Effects of the alpha 1-adrenoceptor agonist phenylephrine in pig heart. Study of the direct action on contractile proteins.

The effects of the α 1 -adrenoceptor agonist phenylephrine (CAS 59-42-7) on Ca ++ sensitivity of the contractile proteins and on force of contraction of the heart were studied in right ventricular preparations isolated from pigs. In contracting trabeculae phenylephrine (3-100 μmol/l) increasesd force of contraction in the presence of propranolol maximally by 91.8±36.2% (n=5). The effect of phenylephrine was antagonized by prazosin, indicating and α-adrenoceptor-mediated positive inotropic effect