Autonomic and arginine vasopressin modulation of the hypoxia-induced atrial natriuretic factor release in immature and mature ovine fetuses

OBJECTIVE: This study investigated the maturational change in the atrial natriuretic factor response to hypoxia in ovine fetuses and the role of the autonomic nervous system and arginine vasopressin in modulating this response. STUDY DESIGN: Chronically catheterized ovine fetuses from 110 to 135 days' gestation were subjected to 30 minutes of hypoxia. The fetuses were either intact, treated with hexamethonium to block the autonomic nervous system, or treated with a pressor antagonist of arginine vasopressin. RESULTS: Hypoxia elevated plasma atrial natriuretic factor levels by 1635 ± 265 pg/ml in immature fetuses; this response was greater than the increase of 748 ± 189 pg/ml in mature fetuses (p < 0.0001). Blockade of the autonomic nervous system reduced the atrial natriuretic factor response and suppressed the vascular pressure changes to hypoxia in immature but not in mature fetuses. A vasopressin pressor antagonist suppressed the atrial natriuretic factor but not vascular pressure responses to hypoxia in mature fetuses. CONCLUSIONS: This study demonstrates that the immature fetus manifested a greater atrial natriuretic factor response to hypoxia than did the mature fetus. This enhanced response appeared to be dependent on the modulatory effects of the autonomic nervous system on vascular pressures during hypoxia. In addition, arginine vasopressin appeared to augment the atria[ natriuretic factor response to hypoxia in the mature fetus independent of vascular pressure changes.