1 The vascular effects of cicletanine have been studied in vitro on ring preparations of inferior epigastric arteries from normotensive human females and human females with pregnancy-induced hypertension (preeclampsia). 2 Cicletanine (10(-7)-10(-3) M) elicited concentration-dependent relaxation of vessels precontracted with 10(-7) M noradrenaline (NA) or 60 mM K+ but was more potent in the former. Relaxation was significantly greater in rings from preeclamptic patients and was uninfluenced by endothelium removal. 3 The intracellular Ca-dependent contractile responses to 10(-5) M NA in Ca-free medium as well as the subsequent extracellular Ca-dependent contractions (on restoration of external Ca) were significantly attenuated dose-dependently by cicletanine (10(-5) M, 3 x 10(-4)M) in arterial rings from both normotensive and preeclamptic patients. Cicletanine also relaxed rings precontracted by 25 mM K+ but was ineffective against 80 mM K+-induced contractions. 4 The inhibition of intracellular Ca-dependent contractions was significantly greater in rings from preeclamptic than from normotensive patients whereas extracellular Ca-dependent contractions were comparably inhibited in both groups. Nifedipine, on the other hand, had little effect on the intracellular Ca-dependent contractions but significantly depressed extracellular Ca-dependent contractions. 5 Cicletanine-induced relaxation was uninfluenced by pretreatment with propranolol, ouabain, tetraethylammonium, procaine, indomethacin, cimetidine or tetrodotoxin but was antagonized by glibenclamide. 6 The results show that cicletanine inhibits contractile responses of human isolated inferior epigastric arteries by a mechanism unrelated to endothelial factors but associated with inhibition of calcium metabolism. An action of cicletanine on glibenclamide-sensitive K+ channels is also suggested. Cicletanine-induced inhibition was significantly greater in arteries from preclamptic patients.
