Non-mast cell histamine levels in rat tissues after histidine loading

Area of Science:

• Pharmacology
• Biochemistry
• Physiology

Background:

• Histamine is a crucial biogenic amine involved in various physiological processes.
• Non-mast cell histamine synthesis and regulation remain incompletely understood.
• Histidine, the precursor to histamine, plays a key role in its synthesis.

Purpose of the Study:

• To investigate the effect of L-histidine administration on histamine levels in non-mast cell tissues in rats.
• To explore the relationship between histidine loading, histidine decarboxylase activity, and serum histamine concentrations.
• To determine the regulatory mechanisms of non-mast cell histamine concentration.

Main Methods:

• Intraperitoneal administration of L-histidine to rats.
• Induction of histamine depletion using polymyxin B or compound 48/80, and anaphylaxis.
• Measurement of histidine and histamine levels in stomach, lungs, and liver tissues.
• Assay of histidine decarboxylase activity in gastric tissues.
• Quantification of serum histamine concentrations.

Main Results:

• L-histidine administration (500 and 1000 mg/kg) increased histidine levels but did not affect histamine concentrations in the stomach, lungs, or liver.
• Histamine levels in lungs and liver were reduced by polymyxin B or 48/80 treatments, and histidine administration did not restore these levels.
• Histidine loading significantly increased histidine decarboxylase activity in the glandular stomach and elevated serum histamine levels.
• Low stomach histamine levels in treated rats remained unchanged despite excess histidine.

Conclusions:

• Increased serum histamine levels following histidine loading are likely due to enhanced histidine decarboxylase activity and rapid histamine elimination into the blood.
• Histamine flux, rather than solely histamine formation, may be the primary regulator of non-mast cell histamine concentration, particularly in stomach tissue.
• These findings provide insights into the dynamic regulation of histamine metabolism in non-mast cell compartments.