The fetal swallowing and endocrine responses to systemic hypotension were studied in five chronically instrumented ovine fetuses (125 +/- 2 days). Fetuses were prepared with bipolar electrodes inserted in the thyrohyoid muscle, nuchal esophagus, and thoracic esophagus, a flow probe surrounding the thoracic esophagus, and arterial and venous catheters. In response to an intravenous infusion of sodium nitroprusside, fetal mean arterial blood pressure decreased from 50.8 +/- 3.6 to 41.7 +/- 3.8 mmHg. Fetal plasma renin activity (5.0 +/- 1.4-25.1 +/- 10.3 ng.ml-1.h-1) and arginine vasopressin (5.6 +/- 4.5-26.3 +/- 21.0 pg/ml) increased, while fetal swallowing electromyogram activity (7.3 +/- 1.1-1.9 +/- 0.3 swallows/10 min) and esophageal flow (5.5 +/- 3.1-1.2 +/- 0.9 ml/10 min) significantly decreased during the nitroprusside infusion. These results indicate a suppression of fetal swallowing in response to systemic hypotension despite stimulation of the renin-angiotensin system.