1. To examine the effects of rate and pressure on release of vasoactive hormones, 10 healthy subjects were examined.

2. A standardized pacing protocol was used to achieve different haemodynamic responses at two predetermined heart rates. Haemodynamic variables, and plasma concentrations of atrial natriuretic peptide, arginine vasopressin, adrenaline and noradrenaline were measured.

3. Right atrioventricular pacing at a rate of 150 impulses/min resulted in disparate responses in right atrial pressure (slight decrease) and pulmonary capillary wedge pressure (increase). Change in arterial plasma concentration of atrial natriuretic peptide correlated to change in pulmonary capillary wedge pressure, and change in arterial plasma concentration of noradrenaline correlated to change in total systemic vascular resistance, whereas concentrations of adrenaline and arginine vasopressin did not alter significantly during the stimulation periods. A significant influence of rate in addition to the pressure related influence on plasma concentration of atrial natriuretic peptide was found. In contrast, an increase in rate in the absence of an increase in atrial pressures did not raise the plasma concentration of atrial natriuretic peptide. There was no significant relationship between change in atrial natriuretic peptide and noradrenaline.

4. These data support the concept of a rate dependence of atrial natriuretic peptide release in man. Increased atrial pressure and thus presumed atrial stretch seems to be a prerequisite for increased plasma concentration of atrial natriuretic peptide. In addition, these results highlight the importance of monitoring both left and right atrial pressure in clinical investigations assessing modulation of atrial natriuretic peptide release.

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