NO supports right ventricular flow dominance and whole body O(2) utilization in midgestation fetal lambs.
It is unknown if nitric oxide (NO) modulates the relative levels of left (LV) and right (RV) ventricular output, fetal O2 consumption, or blood flow distribution between the body and placenta at midgestation. To address these questions, six fetal lambs were instrumented at 89-96 days gestation (term 147 days), and blood flows were measured with radioactive microspheres 3-4 days later at baseline and after inhibition of NO synthesis with 10 mg/kg (L-NNA10) and 25 mg/kg (L-NNA25) N(omega)-nitro-L-arginine. LV output fell by 74 +/- 15 ml. min(-1). kg(-1) at L-NNA10 (P < 0.005), whereas RV output decreased by 90 +/- 18 ml. min(-1). kg(-1) at L-NNA10 (P < 0.02) and by a further 80 +/- 22 ml. min(-1). kg(-1) at L-NNA25 (P < 0.05). As a result, RV output exceeded LV output at baseline (P = 0.03) and L-NNA10 (P < 0.02) but not at L-NNA25. Fetal body blood flow fell by 95 +/- 25 ml. min(-1). kg(-1) at L-NNA10 (P < 0.01), but because placental blood flow decreased by 70 +/- 22 ml. min(-1). kg(-1) at L-NNA10 (P < 0.01) and a further 71 +/- 21 ml. min(-1). kg(-1) at L-NNA25 (P < 0.01), the fetal body-to-placental blood flow ratio was near unity at baseline and L-NNA10 but rose to 1.5 +/- 0.3 at L-NNA25 (P < 0.05). In association with these flow changes, fetal O2 consumption declined by 1.4 +/- 0.3 ml. min(-1). kg(-1) at L-NNA10 (P < 0.05) and by a further 1.5 +/- 0.6 ml. min(-1). kg(-1) at L-NNA25 (P < 0.02). These findings suggest that, in midgestation fetal lambs, NO supports an RV flow dominance, whole body O2 utilization, and the maintenance of a near-equal fetoplacental blood flow distribution.
Centre for Heart and Chest Research, Department of Medicine and Institute of Reproduction and Development, Monash University, Clayton, Victoria, Australia 3168. joe.smolich@med.monash.edu.au
J J
JJ
Smolich
D000818:Animals; D001783:Blood Flow Velocity / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure; D002245:Carbon Dioxide / Q000097:blood; D005260:Female; D005312:Fetal Blood / Q000502:physiology; D005333:Fetus; D006321:Heart / Q000196:embryology*; D006339:Heart Rate; D006439:Hemodynamics / Q000187:drug effects / Q000502:physiology*; D009569:Nitric Oxide / Q000502:physiology*; D019335:Nitroarginine / Q000494:pharmacology*; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000187:drug effects; D011247:Pregnancy; D012756:Sheep; D016277:Ventricular Function, Left / Q000187:drug effects / Q000502:physiology*; D016278:Ventricular Function, Right / Q000187:drug effects / Q000502:physiology; D019323:omega-N-Methylarginine / Q000494:pharmacology*
D002245:Carbon Dioxide; D019335:Nitroarginine; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D010100:Oxygen