Although the tissue mast cell has been studied intensively by light microscopy during the past seventy-five years, little is known concerning the details of its structure. Such knowledge is of special interest, since the mast cell appears to contain heparin (1) and histamine (2), compounds of considerable physiological interest. The present paper is concerned with the results of electron microscopy of sectioned mast cells obtained from the peritoneal fluid of animals either untreated, irradiated, or injected with toluidine blue, protamine sulfate, or stilbamidine. Protamine and toluidine blue bind heparin (3), stilbamidine liberates histamine (2), and x-irradiation produces marked changes in the cytology of the mast cell (4). Materials and MelhodsTo obtain normal mast cells, adult male Syrian hamsters (100 gin.) and Sprague-Dawley rats (200 gin.) were injected intraperitoneaUy with 3 and S cc., respectively, of buffered Tyrode's solution. After 10 minutes the animals were sacrificed by ether anaesthesia or by cervical fracture. Immediately thereafter the peritoneal fluid was withdrawn and transferred to a tube conta~nlng an equal volume of OsO~ (2 or 4 per cent in buffered Tyrede's solution). Ten minutes later the cells were isolated by centrlfugation. The supernatant was discarded and the cells were resuspended in a wash of Tyrode's solution for 10 minutes. The same procedure was used for dehydration of the cells with alcohol (50, 75, 95, and 100 per cent ethyl alcohol) and for infiltration with plastic (70 per cent butyl methacrylate-30 per cent ethyl methacrylate containing 0.5 per cent 2,4-diehlorobenzoy] peroxide as catalyst). Finally the cells were suspended in a small m o u n t of plastic and tmnderred to gelatin capsules. Polymeri~tion was accomplished under ultraviolet irradiation or in an oven at 50°C. Sections were cut on an lmtemational-Minot thin sectioning microtome and observed with the RCA EMU-2A electron microscope.In the course of this work other technics and tissues were explored in attempts to achieve better preparations. Fixation by means of 10 per cent formalin, alcoholformalin, chromic oxide and formalin, osmium tetroxide and potassium dichromate, 4 per cent basic lead acetate, absolute alcohol, and freeze-drying gave results that were usually inferior and never better that those obtained with osmium tetroxide
Finding( 1-3) of changes in number and cytology of tissue mast cells after administration of adrenworticotropic hormone ( lAICTH) and cortisone has suggested that the pituitaryadrenal system exerts a controlling influence on the mast cell. The present paper describes attempts to explore this possibility further.Methods. Examinations of the behavior of tissue mast cell were made in whole mounts (4) of skin and mesentery of young adult, male Sprague-Dawley rats (20'0 g) at various times after adrenlalectomy, hypophysectomy and treatment with X-irradiation, ACTH, adrenal cortical extract, desoxycorticosterone acetate or cortisone. Adrenalectomized rats and their controls were allowed to drink only 1 a/o NaCl solution; hypophysectomized anim l s and their controls were confined to 20% sucrose solution. In addistion to regular diet of Rockland checkers, the hypophysectomid animals had access to oranges, lettuce, bread, and ground meat. Tissues were fixed in alcohol and stained with toluidine blue, as previously described (4). Tissues from intact or mock-operated controls were simultaneously studied. The radiation factors were 250 kv, 15 ma, 0.5 mm Cu and 3.0 mm Bakelite filters, 26.7 cm target distance, 1.5 mm Cu half-value layer and 215-225 r per minute. Mast cell counts were made on stained tissues, separate note taken of normal cells and atypical cells, i.e. degenerated cells with vacuoles and clumped granules(4,S). On a single slide from each animal, thirty contiguous fields, 0.0676 mm2 each, were counted at a magnification factor of 264.The only change in mast cells which could be identified with certainty was an increase in number of cells showing vacuolation and conglomeration of cytoplasmic granules. The allteratims were similar to those previously found by us in irradiated animals (4) and by others in aged tissue cultures of Results.*With assistance of Sally T. Hartig.mast cells ( 6) , edematous tissue and stimulated urticaria pigmentosa lesions ( 7), and after treatment with toluidine blue( 8), nitrogen mustard (9), ACTH ( 1 ) and cortisone ( 1,2 ) .In none of the present studies were there statistically significant changes in total mast cell number.Adrenalectomy was without influence upun the mast cell or upon its response to X-irradiation. Groups of 3 to 101 rats were examined at 2, 7, 14, 21, 28 and 316 days after a d r e n a b 'tomy. Number of cells countedr2.028 mm2 of skin varied between 404 land 6 10 in adrenalectomized and 458 and 608 in mock-operated animals. The per cent of abnormal cells was approximately the same in both groups of animals (.2 to 1.2% of all cells). At 2 weeks after adrenalectomy or mock-operation rats were subjected to single, total-body exposures to 600 r. Groups of 3 rats were examined at various intervals after irradiation. Number of cells counted/2.028 mm2 of skin varied between 328 and 676 in adrenalectomized, irradiated land 339 and 8316 in mock-operated, irradiated rats. The per cent of abnormal cells was 10, 33.3,33.6, 7.0, 3.4 and 2.9 in the adrenalectomized and 10.1, 42...
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