McNulty J A, Prechel M M
Department of Cell Biology, Loyola University Stritch School of Medicine, Maywood, Ill. 60153.
Biol Signals. 1992 May-Jun;1(3):150-9. doi: 10.1159/000109320.
Levels of vasotocin-like immunoreactivity (iVT) and the indoles serotonin (5HT), 5-hydroxyindole acetic acid, N-acetyl-serotonin (NAS) and melatonin were measured over 24-hour periods at monthly intervals in the pineal gland of male rats kept under constant laboratory conditions of photoperiod and temperature. The 8- to 10-fold increase in pineal iVT, which occurred during mid-August, was not related to variations over the 24-hour light:dark (L:D) cycle. Tryptophan and 5HT exhibited seasonal variations over the 24 h L:D cycle with a single peak during the winter months. Twenty-four-hour levels of NAS tended to increase during the fall and spring. Seasonal effects on indole metabolism were further suggested by a marked decline during the fall in the correlation between NAS versus melatonin in individual pineal glands. Positive correlations between 5HT versus NAS and 5HT versus melatonin tended to be significant only during the summer months. These data suggest that environmental cues other than photo-period and temperature can regulate pineal neuroendocrine functions.
