Effects of Insulin and Catecholamines on Inotropy and Oxygen Uptake
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The purpose of this study is to identify the best perfusate after blood for maintaining skeletal muscle inotropy, muscle peak oxygen consumption (peak VO2), and oxygen consumption at rest (resting VO2) in in situ isolated canine gastrocnemius-plantaris muscle. Rejuvenated red cells suspended in perfusate at hematocrit 30% and 45%, perfusate contained insulin (100 µU·ml−1), adrenalin (0.3 and 3 ng·ml−1), and noradrenaline (3 ng·ml−1). Insulin significantly augmented resting VO2 and contracting muscle peak VO2, and developed isometric twitch tension at 4 Hz, compared with control. Insulin-induced increase in resting muscle VO2 was abrogated by catecholamines. In addition to insulin and catecholamines, the developed twitch tension increased significantly by 178% with the accompanied increase in flow rate. O2 cost (peak VO2 / tension) significantly decreased by 52%. The developed tension did not correlate with O2 delivery but with flow rate and peak VO2 of contracting muscle. We successfully identified the characteristics of the best perfusate after blood. Our results suggest that the positive inotropy by insulin and catecholamines is attributed partly to an O2 delivery-independent increase in flow to contracting muscle and redistribution of flow within the contracting muscle, which suffered from low perfusion by perfusate containing rejuvenated red cells.
KeywordsGastrocnemius Muscle Positive Inotropic Effect Contracting Muscle Contraction Time Fatigue Rate
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