Plasma adenosine responses during repeated episodes of umbilical cord occlusion, , ,

Objective: The purpose of this study was to measure changes in adenosine concentration in fetal arterial blood with use of an animal model of intermittent cord occlusion. Adenosine has been shown to be a potent vasodilator and inhibitor of metabolic processes in the adult, actions that help maintain a balance between oxygen supply and oxygen use. Study design: After a 30-minute control period, five chronically instrumented fetal sheep (125 ± 2.2 daysʹ 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 a 1-hour interim, the same 20 cycles of occlusion were repeated. Fetal blood was collected during cord occlusion and 30 seconds after release. Results: The plasma adenosine concentration averaged 0.82 ± 0.19 μmol/L during the initial control period. The plasma adenosine concentration increased significantly to 1.06 ± 0.23 μmol/L and 1.19 ± 0.20 μmol/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 ± 0.28 μmol/L after the twentieth cord occlusion. The concentration during the second group of occlusions was also higher than that during the control period (p < 0.05) but not higher than that during the first recovery period. By the conclusion of the study the plasma adenosine concentration had returned to 0.70 ± 0.16 μmol/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 consistent with a hypoxic protective action of adenosine that is largely restricted to early time periods of continuing intermittent hypoxia. (Am J Obstet Gynecol 1997;177:395-401.)