The Potential Relationship Between β₃-adrenoceptor And Myocardial Hypertrophy Of The Postinfarcted Rats Heart

Background and objective:β3 adrenoreceptor (β3 -AR) is the third member ofβ-AR family, whose structure is similar toβ1 -AR andβ2 -AR to some extent. All the threeβ-AR populations are primarily couple to G s proteins. They share some signal transduction pathways and cross-talk with one another. The fluctuation of one receptor's expression may contribute to the reaction of another. As much effort has gone into the study ofβ3 -AR pharmacologic characteristics, people learned thatβ3 -AR was mainly exerted the metabolic property. Besides, fewβ3 -AR was found in the normal heart but doubly or triply upregulated in the cardiomyocyte of failure heart, which absorbed more attention to its role in the cardiovascular system. What's more, our preliminary work also confirmed an upregulation ofβ3 -AR in the postinfarcted rats'heart, which was considered relative to the development of pathophysiology after myocardial infarction (MI). Cardiac remodeling (CRM) was generally accepted as a determinant pathophysiologic course of the postinfarcted heart, which was defined as genome expression, molecular, cellular and interstitial changes that are manifested clinically as changes in size, shape and function of the heart after cardiac injury.β-AR antagonist had been proved beneficial to the postinfarcted myocardial hypertrophy, whether it cross-talked withβ3 -AR or not remained to be uncovered. Therefore, the selectiveβ1 -AR antagonist metoprolol, nonselectiveβ-AR antagonist and selectiveβ3 -AR agonist were chosen to explore the potential relationship between postinfarcted myocardial hypertrophy andβ3 -AR expression.Materials and Methods:1) Animal assignment and MI model establishment: 130 male Sprague Dawley rats weighing 200-250g were randomly assigned into 3 groups: normal group, sham operated group and MI group (MI-). The MI model was generated by the ligation of left anterior descending (LAD) coronary artery. The survival after 2 hours of ligation were then divided into 6 groups: MI control group (MI-1), MI with aqua destillata intragastrically (MI-2), MI with aqua destillata intraperitoneally (MI-3), MI with metoprolol intragastrically (MI-4), MI with carvedilol intragastrically (MI-5) and MI with BRL37344 intraperitoneally (MI-6).2) Administration and hemodynamic measurement: one week after ligation, the MI-4, MI-5, MI-6 groups were administrated with metoprolol, carvedilol and BRL37344 respectively for 12 weeks. After that, hemodynamic measurement was performed by the right femoral artery cannulation and the left ventricular cannulation via right common carotid artery. Heart rate (HR), mean blood pressure (MBP), left ventricular systolic pressure (LVSP), maximum rise or fall rate of left ventricular pressure (±dp/dt max) were recorded.3) LVBM, RVBM andβ3 -AR determination: after sacrificed by decapitation, the left and right ventricles were weighed then calculated by divided to the body mass. Left ventricle tissue was stored at -80℃for theβ3 -AR protein, mRNA detection by Western-blot and reverse transcribed polymerase chain reaction respectively.4) Statistical analysis: All data were recorded and analyzed using the SPSS 13.0 software program. Results were expressed as mean±SD. Comparison between groups was performed by one-way analysis of variance. Significant difference was considered at p <0.05.Results:1) Postinfarcted myocardial hypertrophy: there was no significant diffecence between the normal group (LVBM: 2.188±0.107, RVBM 0.557±0.024) and the sham operated group (LVBM: 2.209±0.126, RVBM 0.551±0.029) (P>0.05). Compared with the sham operated group, MI control groups (2.529±0.152, 2.545±0.252, 2.596±0.262) induced remarkably increase of the LVBM (P<0.01). No differcence was found among the three MI control groups (P>0.05). With respect to the RVBM, the MI control groups (0.969±0.057, 0.966±0.051, 0.984±0.077) also demonstrated an augmentation relative to the sham