Melatonin levels in the plasma of homing pigeons were measured by radioimmunoassay. In a 12:12 LD cycle a robust daily rhythm of plasma melatonin was found in intact birds. This rhythm is significantly reduced in amplitude after pinealectomy, and disappears completely after the pinealectomized animals have been bilaterally enucleated. The results indicate that in the pigeon 70% of the nighttime peak of blood-borne melatonin comes from the pineal gland, while 17% comes from the retina. In addition, there is a relatively large amount (13%) of non-rhythmic melatonin of unidentified origin. The melatonin rhythm appears to be circadian in nature, since melatonin levels begin to fall before lights-on in LD, and rhythmicity persists in intact and pinealectomized birds for at least two cycles in DD. In conjunction with earlier studies, the present results are consistent with the hypothesis that melatonin serves as mediator of circadian information in the pigeon. © 1988 Springer-Verlag.
Contribution of pineal and retinae to the circadian rhythms of circulating melatonin in pigeons
FOA', Augusto Giuseppe Lorenzo;
1988
Abstract
Melatonin levels in the plasma of homing pigeons were measured by radioimmunoassay. In a 12:12 LD cycle a robust daily rhythm of plasma melatonin was found in intact birds. This rhythm is significantly reduced in amplitude after pinealectomy, and disappears completely after the pinealectomized animals have been bilaterally enucleated. The results indicate that in the pigeon 70% of the nighttime peak of blood-borne melatonin comes from the pineal gland, while 17% comes from the retina. In addition, there is a relatively large amount (13%) of non-rhythmic melatonin of unidentified origin. The melatonin rhythm appears to be circadian in nature, since melatonin levels begin to fall before lights-on in LD, and rhythmicity persists in intact and pinealectomized birds for at least two cycles in DD. In conjunction with earlier studies, the present results are consistent with the hypothesis that melatonin serves as mediator of circadian information in the pigeon. © 1988 Springer-Verlag.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
