HISTAMINE METABOLISM IN THE PREGNANT MOUSE

Multiple sites of L-histidine decarboxylase expression in mouse suggest novel developmental functions for histamine

Histamine mediates many types of physiologic signals in multicellular organisms. To clarify the developmental role of histamine, we have examined the developmental expression of L-histidine decarboxylase (HDC) mRNA and the production of histamine during mouse development. The predominant expression of HDC in mouse development was seen in mast cells. The HDC expression was evident from embryonal day 13 (Ed13) until birth, and the mast cells were seen in most peripheral tissues. Several novel sites with a prominent HDC mRNA expression were revealed. In the brain, the choroid plexus showed HDC expression at Ed14 and the raphe neurons at Ed15. Close to the parturition, at Ed19, the neurons in the tuberomammillary (TM) area and the ventricular neuroepithelia also displayed a clear HDC mRNA expression and histamine immunoreactivity (HA-ir). From Ed14 until birth, the olfactory and nasopharyngeal epithelia showed an intense HDC mRNA expression and HA-ir. In the olfactory epithelia, the olfactory receptor neurons (ORN) were shown to have very prominent histamine immunoreactivity. The bipolar nerve cells in the epithelium extended both to the epithelial surface and into the subepithelial layers to be collected into thick nerve bundles extending caudally toward the olfactory bulbs. Also, in the nasopharynx, an extensive subepithelial network of histamine-immunoreactive nerve fibers were seen. Furthermore, in the peripheral tissues, the degenerating mesonephros (Ed14) and the convoluted tubules in the developing kidneys (Ed15) showed HDC expression, as did the prostate gland (Ed15). In adult mouse brain, the HDC expression resembled the neuronal pattern observed in rat brain. The expression was restricted to the TM area in the ventral hypothalamus, with the main expression in the five TM subgroups called E1-E5. A distinct mouse HDC mRNA expression was also seen in the ependymal wall of the third ventricle, which has not been reported in the rat. The tissue- and cell-specific expression patterns of HDC and histamine presented in this work indicate that histamine could have cell guidance or regulatory roles in development.

Multiple forms of rat stomach histidine decarboxylase may reflect posttranslational activation of the enzyme

Histidine decarboxylase (HDC) catalyzes the formation of histamine, which takes part in a variety of physiological processes including gastric acid secretion, neurotransmission and inflammation. While purified rat HDC is a homodimer of approximately 54 kDa subunits, molecular cloning of mammalian HDC has revealed that HDC mRNA encodes a 74 kDa protein. This discrepancy in molecular mass may be due to a posttranslational processing of the primary translated product of rat HDC mRNA. In the present study we demonstrate that full-length rat HDC expressed in Escherichia coli or in an in vitro transcription/translation system is enzymatically inactive, while expression of a C-terminus truncated HDC (reducing the molecular mass to 54 kDa) gave rise to a protein with high enzyme activity in the same expression systems. COS-7 cells expressing truncated HDC displayed high HDC activity, whereas COS-7 cells expressing full-length HDC displayed low activity. Western blot analysis of fetal rat liver and oxyntic mucosa of gastrin-stimulated rats revealed the presence of both full-length HDC (approximately 73 kDa) and a approximately 53 kDa subunit form in addition to an intermediate form of about 63 kDa. The results are in line with the view that rat HDC may be produced as an enzymatically inactive proenzyme which is processed to give rise to the active enzyme.

Recombinant expression of rat histidine decarboxylase: generation of antibodies useful for western blot analysis

Histidine decarboxylase catalyses the formation of histamine, an important biological messenger. In spite of the essential biological functions exerted by histamine the knowledge about the mechanisms involved in the regulation of histidine decarboxylase is rather limited. This is most likely due to the limited supply of suitable tools, including highly specific antibodies. In the present study we describe the production and characterisation of specific antisera against rat histidine decarboxylase using recombinant protein synthesised in a bacterial expression system. The antisera were shown to effectively immunoprecipitate histidine decarboxylase activity in extracts of fetal rat liver as well as to detect the histidine decarboxylase protein by Western blot analysis of COS-7 cells expressing recombinant rat histidine decarboxylase. The results demonstrate the successful production of highly specific antisera to histidine decarboxylase which may become valuable tools in future studies of the structure and function of this enzyme.

