Ultradian rhythm in rat hypothalamic dopamine levels.

Rats housed under identical conditions were sacrificed with 15-min intervals between 9.30 a.m. and 2.15 p.m. for determinations of DA and NA concentrations in whole hypothalami. The NA levels showed no obvious fluctuation with time, whereas the DAS levels showed an apparent periodicity with a cycle length of approximately 2 hours and with peaks around 11.30 a.m. and 1.45 p.m. A possible relation between this DA rhythm and the secretion of pituitary hormones is discussed.