Catalyzes the reduction of prostaglandin-ethanolamide H(2) (prostamide H(2)) to prostamide F(2alpha) with NADPH as proton donor. Also able to reduce prostaglandin H(2) to prostaglandin F(2alpha) (By similarity). [thioredoxin]-dithiol + prostaglandin H2 = [thioredoxin]-disulfide + prostaglandin F2alpha [thioredoxin]-disulfide + prostamide F2alpha = [thioredoxin]-dithiol + prostamide H2 Belongs to the peroxiredoxin-like PRXL2 family. Prostamide/prostaglandin F synthase subfamily.