MELATONIN SECRETION INVITRO FROM THE PINEAL COMPLEX OF THE LAMPREY PETROMYZON-MARINUS

Melatonin secretion from cultured pineal complexes of the lamprey, Petromyzon marinus, was measured by radioimmunoassay (RIA) for 6 days under either a 12:12 light:dark cycle (L:D) or continuous darkness (D:D) at either 10° or 20°. Under the L:D cycle, melatonin release was completely suppressed during daytime and high during night-time, with larger amplitude at 20° than at 10°. Under D:D conditions, no significant circadian rhythmicity in secretion could be revealed by periodogram analysis at either 10° or 20°. This is the first direct evidence of melatonin secretion in a lamprey, suggesting that both light and temperature can affect in vitro melatonin secretion. © 1993 by Academic Press, Inc.