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The role of histamine in vitro during hematopoiesis has been described by several authors. This work was carried out to determine whether histamine could be available in hemopoietic organs by measuring the HDC activity and the histamine content of developing hemopoietic tissues from C 57 BL/6 mice during fetal life (liver from the 12th day of gestation, spleen from the 14th day, and bone-marrow from the 17th day) and postnatal life. High values were found in the liver, the bone marrow, and especially the spleen between the 17th and the 19th days of gestation. A rapid fall in these values was seen near birth. Interestingly, electron microscopy analysis of day 18 fetal spleen cells, provides evidence for a basophil-rich cell population (25%).

Looked as a specific inhibitor of histidin-decarboxylase, tritoqualine has been injected subcutaneously to Wistar rats immediately after partial hepatectomy and, then, once in 24 hours until 72 hours. It has thus provoked : an unexpected, but transient rise (reaching its apex 3 hours after the operation) of the hepatic and blood histamin concentrations ; then, the expected decrease (more durable and greatest at 48 hours) of the same concentrations. Therefore, an effect of tritoqualine on the liver regeneration might be expected, whether histamin plays some part in this phenomenon.

A quick colorimetric procedure for detection of histidine decarboxylase (HDC) in cultures of Klebsiella, Enterobacter and Serratia is described. Only E. aerogenes could decarboxylate histidine (production of histamine). The interest of HDC test for differentiation of E. aerogenes from K. pneumoniae (especially urease negative strains) is discussed.

Hybridomas secreting monoclonal antibodies directed against Rat gastric L-histidine decarboxylase (H.D.) have been obtained from a partially purified preparation and screened by immunoprecipitation of the enzyme activity. They cross react with Rat brain H.D., indicating at least that these two enzymes share common antigenic determinants.

A specific histidine decarboxylase from rat gastric mucosa has been obtained at high purity and good yield (purification about 600-fold). The purification procedure included double (NH4)2SO4 fractionation, ion-exchange chromatography, preparative isoelectric focusing in a granulated gel and gel filtration. Only the specific histidine enzyme was obtained by that procedure; DOPA decarboxylase, a non-specific enzyme, was absent in our final preparation. Each step of the purification was visualized by polyacrylamide gel electrophoresis and analytical isoelectric focusing. The purified enzyme was apparently homogenous by criteria of electrophoresis and gel filtration and has a molecular weight of 94 000. Several protein bands appeared after isoelectric focusing and the enzyme activity was localized in 3 distinct peaks. The gastric enzyme consists of 3 active forms which could be distinguished by their isoelectric points: 5.4, 5.75 and 6. Moleculare weights estimated by SDS polyacrylamide gel electrophoresis were 97 000, 93 000 and 90 000, and no subunits were observed. Pyridoxal phosphate was required as a coenzyme and resolution of the holoenzyme agreed with a portion of the coenzyme tightly bound to the apoenzyme. The purified enzyme was stable at low ionic strength, near neutral pH; concentrated reducing agents inhibit the enzyme.

The role of histamine in hypersensitivity reactions justifies the use of antagonistic medication. The symptomatic action of the antihistamines has led many workers to forget the role of the drug in reducing histamine (hypohistaminic), in which interest should remain as a curative and mainly preventive medication. The main indications for the action of this drug at the level of physiopathological mechanism involved are: disorders that implicate the production of endogenous histamine, prevention of histamine release, reduction of over-production of histamine by regulation of receptor saturation, symptomatic action without side effects.