Fig. 8.

Schematic illustrating proposed mechanisms underlying the net effects of DA compression on fetal pulmonary blood flow during DA compression, which represent an equilibrium between flow-induced vasodilation and pressure-induced vasoconstriction (myogenic tone). Rho-kinase pathway is related to calcium sensitization, high vascular tone, and myogenic response, which are offset through activation of the nitric oxide (NO) pathway, which induces vasodilation. GC, guanylate cyclase; GTP, guanosine 5′-triphosphate; cGMP, guanosine 3′,5′-cyclic monophosphate; Ca²⁺, intracellular calcium; MLC, myosin light chain; MLC-P, phosphorylated MLC; MLCK, MLC kinase; MLCPh, MLC phosphatase (active); MLCPh-P, phosphorylated MLC phosphatase (inactive).