Fig. 4. L-NMMA inhibits yolk sac vascularization. The vascular morphology of L-NMMA-treated conceptuses was evaluated by PECAM1 staining at 9.5 dpc: (A) D-NMMA, (B) L-NMMA and (C) L-NMMA plus L-arginine. Hematoxylin and Eosin stained images of yolk sacs treated with D-NMMA (D) and L-NMMA (E). (F) Morphometric analysis of images from PECAM1-stained yolk sacs showing vessel diameter distribution. Experiments were repeated at least five times.