operated group (P<0.01) and no significant difference existed among the three MI control groups (P>0.05).2) The expression ofβ3 -AR of the postinfarcted hearts: on the protein and mRNA level, there was no significant difference between the normal group and the sham operated group (P>0.05). Considering the expression ofβ3 -AR of the sham operated group as 1, on the protein level, the three MI control groups were 2.08±0.25, 2.00±0.29, 2.02±0.33 respectively, which were significant upregulation when compared with the sham operated group (P<0.01). On the mRNA level, the three MI control groups were 1.69±0.34, 1.68±0.37, 1.70±0.39 respectively, which were also significant difference when compared with sham operated group (P<0.01).3) The hemodynamics of the postinfarcted rats: the +dp/dt max of normal group and sham operated group were 7092.9±454.9, 7072.6±420.0 respectively, the -dp/dt max were 5460.3±544.5, 5251.3±505.3 respectively, there were no significant difference between the two groups. The +dp/dt max of the three MI control groups were 3950.6±387.7, 3932.7±513.5, 4041.6±439.7 respectively, which were significant increase when compared with the sham operated group (P<0.01) but nonsignificant difference among the three MI control groups (P>0.05). The -dp/dt max of the three MI control groups were 2982.3±343.6, 2919.6±398.7, 2975.6±346.6 respectively, which were significant increase when compared with the sham operated group (P<0.01) but nonsignificant difference among the three MI control groups (P>0.05).4) The effect of the metoprolol, carvedilol and BRL37344 on the postinfarcted rats:①The LVBM of MI-4, MI-5 and MI-6 are 2.431±0.157, 2.525±0.248, 2.537±0.209 respectively, which were significant difference compared with the sham operated group (P<0.01) but nonsignificant difference when compared with the MI control groups (P>0.05). In contrast, the intervention of metoprolol, carvedilol and BRL37344 could ameliorate the RVBM (P<0.01), that were 0.851±0.056, 0.649±0.060, 0.654±0.054 respectively. Carvedilol and BRL37344 were much more favorable than metoprolol (P<0.01).②Considering the expression ofβ3 -AR of the sham operated group as 1, the metoprolol (1.99±0.26) had no effect on the expression ofβ3 -AR on the protein level (P>0.05) but raised the expression on the mRNA level (2.01±0.32) (P<0.01). The carvedilol and BRL37344 promoted the expression ofβ3 -AR on both protein (3.12±0.55, 3.36±0.45) and mRNA (2.74±0.58, 2.84±0.51) level in comparison with MI control groups and MI-4 (P<0.01). No significant difference was presented between carvedilol and BRL37344 groups (P>0.05).③The +dp/dt max of MI-4, MI-5 and MI-6 were 6293.2±447.0, 6394.5±553.3, 6152.7±493.2 respectively. The -dp/dt max were 4084.9±320.8, 4271.5±256.5, 3930.8±370.0 respectively. Both of +dp/dt max and -dp/dt max were significant difference relative to the MI control groups (P<0.01), which indicated great improvement of cardiac function by the intervention of metoprolol, carvedilol and BRL37344.Conclusions:1) The ligation of left anterior descending of coronary artery for 12 weeks produce evidently hypertrophy of the noninfarcted section of left ventricle and the right ventricle, leading to the deterioration of cardiac function.2) The expression ofβ3 -AR of the rats heart is upregulated on both protein and mRNA levels after myocardial infarction.3) The metoprolol, carvedilol and BRL37344 can improve right ventricle hypertrophy but not the left ventricle; carvedilol and BRL37344 are more favorable than metoprolol. Metoprolol can only augment theβ3 -AR mRNA expression while carvedilol and BRL37344 can on both protein and mRNA levels, even to a great extent than metoprolol. All the three medicines can improve the cardiac function.4) We presume that the improvement of RVBM and cardiac function should be associated with the expression ofβ3 -AR protein, the mechanism of which is still incompletely understood. Maybe anti-fibrosis, anti-apoptosis, angiogenesis and cardiac metabolism improvement were involved.