DAY-NIGHT RHYTHM OF ACETYLCHOLINE IN THE RAT PINEAL-GLAND

Using high-performance-liquid-chromatography (HPLC) measurement of ace tylcholine, choline acetyltransferase (ChAT) enzyme assay and anti-ChA T immunohistochemistry, we have investigated the expression of the cho linergic system in pineal glands of male rats. Glands procured during the day period (1200 h) contained significant amounts of acetylcholine (0.5 pmol/gland). A similar content was found in pineal glands after a 48 h culture period, i.e. when the intrapineal nerve fibres have deg enerated. This strongly indicates that the pinealocytes are the cells which contain acetylcholine. To confirm this conclusion we demonstrate substantial ChAT-like immunoreactivity in pinealocytes. ChAT enzyme a ctivity measured in homogenized glands (day period) was 7 +/- 3 nmol/m g per h. Acetylcholine content as well as ChAT enzyme activity increas ed about 10-fold in pineal glands during the night period (2400 h). Th e present study demonstrates for the first time the presence of a day- night rhythm of ChAT and acetylcholine in rat pinealocytes. The functi on of pineal acetylcholine is not clear, but there are indications tha t acetylcholine may depress noradrenaline release from intrapineal sym pathetic fibres and hence melatonin synthesis. (C) 1997 Elsevier Scien ce Ireland Ltd.