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1 Department of Surgery, University Hospital Maastricht, and Departments of 2 Pharmacology, 3 Biophysics, and 4 Physiology, Cardiovascular Research Institute Maastricht, Maastricht University, 6200 MD Maastricht, the Netherlands
Changes in mesenteric arterial diameters were studied
using intravital microscopy in chick fetuses at days 13 and
17 of incubation, corresponding to 0.6 and 0.8 fetal
incubation time, both during 5 min of hypoxia followed by 5 min of
reoxygenation and after topical administration of increasing
concentrations (10
6-10
2 M) of
norepinephrine (NE) and acetylcholine (ACh). Baseline diameters of
second-order mesenteric arteries increased from 56 µm at 0.6 incubation to 75 µm at 0.8 incubation. Acute hypoxia induced a reduction in arterial diameter to 87 ± 4.4% of baseline at 0.6 incubation and to 44 ± 6.7% at 0.8 incubation (P < 0.01). During reoxygenation, mesenteric arteries dilated to 118 ± 6.5% and 121 ± 7.5% of baseline at 0.6 and 0.8 fetal
incubation time, respectively. Phentolamine did not affect the
vasoconstriction during hypoxia at 0.6 incubation, whereas this
-adrenergic antagonist significantly attenuated the
vasoconstrictor response at 0.8 incubation (to 93 ± 2.7% of
baseline, P < 0.01). Topical NE induced maximal
vasoconstriction to 71 ± 3% of baseline at 0.6 incubation and to
35 ± 3.8% at 0.8 incubation (P < 0.01). Maximal
vasodilation to topical ACh was 113 ± 4.4% and 122 ± 4.8%
of baseline at 0.6 and 0.8 incubation, respectively. These in vivo
findings show that fetal mesenteric arteries constrict in response to
acute hypoxia and that the increase in magnitude of this
vasoconstrictor response from 0.6 to 0.8 of fetal development results
from an increase in adrenergic constrictor capacity.
cardiovascular development; hypoxia; necrotizing enterocolitis; norepinephrine; acetylcholine
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