Key result
Noradrenaline maintains stroke volume and boosts cardiac output during pacing in the anaconda heart.
Why the study?
Intrinsic autoregulation of cardiac output limits stroke volume at increased heart rates, and the capacity of noradrenaline to overcome this in the anaconda heart was unexplored.
Does noradrenaline overcome intrinsic autoregulation of cardiac output in the anaconda heart compared to electrical pacing?
Does noradrenaline overcome intrinsic autoregulation of cardiac output in the anaconda heart compared to electrical pacing?
Adrenergic stimulation with noradrenaline overcomes intrinsic autoregulation in the anaconda heart by increasing contractility to maintain stroke volume at high heart rates.
Noradrenaline may preserve output at high rates in anacondas; leaves open relevance to mammalian cardiac autoregulation.
Most vertebrates increase cardiac output during activity by elevating heart rate with relatively stable stroke volume. However, several studies have demonstrated 'intrinsic autoregulation' of cardiac output where artificially increased heart rate is associated with decreased stroke volume, leaving cardiac output unchanged. We explored the capacity of noradrenaline to overcome autoregulation in the anaconda heart. Electrically pacing in situ perfused hearts from the intrinsic heart rate to the maximum attainable resulted in a proportional decrease in stroke volume. However, noradrenaline, which increased heart rate to the same frequency as pacing, maintained stroke volume and thus increased cardiac output. In atrial and ventricular preparations, noradrenaline significantly increased the force of contraction and contraction kinetics. Thus, the increased contractility associated with adrenergic stimulation ameliorates filling limitations at high heart rates. Although heart rate appears the primary regulated variable during activity, this may only be achieved with compensatory amendments in myocardial contractility provided by adrenergic stimulation.
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Joyce et al. (2016) studied this question. Noradrenaline vs. Electrical pacing was evaluated on Cardiac output and stroke volume. Noradrenaline maintained stroke volume and increased cardiac output in the anaconda heart, overcoming the intrinsic autoregulation that decreases stroke volume during electrical pacing.
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