This study tested the hypothesis that coronary artery adaptations during the postpartum period are related to underlying reductions in endothelium-dependent relaxation and/or augmented smooth muscle vasoconstrictor responsiveness. In vivo experiments were performed in control (nonpregnant) and postpartum swine 35-45 days post-delivery, with isometric tension experiments performed in isolated coronary arteries from those animals. Coronary artery rings demonstrated increases in active tension generation following incremental increases in passive stretch with no differences between groups. Endothelium-dependent relaxation to bradykinin was attenuated in postpartum vs. control swine (P < 0.005). Contractions to the thromboxane A2 mimetic U46619 (0.1 nM - 1 µM) were shifted rightward (EC50 27 ± 10 nM vs. 238 ± 66 nM; P < 0.01) in arteries from postpartum swine, with no changes in maximum responses (P = 0.68). Intracoronary administration of U46619 (1 nM - 1 µM) in open-chest swine decreased coronary flow ~45 ± 3% in nonpregnant controls but had no effect on coronary blood flow in postpartum swine. Contractions to KCl (5 - 90 mM) showed a rightward shift in arteries from postpartum swine (15.6 ± 1.4 mM vs. 21.8 ± 1.9 mM; P = 0.03), with no change in maximum response. Taken together, the postpartum period is associated with reduced endothelium-dependent relaxation and responsiveness to receptor-dependent and independent vasoconstrictor stimuli.
S. Karger AG, Basel.