The antiadrenergic effect of neuropeptide Y on the ventricular cardiomyocyte

The effect of neuropeptide Y (NPY) on adenylate cyclase activity was examined in ventricular myocytes isolated from the adult rat heart. In the presence of the phosphodiesterase inhibitor Ro 20-1724 (0.5 mM) and adenosine deaminase (5 U/ml), these intact cells accumulate cyclic AMP when stimulated by isoproterenol. NPY (10−9 to 10−6 M) reduced the degree of cAMP accumulation achieved by 10−7 M isoproterenol in a dose dependend manner by 10 to maximally 48%. The IC 50 value was 3 x 10−8 M NPY. A maximal concentration (10−6 M) of N6-phenylisopropyladenosine (PIA) decreased cAMP levels by 39%, i.e. to a similar extent. Prior treatment of the myocytes with pertussis toxin (1 μg/ml for 6 h) increased the mean stimulated values in the presence of isoproterenol (10−7 M) by a factor 4.1. In such cells, NPY and PIA were ineffective in antagonizing the stimulation of cAMP production by isoproterenol. These results indicate that the ventricular myocyte has receptors for NPY, similar to the A1 adenosinereceptor in that they are linked to the adenylate cyclase by an inhibitory guanylate binding protein.