Expressions of cardiac sympathetic norepinephrine transporter and β1-adrenergic receptor decreased in aged rats

Evidence suggests that the deterioration of communication between the sympathetic nervous system and cardiovascular system always accompanies the aging of human and animals. Cardiac sympathetic norepinephrine (NE) transporter (NET) on presynaptic membrane is a predominant component to eliminate released NE in the synaptic cleft and maintains the sensitivity of the beta-adrenergic receptor (beta-AR). In the present study, we investigated NET and beta 1-AR mRNA levels and sympathetic nerve density in cardiac sympathetic ganglion and left ventricular myocardium in 2- and 16-month-old rats with Northern blot analysis and immunohistochemistry. The expression levels of NET mRNA, NET protein and beta(1)-AR mRNA in the ganglia or myocardia of 16-month-old rats were markedly reduced by 67%, 26%, and 43%, respectively, in comparison with those in 2-month-old rats. Our results also show that aging induces a strong decrease of the catecholaminergic nerve fiber density.