Reduced responses of nitrendipine in PGF2 alpha-precontracted porcine isolated arteries after pretreatment with methylene blue.

Vascular activity of nitrendipine (NTD) in different depolarized and prostaglandin F2 alpha (PGF2 alpha)-precontracted isolated porcine arteries was examined in the presence and absence of methylene blue (MB). Presence of MB potentiated the PGF2 alpha-induced contractions in all vessels studied and reduced the response of NTD in coronary and basilar arteries seven- to 23-fold. Only in ulnar arteries was the affinity of NTD slightly increased. In contrast, MB did not modify the affinity of papaverine under these conditions. Furthermore, MB had no influence on KCl-induced contractions and subsequent vasorelaxation by NTD. It is proposed that MB impaired endothelium derived relaxing factor, thereby stimulating and/or increasing the calcium influx through receptor-operated calcium channels.