1. Indomethacin treatment of renomedullary interstitial cells (RIC) causes a marked increase in number and size of their lipid droplets. The anti-hypertensive function is retained.
2. After multiple passages in tissue culture, RIC lose their ability to produce an anti-hypertensive effect in hypertensive animals. Along with this functional loss, lipid droplets and a prominent cisternal system become attenuated or disappear.
3. We conclude that preservation of the lipid granule—cisternal organelle relationship is important in preservation of the anti-hypertensive endocrine function of RIC.