N-Acetyltransferase activity, hydroxyindole-O-methyltransferase activity, and melatonin levels in the Harderian glands of the female Syrian hamster: Changes during the light: Dark cycle and the effect of 6-parachlorophenylalanine administration

Melatonin Synthesis in the Rat Harderian Gland: Age- and Time-related Effects

“…1), in the Harderian gland of the Wistar rat, a species commonly used in investigations dealing with melatonin synthesis. By contrast to Sprague± Dawley rats and female Syrian hamsters (Reiter et al, 1983;Hoffman et al, 1985;Menendez-Pelaez et al, 1987), and similarly to male Syrian hamsters and Richardson's ground squirrels (Reiter et al, 1981;Hoffman et al, 1985;Menendez-Pelaez et al, 1989), we found no signi®cant changes in the melatonin content over the 24 hr span, which strongly suggest a lack of diurnal rhythm of melatonin in the Harderian gland of Wistar rats. These differences suggest interspecies variations, but may also well be related to seasonal modulation of the diurnal rhythm of melatonin content in the Harderian gland.…”

“…By contrast to the voluminous literature on pineal melatonin synthesis, its circadian rhythmicity and the effects of aging, few studies dealing with the circadian variations of melatonin in the rodent Harderian gland have been performed. There is increasing evidence that numerous differences exist between rodent species with respect to daily pro®les of melatonin Hurlbut, 1981, Reiter et al, 1983;Hoffman, Johnson and Reiter, 1985;Menendez-Pelaez et al, 1987, 1989. The purpose of this study was therefore to evaluate in the Wistar rat Harderian gland, the time-and age-related effects on melatonin content as well as on its synthesizing enzymes, namely, NAT and HIOMT.…”

Nuclear localization of melatonin in different mammalian tissues: Immunocytochemical and radioimmunoassay evidence

“…Heretofore, it was generally felt that melatonin acts more or less exclusively via specific membrane binding sites located at rather discrete locations throughout the organism [Krause and Dubocovich, 19911. However, the importance of membrane "receptors" has been questioned [Kennaway and Hugel, 19921, and many of the actions of melatonin are not readily explained on the basis of the rather small number of membrane receptors that have been described [Reiter, 1991aI. On the other hand, genomic effects of melatonin have been proposed in tissues as different as the adrenal glands and the Harderian glands [Menendez-Pelaez et al, 1991;Persengiev et al, 19911. The results described herein provide a further justification for this suggestion since melatonin appears to have specific nuclear binding sites.…”

“…However, melatonin exerts an important role in other areas, such as the liver, the gut, and the heart, where melatonin receptors have not been fully characterized. Although the 24 h rhythm in circulating melatonin seems to be exclusively dependent on pineal melatonin production, there is evidence suggesting that organs in addition to the pineal gland produce melatonin, Thus, melatonin is known to be synthetized in the retina [Pang and Allen, 19861, the Harderian gland [Menendez-Pelaez et al, 19871, the extraorbital lacrimal gland [Mhatre et al, 19881, and the gut [Huether et al, 19921. Proof that melatonin is not an exclusive product of the pineal gland also comes from the observation that melatonin is found in invertebrates including Drosophila [Finocchiaro et al, 19881 and in a unicellular organism, Gonyaulax polyedra [Poeggeler et al, 19911; in the latter species melatonin exhibits a dayinight associated rhythm.…”

Rhythmic Release Pattern of Pineal Melatonin in Rodents

“…These findings suggest that the release of pineal melatonin into the confluens sinuum is under the regulation of the cervical sympathetic system. The sympathetic influence on pineal melatonin secretion systemic blood melatonin appeared to be the results of changes iThe synthesis and secretion of melatonin occur in a variety of organs, including the pineal gland, retina, lacrimal gland, Harderian gland, brain and gut in mammals [Quay, 1965;Bubenik et al, 1974; Pangetal., 1977;Ralph, 1980;Menendez-Pelaez et al, 1987;Mhatre et al, 1988], It is unclear as to whether or not all these organs secrete melatonin into the systemic circula tion. Surgical removal of the retina and/or Harderian gland in rats did not alter the melatonin concentration in the blood [Tang and Pang, 1982].…”