Stimuli for fetal swallowing: systemic factors

Abstract

Although the fetal gastrointestinal tract is believed to be a major site of amniotic fluid absorption, there is little information with regard to the acute regulation of fetal swallowing. A model for the study of ovine fetal swallowing was developed to incorporate electromyograms, an esophageal flow probe, and a computer data acquisition and analysis program. The fetal swallowing responses to two primary thirst stimuli, plasma hyperosmolality and angiotensin II, were studied. On alternate days, chronically prepared fetal lambs (131 +/- 2 days) received an intravenous infusion of angiotensin II (100 ng/kg per minute) or bolus injections (3 ml) of 0.15 and 3.97 mol/L saline solution. In response to the angiotensin II infusion, fetal systolic (49.3 to 64.7 mm Hg; p less than 0.05) and diastolic (31.1 to 40.5 mm Hg; p less than 0.05) blood pressures significantly increased. However, fetal swallowing did not change from basal rates of 0.85 swallows per minute and a net esophageal flow of 0.98 ml/min. In response to the injection of 3.97 mol/L saline solution, fetal plasma osmolality increased (292 to 306 mOsm; p less than 0.05) and subsequently decreased to 300 mOsm at 15 minutes after the injection. Within 1 minute after injection of the hypertonic saline solution, fetal swallowing activity (6.0 swallows per minute; p less than 0.05) and net esophageal flow (2.4 ml/min; p less than 0.05) significantly increased. Swallowing returned to basal values within 5 minutes after the injection. The data indicate that ovine fetal responses to osmolar thirst challenges are intact at 130 days' gestation. Fetal swallowing and thus amniotic fluid volume may be affected by fetal responses to in utero stimuli.