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  • Title: Catecholamine response to maximal exercise following 16 days of simulated microgravity.
    Author: Engelke KA, Convertino VA.
    Journal: Aviat Space Environ Med; 1996 Mar; 67(3):243-7. PubMed ID: 8775402.
    Abstract:
    INTRODUCTION: We tested the hypothesis that the elevated peak heart rate (HR) response to maximal exercise following microgravity exposure is associated with increased plasma levels of catecholamines. METHODS: To do this, plasma norepinephrine (NE) and epinephrine (E) were measured in venous blood samples obtained from 7 subjects before and immediately after graded supine cycle exercise to volitional fatigue performed prior to and at the conclusion of 16 d of 6 degrees head-down tilt (HDT). RESULTS: Resting HR was increased (p = 0.014) following HDT (56 +/- 3 to 63 +/- 2 bpm), but pre-exercise NE concentration (217 +/- 18 pg.ml-1) was not different (p = 0.224) from that measured before HDT (183 +/- 23 pg.ml-1). Peak exercise HR was greater (p = 0.001) after simulated microgravity exposure compared to pre-HDT (181 +/- 3 bpm vs. 172 +/- 4 bpm). NE measured at volitional fatigue was 64% higher (p = 0.004) after HDT compared to that measured prior to HDT (1337 +/- 181 vs. 2191 +/- 189 pg.ml-1 for pre- and post-HDT, respectively). Plasma E concentration at exhaustion was unchanged by microgravity exposure. CONCLUSIONS: Our observation of greater levels of plasma NE and peak exercise HR suggests that sympathetic influences on cardiac chronotropic control may be altered by exposure to prolonged microgravity.
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