Fig. 3.

(A–C) HP ¹³C-urea behavior observed for n = 3 pregnant rats treated with l-NAME as described in the text. Highlighted are maternal arteries and a number of placentas showing dissimilar behaviors. (D) Time course of the regions indicated in A–C, normalized to their maximum intensities. Notice the distinctly different behaviors shown by the placentas; that is, in P2 and P5, signals wash away as in the maternal arteries, whereas in P1 and P4 they last for ≥40 s as in the normal cases illustrated in Fig. 2. Unlabeled ¹³C signals in C arise from placentas and other organs, in the periphery of the region detectable with the surface coil used. See SI Appendix, section 6, Figs. S11 and S12, and Table S1, for further details of this kinetics.