REGULATION OF NERVE GROWTH-FACTOR SYNTHESIS AND RELEASE IN ORGAN-CULTURES OF RAT IRIS

The synthesis and release of nerve growth factor (NGF) was studied in cultured rat iris with a 2-site enzyme immunoassay by measuring the time course of NGF levels remaining in the iris and released into the medium up to 72 h. For up to 3 h, the NGF levels in the iris did not change significantly. After that, they increased to a maximal level of 350 .+-. 30 pg NGF/iris at 19 h, which is 200 times higher than the in vivo content. Between 20 and 72 h in culture, the NGF level decreased to 130 .+-. 10 pg NGF/iris, whereas general protein synthesis did not change during that time period. Maximal rate of NGF production (203 pg NGF/h per iris) was seen between 9 and 12 h in culture. In the medium, NGF levels were first detectable after 6 h. Levels then increased with a time course similar to that seen within the iris, reaching a maximal level of 1180 .+-. 180 pg after 19 h in vitro, and then did not significantly change for up to 48 h. The NGF production of the densely sympathetically innervated dilator was 3 times higher than that of the predominantly cholinergically innervated sphincter. The NGF production was blocked by inhibitors of mRNA synthesis (actinomycin D) and of polyadenylation (9-.beta.-D-arabinofuranosyladenine) as well as by inhibitors of translation (cycloheximide). Monensin, which interferes with the transport of proteins through the Golgi apparatus, decreased NGF levels to 8-12% of controls in the medium, suggesting that the Golgi apparatus is involved in the intracellular processing of NGF.