Study of in vitro effects of hydralazine metabolites--comparative evaluation of products of hydroxylation, hydrolysis and conjugation.

K+ contractures were induced in paired strips of rabbit aortic smooth muscle. The relationship between relaxant effects and the bath concentration of hydralazine acetone hydrazone (HA), 4-OH-hydralazine (HH) and phthalazine (P) was studied over the concentration range 10(-5)-10(-3)M. All compounds were active, HA = HH greater than P (p less than 0.05; n = 6) at concentrations in the range 10(-4)-10(-3M, HA greater than HH at a concentration of 10(-3M (pgreater than 0.01). The activity of HA did not depend on significant reconversion to hydralazine (H) in the bath ( less than 0.5%). A range of H derivatives may contribute to the hypotensive effects of administered H.