Enhanced -adrenergic mediated cardiovascular responses in en durance athletes. Hopkins, Michael G., Robert J. Spina, Ali A. Ehsani. Section of Applied Physiology, and Cardiovascular Division, Washington University School of Medicine, St. Louis, MO
APStracts 2:0451A, 1995.
To determine whether the adaptive increase in left ventricular systolic function in the trained state is mediated by enhanced responses to -adrenergic stimulation, we studied eight male endurance athletes (age 27 +/- 1.8 yrs, O2max: 60 +/- 0.9 ml/kg/min; mean +/- SE) and eight sedentary men (age: 27 +/- 1.4 yrs, O2max: 43.1 +/- 1.7 ml/kg/min). Left ventricular function was evaluated with 2-D echocardiography and pulsed Doppler transmitral flow velocity profile in the basal state, following parasympathetic blockade by atropine, and during infusion of Dobutamine. Cardiac output () and stroke volume (SV), determined with the acetylene rebreathing technique, during maximal exercise were significantly higher in the endurance athletes than in the sedentary men (max: 28.9 +/- 1.7 vs 23 +/- 1.23 l/min, p = 0.019, and SVmax: 162 +/- 12 vs 125 +/- 7 ml/min, p = 0.029). Endurance athletes showed 1) physiological volume-overload left ventricular hypertrophy, and 2) greater enhancements of left ventricular systolic function and filling dynamics in response to Dobutamine than did the sedentary men as reflected in a) a steeper slope of the fractional shortening (FS)-end systolic wall stress ([sigma]es) relationship (FS-[sigma]es: - 0.986 +/- 0.16 vs -0.508 +/- 0.054 p = 0.014, athletes vs controls), and (b) a higher early -to-late transmitral diastolic Doppler velocity ratio (2.14 +/- 0.14 vs 1.74 +/- 0.12, p = 0.016) at a comparable heart rate. Although endurance athletes had a significantly greater inotropic response to Dobutamine, they demonstrated a markedly attenuated chronotropic response to 1-adrenergic stimulation compared to sedentary subjects. Our findings suggest that even with a blunted chronotropic response, endurance trained young men show an augmented inotropic response to a 1-adrenergic agonist which, along with physiologic volume over-load hypertrophy and increased diastolic filling, can contribute to a larger stroke volume during maximal exercise in the trained state. 

Received 21 April 1995; accepted in final form 19 September 1995.
APS Manuscript Number A437-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95