Role of glucocorticoids in local regulation of blood flow

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Abstract
Experiments were designed to evaluate further the proposed role of intrinsic histamine and glucocorticoids in the local regulation of blood flow. This was done by means of direct microscopic observation of the rat mesocecal microcirculation. Various pure synthetic glucocorticoids even when given in large doses did not constrict any of the muscular components of the capillary bed. These steroids, however, enhanced vascular reactivity to various constrictors while suppressing histamine and bradykinin-induced vasodilation. Furthermore these steroids were able to restore microvascular responsiveness to constrictor materials whose peripheral actions had been suppressed or absent in animals depleted of their mast cells. Fourteen-day salt-maintained, adren-alectomized animals showed enhanced constrictor responses to locally applied catecholamines and serotonin even though endogenous histamine levels are known to be elevated in such animals. Such findings may not be compatible with the hypothesis of microcirculatory regulation through the synthesis of intrinsic histamine. Overall, our findings reinforce the hypothesis that glucocorticoids may function as regulators of local blood flow via their modulation of vascular smooth muscle responsiveness to other endogenous humoral agents.