Left thoracic duct lymph flow responses to angiotensin II or atrial natriuretic factor infusion in the ovine fetus

Abstract

In the ovine fetus it is known that left thoracic duct lymph flow rate relative to body weight is four to five times adult levels, but it is not known whether the circulating hormones modulate fetal lymph flow. To explore this, we intravenously infused either angiotensin II (10 to 400 ng/min, n = 8) or atrial natriuretic factor (500 to 1000 ng/min, n = 8) into chronically catheterized fetal sheep for 30 minutes. Significant increases occurred in fetal arterial (p less than 0.0001) and venous (p = 0.018) pressures during the angiotensin II infusion, and thoracic duct lymph flow rate underwent a dose-dependent increase (r = 0.888, p = 0.0033). With termination of the angiotensin II infusion, fetal vascular pressures rapidly returned to control levels, and lymph flow fell from 18.8% +/- 10.1% (mean +/- SE) above control to 13.7% +/- 7.7% below preinfusion levels (p less than 0.01). During the atrial natriuretic factor infusion, fetal arterial pressure and circulating blood volume decreased significantly (p less than 0.01), whereas thoracic duct lymph flow was unchanged. After termination of the atrial natriuretic factor infusion, fetal arterial pressure returned toward control, blood volume remained reduced, and lymph flow rate underwent a transient rise to 35.6% +/- 15.7% (p less than 0.05) above control levels. These data suggest that angiotensin II and atrial natriuretic factor have significant but opposite effects on fetal thoracic duct lymph flow rate, with angiotensin II stimulating and atrial natriuretic factor suppressing lymph flow.