Effect of retinoic acid on organ-cultured transitional epithelium

In view of the correlation shown in vivo between vitamin A deficiency and increased transitional cell proliferation, the ability of retinoic acid to block hyperplasia in organ-cultured bladder epithelium was investigated. Retinoic acid, at concentrations shown to block hyperplasia in other in vitro systems, was ineffective in blocking hyperplasia in bladder epithelium. The data suggest the possibility that, in vivo, vitamin A may not act directly on the transitional epithelium to control cell proliferation. The cytoplasmic volume, which normally decreases during the period of hyperplasia in vitro, was increased by retinoic acid. The increase in cytoplasmic volume stimulated by 0.3 micrometer retinoic acid was sufficient to maintain normal nuclear:cytoplasmic ratios during the hyperplastic response. The increase in cytoplasmic volume could not be correlated with increased protein, mucin, or glycogen synthesis. The data suggest that retinoic acid may have increased the permeability of the luminal membrane to water, possibly by interfering with the synthesis of the keratin component of the membrane.