Effect of adrenergic agonists on phosphoinositide breakdown in rat skeletal muscle preparations

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Abstract
Adrenergic regulation of phosphoinositide breakdown in rat skeletal muscle was investigated in 30‐min incubations with 10 mM LiCl. In rat hemidiaphragms, prelabelled with D‐myo‐[2‐3H]inositol, addition of α‐agonists (epinephrine, norepinephrine, phenylephrine) induced a 5‐8‐fold increase of [3H]inositol monophosphate accumulation. This could be prevented by inclusion of α‐antagonists (phentolamine, prazosin). β‐Agonists and/or β‐antagonists had no effect. Similar experiments with isolated flexor digitorum brevis muscle fibers yielded confirmatory results. Functional integrity of β‐receptor mediated processes was suggested by the β‐agonist‐induced increase of glucose 6‐phosphate in hemidiaphragms and cAMP in fiber preparations. The results indicate that phosphoinositide breakdown in differentiated rat skeletal muscle is, at least in part, under α‐adrenergic control.