Fetal Swallowing Activity Research Articles

Ovine fetal swallowing and renal responses to oligohydramnios

Amniotic fluid (AF) volume regulation is dependent on a balance between fluid production and fluid resorption. We examined the effects of reduced AF volume on AF production by fetal urine and resorption by fetal swallowing and the response of these parameters to AF volume replacement. Eight time-dated pregnant ewes (125 +/- 1 days gestation) were studied before (day 1) and after (day 3) AF and fetal urine drainage. Drainage resulted in a significant decrease in AF volume (415 +/- 89 to 157 +/- 36 ml). Fetal urine osmolality increased (139 +/- 10 to 286 +/- 33 mosmol/kgH2O), while urine flow did not change significantly (0.31 +/- 0.04 to 0.23 +/- 0.06 ml/min), resulting in nonsignificant increases in osmolar, sodium, and chloride excretions. Fetal electromyographic swallowing activity decreased 30% (1.0 +/- 0.1 to 0.7 +/- 0.1 swallows/min; P < 0.05), while net esophageal flow decreased 74% (0.31 +/- 0.12 to 0.07 +/- 0.04 ml/min; P < 0.05). On day 4, 0.15 M NaCl (500 ml; 37 degrees C) was administered into the AF over 30 min. During the 2 h after reinfusion, urine flow (0.29 +/- 0.07 to 0.40 +/- 0.09 ml/min) and osmolar sodium and chloride excretion significantly increased, though fetal swallowing activity and esophageal flow did not change. Thus the ovine fetus responded to reduced AF volume by maintaining AF production and decreasing AF resorption. In response to AF replacement, urine flow increased while fetal swallowing activity did not change, consistent with an intramembranous pathway for fetal AF resorption.

Central angiotensin II stimulation of ovine fetal swallowing.

In the late-gestation ovine fetus, spontaneous swallowing occurs primarily during fetal low-voltage electrocortical (ECoG) activity in association with fetal breathing movements. Fetal swallowing activity may be stimulated in response to systemic or carotid plasma hyperosmolality, although not to increased plasma angiotensin II (ANG II) levels. In view of the potent dipsogenic effects of central, but not peripheral, ANG II in adult sheep, the present study investigated the effect of intracerebroventricular (ICV) ANG II on fetal swallowing activity. Six ovine fetuses (127 +/- 1 days) were chronically prepared with electromyogram and cortical electrodes and with vascular and lateral ventricle catheters. After a 2-h control period, fetuses received ICV injections of artificial cerebrospinal fluid and increasing concentrations of ANG II (0.1, 1.0, 10, 100, and 500 ng/kg). Fetal ECoG activity did not change, although fetal swallowing activity significantly increased in response to the 100- and 500- ng/kg ANG II doses (1.20 +/- 0.14 to 3.34 +/- 0.59 and 3.46 +/- 0.81 swallows/min of low-voltage ECoG, respectively). In response to the highest ANG II dose, fetal plasma arginine vasopressin levels significantly increased (5.7 +/- 1.2 to 17.2 +/- 4.6 pg/ml). ICV ANG II stimulation of fetal swallowing and arginine vasopressin secretion demonstrates that central ANG II dipsogenic mechanisms are intact by 0.9 of ovine gestation.

Fetal swallowing: response to graded maternal hypoxemia

A computer-based system, incorporating electromyography (EMG) and esophageal fluid flow measurement, was used to determine fetal breathing and swallowing responses to graded maternal hypoxemia. Five chronically prepared ewes with singleton fetuses at a gestational age of 130 +/- 2 (SE) days were subjected to successive 30-min periods of mild and moderate hypoxemia (inspired O2 fraction = 0.16 and 0.13, respectively). Mild and moderate maternal hypoxemia evoked significant reductions in fetal arterial PO2 (21 +/- 1 to 17 +/- 1 and 13 +/- 1 Torr, respectively), while fetal arterial pH, hematocrit, plasma osmolality, heart rate, and mean blood pressure did not change. Moderate hypoxemia was associated with significant increases in fetal plasma arginine vasopressin and renin activity and significant reductions from basal values in percent time breathing (53 +/- 4 to 25 +/- 12%), percent time swallowing (11.5 +/- 3.1 to 1.3 +/- 0.7%), and volume swallowed (21.3 +/- 2.1 to 4.8 +/- 2.7 ml/30 min). Fetal swallowing activity was better correlated with arterial PO2 (r = 0.8) than breathing activity (r = 0.45). We conclude that fetal swallowing is suppressed during mild and moderate hypoxemia. It is suggested that several sites and/or mechanisms may account for the hypoxemic inhibition of fetal activities.

Ovine Fetal Breathing and Swallowing Activity in Response to Plasma Glucose Changes

Fetal swallowing activity generally occurs simultaneously with fetal breathing movements (FBM) in sheep. The present study investigated the FBM and swallowing responses to altered fetal plasma glucose. Fetal lambs were chronically prepared with laryngeal, esophageal and diaphragm electromyogram (EMG) wires, an esophageal flow probe and vascular catheters. Beginning at 138 +/- 1 day, FBM and swallowing were monitored during control periods and in response to intravenous glucose infusions (14 mg/kg/min for 120 min) to fetuses of fed and fasted ewes. Glucose infusions to fetuses of fed ewes resulted in significant increases in fetal plasma glucose (21.2 +/- 0.7 to 40.5 +/- 1.9 mg/dl) and time breathing (46.2 +/- 6.3 to 60.0 +/- 9.5 min/2 h). In response to maternal fasting, fetal glucose levels (13.4 +/- 1.0 mg/dl) and time breathing (23.0 +/- 7.2 min/2 h) decreased significantly. Glucose infusion to fetuses of fasted ewes resulted in significant increases in time breathing (50.3 +/- 13.4 min/2 h) and diaphragmatic EMG activity (1,295 +/- 654 to 3,012 +/- 1,182 spikes/2 h). There was no change from basal levels of fetal EMG swallows (83.2 +/- 4.3 swallows/2 h) or esophageal flow (40.8 +/- 7.9 ml/2 h) in response to maternal fasting or fetal glucose infusions.

Stimuli for fetal swallowing: Systemic factors

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.