Relaxation induced by PDE1 inhibition is reduced by inhibition of PKG and the NO‐cGMP pathway. Cumulative concentration–response curves for the PDE1 inhibitor, Lu AF58027, in the presence of the PKG inhibitor, Rp‐8 (10 μM), or the PKA inhibitor, H89 (1 μM) (A), or in the presence of the NOS inhibitor, l‐NAME (100 μM), the soluble guanylate cyclase inhibitor, ODQ (3 μM), and in arterial segments without endothelium (B). (C) and (D) illustrate the pEC50 values for Lu AF58027 for the different treatments in (A) and (B). Mesenteric arteries were contracted with U46619 to approximately 80% of maximal contraction. Data are mean ± SEM. n = 6 arteries from separate rats. Student's t‐test with Bonferroni's multiple comparisons test. *P < 0.05 from control.