Increase in plasma noradrenaline concentration after the administration of phentolamine in the patients with “latent” left-sided heart failure

We measured increments of peripheral venous pressure induced by dynamic leg exercise (ΔVP) in 10 healthy subjects (Group C) and 70 patients with heart diseases which primarily affect the left-side of the heart. None of the subjects showed apparent symptoms of left- or right-sided heart failure. The patients were divided into 2 groups on the basis of ΔVP, namely, Group N (ΔVP<35 mmH₂O, n=30, normal reaction) and Group H (ΔVP≥35 mmH₂O, n=40, abnormal reaction). We measured the increments of plasma concentrations of noradrenaline (ΔNAPH) and adrenaline (ΔAPH) with infusion of phentolamine (PH). Parallel studies with nitroglycerin and prozosin supplied strong evidence that ΔNAPH was brought about mainly by the blockade of α₂-receptors at the sympathetic nerve terminals. Thus, we estimated the degree of sympathetic nerve activity from the central nervous system by opening using PH the negative feed-back loop for noradrenaline (NA) release at the sympathetic nerve terminals, and this degree of sympathetic nerve activity was compared with the degree of ΔVP. The results obtained were 1) there was a rough overall correlation between ΔVP and ΔNAPH in the subjects of Groups C, N and H, and 2) ΔNAPH was significantly higher in Group H than in Groups C and N. These results suggest that much reliance can be placed on the measured increment of plasma NA concentration in response to the administration of PH in assessing the degree of enhanced sympathetic nerve activity in the patients with “latent” left-sided heart failure.