Local effects of catecholamines on radioiodide clearance in skeletal muscle

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Abstract
The clearance method of detecting changes in tissue blood flow has been explored by injecting sodium radioiodide into the gastrocnemii of anesthetized cats and phenolsulfonphthalein into the deltoids of healthy men. Among several questions investigated were the choice of a labeled substance, ways of injecting it, ways of detecting it in-situ, ways of analyzing and interpreting clearance curves and ways of adapting the technique for measuring local vasomotor reactions to drugs. Significantly more reproducible clearance rates were obtained by isotope injections through a plastic catheter acutely imbedded in muc-cle than by blind intramuscle unjections. By giving mixtures of isotope and drug, localized drug effects were produced without systemic reactions. In terms of clearance ratios, dose-response curves were established for epinephrine, norepinephrine and isoproterenol. The results are interpreted to indicate that isoproterenol caused only vasodilatation, norepinephrine only vasoconstriction and epinephrine one or the other, depending on its concentration. Used with precautions, the clearance method is judged to be uniquely satisfactory for detecting changes in blood flow within the microcirculation of skeletal muscle.