Hypothalamic 24-hour rhythms in histamine, histidine, decarboxylase and histamine-N-methyltransferase

Endocrinology. 1975 Apr;96(4):941-5. doi: 10.1210/endo-96-4-941.


Twenty-four hour rhythms of histamine (H), its biosynthetic enzyme, L-histidine decarboxylase (EC, HD) and its inactivation enzyme, histamine N-methyltransferase (EC, HMT) were assayed in the 63-day-old male rat hypothalamus using a modified single isotopeenzyme microassay. H was found to have a 24-h rhythm with a maximum concentration at 11:00 h (lights on 10:00-22:00 h) and a minimum at 23:00 h. In vitro HD and HMT activities were also found to have 24-h rhythms with peak activites in both occurring at 04:00 h. HMT also had a broad secondary peak throughout the day, whereas HD activity during the day was dominated by a mid-light trough at 16:00 h. These rhythms are considered significant for evaluation of the control and physiological role of histamine in the mammalian hypothalamus.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Carboxy-Lyases / metabolism*
  • Circadian Rhythm*
  • Histamine / metabolism
  • Histidine
  • Histocytochemistry
  • Hypothalamus / enzymology*
  • Light
  • Male
  • Methyltransferases / metabolism*
  • Rats


  • Histidine
  • Histamine
  • Methyltransferases
  • Carboxy-Lyases