Continuous in vivo treatment with catecholamines suppresses in vitro reactivity of rat peripheral blood T-lymphocytes via α-mediated mechanisms

A 20 h continuous treatment of rats with catecholamines, using subcutaneously implantable retard tables, had either no (adrenaline, isoproterenol, midodrine) or a slight (noradrenaline) suppressive effect on the in vitro responsiveness of peripheral blood T-lymphocytes. A marked suppression of the mitogen response ensued when adrenaline, noradrenaline or midodrine, but not isoproterenol, was applied together with the β-receptor blocker propranolol, whereas the combination with the α-receptor blocker phentolamine had no effect. The mitogen response of splenic lymphocytes was not affected by any of these treatments. This α-mediated adrenergic suppression of peripheral blood T-cells was not correlated with general metabolic alterations, shifts in white blood cell counts or CD4 +/CD8 + subsets, or with elevated glucocorticoid levels. The data suggest that to consistently influence the reactivity of rat peripheral blood lymphocytes by chronic adrenergic stimuli in vivo requires both high catecholamine levels and a bias towards α-adrenergic receptivity.