Stimulation of uterine ornithine decarboxylase in organ culture by decreasing osmolality: possible relation to in vivo mechanisms.

Ornithine decarboxylase (ODC) activity increases during many growth responses. Some cells and tissues in culture also exhibit elevated enzyme activity with decreasing osmolality of the culture medium. We have found that this also occurs with uterine tissue from ovariectomized rats. Organ culture incubation under hypotonic conditions caused maximal stimulation of uterine ODC activity at 4 hr. This stimulation was observed when either NaCl or sucrose was used to adjust the osmolality. Incubation under isotonic conditions also increased ODC activity relative to hypertonic conditions. This increase was similar in magnitude to that seen with unincubated uterine tissue from animals receiving systemic estradiol or intrauterine cholera toxin. Both estradiol and cholera toxin increase vascular permeability, and the resultant edema changes the extracellular microenvironment of the uterine cells. We suggest that this change somehow is mimicked by organ culture under hypotonic or isotonic conditions and is responsible for the stimulation of uterine ODC activity.