PLASMA ADENOSINE RESPONSES DURING REPEATED EPISODES OF UMBILICAL-CORDOCCLUSION

OBJECTIVE: The purpose of this study was to measure changes in adenosi ne concentration in fetal arterial blood with use of an animal model o f intermittent cord occlusion. Adenosine has been shown to be a potent vasodilator and inhibitor of metabolic processes in the adult, action s that help maintain a balance between oxygen supply and oxygen use. S TUDY DESIGN: After a 30-minute control period, five chronically instru mented fetal sheep (125 +/- 2.2 days' gestation) were subjected to a 1 -minute cord occlusion, followed by a 2-minute recovery. The occlusion -release cycle was repeated 20 times. Then, after 1-hour interim, the same 20 cycles of occlusion were repeated. Fetal blood was collected d uring cord occlusion and 30 seconds after release. RESULTS: The plasma adenosine concentration averaged 0.82 +/- 0.19 mu mol/L during the in itial control period. The plasma adenosine concentration increased sig nificantly to 1.06 +/- 0.23 mu mol/L and 1.19 +/- 0.20 mu mol/L during and after the fifth occlusion (p < 0.05 and 0.01, respectively). The plasma adenosine concentration reached a maximal level of 1.31 +/- 0.2 8 mu mol/L after the twentieth cord occlusion. The concentration durin g the second group of occlusions was also higher than that during the control period lo < 0.05) but not higher than that during the first re covery period. By the conclusion of the study the plasma adenosine con centration had returned to 0.70 +/- 0.16 mu mol/L. CONCLUSION: Plasma adenosine increases cyclically with intermittent cord occlusion in the near-term fetal sheep, but the response is attenuated or lost after 2 hours. These results together with those of earlier studies are consi stent with a hypoxic protective action of adenosine that is largely re stricted to early time periods of continuing intermittent hypoxia.