Response of the Fetal Mesenteric Microvascular System to Maternal Hypoxia 1

Summary

The effect of maternal hypoxia on the microvascular system of fetal and pregnant adult rabbits was studied. The response of the fetal mesenteric microvasculature to hypoxia was vasoconstriction, reduced flow in the large arterioles and venules, and severely reduced flow in most capillaries. This response occurred within 30 min after initiation of 8% O₂; recovery occurred within 20 min after removal of the low oxygen mixture. Similar findings were obtained in the maternal mesenteric microvaseulature but the responses were more rapid, occurring within 20 min, with recovery within 5–10 min. The responses appeared to be mediated by an oxygen dependant, alpha-adrenergic mechanism since, during recovery, flow and vascular diameter were restored in parallel with the blood pO₂ even though blood pH still was depressed and pCO₂ was elevated, and since the vasoconstrictive response could be blocked by phentolamine but not by propranolol.