Catecholamines contribute to exertional dyspnoea and to the ventilatory response to exercise in normal humans.
BACKGROUND
Exogenous catecholamine administration in humans stimulates ventilation. The present study was designed to investigate whether increased endogenous catecholamine release influences objective measures of ventilation and subjective measures of breathlessness in normal subjects.


METHODS
Yohimbine, a pre-synaptic alpha 2 adrenoceptor antagonist, or placebo was administered to 10 normal male subjects in a double-blind cross-over fashion. Ventilation and metabolic gas exchange were measured during steady state exercise at 60% of previously determined maximal oxygen consumption. Venous lactate and noradrenaline were measured during exercise. Subjects' sensation of breathlessness and fatigue were recorded using visual analogue scales.


RESULTS
Plasma noradrenaline was higher following yohimbine administration (at 6 min exercise; 4.58 +/- 0.56 nmol.l-1 vs 8.74 +/- 1.53; P < 0.05). Oxygen consumption was unchanged, but ventilation was greater throughout exercise following yohimbine. The sensation of exertion was greater following yohimbine, and at any given level of ventilation, the sensation of exertion was greater.


CONCLUSIONS
Yohimbine administration causes increased noradrenaline release. This is associated with an increased ventilatory response and an increase in the sensation of exertion during steady state exercise. An increase in circulating noradrenaline might be a mechanism for both increased ventilation and pathological conditions of breathlessness such as chronic heart failure.
Clark
A L
AL
Department of Physiology, University of Glasgow, UK.
Galloway
S
S
MacFarlane
N
N
Henderson
E
E
Aitchison
T
T
McMurray
J J
JJ
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000328:Adult; D002395:Catecholamines / Q000502:physiology*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004417:Dyspnea / Q000503:physiopathology*; D006801:Humans; D007773:Lactates / Q000097:blood; D008297:Male; D009638:Norepinephrine / Q000097:blood; D005082:Physical Exertion; D015016:Yohimbine / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D002395:Catecholamines; D007773:Lactates; D015016:Yohimbine; D009638:Norepinephrine