Enzymatic histamine catabolism in vertebrate ontogenesis. A comparative study

Area of Science:

• Biochemistry
• Developmental Biology
• Pharmacology

Background:

• Histamine plays crucial roles in physiological processes.
• Understanding histamine metabolism is vital for developmental studies.
• Enzymatic control of histamine levels is not fully elucidated in embryonic tissues.

Purpose of the Study:

• To investigate the enzymatic activities of histamine synthesis and degradation in developing guinea pig and chick embryos.
• To compare the relative activities of histamine-N-methyltransferase (HMT) and diamine oxidase (DAO) with histidine decarboxylase (HDC).
• To correlate enzyme activities with histamine levels in embryonic tissues.

Main Methods:

• Enzyme assays were performed on liver and small intestine tissues from developing guinea pig and chick embryos.
• Histidine decarboxylase (HDC) activity was measured to assess histamine synthesis.
• Histamine-N-methyltransferase (HMT) and diamine oxidase (DAO) activities were measured to assess histamine degradation.
• Histamine concentrations were quantified in tissue samples.

Main Results:

• Histidine decarboxylase (HDC) activity increased with age but was significantly lower (2-3 orders of magnitude) than degradation enzyme activities.
• Diamine oxidase (DAO) activity was consistently 10-100 fold higher than histamine-N-methyltransferase (HMT) activity across all studied ages.
• Histamine levels were generally higher in developing guinea pig tissues compared to chick embryos.
• Intestinal histamine concentration in laying hens was notably higher than in adult guinea pigs.

Conclusions:

• Oxidative deamination by DAO appears to be the primary mechanism controlling tissue histamine levels during embryonic development.
• The balance between histamine synthesis and degradation shifts towards degradation, with DAO playing a dominant role.
• Species and tissue-specific differences in histamine levels and enzyme activities exist during development.