Effect of oral sucrose on ingestive behavior in the near-term ovine fetus

BACKGROUND: Dipsogen-mediated ingestion matures acutely in late gestation because the preterm fetus may demonstrate absent responses to putative dipsogens, Although central appetite-mediated ingestive behavior is functional near term, it is unknown whether peripheral mechanisms for stimulation of appetite also are functional. In the adult, sweet taste stimulates and potentiates ingestive behavior, We sought to determine whether oropharyngeal sucrose exposure stimulates ingestive behavior in the near-term ovine fetus. STUDY DESIGN: Time-dated pregnant ewes with near-term singleton fetuses (n = 6) were chronically prepared with fetal vascular and sublingual catheters and esophageal electromyogram electrodes and studied at 129 +/- 1 days of gestation. After an initial 2-hour baseline period, successive solutions of distilled water and 2.5%, 101%, and 40% sucrose were infused sublingually (0.25 mL/min), each for 2 hours. Maternal and fetal arterial blood samples were drawn at timed intervals. RESULTS: During the basal period, fetal swallowing averaged 0.9 +/- 0.1 swallows per minute. Swallowing did not change in response to distilled water (0.9 +/- 0.2 swallows per minute) but significantly increased after sublingual infusion of 2.5% sucrose (1.3 +/- 0.1 swallows per minute), 10% sucrose (1.8 +/- 0.1 swallows per minute), and 40% sucrose (1.3 +/- 0.1 swallows per minute, P =.001). There were no significant changes in other fetal or maternal parameters. CONCLUSIONS: The stimulation of fetal swallowing in response to sublingual sucrose infusion suggests that taste-mediated ingestive behavior is functional in the near-term fetus and that both central and systemic appetite mechanisms are intact near term. Fetal swallowing increased in response to an increase in sucrose concentration to peak at 10% and then decreased with further rises in concentration, possibly mediated by aversive fetal reaction to a high-intensity sucrose concentration.