Leukocyte adhesion is a key factor in the pathogenesis of organ injury following a variety of stimuli. In this study we have addressed the role of leukocyte adhesion in hypertensives as a risk factor for organ injury. In the spontaneously hypertensive rat (SHR), the number of circulating leukocytes and their level of activation are significantly increased compared with its normotensive control, the Wistar-Kyoto rat (WKY). We have demonstrated that elevated levels of glucocorticoid in SHR suppress P-selectin-mediated leukocyte-endothelial interaction in the microcirculation. It is possible that the disturbance in leukocyte-endothelial interactions may result in an elevated number of leukocytes in the circulation. The aim of the present study was to investigate the contribution of the adrenal glands to the disturbance in leukocyte behavior in SHR by subjecting the animals to bilateral adrenalectomy and investigating the effect of hydrocortisone. In addition, we have studied by immunohistochemistry the expression of the endothelial adhesion molecule, P-selectin, in response to histamine in the mesenteric venules of normal and adrenalectomized SHR and WKY. The elevated blood pressure, above-normal leukocyte counts, and elevated number of activated neutrophils (nitroblue tetrazolium test) in SHR were blunted after adrenalectomy. The blunted histamine-induced leukocyte-endothelial interaction in the mesenteric venules of SHR was restored after adrenalectomy. Treatment with hydrocortisone significantly attenuated the elevated leukocyte adhesion in the adrenalectomized SHR as well as in WKY. The suppressed P-selectin expression in SHR mesentery was restored after adrenalectomy. In conclusion, the subnormal leukocyte-endothelial interaction in response to an inflammatory stimulation in SHR is abolished after adrenalectomy, suggesting a relationship between the altered leukocyte adhesiveness and the adrenal corticosteroids in hypertensives.