5-METHOXYTRYPTOPHOL RHYTHMS IN THE CHICK PINEAL-GLAND - EFFECT OF ENVIRONMENTAL LIGHTING CONDITIONS

5-Methoxytryptophol (5-ML) rhythms were studied in the pineal glands o f chicks which were adapted to three different lighting conditions: 12 h light: 12 h dark (LD), constant darkness (DD) and continuous light (LL). Pineal glands of chicks kept under LD conditions exhibited rhyth mic fluctuations in 5-ML content. 5-ML levels were low (18 +/- 2 pg/pi neal) during the dark phase of the cycle, they increased approximately 9-fold at the end of the dark phase, and remained high (176 +/- 6 pg/ pineal) throughout the light period. This pattern of 5-ML content also persisted under conditions of DD, indicating that the 5-ML rhythm is circadian in nature. This is the first evidence of circadian rhythmici ty of 5-ML. Pineal 5-ML levels in chicks kept under LL were high (168 +/- 8 pg/pineal), but did not fluctuate in a rhythmic fashion. Under L D and DD, but not LL, the rhythm of 5-ML in the chick pineal is 180 de grees out of phase with the rhythm of melatonin biosynthesis, an obser vation suggesting that, at least in this species, the pineal productio n of these two hormones may be inversely correlated. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.