Effects of nitroprusside on the bradykinin responsiveness of human fibroblasts

The effects of agents that cause vasodilatation and hypotension, such as endogenously produced bradykinin (BK) or the drug nitroprusside (NP), appear to result from effects on cyclic nucleotides (cGMP, cAMP) and arachidonate metabolism. Cultured human fibroblasts, which possess B2 BK receptors and respond to NP with an increase in cGMP, were used to study the interaction of these agents at the molecular level. Addition of BK or NP to cultured human fibroblasts caused a rapid increase in cGMP. The effect of NP was usually maximal within 30 sec, after which cGMP content declined. The increase in cGMP produced by BK reached a maximum at approximately 1 min and then fell; the rise with NP was more than 10 times that with BK. At 30 sec, cGMP content with NP plus BK was less than with NP alone. At later times, however, effects of BK and NP were slightly more than additive and maximal cGMP levels were reached at 90 sec. BK increased prostaglandin production by the fibroblasts; it is believed that the kinin-induced elevation in cAMP content is secondary to increased prostaglandin formation. NP caused a small, early increase in cAMP without significant effect on prostaglandin I2 (PGI2); after 2.5 min, effects on PGI2 and cAMP were greater with BK and NP than with BK alone. To study further the roles of arachidonate metabolites in the fibroblast response to BK and NP, the cyclooxygenase inhibitor, indomethacin, and the combined lipoxygenase and cyclooxygenase inhibitor, 5,8,11,14-eicosatetraynoic acid (ETYA), were added to fibroblasts prior to BK or NP. Increases in cAMP or PGI2 with BK or BK plus NP were blocked by indomethacin or ETYA. These effects of BK or BK plus NP on cAMP thus appear to be mediated through cyclooxygenase products of arachidonate metabolism. Indomethacin and ETYA did not affect cGMP in the presence of BK plus NP but enhanced NP-stimulated cGMP accumulation by 40-50%; effects of NP on cGMP may be independent of or perhaps inhibited by cyclooxygenase derivatives. Cellular responses to BK plus NP differed quantitatively and temporally from the sum of effects of BK and NP alone. Through interactions of this type, in vivo responses to drugs like NP may be influenced by levels of BK or similar endogenous mediators.