Diurnal variations of S-adenosyl-L-methionine and adenosine content in the rat pineal gland

S-adenosylmethionine and adenosine levels in the rat pineal gland were determined by high-performance liquid chromatography after fractionation of the pineal extracts. The concentration of S-adenosylmethionine follows a circadian rhythm and is about three times higher during the day (2.5 nmol/gland) than the night (1.1 nmol/gland). The variations in the level of adenosine are apparently more complex. Over the 24 hours period there are two maxima at 03.00 (120 pmol/gland) and 15.00 hrs (100 pmol/gland) and one minimum at 09.00 hrs (50 pmol/gland). In addition, only an ultradian rhythm with a period of 12 hrs and an acrophase of 3 hrs can be evinced by computer analysis.