Functional Adaptations in Coronary Reactivity following Healthy Pregnancy in Swine

This study was designed to test 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 of postdelivery, 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 arteries from postpartum swine versus control (p < 0.005). Concentration-dependent 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 contractile responses (p = 0.68). Intracoronary administration of U46619 (1 nm-1 µm) in open-chest swine decreased coronary blood flow ∼45 ± 3% in nonpregnant controls but had no effect on coronary blood flow in postpartum swine. Concentration-dependent 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.

These findings indicate that chronic exposure of the coronary circulation to the pregnancy/postpartum milieu results in functional adaptations in sensitivity to paracrine/hormonal compounds that should be further explored.