Propranolol reduces rat dopamine-beta-hydroxylase activity and catecholamine levels

Contractile effects of stimulation of D1-dopamine receptors in the isolated human atrium

Dopamine receptors have been claimed not to directly increase contractility in the human heart. Therefore, we performed contraction experiments in isolated electrically driven human atrial preparations (HAP). For comparison, we performed contraction experiments with left atrial preparations of transgenic mice which harbor a cardiac overexpression of human D1-dopamine receptors (D1-TG). In D1-TG, first we noted that dopamine (10 nM-10 µM cumulatively applied) in the presence of propranolol exerted a concentration- and time-dependent positive inotropic effect in D1-TG. In a similar fashion, dopamine increased force of contraction in the presence of 0.4 µM propranolol in HAP and these effects were amplified by pre-treatment with inhibitor of phosphodiesterase III (1 µM) cilostamide. Moreover, contractile effects of dopamine in the presence of propranolol 0.4 µM in HAP were antagonized by odapipam, haloperidol, or raclopride. Ten micromolars of fenoldopam in the presence of cilostamide increased force of contraction in HAP and this effect was antagonized by SCH 23390. We conclude that stimulation of human D1-dopamine receptors can increase force of contraction in the HAP.

Role of Dopamine in the Heart in Health and Disease

Dopamine has effects on the mammalian heart. These effects can include an increase in the force of contraction, and an elevation of the beating rate and the constriction of coronary arteries. Depending on the species studied, positive inotropic effects were strong, very modest, or absent, or even negative inotropic effects occurred. We can discern five dopamine receptors. In addition, the signal transduction by dopamine receptors and the regulation of the expression of cardiac dopamine receptors will be of interest to us, because this might be a tempting area of drug development. Dopamine acts in a species-dependent fashion on these cardiac dopamine receptors, but also on cardiac adrenergic receptors. We will discuss the utility of drugs that are currently available as tools to understand cardiac dopamine receptors. The molecule dopamine itself is present in the mammalian heart. Therefore, cardiac dopamine might act as an autocrine or paracrine compound in the mammalian heart. Dopamine itself might cause cardiac diseases. Moreover, the cardiac function of dopamine and the expression of dopamine receptors in the heart can be altered in diseases such as sepsis. Various drugs for cardiac and non-cardiac diseases are currently in the clinic that are, at least in part, agonists or antagonists at dopamine receptors. We define the research needs in order to understand dopamine receptors in the heart better. All in all, an update on the role of dopamine receptors in the human heart appears to be clinically relevant, and is thus presented here.

Morphogenesis of Hepatitis E Virus

Hepatitis E virus, a leading cause of acute hepatitis worldwide, has been recognized as non-enveloped virus since its discovery in the 1980s. However, the recent identification of lipid membrane-associated form termed as "quasi-enveloped" HEV has changed this long-held notion. Both naked HEV and quasi-enveloped HEV play important roles in the pathogenesis of hepatitis E. However, the biogenesis and the mechanisms underlying the composition, biogenesis regulation, and functions of the novel quasi-enveloped virions remain enigmatic. In this chapter, we highlight the most recent discoveries on the dual life cycle of these two different types of virions, and further discuss the implication of the quasi-envelopment in our understanding of the molecular biology of HEV.

Chronic propranolol treatment affects expression of adrenoceptors on peritoneal macrophages and their ability to produce hydrogen peroxide and nitric oxide

Using both immunocytochemical and flow cytometric analyses of rat peritoneal exudate cells constitutive expression of tyrosine hydroxylase and both beta(2)- and alpha(1)- adrenoceptors on macrophages was revealed. Furthermore, according to the characteristic assemblage of tyrosine hydroxylase and adrenoceptor subtype expression different macrophage subsets were identified. In vitro treatment of macrophages with the non-selective alpha,beta-adrenoceptor agonist arterenol and/or the beta-adrenoceptor antagonist propranolol indicated that beta-adrenoceptors potentiated nitric oxide (NO) production and suggested alpha-adrenoceptor-mediated suppression of hydrogen peroxide (H(2)O(2)) production. An increase in H(2)O(2) production in the presence of the alpha(1)-adrenoceptor antagonist ebrantil provided support for this. Chronic propranolol treatment in vivo led to increased NO and H(2)O(2) production by peritoneal macrophages. Furthermore, this treatment resulted in opposing effects on the expression of beta(2)- and alpha(1)-adrenoceptors on peritoneal macrophages (a stimulatory effect on beta(2)-adrenoceptors and a suppressive effect on alpha(1)-adrenoceptors). In conclusion, a subset of resident peritoneal macrophages synthesizes catecholamines, which may exert differential effects on H(2)O(2) and NO production via distinct adrenoceptors. Finally, chronic propranolol treatment affected adrenoceptor expression on peritoneal macrophages and altered their capacity to generate NO and H(2)O(2).

