Abstract
In 1958 Lerner isolated a “blanching principle” from bovine pineal extracts (1), which proved to be 5-methoxy-N -acetyltryptamine (melatonin). Subsequent investigations into the properties of melatonin showed effects upon the plasma levels of prolactin and thyroid stimulating hormone (2,3). The importance of these two hormones in mammals is well appreciated, and in teleosts they are strongly implicated in the physiological predisposition for migration (4, 5). Another important element in migratory behavior is the influence of photoperiod. Since the pineal gland of teleosts is capable of photoreception (6), and is a prime source of melatonin, the pineal may act as a photochemical transducer, instrumental in the proper timing of essential endocrine adjustments prior to migration. Photoperiod dependence of the activity of pineal acetylserotonin methyltransferase (ASMT), the enzyme catalyzing the final step in melatonin synthesis, has already been shown to exist in rats (7).
It was the purpose of this study to determine whether a diurnal fluctuation in ASMT activity exists in the pineal of the migratory species of trout, Salmo gairdneri (steelhead trout), when exposed to natural photoperiod.
Methods and Materials. Juvenile steelhead trout averaging 20 cm in length were maintained in an outdoor tank at the Alsea Trout Hatchery near Alsea, Oregon.
Sampling was done by weighing and sacrificing the fish, and then excising the top of the skull. Two such skull fragments were placed in a single vial that was kept on dry ice. The two skull fragments later yielded two pineals that were pooled and assayed as a single sample. Pineal removal usually began at noon and was repeated every 4 hours over a 24 hr period. At each 4 hour sampling time ten fish were processed as described above.
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