Abstract
We have investigated the possibility that the various left ventricular load conditions may exert different effects on the sympathetic function by comparing the influence of volume (VOL) and pressure (POL) overload on platelet α-adrenoceptor activity, plasma catecholamines and cAMP in 44 patients with rheumatic heart valvular disease. Receptor activity was determined by radioligand binding methods, catecholamines by HPLC using an electrochemical detector, and cAMP by radioimmunoassay. The mean a-adrenoceptor density (B
max) of the control group (
n = 29) was 4.71±0.41 fmol per 10
7 platelets and the corresponding dissociation constant (
K
d
) was 2.47±0.15 nM. In VOL patients, the density was elevated by 70% (
P<0.001), but it remained unchanged in the POL patients. In contrast to the B
max the
K
d
of the VOL group was not changed, and it increased by 34% (
P<0.01) in the POL group. Norepinephrine was elevated by 91% (
P<0.05) in POL, and epinephrine increased by 65% (
P<0.05) in POL and 71% (
P<0.05) in VOL. These results suggest that the sympathetic nervous system responds to left ventricular volume overload by increasing α-adrenoceptor density with no apparent change in receptor affinity toward [
3H]-yohimbine binding, and to left ventricular pressure overload by decreasing their binding affinity without a parallel decrease in receptor density. The increase in receptor density in VOL is accompanied by an increase in plasma epinephrine, and the decrease in binding affinity in POL is associated with increased plasma norepinephrine and epinephrine levels