Vascular responses of umbilical-placental circulation to vasodilators in fetal lambs.
It has been suggested that the umbilical-placental circulation is maximally vasodilated under normal conditions. To test this hypothesis, we investigated the effect of vasodilators on umbilical-placental vascular resistance. In nine chronically instrumented fetal lambs, catheters were placed in the descending aorta, umbilical artery, umbilical vein, and inferior vena cava. Umbilical-placental blood flow was measured by an electromagnetic flow probe placed around the common umbilical artery. Forskolin and nitroglycerin both dilated the umbilical-placental circulation, causing a dose-dependent decrease in umbilical-placental resistance to approximately 80% of baseline, indicating that the umbilical-placental circulation has some dilatory reserve. Both the adenosine 3',5'-cyclic monophosphate and the guanosine 3',5'-cyclic monophosphate mechanisms, which are directly stimulated by forskolin and nitroglycerin, respectively, are functional in the umbilical-placental circulation. However, the vasodilators prostacyclin and adenosine, which act through specific cell membrane receptors, have no effect on the umbilical-placental resistance. The inability of these agents to dilate the umbilical-placental circulation could be due to a lack of the appropriate receptors in the umbilical-placental vasculature.
Paulick
R P
RP
Cardiovascular Research Institute, University of California, San Francisco 94143.
Meyers
R L
RL
Rudolph
A M
AM
D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D005576:Colforsin / Q000494:pharmacology; D011464:Epoprostenol / Q000494:pharmacology; D005333:Fetus / Q000502:physiology*; D005996:Nitroglycerin / Q000494:pharmacology; D010920:Placenta / Q000098:blood supply*; D012039:Regional Blood Flow / Q000187:drug effects; D012756:Sheep; D014470:Umbilical Cord / Q000098:blood supply*; D014655:Vascular Resistance / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology*
D014665:Vasodilator Agents; D005576:Colforsin; D011464:Epoprostenol; D005996:Nitroglycerin; D000241:Adenosine