Saskia van der Sterren

Morphological and Functional Alterations of the Ductus Arteriosus in a Chicken Model of Hypoxia-Induced Fetal Growth Retardation

The hypoxic conditions in which children with intrauterine growth retardation (IUGR) develop are hypothesized to alter the development of the ductus arteriosus (DA). We aimed to evaluate the effects of in ovo hypoxia on chicken DA morphometry and reactivity. Hypoxia (15% O2 from day 6 to 19 of the 21-d incubation period) produced a reduction in the body mass of the 19-d fetuses and a shortening of right and left DAs. However, ductal lumen and media cross-sectional areas were not affected by hypoxia. The ductal contractions induced by oxygen, KCl, H2O2, 4-aminopyridine, and endothelin-1 were similar in control and hypoxic fetuses. In contrast, the DAs from the hypoxic fetuses showed increased contractile responses to norepinephrine and phenylephrine and impaired relaxations to acetylcholine, sodium nitroprusside, and isoproterenol. The relaxations induced by 8-Br-cGMP, forskolin, Y-27632, and hydroxyfasudil were not altered by chronic hypoxia. In conclusion, chronic in ovo hypoxia-induced growth retardation in fetal chickens and altered the response of the DA to adrenergic agonists and to endothelium-dependent and -independent relaxing agents. Our observations support the concept that prolonged patency of the DA in infants with IUGR may be partially related with hypoxia-induced changes in local vascular mechanisms.

Prenatal cardiovascular shunts in amniotic vertebrates

During amniotic vertebrate development, the embryo and fetus employ a number of cardiovascular shunts. These shunts provide a right-to-left shunt of blood and are essential components of embryonic life ensuring proper blood circulation to developing organs and fetal gas exchanger, as well as bypassing the pulmonary circuit and the unventilated, fluid filled lungs. In this review we examine and compare the embryonic shunts available for fetal mammals and embryonic reptiles, including lizards, crocodilians, and birds. These groups have either a single ductus arteriosus (mammals) or paired ductus arteriosi that provide a right-to-left shunt of right ventricular output away from the unventilated lungs. The mammalian foramen ovale and the avian atrial foramina function as a right-to-left shunt of blood between the atria. The presence of atrial shunts in non-avian reptiles is unknown. Mammals have a venous shunt, the ductus venosus that diverts umbilical venous return away from the liver and towards the inferior vena cava and foramen ovale. Reptiles do not have a ductus venosus during the latter two thirds of development. While the fetal shunts are well characterized in numerous mammalian species, much less is known about the developmental physiology of the reptilian embryonic shunts. In the last years, the reactivity and the process of closure of the ductus arteriosus have been characterized in the chicken and the emu. In contrast, much less is known about embryonic shunts in the non-avian reptiles. It is possible that the single ventricle found in lizards, snakes, and turtles and the origin of the left aorta in the crocodilians play a significant role in the right-to-left embryonic shunt in these species.

Vasoactivity of the gasotransmitters hydrogen sulfide and carbon monoxide in the chicken ductus arteriosus

Besides nitric oxide (NO) and carbon monoxide (CO), hydrogen sulfide (H(2)S) is a third gaseous messenger that may play a role in controlling vascular tone and has been proposed to serve as an O(2) sensor. However, whether H(2)S is vasoactive in the ductus arteriosus (DA) has not yet been studied. We investigated, using wire myography, the mechanical responses induced by Na(2)S (1 μM-1 mM), which forms H(2)S and HS(-) in solution, and by authentic CO (0.1 μM-0.1 mM) in DA rings from 19-day chicken embryos. Na(2)S elicited a 100% relaxation (pD(2) 4.02) of 21% O(2)-contracted and a 50.3% relaxation of 62.5 mM KCl-contracted DA rings. Na(2)S-induced relaxation was not affected by presence of the NO synthase inhibitor l-NAME, the soluble guanylate cyclase (sGC) inhibitor ODQ, or the K(+) channel inhibitors tetraethylammonium (TEA; nonselective), 4-aminopyridine (4-AP, K(V)), glibenclamide (K(ATP)), iberiotoxin (BK(Ca)), TRAM-34 (IK(Ca)), and apamin (SK(Ca)). CO also relaxed O(2)-contracted (60.8% relaxation) and KCl-contracted (18.6% relaxation) DA rings. CO-induced relaxation was impaired by ODQ, TEA, and 4-AP (but not by L-NAME, glibenclamide, iberiotoxin, TRAM-34 or apamin), suggesting the involvement of sGC and K(V) channel stimulation. The presence of inhibitors of H(2)S or CO synthesis as well as the H(2)S precursor L-cysteine or the CO precursor hemin did not significantly affect the response of the DA to changes in O(2) tension. Endothelium-dependent and -independent relaxations were also unaffected. In conclusion, our results indicate that the gasotransmitters H(2)S and CO are vasoactive in the chicken DA but they do not suggest an important role for endogenous H(2)S or CO in the control of chicken ductal reactivity.

Contractile effects of 15-E2t-isoprostane and 15-F2t-isoprostane on chicken embryo ductus arteriosus.

Isoprostanes (IsoPs) are prostaglandin (PG)-like compounds produced nonenzymatically by free radical-catalyzed peroxidation of arachidonate. Cyclooxygenase-derived PGs play a major role in ductus arteriosus (DA) homeostasis but the putative role of IsoPs has not been studied so far. We investigated, using wire myography, the vasoactive effects of 15-E(2t)-IsoP and 15-F(2t)-IsoP in the chicken embryo DA, pulmonary artery (PA) and femoral artery (FA). 15-E(2t)-IsoP and 15-F(2t)-IsoP contracted DA, PA, and FA rings in a concentration-dependent manner. 15-E(2t)-IsoP was equally efficacious (mean±SE E(max)=1.25±0.06 mN/mm) as and more potent (-log of molar concentration producing 50% of E(max)=pEC(50)=7.00±0.04) than the thromboxane-prostanoid (TP) receptor agonist U46619 (E(max)=1.49±0.11 mN/mm; pEC(50)=6.48±0.05) in contracting chicken DA (pulmonary side). 15-F(2t)-IsoP was less potent (pEC(50)=5.74±0.11) and less efficacious (E(max)=0.96±0.11) than U46619. Concentration-dependent contractions to 15-E(2t)-IsoP and U46619 in DA rings were competitively inhibited by the TP receptor antagonist SQ29548 (0.1 μM to 10 μM) with no decrease in the E(max) values. SQ29548 also inhibited concentration-dependent contraction to 15-F(2t)-IsoP but this inhibition was associated with a decrease in E(max). Pre-incubation of DA rings with 15-F(2t)-IsoP inhibited responses to U46619 and, in vessels contracted with U46619 (1 μM), 15-F(2t)-IsoP (>1 μM) evoked a relaxant response. Enzyme immunoassay did not show a measurable release of 15-F(2t)-IsoP by DA rings. In conclusion, 15-E(2t)-IsoP is a potent and efficacious constrictor of chicken DA, acting through TP receptors. In contrast, 15-F(2t)-IsoP is probably acting as a partial agonist at TP receptors. We speculate that IsoPs play a role in the control of chicken DA tone and could participate in its closure.