Fig. 6. Induction of lumen formation by RAR-pan-reactive and RAR-selective synthetic retinoids. (A) J3B1A cells were suspended in collagen gels and incubated either with 0.1% DMSO (control) or with a wide range of concentrations of the RAR-selective agonist TTNPB. (B) J3B1A cells were suspended in collagen gels and incubated either with 0.1% DMSO (control) or with different concentrations of Am-580, a selective RAR ligand. Lumen formation was quantified after 6 days as described in Materials and Methods. Results are expressed as mean percentage of cysts±s.e.m. in 20 randomly selected photographic fields (five fields from each of four separate experiments) per experimental condition. In A, 1=P<0.05; 2=P<0.025; 3=P<0.0005 (compared with control values); in B, ^*=P<0.0005 (compared with control values).