms' mean levels (Co) were reduced for ACTH and augmented for B. The amount of total motor activity per day decreased progressively down to 60% of controls at 60 d. Under otherwise non-fluctuating conditions the photoperiod appears, therefore as a main synchronizer to the endogenous pace-maker(s) driving those hormonal and behavioral rhythms.