Protective Role of L-arginine on the Suprarenal Gland of Adult Male Albino Rats Subjected to Recurrent Acute Restraint Stress: A Histological and Immunohistochemical Study

Abstract

ABSTRACTBackground: The adrenal glands are small flattened glands closely applied to the upper pole of each kidney. The adrenal cortex consists of three layers that vary primarily in the arrangement of the secretory cells comprising each layer. The gland adapts to various forms of acute and chronic stress. Nitric oxide (NO) is an important endogenous biological modulator, produced by various cell types in different tissues and has diverse physiological actions, including the modulations of vascular resistance, tissue perfusion, blood pressure, and cell proliferation. L-arginine is one of the most metabolically versatile amino acids. In addition to its role in the synthesis of nitric oxide, L-arginine serves as a precursor for the synthesis of polyamines, proline, glutamate, creatine, agmatine and urea.Aim of work: To study the microscopic changes that might occur in the suprarenal gland of adult male albino rats in response to recurrent episodes of acute restraint stress and the role of L-arginine in relieving or blocking these changes.Material and Methods: Thirty adult male Albino rats, 200 - 250 gm body weight each, were used in the present study. The rats were divided into three groups (ten rats/group). Group I: Control group: were not exposed to stress and allowed to move freely. Group II: Rats subjected to recurrent episodes of acute restraint stress: rats were exposed to immobilization stress. The fore limbs and hind limbs of rats were tied separately and then together securing them with adhesive tape thereby immobilizing them for 2 hours daily for 7 days. Group III: Rats treated with L-arginine and subjected to recurrent episodes of acute restraint stress: rats were administered L-arginine by gastric gavage, at a dose of 300 mg/kg/day.At the end of the experiment, the rats were anaesthetized and their adrenals were extracted and processed for light microscopic examination, immunohistochemical studies and quantitative image analysis.Results: Exposure of adult male rats to recurrent episodes of acute restraint stress resulted in diffuse vacuolar degeneration within the three zones of suprarenal cortex, with distortion of cellular cords, widened intercellular spaces and localized hemorrhage in suprarenal medulla. Acute restraint stress also caused statistically highly significant increase in the distribution of iNOS in both cortex and medulla within nerve cells and nerve fibers compared to the control group.On the other hand, concomitant treatment with L-arginine caused an apparent improved cellular architecture with marked decrease in the extent of vacuolar degeneration within all the three zones of suprarenal cortex, but areas of hyperemia within the cortex and congested blood capillaries in the medulla could be observed. Moreover, treatment with L-arginine resulted in statistically highly significant decrease in the distribution of iNOS within suprarenal gland with shift of activity of iNOS from suprarenal medulla to suprarenal cortex compared to the stress group. Still, there were, statistically, highly significant increase in the distribution of iNOS in suprarenal cortex within nerve cells and nerve fibers compared to the control group.Conclusion: The present study revealed that recurrent episodes of acute restraint stress caused microscopic degenerative changes in the suprarenal glands of adult male albino rats with decreased NOS activity within the suprarenal medulla. L-arginine improved such degenerative changes with increased NOS activity within the suprarenal medulla. However, a further study will be planned to correlate the dose and duration of L-arginine administration on the quality of such improvement.