Mesenteric artery reactivity and small intestine morphology in a chicken model of hypoxia-induced fetal growth restriction.

Infants with intrauterine growth retardation are prone to intestinal disorders. The morphological and molecular mechanisms that lead to these complications are not completely understood and suitable experimental models are necessary. The aim of this study was to characterize mesenteric artery (MA) reactivity, small intestine morphometry and intestinal expression of vascular endothelial growth factor (VEGF) in a chicken model of hypoxia-induced fetal growth restriction. Chicken embryos (15 and 19 incubation days) and hatchlings (<3-h-old and 1-d-old) were incubated under hypoxic (15% O2 from day 0 to day 19 of incubation) or normoxic conditions. Vascular reactivity was studied using wire miography. Intestinal morphometry was assessed in hematoxyline-eosine-stained sections. VEGF mRNA expression was determined by RT-PCR analysis. Hypoxia increased the responsiveness of chicken embryo MAs to the adrenergic agonist norepinephrine, the polypeptide endothelin (ET)-1, and the nitric oxide donor sodium nitroprusside and decreased the responsiveness to the endothelium-dependent relaxant agonist acetylcholine. However, the majority of these alterations, with the exception of the hyperresponsiveness to ET-1, were not present in the hypoxic hatchlings. When intestinal histology was analyzed, subtle hypoxia-induced changes were noted in the villi and the muscularis propria from the hatchlings. Hypoxic incubation also diminished the expression of VEGF mRNA in the terminal ileum of the hatchlings. In conclusion, chronic moderate hypoxia during incubation results in subtle but significant alterations in chicken MA reactivity, small intestine morphology and VEGF expression. Whether these alterations may have a direct effect on the functional status of the intestine remains to be investigated.

Chronic moderate hypoxia during in ovo development alters arterial reactivity in chickens.

We previously observed arterial sympathetic hyperinnervation and endothelial dysfunction in the chicken embryo after exposure to chronic hypoxia. We now investigate whether changes in arterial properties could also be observed at 14-15 weeks of life. Eggs of White Leghorn chicken were incubated under normoxic or moderately hypoxic (15% O2 from days 6-19 of a 21-day incubation) conditions. Experiments were performed at 14-15 weeks of life under standard conditions (Hm: males exposed to hypoxia; Hf: females exposed to hypoxia; Nm: males exposed to normoxia; Nf: females exposed to normoxia). Body weight at hatching and at 14-15 weeks was not affected by in ovo exposure to hypoxia. Mean arterial pressure and heart rate were not significantly altered by chronic in ovo hypoxia. However, isolated femoral arteries were more sensitive to electrical stimulation (frequency in Hz of half-maximal contraction, Hm: 1.62+/-0.33, Hf: 1.92+/-0.88, Nm: 2.49+/-0.49, Nf: 2.83+/-0.31) and pharmacological stimulation of peri-arterial sympathetic nerves (contraction in N/m in response to tyramine: Hm: 5.27+/-0.85, Hf: 4.10+/-0.9, Nm: 2.26+/-0.67, Nf: 3.65+/-0.51, p=0.07) after in ovo hypoxia. In side branches of the femoral artery, the effect of NO synthase blockade with L-NAME on contraction (in N/m) in response to high K+ (Hm: 0.35+/-0.91, Hf: 1.29+/-0.36, Nm: 2.88+/-0.19, Nf: 2.79+/-0.58) and on the sensitivity to acetylcholine (DeltapD2, H: 0.32+/-0.11, N: 0.62+/-0.05) was reduced after in ovo hypoxia. The present study shows that exposure to chronic moderate hypoxia during development affects the contractile and relaxing arterial responses of 14- to 15-week-old chickens. Although hypoxia did not lead to changes in blood pressure at this age, the observed effects on arterial sympathetic and endothelial function may represent early signs of future cardiovascular abnormalities.

Direct effects of acute hypoxia on the reactivity of peripheral arteries of the chicken embryo.

In the chicken embryo, acute hypoxemia results in cardiovascular responses, including an increased peripheral resistance. We investigated whether local direct effects of decreased oxygen tension might participate in the arterial response to hypoxemia in the chicken embryo. Femoral arteries of chicken embryos were isolated at 0.9 of incubation time, and the effects of acute hypoxia on contraction and relaxation were determined in vitro. While hypoxia reduced contraction induced by high K(+) to a small extent (-21.8 +/- 5.7%), contractile responses to exogenous norepinephrine (NE) were markedly reduced (-51.1 +/- 3.2%) in 80% of the arterial segments. This effect of hypoxia was not altered by removal of the endothelium, inhibition of NO synthase or cyclooxygenase, or by depolarization plus Ca(2+) channel blockade. When arteries were simultaneously exposed to NE and ACh, hypoxia resulted in contraction (+49.8 +/- 9.3%). Also, relaxing responses to ACh were abolished during acute hypoxia, while the vessels became more sensitive to the relaxing effect of the NO donor sodium nitroprusside (pD(2): 5.81 +/- 0.21 vs. 5.31 +/- 0.27). Thus, in chicken embryo femoral arteries, acute hypoxia blunts agonist-induced contraction of the smooth muscle and inhibits stimulated endothelium-derived relaxation factor release. The consequences of this for in vivo fetal hemodynamics during acute hypoxemia depend on the balance between vasomotor influences of circulating catecholamines and those of the endothelium.