BACKGROUND We evaluated the clinical effectiveness of variable courses of paracetamol on patent ductus arteriosus (PDA) closure and examined its effect on the in vitro term and preterm murine ductus arteriosus (DA). METHODS Neonates received one of the following three paracetamol regimens: short course of oral paracetamol (SCOP), long course of oral paracetamol (LCOP), and intravenous paracetamol (IVP) for 2–6 d. Pressure myography was used to examine changes in vasomotor tone of the preterm and term mouse DA in response to paracetamol or indomethacin. Their effect on prostaglandin synthesis by DA explants was measured by mass spectroscopy. RESULTS Twenty-one preterm infants were included. No changes in PDA hemodynamics were seen in SCOP infants (n = 5). The PDA became less significant and eventually closed in six LCOP infants (n = 7). PDA closure was achieved in eight IVP infants (n = 9). On pressure myograph, paracetamol induced a concentration-dependent constriction of the term mouse DA, up to 30% of baseline (P < 0.01), but required >1 μmol/l. Indomethacin induced greater DA constriction and suppression of prostaglandin synthesis (P < 0.05). CONCLUSION The clinical efficacy of paracetamol on PDA closure may depend on the duration of treatment and the mode of administration. Paracetamol is less potent than indomethacin for constriction of the mouse DA in vitro.

Nitric oxide (NO) and cyclooxygenase (COX)-derived prostaglandins are critical regulators of the fetal ductus arteriosus. To examine the interaction of these pathways within the ductus wall, the ductus arteriosus of term and preterm fetal mice was evaluated by pressurized myography. The isolated preterm ductus was more sensitive to NOS inhibition than at term. Sequential NOS and COX inhibition caused 36% constriction of the preterm ductus regardless of drug order. In contrast, constriction of the term ductus was dependent on the sequence of inhibition; NOS inhibition prior to COX inhibition produced greater constriction than when inhibitors were given in reverse order (36±6% versus 23±5%). Selective COX-1 or COX-2 inhibition prior to L-NAME induced the expected degree of constriction. However, NOS inhibition followed by selective COX-2 inhibition caused unexpected ductal dilation. These findings are consistent with NO-induced activation of COX in the ductus arteriosus wall and the production of a COX-2-derived constrictor prostanoid that contributes to the balance of vasoactive forces that maintain fetal ductus arteriosus tone.

Although prostaglandin E2 (PGE2) vasodilates the ductus arteriosus, tocolysis with cyclooxygenase (COX) inhibitors delays postnatal ductus arteriosus closure. We used fetal mice and sheep to determine if PGE2 has a role in the development of ductus contractility that is distinct from its function as a vasodilator. Prolonged exposure of fetal ductus to PGE2, in vitro, increased expression of CaL- and K+-channel genes (CaLα1c, CaLβ2, Kir6.1, Kv1.5) (which regulate oxygen-induced constriction) without affecting genes that regulate Rho-kinase-mediated calcium sensitization. Conversely, chronic exposure to cyclooxygenase inhibitors in utero decreased expression of CaL- and K+-channel genes, without affecting Rho-kinase-associated genes. Chronic cyclooxygenase inhibition in utero decreased the ductus’ in vitro contractile response to stimuli that utilize CaL- and K+-channels (like O2 and K+), whereas the response to stimuli that act through Rho-kinase–mediated pathways (like U46619) was not significantly affected. Phosphodiesterase expression, which decreases the ductus’ sensitivity to cAMP/cGMP-dependent vasodilators, was increased by PGE2 exposure and decreased by cyclooxygenase inhibition, respectively. These studies identify potential downstream effectors of a PGE2-mediated, developmental program, regulating oxygen-induced ductus closure. Alterations in these effectors may explain the increased risk of patent ductus arteriosus (PDA) after in utero cyclooxygenase inhibition.

Vascular smooth muscle cells (VSMCs) are derived from distinct embryonic origins. Vessels originating from differing smooth muscle cell populations have distinct vascular and pathological properties involving calcification, atherosclerosis, and structural defects such as aneurysm and coarctation. We hypothesized that domains within a single vessel, such as the aorta, vary in phenotype based on embryonic origin. Gene profiling and myographic analyses demonstrated that embryonic ascending and descending aortic domains exhibited distinct phenotypes. In vitro analyses demonstrated that VSMCs from each region were dissimilar in terms of cytoskeletal and migratory properties, and retention of different gene expression patterns. Using the same analysis, we found that these same two domains are indistinguishable in the adult vessel. Our data demonstrate that VSMCs from different embryonic origins are functionally distinct in the embryonic mouse, but converge to assume a common phenotype in the aorta of healthy adults. These findings have fundamental implications for aortic development, function and disease progression.

BACKGROUND Increased oxygen tension at birth regulates physiologic events that are essential to postnatal survival, but the accompanying oxidative stress may also generate isoprostanes. We hypothesized that isoprostanes regulate ductus arteriosus (DA) function during postnatal vascular transition. METHODS Isoprostanes were measured by gas chromatography–mass spectrometry. DA tone was assessed by pressure myography. Gene expression was measured by quantitative PCR. RESULTS Oxygen exposure was associated with increased 8-iso-prostaglandin (PG)F2α in newborn mouse lungs. Both 8-iso-PGE2 and 8-iso-PGF2α induced concentration-dependent constriction of the isolated term DA, which was reversed by the thromboxane A2 (TxA2) receptor antagonist SQ29548. SQ29548 pretreatment unmasked an isoprostane-induced DA dilation mediated by the EP4 PG receptor. Exposure of the preterm DA to 8-iso-PGE2 caused unexpected DA relaxation that was reversed by EP4 antagonism. In contrast, exposure to 8-iso-PGF2α caused preterm DA constriction via TxA2 receptor activation. Further investigation revealed the predominance of the TxA2 receptor at term, whereas the EP4 receptor was expressed and functionally active from mid-gestation onward. CONCLUSION This study identifies a novel physiological role for isoprostanes during postnatal vascular transition and provide evidence that oxidative stress may act on membrane lipids to produce vasoactive mediators that stimulate physiological DA closure at birth or induce pathological patency of the preterm DA.