[Persistence of circadian rhythms of plasma ACTH and corticosterone after pinealectomy in sighted or blind rats].

The possible effects of pinealectomy on the corticotropic system was studied in either sighted or ocular enucleated adult female Rats. Individual ACTH and corticosterone measurements were performed on sequential plasma samples obtained over a 48 hrs period from a carotid implanted cannula. Compared with their respective sighted or blind controls, pinealectomized Rats displayed no alteration in the hormonal rhythms' periodicity, phase, mean level and amplitude. On the other hand, ocular enucleation, whether or not associated with pinealectomy depressed the amplitude and to a lesser extent the mean level of the ACTH rhythm, and paradoxically increased the corticosterone rhythm's mean level. While no pineal factors appear therefore required for a normal corticotropic rhythmicity, the possible regulating role of retinal melatonin may be discussed.