Nitric oxide: Biphasic dose responses

The capacity of nitric oxide (NO) to affect biphasic dose responses in phar macological and toxicological systems was assessed. Numerous examples of su ch biphasic responses were documented, including osteoclast differentiation , various vascular responses, neutrophil migration, superoxide anion format ion, exploratory behavior in rodents, vitamin D-3 levels in macrophages, hu man sperm motility and mobility, myocardial contraction, and other function s. The quantitative features of the dose response indicated a maximum stimu latory response usually less than twofold greater than the controls. While the stimulatory range was variable, ranging from similar to2.5 to 500-fold, the majority was less than or equal to 10-fold. These findings indicate th at biphasic dose-response relationships are common manifestations of the NO -induced effects.