ADENOSINE MEDIATES HYPOXIC RELEASE OF ARGININE-VASOPRESSIN IN FETAL SHEEP

The effects of adenosine on plasma arginine vasopressin (AVP) concentr ations were determined in chronically catheterized fetal sheep (>0.8 t erm). Infusion of adenosine [0.35 +/- 0.01 (SE) mg.min(-1).kg(-1)] int o the inferior vena cava of six fetuses caused a transient fall in art erial PO2 (by similar to 3 Torr), a slight reduction in arterial pH, a nd a 5- to 6-mmHg decrease in diastolic pressure without significantly affecting systolic or mean arterial values. A lower rate of infusion (0.19 +/- 0.01 mg.min(-1).kg(-1)) in five fetuses had virtually no eff ect on arterial blood gases, pH, or arterial pressures. Both the low- and high-dose adenosine infusions significantly increased fetal plasma AVP concentrations (1.7 +/- 0.2 to 25 +/- 7 pg/ml and 1.6 +/- 0.1 to 54 +/- 8 pg/ml, respectively). Intravenous infusion of papaverine lowe red fetal diastolic and mean arterial pressures by similar to 8 mmHg b ut had no significant effect on plasma levels of AVP. During an hour o f isocapnic hypoxia (arterial PO2 12-13 Torr), fetal plasma AVP levels increased from 1.7 +/- 0.2 to 40 +/- 6 pg/ml. Intra-arterial infusion of the adenosine receptor antagonist 8-(p-sulfophenyl)-heophylline si gnificantly blunted the hypoxia-induced rise in plasma AVP concentrati ons to a maximum mean level of 11 +/- 6 pg/ml. These results indicate that 1) adenosine causes a dose-dependent increase in plasma AVP conce ntrations and 2) a hypoxia-induced rise in fetal adenosine levels trig gers vasopressin release.