Histamine synthesis in intact and disrupted rat mast cells

Altered methylprednisolone pharmacodynamics in healthy subjects with histamine N-methyltransferase C314T genetic polymorphism

This study investigated the potential differences in methylprednisolone pharmacodynamics between healthy subjects with different histamine N-methyltransferase (HNMT) C314T genotypes. Six individuals with C/C genotype and 4 with C/T genotype were administered a single intravenous dose of methylprednisolone 0.6 mg/kg ideal body weight in a randomized 2-period manner. Methylprednisolone plasma concentrations were fitted with a 1-compartment model. Cortisol and whole blood histamine suppression were assessed by indirect response models, with circadian baseline cortisol analyzed by Fourier analysis. The area between the baseline and effect curve and the area under the effect versus time curve suppression ratio were used to characterize plasma histamine suppression. Methylprednisolone pharmacokinetics and plasma and whole blood histamine suppression were similar between the 2 genotype groups. Median nadir of cortisol and the 50% inhibitory concentration for cortisol were significantly higher in subjects with C/T genotype than those with C/C genotype (P=.031 and .033, respectively, Wilcoxon rank sum test). Subjects who are heterozygous for the T314 variant allele thus appeared less sensitive to the suppressive effects of methylprednisolone on cortisol secretion.

Maximal activities of glutaminase, citrate synthase, hexokinase, 6-phosphofructokinase and lactate dehydrogenase in skin of immune-competent Balb/c and immune-deficient Balb/c (nu/nu) mice during wound healing

1. The maximal activities of hexokinase (HK), 6-phosphofructokinase (PFK), lactate dehydrogenase, citrate synthase (CS) and glutaminase (GLU) which provide quantitative and qualitative indices of flux through several important metabolic pathways have been examined in the wounded skin of haired immune competent Balb/c mice and hairless immune deficient Balb/c (nu/nu) mice of various ages during the first ten days of wound healing. 2. The potential for glucose utilization and for aerobic metabolism as suggested by the maximal activities of HK, PFK, CS, were raised in the skin of Balb/c mice of various ages on all post wounding days. Increases in the maximal activity of GLU was observed only in the skin of 6 and 10 weeks old Balb/c mice during wound healing. 3. There was no evidence of a contribution to the maximal activity of GLU by infiltrating cells of the immune system to the wound site in the skin of either haired or hairless mice.

Histidine decarboxylase from rat mast cells. Enhanced recovery in cell-free extracts and isotopic labelling

A procedure for obtaining rat mast-cell histidine decarboxylase in greater than 50% yield in cell-free extracts was developed. The enzyme was found in the supernatant fractions from a 3,500 g and a 105,000 g centrifugation step and was demonstrated to be sensitive to inhibition by alpha-fluoromethylhistidine but not by phenylalanine. Although the enzyme shows a half-life of only 3 h in cell-free extract, the initial high recovery of activity allowed for active-site labelling of the enzyme by [3H]histidine and NaBH4. Labelled protein migrated on non-denaturing polyacrylamide-gradient-gel electrophoresis as a 55,000 Da species.

Evidence for rapid histamine turnover and loss of histamine from immature rat mast cells

Histamine synthetic activity which is high in young mast cells decreases as the cells mature [Beaven et al., J. Pharmac. exp. Ther. 224, 620 (1983)]. In this study we show that a substantial proportion of newly formed histamine in young mast cells leaked to the extracellular environment. The cells acquired the full ability to sequester newly formed histamine once the numbers of intracellular granules and the supply of sulfated mucopolysaccharide material within them had increased. Rat peritoneal mast cells were separated into successive fractions of increasing size and maturity by counter current elutriation. Loss of histamine from fractions of immature cells was demonstrated by a progressive accumulation of histamine in the medium without any decrease in intracellular histamine content. The estimated turnover time of histamine was less than 10 hr. In fractions of more mature cells, the proportion of cellular histamine released into the medium was substantially lower, giving estimated turnover times of 20 hr or longer. Studies with radiolabeled histidine also indicated that little, if any, newly formed histamine was lost from fractions of mature cells. Both release of endogenous histamine and formation of radiolabeled histamine from labeled histidine were inhibited by the histidine decarboxylase inhibitor alpha-fluoromethylhistidine (10 microM). Histamine turnover times were similar in the presence or absence of external histidine, a possible indication that the supply of intracellular histidine was sufficient to maintain normal histamine synthetic activity.