Early reduction in plasma norepinephrine during beta-blocking therapy with metoprolol in chronic heart failure

BACKGROUND

The possible role exerted by modulation of sympathetic outflow in the clinical effects of beta-blockade in chronic heart failure was tested during short- and long-term treatment.

METHODS AND RESULTS

Oral metoprolol (30-150 mg/day) was added to conventional therapy in 14 patients with idiopathic dilated cardiomyopathy, left ventricular ejection fraction (LVEF) of <0.45, and New York Heart Association class II or III. Norepinephrine plasma levels, which are an index of sympathetic activation, decreased by 27.57 +/- 18.03% after 1 month (P < .005), but returned to pretreatment levels after 6 months. LVEF increased by 7.7 +/- 6.0 ejection fraction units after 6 months (P < .005 vs baseline and P < .05 vs 1 month). Long-term beta-blockade resulted in nonsignificant improvements in functional class, symptom score, and oxygen consumption at peak exercise. After 1 month, the reduction in plasma norepinephrine levels and the changes in LVEF were inversely correlated (P < .01). No other correlation emerged during short- or long-term treatment.

CONCLUSION

In conclusion, the reduction in plasma norepinephrine levels during short-term beta-blockade was not proportional to the clinical benefits and may have been attributed to the direct inhibition of sympathetic outflow. The early reduction in circulating norepinephrine levels may decrease cardiac performance through withdrawal of sympathetic support when the favorable effects of beta-blockade have not had time to occur. The role that sympathetic modulation may exert in the long-term clinical benefits of metoprolol deserves further investigation.

Localization of the dopamine D1 receptor protein in the human heart and kidney

The dopamine D1 receptor has recently been identified in the rat heart and kidney. In the present study, using Western blot analysis and light microscopic immunohistochemistry, we examined D1 receptor protein expression in the human kidney and heart. Antipeptide polyclonal rabbit antiserum was raised against the third extracellular domain of the native receptor and affinity-purified using a protein-A column. Selectivity of the antiserum was validated by recognition of the D1 receptor expressed in stably transfected LTK- cells and Sf-9 cells. The immunohistochemical staining for D1 receptor protein was distributed throughout the atrium and ventricular myocardium and in the coronary vessels. In the kidney, positive immunoreactive signal was detected in the proximal and distal tubules, the collecting ducts, and the large intrarenal vasculature, whereas staining was absent in the juxtaglomerular (JG) cells and the glomeruli. D1 receptor antiserum preadsorbed against the immunizing peptide did not produce significant staining. In Western blot analysis, a single 55-kD band was detected for the D1 receptor in membranes from the D1 receptor transfected Sf-9 cells but not in nontransfected cells. In the heart and kidney, we detected a 55-kD band as well as an additional 40-kD band, which may reflect partial degradation of the receptor protein. These results provide the first evidence for the localization of the dopamine D1 receptor protein in the human heart and kidney. The similar distribution of this subtype receptor in the human heart and kidney to that in the rat supports the possible (patho)physiological significance of the peripheral dopamine system in humans.

Expression of the subtype 1A dopamine receptor in the rat heart

The subtype 1A dopamine receptor (D1A) has recently been detected in the rat kidney. In the present study using light microscopic immunohistochemistry, electron microscopic immunocytochemistry, and in situ amplification of mRNA, we demonstrate the D1A receptor in Sprague-Dawley and Wistar Kyoto rat hearts. For immunohistochemistry and immunocytochemistry, anti-peptide polyclonal antibodies were directed toward amino acid sequences of the third extracellular and intracellular domains of the native receptor. Selectivity was validated by recognition of the D1A receptor expressed in stably transfected LTK- cells. D1A receptor mRNA was detected with a novel transcription-based isothermal in situ amplification system as well as with reverse transcription-polymerase chain reaction. D1A receptor protein was distributed throughout the atrium and ventricular myocardium. Preimmune and preabsorption controls were negative. Electron microscopic immunocytochemistry using the protein A gold method demonstrated the D1A receptor along the cellular membranes of coronary smooth muscle cells and ventricular myocytes and in the myosin thick filaments and M-lines. D1A receptor mRNA was present in coronary vessels and myocardium in amplified but not in unamplified sections. Western blot analysis showed specific D1A bands in transfected LTK- cells and the atrium but not in nontransfected LTK- cells and the ventricle. The selective D1-like receptor agonist SKF38393 stimulated adenylyl cyclase in ventricular myocardial plasma membranes in a dose-related fashion, and the response was abolished by the selective D1-like receptor antagonist SCH23390. These results demonstrate that the D1A receptor gene and protein are expressed in normal rat heart. The physiological and pathophysiological roles and predominant cell signaling mechanism or mechanisms of this receptor remain to be determined.