6α-PGI1 is a stable PGI2 analog resistant to hydrolysis in aqueous solutions. 6α-PGI1 promotes cAMP accumulation in human thyroid slices and cells in a concentration dependent manner. However, it is about 10-fold less potent than the β-isomer and 100-fold less potent than PGI2 in eliciting the response. 6α-PGI1 exhibits an IC50 of 350 ng/ml for inhibition of ADP-induced platelet aggregation, which is nearly 900-fold higher than that observed for PGI2 (0.4 ng/ml).