Alpha-adrenergic reactivity of the microcirculation in conscious spontaneously hypertensive rats
Abstract The goal of this study was to determine the functional distribution of α 1 - and α 2 -adrenoceptors in the striated muscle microcirculation. Experiments were performed in intact conscious spontaneously hypertensive rats (SHR) that were provided with a dorsal microcirculatory chamber to allow microvascular diameter measurements. Administration of selective α 1 - and α 2 -agonists, phenylephrine and azepexole, respectively, induced different patterns of microvascular constriction. α 1 -Adrenoceptor stimulation showed a preferential constriction of large arteries and venules. The entire arteriolar microvasculature was sensitive to α 2 -adrenoceptor stimulation, whereas the venular vessels did not respond to azepexole. The selective α 1 - and α 2 -antagonists prazosin and yohimbine showed patterns of vasodilator activity comparable to those of the corresponding agonists. The specificity of the drug-induced effects was verified by comparing their effects with those of graded hemorrhage, a non-pharmacological method for blood pressure lowering. In the range of blood pressure decreases comparable to that obtained by α-adrenoceptor antagonists, graded hemorrhage did not influence microvascular diameters. These results show a differential functional distribution of α 1 - and α 2 -adrenoceptors along the microvascular tree in striated muscle of conscious SHR.
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