The pathophysiological effects of congestive heart failure and physiological effects of exercise training on skeletal muscle may be mediated in part by modulation of β-adrenergic receptor density. To shed light on the physiological role of skeletal muscle β-receptors, their density and distribution were characterized in muscle fibers and resistance arterioles of whole tissue slices of three rat inndquarter muscles differing markedly in fiber type composition and capacities for oxidative metabolism and vasodilatation. Binding isotherms and quantitative light microscopic autoradiograpinc localization of receptors were performed by incubating tissue slices in selected concentrations of [125I]cyanopindolol with and without 10-5M T-propranolol. Muscle fiber types were delineated in adjacent sections by histochemical staining of myofibrillar ATPase activity at pH 4.5-4.55. The total tissue content of receptors (Bmaxwas nearly threefold greater in the soleus, a muscle consisting almost entirely of slow-twitch (type I) fibers than in superficial white vastus lateralis, a muscle composed of >95percent; fast-twitch (type IIb) fibers. Bmaxwas intermediate in gastrocnemius, a mixed fiber muscle (all differences p<0.01). Receptor affinity for radioligand was higher in the white vastus than in the mixed fiber and slow-twitch muscles (Kd= 3.5±0.4 pM for white vastus versus 6.8±0.8 and 6.4±1.1 pM in gastrocnemius and soleus, respectively; both p<0.01 versus white vastus). Disparities in Bmaxamong muscles were due entirely to differences in receptor densities of skeletal muscle cells as shown autoradiographically. Furthermore, variations in Bmaxof the three skeletal muscles were directly related to percentage of type I fibers (r=0.99; p<0.001), winch had a β-receptor density that was approximately 4.5-fold greater than in superficially located type IIb fibers, 3.2-fold greater than in intermediate depth type IIb fibers, and 2.0-fold greater than in type IIa fibers. In contrast, grain densities of resistance arterioles were similar regardless of surrounding skeletal muscle fiber type composition. However, resistance arterioles were 2.5- and 6.1-fold more numerous in the slow-twitch soleus than in the gastrocnemius and superficial white vastus, respectively (all differences p<0.01). We conclude that β-receptor density of rat hindquarter skeletal muscles is directly proportional to percentage of slow-twitch fibers, while receptor affinity for antagonist is ingher in fast-twitch than in slow-twitch or mixed fiber muscles, β-receptor density of resistance arterioles is similar among types of muscles but these vessels are far more numerous in the slow-twitch soleus. Such differences reflect the diverse metabolic and physiological characteristics of the rat hindquarter musculature.