Nerve growth factors in the rat iris.

Nerve growth factor (NGF) activity was not detected by bioassay in irides killed immediately after excision but NGF appeared within 24 h in living irides placed in culture or grafted to a host eye. Furthermore, sensory and, although less effective, sympathetic denervation of irides in situ led within 10 days to the appearance of NGF activity. In addition, freezing and thawing released a parasympathetic neuronotrophic factor activity from irides.