Beta adrenoceptor density in patients with left-sided valvular regurgitation

Afterload Reduction May Halt and Beta-Adrenergic Blockade May Worsen Progression of Left Ventricular Dysfunction in Patients With Chronic Compensated Mitral Regurgitation: A Retrospective Cohort Study

Severe chronic mitral regurgitation (MR) is associated with progressive left ventricular (LV) systolic dysfunction. Both afterload reduction and beta-adrenergic blockade have been suggested as methods for preventing LV dysfunction in asymptomatic patients with MR and normal LV function, who are therefore not yet candidates for surgical intervention. The objective of this study was to determine if afterload reduction reduces progression of LV dysfunction in patients with severe MR. The reports of echocardiographic studies performed 20 ±14 months apart were compared in a retrospective cohort of 134 asymptomatic patients with moderate-severe chronic MR and baseline ejection fraction (LVEF) >50%. Groups were defined by exposure to any afterload-reducing drug: Group 0, no exposure; Group 1, exposure beginning after the first echocardiogram; and Group 2, drug exposure beginning before the baseline echocardiogram. The groups differed importantly only in treatment duration. In 72 patients not exposed to beta-adrenergic blockade, LVEF decreased by a relative —3.2% in Group 0, while Group 1 increased by 3.4% and Group 2 increased by 5.1%, p <0.01. Among 62 patients exposed to beta-adrenergic blockade, LVEF consistently worsened (Group 0, 4.8%; Group 1, —3.3%; Group 2, —1.7%; p = 0.71) compared to the 72 patients without beta-adrenergic blockade. In a multivariate model that included treatment duration and exposure to other medications, the beneficial effect of afterload reduction (p <0.03) and the deleterious effect of beta-adrenergic blockade (p < 0.02) were significant. Afterload reduction halted or reversed the progressive worsening of left ventricular function while beta-adrenergic blockade had a deleterious effect.

Changes in systemic sympathetic nervous system activity after mitral valve surgery and their relationship to changes in left ventricular size and systolic performance in patients with mitral regurgitation

BACKGROUND

We have shown that the systemic sympathetic nervous system (SNS) is activated in patients with chronic mitral regurgitation (MR). However, the fate of systemic SNS activity after surgical correction of MR is currently unknown.

METHODS

We examined 14 patients with MR who had normal sinus rhythm with an investigational, preoperative cardiac catheterization, including arterial norepinephrine (NE) sampling and [(3)H]-NE infusions and arterial blood sampling to determine NE kinetic parameters using a 2-compartment modeling analysis. The arterial NE and NE kinetic parameters were determined in all patients after mitral valve surgery (MVS) at a mean of 12 months. A 2-dimensional echocardiographic examination was also performed before and after MVS.

RESULTS

The average extravascular NE release rates (NE(2)) before and after MVS were 1.89 +/- 0.66 and 2.26 +/- 0.82 microg/min/m(2) (P =.24), respectively. The average left ventricular (LV) end-diastolic dimension, fractional shortening, and ejection fraction decreased, whereas the mean LV end-systolic dimension did not change between the pre- and post-MVS echocardiographic studies. However, these group averages were comprised of patients with MR in whom the NE(2) and echocardiographic values both increased and decreased. This lack of homogeneity was a reflection of our new observation that the pre- to post-MVS changes in NE(2) were directly proportional to the changes in LV end-systolic dimension (r = 0.91, P <.001) and inversely related to the changes in LV fractional shortening (r = -0.82, P <.001) and ejection fraction (r = -0.78, P <.001).

CONCLUSIONS

The response in systemic SNS activity in patients with MR after MVS is not homogeneous, and these changes are concordant with the post-MVS changes in LV size and systolic performance. These data further support our earlier observations and extend them to suggest that systemic SNS activation in patients with chronic MR is related to LV remodeling and impaired systolic performance.

Characterization of lymphocyte beta 2-adrenoceptor signalling in patients with left ventricular volume overload disease

1. Studies using animal experimental models have suggested that the beta2-adrenoceptor is uncoupled in association with alterations in the expression of G-protein-coupled receptor kinases (GRK) 2/3 in heart failure. However, the functional expression of the components of this pathway in human disease has not been fully elucidated yet. In the present study, we evaluated the possibility that the regulation of beta2-adrenoceptor signalling components in patients with left ventricular volume overload (VOL) depends on the severity of the overload. 2. We characterized the lymphocyte GRK 2-6, beta-arrestins 1 and 2, beta2-adrenoceptor expression at the mRNA and protein levels, as well as the activity of adenylyl cyclase, protein kinases (PK) A and PKC in patients with VOL using healthy blood donors as controls. 3. In the patient group, GRK2 mRNA was increased by 61% (P < 0.001), GRK3 was increased by 54% (P < 0.005), GRK5 was increased fivefold (P < 0.001) and the beta-arrestin 2 mRNA was increased by 40% (P < 0.05). These increases were paralleled with a sixfold increase in GRK2, a twofold increase in GRK3 and a 1.3-fold increase in GRK5 protein levels. These changes were associated with a significant decrease in beta2-adrenoceptor mRNA, the basal, catalytic and receptor-mediated activity of adenylyl cyclase and sensitization of the forskolin-stimulated activity towards augmented inhibition by guanylimidodiphosphate. In general, the increase in GRK2 and 5 mRNA exhibited a positive correlation with the gravity of the haemodynamic load, as determined by changes in left ventricular fractional shortening. 4. The results suggest that VOL induces an increase in the expression of lymphocyte beta2-adrenoceptor-specific GRK and beta-arrestin 2 in association with an attenuation in beta2-adrenoceptor levels. It can be speculated that the cardiac circulatory system adapts itself to altered haemodynamic functional demands partly by altering beta2-adrenoceptor signalling.