Intervascular and stimulus selectivity of nitrendipine and related derivatives in KCl and prostaglandin F2 alpha precontracted porcine arteries.

1. Dihydropyridine-type calcium entry blockers exhibit a different vasodilator potency depending on the arterial tissue (intervascular selectivity) as well as on the precontracting stimulus used (stimulus selectivity). In addition, the structure of their ester side chains seems to influence their activity. 2. Vascular activity of nitrendipine and six related 3-ester side chain derivatives was investigated in isolated coronary, ulnar and basilar arteries of the pig following precontraction with KCl or prostaglandin F2 alpha (PGF2 alpha). 3. After depolarization, all dihydropyridines exhibited a weak preferential action on coronary arteries. Bay E 6927 produced the strongest effect in all vessel types. By contrast, precontraction with PGF2 alpha resulted in a marked preferential action in basilar arteries, although higher concentrations of the dihydropyridines were required for half maximal vasorelaxation. In each case, ulnar arteries were less sensitive. 4. Except with Bay O 5572, the most bulky substituted and least active derivative, only moderate differences were observed within the dihydropyridines studied. On the other hand, there was a pronounced increase in the ratios of the half maximal active concentrations required after precontraction of the vessels with PGF2 alpha compared to KCl (stimulus selectivity) following a limited prolongation of the 3-ester side chain up to an isopropyl-group. 5. It is suggested that the observed shift in the intervascular selectivity after precontraction with PGF2 alpha is a consequence of different contractile mechanisms in the three vessel types studied. The degree of the stimulus selectivity may also depend on the structure of the dihydropyridines.