Major vasodilator role for nitric oxide in the gastrointestinal circulation of the mid-gestation fetal lamb.
As nitric oxide (NO) may be a particularly important vasodilator in early life, we investigated its role in the regulation of the gastrointestinal (GI) circulation at mid-gestation. Cardiac output and GI blood flow were measured by the radioactive microsphere technique in eight chronically instrumented and unanesthetized mid-gestation fetal sheep. Mean arterial pressure (MAP), heart rate, blood flow, oxygen delivery, and vascular resistance were determined before and after infusion of the specific NO synthase inhibitor, Nomega-nitro-L-arginine (L-NNA) at doses of 10 and 25 mg/kg. In response to L-NNA infusion, MAP increased (p < 0.01) and combined ventricular output decreased (p < 0.001). GI blood flow and oxygen delivery decreased and vascular resistance increased in the stomach and all segments of the small and large intestine (all p < 0.001). The greatest reduction in blood flow was in the small intestine (p < 0.01) and the basal differential pattern of small intestinal blood flow exceeding large intestinal flow was completely abolished. These changes were much greater than those previously described in late-gestation fetuses. Our results suggest that, at mid-gestation, NO plays a major role in the regulation of blood flow and vascular tone across all segments of the fetal GI tract, with its effects being more pronounced than later in development.
Fan
W Q
WQ
Institute of Reproduction and Development, Monash University, Clayton, Victoria, Australia.
Smolich
J J
JJ
Wild
J
J
Yu
V Y
VY
Walker
A M
AM
D000818:Animals; D004064:Digestive System / Q000098:blood supply*; D005314:Embryonic and Fetal Development; D005260:Female; D005333:Fetus / Q000502:physiology*; D005865:Gestational Age; D006340:Heart Rate, Fetal; D009569:Nitric Oxide / Q000502:physiology*; D010101:Oxygen Consumption; D011247:Pregnancy; D012039:Regional Blood Flow / Q000502:physiology; D012756:Sheep; D014664:Vasodilation / Q000502:physiology*
D009569:Nitric Oxide