Two biochemically distinct populations of histaminocytes separated by isokinetic sedimentation of dispersed rat gastric cells

Two populations of histaminocytes, with different sedimentation rates (SR), were separated by a computer developed isokinetic gradient using dispersed rat gastric mucosal cells. Histamine content, histidine decarboxylase (HDC) activity and incorporation of radiolabelled histidine metabolites were used to assess the migration of specific cells throughout the gradients. One histaminocyte population, with cells of lower SR, contained high HDC activity and undetectable levels of histamine, whereas the other population, with cells of higher SR, contained lower HDC activity and high concentration of histamine. Both types of histaminocytes incorporated 3H-histidine metabolites. Electron microscopy showed that the fractions containing histaminocytes with lower SR had 3.5 times more endocrine ECL cells than the original population of dispersed fundic cells and lacked A and D cells, whereas the fractions with histaminocytes of higher SR were associated with a 2.7 times higher concentration of A and D cells and with a 7.7 times higher ratio of a variety of partial cells with a distinct mitochondrial morphology. These results are consistent with prior novel information regarding the separation of two populations of rat histaminocytes using different sedimentation techniques.

Inhibitory effect of tritoqualine (TRQ) on histamine release from mast cells

Tritoqualine (TRQ), used clinically as an antiallergic drug, did not inhibit histidine decarboxylase activity (HDC, EC. 4.1.1.22.) partially purified from fetal rats and the enzymes prepared from mastocytoma P-815 cells. However, TRQ inhibited the histamine release from rat peritoneal mast cells induced by compound 48/80 and ATP. TRQ was also effective in inhibiting antigen-induced histamine release in rat mast cells sensitized actively or passively by the homologous anti-DNP-Ascaris antibody. Preincubation of cultured mastocytoma P-815 cells in a medium including TRQ inhibited non-cytotoxically the histamine release of mastocytoma cells induced by compound 48/80, and the effect of TRQ became more marked with lengthening of the culture period in the presence of TRQ. It was concluded from these results that one of the main actions of TRQ as an antiallergic drug was not the inhibitory action on HDC, but might be ascribed to its inhibitory effect on histamine release from mast cells.

Radiation effects on mast cells: secretory ability, histamine release and recovery, and cell number

We studied the effects of irradiation with a single fraction of high-energy electrons, in the absorbed dose range used in radiotherapy, on features related to the rat mesenteric mast-cell (MC) population. Such features were energy dispersive X-ray microanalysis for zinc, light and transmission electron microscopic changes, histamine content, and secretory ability of MCs when exposed to the potent secretagogue 48/80. The observation period was 14 days. Also studied were the effects of radiation on the number and histamine content of free peritoneal MCs. Irradiation-induced decrease in histamine content was delayed for at least two days and the rate of subsequent recovery of mesenteric histamine was approximately 70% below normal. This was corroborated by the findings of necrotic and fragmented mesenteric MCs during the entire experimental period. Fibroblasts and macrophages phagocytosed groups of MC granules as well as individual MC granules. A fraction of the extruded MC granules retained an almost normal appearance. This suggests that they were solubilized unduly slow presumably because the irradiation destroyed the mechanisms and enzymes which normally degrade the heparin-protein granule matrix and its heparin. Moreover, the irradiation suppressed the secretory ability of mesenteric MCs and significantly reduced the number of free peritoneal MCs. The findings indicate that the MC is a remarkably radiosensitive connective-tissue cell.

Histamine content and histidine decarboxylase activity in the spleen of the magnesium-deficient rat: comparison with the skin and peritoneal mast cells

In young rats, some effects of magnesium (Mg) depletion in the diet on histamine content and histidine decarboxylase (HDC) activity in spleen were studied in comparison with those in the skin and peritoneal mast cells. In the case of the young rats fed a Mg-deficient diet (0.001% Mg), the splenic histamine contents increased to levels about 1.3, 2.8 and 23 times as high as those in the rats fed a control diet (0.07% Mg) on the 4th, 6th and 8th day, respectively; histamine contents in the peritoneal mast cells also increased to about 1.2 and 1.8 times the control levels on the 6th and 8th day, respectively; no change was observed in histamine contents in the skin during 8 days of Mg depletion. HDC activities in the spleen of Mg-deficient rats on the 4th, 6th and 8th day increased to levels about 5.5, 15.5 and 35 times as high as the respective control values; the activities in the skin increased to about 37, 7 and 10 times the control values on the 4th, 6th and 8th day, respectively; while in the peritoneal mast cells, the activities increased to about 1.2 and 2.2 times the control values on the 6th and 8th day, respectively. On the 8th day of the Mg deficiency, some studies were made on the effects of histamine releasers on histamine contents in the spleen and peritoneal mast cells. Compound 48/80 (0.5 microgram/ml) or polymyxin B (5 micrograms/ml) induced a release of histamine from the peritoneal mast cells, but not from the spleen cells isolated from the Mg-deficient rat in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)