The role of the adrenergic system in the heart: regulation of contractility by cardiac adrenoceptors

Beta adrenoceptor density in patients with left-sided valvular regurgitation

Aortic regurgitation differs from mitral regurgitation in that it is a result of combined volume and pressure overload, while the latter represents an almost pure volume overload. In this study, we tested the possibility that these two forms of left ventricular volume overload exert different effects on beta-adrenoceptor density. Lymphocyte (n = 33) and myocardial (n = 22) beta-adrenoceptor densities were evaluated by [125I]-iodocyanopindolol binding in volume-overload patients with left heart valvular disease, compared with 31 healthy donor blood and 15 donor heart controls, made available as a result of failing to get matching recipient. The total lymphocyte (LC) beta-adrenoceptor density decreased from 43.4 +/- 5.5 fmol mg-1 protein in controls to 9.2 +/- 2.7 fmol (P < 0.001) in heart valvular patients. In the myocardial controls, the left ventricular (LV)-receptor density was 126.7 +/- 19.5 fmol; right ventricular (RV), 123.1 +/- 14.6 fmol; left atrial (LA), 81.6 +/- 10.5 fmol; and right atrial (RA), 108.1 +/- 14.5 fmol mg-1 protein. Compared to this group, the total LV-receptor density of the patients decreased by 63%, RV by 54%, LA by 31% and RA by 34%. The decrease in receptor density exhibited a positive correlation with increasing ejection fractions in both the left (r = 0.38) and right (r = 0.44) ventricles, indicating that the former was dependent on the extent of the disease. These changes were accompanied by a 44% increase in plasma epinephrine, 13% in norepinephrine and a 27% decrease in dopamine levels. Based on the predominant left ventricular volume overload classified as aortic regurgitation (AVR), mitral regurgitation (MVR), and mixed aortic and mitral regurgitation (MOL), the attenuation in myocardial-receptor densities showed the following trend: MOL > AVR > AVR. The results show a global reduction in myocardial and LC beta-adrenoceptor density, which depends on the origin and the gravity of the LV volume overload.

Effects of different left ventricular load conditions on myocardial beta-adrenoceptor density in patients with rheumatic heart valvular disease

1. The possibility that different left ventricular load conditions may influence myocardial beta-adrenoceptor function in various ways was evaluated by determining the receptor density in all four chambers of 69 patients with rheumatic heart valvular disease. 2. The left ventricular beta-adrenoceptor density was reduced by 44% in patients with left ventricular pressure overload (LVP), 66% in left ventricular volume overload (LVV), 56% in mixed volume and pressure overload (MOL), and 60% in those with no left ventricular pressure overload (NOL). Similarly, the right ventricular receptor density decreased significantly by 46%, 54%, 43%, and 46%, left atrial by 15%, 29%, 14%, and 21%; and right atrial by 27%, 30%, 28%, and 12% in LVP, LVV, MOL, and NOL, respectively. Thus, the general trend in the decrease in receptor density was LVV > MOL = NOL > LVP. 3. Furthermore, the LVV patients with the largest decrease in receptor density in all four chambers, similarly exhibited the largest ejection fractions (EF) and left ventricular internal diastolic and systolic diameters. 4. The results show that left ventricular volume overload is a major cause of attenuation in myocardial beta-adrenoceptor density, compared to other forms of ventricular overload in heart valvular disease. 5. Since elevated EF in volume overload patients is an indication of the severity of the disease, the decrease in their myocardial receptor density may be a reflection of the degree of influence of the disease on their sympathetic activity.

Comparison of the effect of left ventricular volume and pressure overload on beta-adrenoceptor density in left heart valvular disease

The sympathetic responses in left heart valvular disease may depend on the ventricular load conditions. We proposed to evaluate this possibility by comparing the effects of left ventricular pressure (LVP) and volume (LVV) overload on beta-adrenoceptor density and ligand binding affinity in lymphocytes and in the four myocardial chambers in rheumatic heart valvular patients. Receptor activity was determined by radioligand binding using [125I]iodocyanopindolol. In the lymphocytes (n = 45), the beta-adrenoceptor density was reduced by 88% (P < 0.001) in LVP patients (n = 15) and 79% (P < 0.001) in LVV patients (n = 30) compared with 23 controls. In the myocardium, the receptor density of the LVP (n = 12) was attenuated by 55% (P < 0.05) in the left ventricle, 42% in the right ventricle, 13% in the left atrium, and 37% in the right atrium, while in LVV patients (n = 22) it decreased by 73% (P < 0.01) in the left ventricle, 62% (P < 0.05) in the right ventricle, 30% in the left atrium, and 34% in the right atrium compared with 15 controls. Thus, the reduction in density was greatest in lymphocytes and least in the atria in both groups. The decrease in ventricular density of the LVV group was similar to the reduction in the lymphocytes and two-fold higher than in the atrial density. These alterations were significantly greater for the LVV than for the LVP group. The Kd for the myocardial receptor binding to [125I]iodocyanopindolol was not significantly influenced in either group, but was lower in the lymphocytes. These findings suggest that in patients with left heart valvular disease, there is a significant attenuation in both peripheral and myocardial beta-adrenoceptor density. The decrease in receptor density is significantly greater in the left ventricular volume overload than in the left ventricular pressure overload patients.

Characterization of lymphocyte beta-adrenoceptor activity and Gs-protein in patients with rheumatic heart valvular disease

In order to test whether the beta-adrenoceptor activity in rheumatic heart valvular disease depends on the ventricular load conditions, we determined their density and binding affinity to [125I]-iodocyanopindolol in lymphocytes, as well as plasma catecholamine and cAMP levels in 69 patients with regurgitant and stenotic lesions of the aortic and mitral valves. The patients were classified as having left ventricular pressure overload (LVP), left ventricular volume overload (LVV), mixed lesions (MOL) or right ventricular pressure overload (RVP). The beta-adrenoceptor activity was determined by radioligand binding methods, catecholamines by high performance liquid chromatography using an electrochemical detector and cAMP by radioimmunoassay. The mean beta-adrenoceptor density (Bmax) of the control group was 60.1 +/- 9.5 fmol (n = 29) per 10(6) lymphocytes. In the study population, the density was decreased by 83% in LVP, 78% in LVV, 87% in MOL and 86% in RVP. Plasma norepinephrine was elevated by 89% in LVP and 60% in MOL, epinephrine by 43% in LVP, 50% in VOL, 115% in MOL and 20% in RVP, while dopamine was not significantly changed, and cAMP was slightly elevated in all four groups. Screening for activating mutational changes in the Gs alpha-protein gave negative results, possibly dissociating the elevation in plasma cAMP from stimulatory effects of such abnormalities in the Gs-protein signaling.(ABSTRACT TRUNCATED AT 250 WORDS)