Effects of 1-(2,6-dimethylphenoxy)-2-(3,4-dimethoxy phenylethylamino) propane hydrochloride on rabbit papillary muscles

The effects of l-(2, 6-dime thylphenoxy)-2-(3, 4-dimethoxyphenylethyla mino) propane hydrochloride (DDP) on the oontractility, functional refractory period (FRP), automaticity and excitability were studied in rabbit papillary muscles. DDP decreased field stimulation-evoked contraction of papillary muscles dose-dependently with a threshold concentration above 10 μM. In the presence of propranolol (5 μM) DDP 1 μM shifted the dose-response curve for phenylephrine to enhance field stimulation evoked contraction of the papillary muscles to the right in parallel manner with a pA2value of 6.8. DDP 30 μM reduced the automaticity induced by adrenaline and prolonged the FRP, but exerted no obvious influence upon the excitability. The results demonstrate again that DDP can block α1 adrenoceptors and also reveal that DDP in higher concentration possesses possibly a calcium antagonistic effect