Visceral MCT is uncommon in dogs, and the prognosis is extremely poor. Biological behavior and drug susceptibility of visceral MCT may be different from cutaneous MCT. The lack of specific clinical signs may result in delay of a definitive diagnosis. The rapid progression of clinical signs and difficulty in diagnosis contributes to a short survival time.

Background: Recent data suggest that normal tissue mast cells can express functional receptors for IgG under certain conditions. However, little is known about IgG receptor expression and functional consequences in mast cell neoplasms. Methods: In this study, neoplastic mast cells were obtained from a dog with cutaneous mastocytoma (CM-MC) and from a dog with visceral mastocytoma (VI-MC). Both cell populations were characterized morphologically and functionally. Results: Most cells proliferated constantly in suspension without particular supplements. Doubling times of CM-MC and VI-MC were 52.2 and 27.5 h, respectively. Both cell types were sensitive to formalin fixation, did not contain heparin and were tryptase and chymase positive. Electron microscopy showed fine granules with electron-dense content in both cell populations. The total histamine content of CM-MC and VI-MC was 0.25 and 0.10 pg/cell, respectively. Calcium ionophore A23187 and substance P induced dose-dependent histamine release, whereas compound 48/80 had no effect. Most significantly, both cell types, when sensitized with monomeric dog IgG, released histamine upon stimulation by anti-dog IgG. Conclusions: Dog mastocytoma-derived cells may be useful to study the regulation of neoplastic mast cell growth and differentiation, as well as IgG receptor-mediated activation in neoplastic mast cells. Further research is required to clarify the pathophysiological significance of constitutive expression of IgG receptors in neoplastic (canine) mast cells.

ABSTRACT. The inhibitory effect of glucocorticoids (GCs) on proliferation of canine mast cell tumor (MCT) was studied using two types of MCT cells; JuMC cells and LuMC cells derived from spontaneous canine cutaneous and intestinal MCT, respectively. In in vitro study, growth of JuMC cells was significantly inhibited with more than 1 nM GCs and apoptotic-like cell death was seen, while that of LuMC cells was never inhibited even with 10 µM GCs. Growth rate of masses in nude mice developed by inoculation of JuMC cells was reduced in a dose-dependent manner by administration of GC, while growth inhibition of masses developed by inoculation of LuMC cells was minimal with increasing GC doses. We have established both cutaneous and intestinal types of canine MCT cells from the spontaneous canine cases [18,19]. In this experiment, in vitro and in vivo inhibitory effects of GCs on these tumor cells were investigated and cytoplasmic GC receptors of these cells were measured. MATERIALS AND METHODS MCT cells and culture method:JuMC cell was derived from spontaneous canine cutaneous MCT clinically categorized as intermediately-differentiated MCT, which had been treated with prednisolone (PRD) as one of the chemotherapeutic agents. This cell was maintained in our laboratory by in vivo passage (subcutaneous inoculation) in female nude mice (5 week old, BALB/c-nu/nu Slc, Nippon SLC Inc., Shizuoka, Japan) in every 6 to 10 weeks. This cell was characterized as rat connective tissue type mast cell by morphology and the manner of degranuration by various stimulations [19]. Doubling time of this cell in vitro was over 300 hr. In this study JuMC cells with 20 to 24 passages were used.JuMC cells were obtained by excision of the mass from the nude mouse. The mass was minced in phosphate buffered saline (PBS( )), filtrated through a 53-µm mesh, washed and centrifuged at 1,000 rpm for 5 min. Then it was resuspended and cultured in RPMI-1640 medium (2 mM L-glutamine, 10 U/ml penicillin, 10 µg/ml streptomycin, 50 µM 2-mercaptoethanol) with 10% heat-inactivated fetal bovine serum (FBS) (JRH Biosciences, U.S.A.) at 37°C in humidified air with 5% CO 2 .LuMC cells were derived from spontaneous canine intestinal MCT. The case also had a history of receiving PRD treatment for indistinct eosinophilia. This cell was Mast cell tumor (MCT) accounts for 7 to 21% of all skin tumors and 11 to 27% of all malignant skin tumors in dogs [9,23]. Canine MCT occurs primarily in the dermis and subcutaneous tissues, which is called as cutaneous MCT. Mast cell tumor cells have cytoplasmic granules containing several vasoactive substances like histamine and heparin, which often cause various clinical symptoms such as gastric ulcer and bleeding tendency in the tumor patients. Surgical excision is the choice of treatment for cutaneous MCT, however it often metastasizes to the adjacent and/or distant skin and visceral lymph nodes. In addition, the vasoactive substances of this tumor affect the systemic conditions. Another MCT, called as intestinal MCT, is derived f...

Results of our study indicate that an unknown mast cell-degranulating substances contained in HW extract may degranulate mast cells directly, consequently releasing histamine that may participate in the onset of shock in HW extract-induced shock in dogs.

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