Both hydroxy- and methoxyindoles modify basal temperature in the rat

The various pineal gland tryptophan metabolites were administered to male rats intraperitoneally (100 micrograms/kg) and rectal temperatures were recorded. Of the compounds tested, hydroxytryptophan, N-acetylserotonin, hydroxytryptophol, and their corresponding methoxyindoles all caused a marked hypothermia, indicating that several indolic products may be involved in thermoregulation. Although the brain penetration of indoles is poor, a central site of action would be most likely, although peripheral actions cannot be excluded. The mechanism of induction of hypothermia may involve peptides, the pituitary-thyroid axis, the adrenal gland, or a combination of these. These results may suggest that the pineal gland integrates environmental cues to act in concert with physiological thermostats in the fine tuning of thermoregulation.