Gibberellic acid, a plant growth hormone, enhances mammalian guanylate cyclase activity.

In vivo injections of gibberellic acid, a potent plant growth hormone, are known to increase the growth of animals as well as plants. Investigation into gibberellic acid's growth promoting mechanism in animals at the cellular level focused on guanylate cyclase (E.C.4.6.1.2.), an enzyme known to be associated with growth. Gibberellic acid enhanced the activity of rat lung guanylate cyclase over a concentration range of .00001 mM to 1 mM with no stimulation being observed at .000001 mM. Varying the concentration of the guanylate cyclase co-factor manganese had no effect on gibberellic acid's enhancement of guanylate cyclase activity. Since human and rat growth hormones also enhance guanylate cyclase activity, it appears that at cellular level the mechanism of action of growth promoting hormones may include a common process that involves enhancement of guanylate cyclase activity.