Calcium entry blocking activities of MPC-1304 and of its enantiomers and metabolites.

The Ca2+ entry blocking effects of MPC-1304, a new Ca2+ entry blocker of the 1,4-dihydropyridine type, and of its (S) and (R) enantiomers and metabolites were examined on Ca(2+)-induced contractions in isolated rabbit arteries. The Ca2+ entry blocking activity of the (S) enantiomer of MPC-1304 was approximately 150 times greater than that of its (R) enantiomer. Likewise, the antihypertensive effect of the (S) enantiomer was twice as great as that of MPC-1304 (racemate) in conscious spontaneously hypertensive rats, while the (R) enantiomer was ineffective. Thus, most of the pharmacological activity of MPC-1304 resides in its (S) configuration. The main metabolic products of MPC-1304 also inhibited the Ca(2+)-induced contraction in the isolated vascular smooth muscles. These active metabolites showed a stereoselectivity similar to that of MPC-1304 for Ca2+ entry blocking activity, and may contribute to the potent antihypertensive action of MPC-1304.