Distribution of histamine in the rat kidney during pregnancy and development

An antiserum against conjugated histamine and two oligonucleotide probes that detect the mRNA encoding L-histidine decarboxylase (HDC) involved in histamine synthesis were used to study the appearance of histamine and its location in the kidneys of fetal, newborn and young postnatal rats and in the kidneys of pregnant rats. On embryonic days 16 and 18 (E16 and E18), some HA-immunoreactive (HA-ir) cells were found within the largest S-shaped bodies. Histamine was found to appear rapidly between the 18th and 20th embryonic days in the convoluted tubules of the kidneys. On postnatal day 0 (P0), the distal convoluted tubules and collecting ducts exhibited bright fluorescence, the intensity of which decreased quickly so that it was faint on day P4 and absent at later stages. In kidneys of pregnant rats HA-ir was found in the epithelium of both the Bowman's capsule, collecting ducts and in a few cells within the tubules. Nonuniform HA-ir was also detected within glomeruli. No evidence for the presence of L-histidine decarboxylase mRNA in kidneys of fetuses or pregnant rats was seen. It is concluded that distinct structures in the developing rat kidney contain histamine during a period around birth from day E20 to day P4. In the pregnant rat, the epithelium that is in direct contact with the urine flow is immunoreactive for histamine from day 16 to 20 of pregnancy. The results suggest that histamine is not synthesized locally in the kidneys but rather originates from other tissues.

Autoradiography of 3H-alpha-fluoromethyl histidine in mice: correlation with the kidney histidine decarboxylase activity

Tritium-alpha-fluoromethyl histidine (3H-alpha-FMH), designed as a kcat-inhibitor of mammalian histidine decarboxylase (EC 4.1.1.22), was administered intravenously in male and pregnant female mice of the NMRI strain and the distribution of tritium in the body recorded by whole-body and microautoradiography. The results showed penetration of radioactivity into most tissues within 5 min. after the injection. After 4 hrs the highest levels of radioactivity were present in the intestinal content and in the kidneys. In the pregnant animal there was also a high labelling of the foetal tissues. When whole-body sections were washed in TCA prior to the autoradiographic exposure to retain only protein-bound radioactivity, a distinct labelling pattern was seen in the kidneys of the pregnant female mice but not in those of the male mice. Microautoradiography of the kidneys showed that the cells involved were located within the proximal convoluted tubuli. In several mouse strains, including the NMRI, the activity of kidney histidine decarboxylase is low in the males but high in females during a transient period of pregnancy. Incorporation of tritium into kidney protein after treatment with 3H-alpha-FMH, was correlated to a loss in histidine decarboxylase activity. The isotopic labelling was confined mainly to a component which cofractionated with histidine decarboxylase in polyacrylamide gel electrophoresis (PAGE) under non-denaturing conditions. Our data indicate that the cells described above represent the location of kidney histidine decarboxylase.

Effects of alpha-fluoromethylhistidine on increase in histidine decarboxylase activity of maternal mouse kidney observed during late pregnancy and evidence for its non-mast cell origin by using estrogen and W/WV mice

The increase of histidine decarboxylase (HDC) activity during late pregnancy in the whole bodies of fetal mice and the kidneys of their mothers were almost completely inhibited by i.p. administration of 25 mg/kg of alpha-fluoromethylhistidine (alpha-FMH), a suicide inhibitor of HDC, starting on day 13 of pregnancy. The increase of HDC in fetal mice was previously shown to be in mast cells [T. Watanabe et al., Proc. Natl. Acad. Sci. U.S.A. 78, 4209-4212 (1981)]. The increase of HDC in maternal kidneys was examined by using estrogen and W/WV mice, which were devoid of mast cells and infertile. Treatment of castrated mice with 17-beta-estradiol increased the HDC activity of the kidney, and this increase was antagonized by concomitant treatment with clomiphene, an antiestrogen, confirming that the increase is mediated through an estrogen receptor. HDC activity in the kidney of W/WV mice was also increased by estradiol treatment, indicating that HDC activity was associated with non-mast cells.

Absence of increase of histidine decarboxylase activity in mast cell-deficient W/W mouse embryos before parturition

The histidine decarboxylase (L-histidine carboxylase, EC 4.1.1.22) activity of whole W/W mouse embryos, which are devoid of mast cells, remained very low and did not show the rapid increase before birth (17-20 days of gestation) seen in wild-type +/+ embryos. During the same period, the histamine content also remained very low and no mast cells were detected in the W/W embryos, in the contrast to the large increase in both histamine content and number of mast cells in wild-type embryos. These findings imply that the histamine in embryos is largely derived from mast cells. In +/+ mice, histidine decarboxylase activity decreased rapidly soon after birth without concomitant decrease in histamine content or number of mast cells, suggesting that the enzyme activity in mast cells is regulated by some unknown mechanism.

