Correlations of Melatonin Content in Pineal Gland, Blood, and Brain of Some Birds and Mammals

Abstract

Diurnal, rhythmic variation of melatonin content in the pineal gland, blood serum, and brain have been found in chickens, with greater amounts present in all tissues during nighttime than during daytime. Similar daily rhythms appear to occur in the pineal gland and serum of rats and in the serum and urine of humans. It is proposed that these correlated fluctuations in melatonin levels are causally related, elevated pineal content resulting in increased melatonin content of the blood and increased accumulation by the brain. The brain of chickens, especially the hypothalamus, appears to accumulate melatonin and is probably a primary site of action of melatonin.