Maternal ovine placental vascular responses to adenosine.

We have examined the effect of adenosine given via retrograde uterine artery catheter at 25 mg/min to nine chronically catheterized near-term sheep pretreated with angiotensin II, 5 micrograms/min, via the jugular vein. Blood flows were measured by the microsphere technique. Flows were measured at rest, after 10 minutes of angiotensin II infusion, and after 1.5 minute of adenosine infusion. Blood pressure increased with angiotensin II infusion from 101 +/- 2.63 to 130 +/- 4.33 mm Hg (p less than 0.05) and then remained unchanged with local adenosine infusion at 129 +/- 4.33 mm Hg (NS). Organ resistances were: Tissue Control Angiotensin II Adenosine Uterine resistance/gm 299 +/- 0.04 767 +/- 83 (p less than 0.05) 355 +/- 37.7 (p less than 0.05) Cotyledonary resistance/gm 37.9 +/- 4.83 48.1 +/- 4.93 (p less than 0.05) 50.10 +/- 5.27 (p less than 0.05) The experimental uterine tissue resistance increased with angiotensin II and showed vasodilation in response to adenosine. The cotyledonary resistance increased with angiotensin II infusion but showed no change in response to adenosine. The maternal-placental response was anomalous. Angiotensin II-induced maternal-placental vasoconstriction cannot be opposed by the exogenous administration of adenosine.