Effect of corticosteroids on argyrophilic premedullary thymocytes

Abstract

Cells in the premedullar zone of the thymus contain serotonin and catecholamines and show argyrophilicity in the Grimelius test. Their cytoplasm is packed with granules. Glucocorticoids (hydrocortisone) provoke an increase in the number of argyrophilic premedullary cells and in their content of serotonin and catecholamines. Mineralocorticoids induce a prolonged (1-14 days) increase in the number of argyrophilic premedullary cells, enhance their degranulation, and increase their contents of serotonin (2-3 fold) and catecholamines.Key Words: argyrophilic premedullary thymocytes; serotonin; catecholamines; hydrocortisone; deoxycorticdsterone acetate Serotonin and catecholamines (CA) are important neurohumoral factors regulating the function of lymphatic tissues and organs [3,4]. These compounds were found in the aminocytes, specific cells in the thymic premedullary zone [3]. The nature of these cells so far remains unknown. Some researchers believe that aminocytes are APUD ceils [1,6,11], while others claim that they are macrophages/ APUD cells [7].We have found that monoamine-containing cells in the premedullary zone of rat thymus can be stained by the method of Grimelius [10]. This is a conventional technique for the identification of APUD cells. However,. it was never used for the investigation of rat thymus. Thymus is highly sensitive to adrenal hormones, therefore, it was interesting to examine the effects of glucocorticoids (hydrocortisone), which are known to inhibit lymphopoiesis and immunogenesis [2,9], and those of mineralocorticoids (DOCA), which stimulate these processes, on argyrophilic premedullary cells (APC), specifically, on their count, localization, structure, and changes in the serotonin and CA contents. MATERIALS AND METHODSExperiments were performed on 50 outbred male albino rats weighing 160-200 g. Control group included 20 rats. Two series of experiments were carried out. DOCA (10 mg/kg intramuscularly) was injected in the first series (n=25), and hydrocortisone (I0 mg/ kg intramuscularly) was injected in the second series (n=25). The animals were decapitated under light ether anesthesia on days 1, 3, 7, and 14 after administration of these hormones. Part of the thymus was fixed in Bouin's fluid, embedded in paraffin, and 5-g think sections were prepared. The sections were used in the Grimelius test with our modifications (optimization of fixation and exposure times). The size of APC was measured with an ocular micrometer [9].Serotonin and CA were identified on 7-g thick cryostat sections which were treated with 2% glyoxylic acid as described [10]. Microspectrofluorimetry was carried out in a LYuMAM-I1 microscope at an output voltage of 1900 V and magnification 200. The serotonin and CA contents were measured using a probe 0.2 mm in diameter and interference filters (525 nm for serotonin and 480 nm for CA). The intensity of fuorescence was expressed in arbitrary units [5].

Effect of hydrocortisone on amine content in the thymus

“…exhibit anti-inflammatory, antishock, antiallergic, and immunosuppressive activities, which are of importance in tissue and organ transplantation for prevention of their rejection. An important role in these processes is played by the thymus [5][6][7][8].Hydrocortisone exerts an antimitotic effect on cortical lymphocytes of the thymic lobules and induces a dose-dependent involution of the thymus [5]. This is accompanied by a 50% reduction of organ weight and its DNA content, inhibition of lymphocyte differentiation, and intensification of destructive processes.…”