ACTIONS OF 1,4-DIHYDROPYRIDINES IN ISOLATED MESENTERIC VASCULAR BEDS

Recent studies indicate that the vasorelaxation induced by nitrendipine may be mediated partially by increased release of nitric oxide (NO). To study this effect in more detail and to examine the vasodilating effect of other 1,4-dihydropyridines (1,4-DHP) with regard to a possible involvement of NO, we investigated the effects of nitrendipine, nifedipine, nisoldipine, and nimodipine on isolated mesenteric vascular bed and the influence of L-N-G-nitroarginine (L-NNA) on 1,4-DHP-induced vasorelaxation. Perfusion with these I,4-DHP resulted in a concentration-dependent increase in global flow and vascular diameter in all vessel branches. Nifedipine exhibited a more pronounced effect on G4 vessels, whereas the actions of the other 1,4-DHP on the investigated vascular tree were more homogeneous, The dilating and flow increasing effects of nitrendipine and nifedipine could be significantly antagonized by treatment with LNNA. The vasodilating effects of nisoldipine and nimodipine could also be antagonized with L-NNA. We conclude that NO release plays an additional role in the relaxation of small resistance vessels by 1,4-DHP.