Alterations in the activities of ornithine and histidine decarboxylases provoked by testosterone in mice

1. The urinary excretion of putrescine has been determined in female mice before and during repeated injections of testosterone.2. Testosterone administration effected a striking increase in the excretion of free putrescine.3. Ornithine decarboxylase (L-ornithine carboxy-lyase; E.C. 4.1.1.17) and histidine decarboxylase (L-histidine carboxy-lyase; E.C. 4.1.1.22) activities of mouse kidney and liver were examined. In the kidney, following testosterone administration, ornithine decarboxylase activity was found to be substantially elevated, whereas that of histidine decarboxylase was depressed. In the liver, by contrast, the activity levels of these enzymes were not significantly altered by testosterone treatment.4. The possibility of a functional interrelation between putrescine and histamine, via the two enzyme activities investigated, is discussed.

Alterations of histamine metabolism after injections of sex hormones in mice

1. Urinary excretion of histamine in female mice was determined after the injection of oestradiol, progesterone or testosterone. Histamine excretion was increased by oestradiol but was not affected by progesterone. Testosterone administration, by contrast, effected a striking reduction of histamine excretion.2. After injection of oestradiol, the kidney histamine forming capacity was greatly elevated, but in the other tissues investigated no significant change occurred.3. Testosterone administered in vivo but not in vitro reduced the histidine decarboxylase activity of female mouse kidney to a small fraction of normal.4. On thin-layer chromatography, after extraction and coupling of the amines to 2,4-dinitrofluorobenzene, the amount of histamine and to a lesser extent, methyl histamine in urine was reduced after testosterone administration. On the chromatogram of urine from untreated mice, an unidentified yellow spot appeared and the quantity of this spot was increased during testosterone treatment.

Retardation of protein synthesis in rat foetal liver on inhibiting rate of histamine formation

1. The rate of protein synthesis, as gauged by the incorporation of [(14)C]leucine, has been determined in vitro in foetal and 5-day-old rat liver, tissues with respectively high and low histidine decarboxylase activity.2. Incorporation of [(14)C]leucine was considerably faster in foetal liver than in liver of the young.3. Following inhibition of histamine formation by alpha-methyl histidine, a specific inhibitor of histidine decarboxylase, the rate of incorporation of [(14)C]leucine was substantially diminished in foetal but not in liver of the young.4. The retarded incorporation of [(14)C]leucine consequent on inhibition of endogenous histamine formation could not be restored by extracellular histamine, i.e. by adding histamine to foetal liver tissue.5. On complete inhibition of protein synthesis by puromycin in foetal and 5-day-old rat liver the rate of histamine formation was not affected.6. The present observations support the view of endogenous histamine formation, ;nascent histamine', as an essential part of the metabolic machinery in some rapidly growing tissues.

Accelerated mobilization and formation of histamine in the gastric mucosa evoked by vagal excitation

1. The changes in the rate of histamine formation and in the histamine content of the parietal cell containing region of the gastric mucosa have been studied in rats under the influence of agents which evoke or abolish vagal excitation.2. The hypoglycaemia producing agents, insulin and 2-deoxyglucose (2-DG), raised the mucosal histamine-forming capacity (HFC) in a way similar to that previously observed on re-feeding, gastrin injection, and distension of the stomach wall.3. In cats, insulin injection elicited an elevation of mucosal HFC similar to the corresponding effect of insulin in rats.4. Hoechst 9980, which inhibits post-ganglionic cholinergic transmission, counteracted the elevation of mucosal HFC following vagal excitation, but did not inhibit changes produced by gastrin, thus indicating the absence of a cholinergic intermediary link between gastrin and changes in mucosal histamine.5. It is emphasized that although re-feeding, vagus excitation, gastrin and distension all produce similar changes in mucosal histamine, the clarification of the precise role of histamine as a natural stimulant for the parietal cells may require a fresh kind of approach.

Gastric secretion during pregnancy and lactation in the rat

1. Gastric acid secretion has been studied in the rat before, during and after pregnancy using different types of stomach preparation. During the same periods the histamine-forming capacity (HFC) has been determined in gastric mucosa and mammary gland.2. In rats with a whole stomach fistula interdigestive acid secretion is increased during pregnancy and lactation.3. In rats with a denervated chronic pouch secretory response to stimulation with gastrin and histamine is augmented during pregnancy and lactation.4. The histamine forming capacity (HFC) of the gastric mucosa is increased 2-3 times during the last days of pregnancy and also during lactation.5. The HFC of the mammary gland is increased 2-3 times during lactation as compared with the fully developed gland in pregnancy.

Histidine decarboxylase in experimental tumours

Histidine decarboxylase activity has been demonstrated in some experimental tumours by direct enzyme assay. The kinetic properties of semi-purified preparations of the histamine-forming enzyme from Rous rat sarcoma and Walker rat mammary carcinoma were similar to those of the “specific” histidine decarboxylase of the foetal rat. Transplants from a malignant hamster melanoma had no “specific” histidine decarboxylase but high dopa decarboxylase activity. The lack of histidine decarboxylase in this tumour seems to indicate that a high histamine-forming capacity is not indispensable for tumour growth.