TY - JOUR
T1 - Maternal plasma hypo-osmolality
T2 - Effects on spontaneous and stimulated ovine fetal swallowing
AU - Nijland, Mark J.M.
AU - Kullama, Linda K.
AU - Ross, Michael G.
N1 - Funding Information:
Contract grant sponsor: March of Dimes Birth Defects Foundation; Contract grant sponsor National Institutes of Health Awards; Contract grant numbers: HLA0899 and DK43311. *Correspondence to: Michael G. Ross, Harbor-UCLA Medical Center, 1 1 24 West Carson Street, RB-1, Torrance, CA 90502. Received 29 September 1997; revised 25 March 1998; accepted 15 April 1998
PY - 1998
Y1 - 1998
N2 - Fetal swallowing is a major route of amniotic fluid resorption, and thus swallowing activity may alter amniotic fluid volume. Near-term ovine fetal swallowing increases in response to plasma and/or cerebrospinal fluid hypertonicity. As maternal hydration status alters amniotic fluid volume, we hypothesized that maternal plasma hypotonicity may alter fetal swallowing activity. Pregnant ewes (130 ± 1 d; n = 6) were chronically prepared with maternal and fetal vascular catheters, a fetal esophageal flow probe, and fetal thyrohyoid and nuchal and thoracic esophagus electromyogram electrodes. Spontaneous fetal swallowing and hypertonic saline thresholds for stimulated swallowing were determined prior to and following maternal hypotonicity induced with water loading and intravenous DDAVP (arginine vasopressin V2 agonist). Fetal swallowing thresholds were determined with intracarotid injections (0.15 ml/kg) of increasing sodium chloride concentrations (0.15-1.2 M) at 2-min intervals. Maternal DDAVP infusion significantly decreased mean (±SEM) maternal and fetal plasma osmolalities (298 ± 2-284 ± 3; 295 ± 2-278 ± 3 mOsm/kg, respectively) and sodium concentrations (1473 ± 0.4-137.5 ± 0.9; 142.7 ± 0.8-133.5 ± 1.0 mEq/l, respectively), suppressed spontaneous swallowing activity and volume (1.1 ± 0.2-0.6 ± 0.1 swallows/min; 0.7 ± 0.2-0.5 ± 0.1 ml/min, respectively) and significantly increased the osmotic threshold for swallowing stimulation (0.77 ± 0.08-1.03 ± 0.09 M NaCl). We conclude that: (1) maternal, and thus fetal, plasma hypotonicity results in suppression of spontaneous fetal swallowing activity and a decrease in volume swallowed, suggesting that spontaneous fetal ingestive behavior results, in part, from tonic dipsogenic stimulation, and (2) under hypotonic conditions, the intracarotid NaCl injection concentration for swallowing stimulation increases. These results suggest that the reset (lower) maternal plasma osmolality during human pregnancy may serve to minimize fetal ingestive and perhaps arginine vasopressin-mediated antidiuretic responses to acute maternal hypertonicity.
AB - Fetal swallowing is a major route of amniotic fluid resorption, and thus swallowing activity may alter amniotic fluid volume. Near-term ovine fetal swallowing increases in response to plasma and/or cerebrospinal fluid hypertonicity. As maternal hydration status alters amniotic fluid volume, we hypothesized that maternal plasma hypotonicity may alter fetal swallowing activity. Pregnant ewes (130 ± 1 d; n = 6) were chronically prepared with maternal and fetal vascular catheters, a fetal esophageal flow probe, and fetal thyrohyoid and nuchal and thoracic esophagus electromyogram electrodes. Spontaneous fetal swallowing and hypertonic saline thresholds for stimulated swallowing were determined prior to and following maternal hypotonicity induced with water loading and intravenous DDAVP (arginine vasopressin V2 agonist). Fetal swallowing thresholds were determined with intracarotid injections (0.15 ml/kg) of increasing sodium chloride concentrations (0.15-1.2 M) at 2-min intervals. Maternal DDAVP infusion significantly decreased mean (±SEM) maternal and fetal plasma osmolalities (298 ± 2-284 ± 3; 295 ± 2-278 ± 3 mOsm/kg, respectively) and sodium concentrations (1473 ± 0.4-137.5 ± 0.9; 142.7 ± 0.8-133.5 ± 1.0 mEq/l, respectively), suppressed spontaneous swallowing activity and volume (1.1 ± 0.2-0.6 ± 0.1 swallows/min; 0.7 ± 0.2-0.5 ± 0.1 ml/min, respectively) and significantly increased the osmotic threshold for swallowing stimulation (0.77 ± 0.08-1.03 ± 0.09 M NaCl). We conclude that: (1) maternal, and thus fetal, plasma hypotonicity results in suppression of spontaneous fetal swallowing activity and a decrease in volume swallowed, suggesting that spontaneous fetal ingestive behavior results, in part, from tonic dipsogenic stimulation, and (2) under hypotonic conditions, the intracarotid NaCl injection concentration for swallowing stimulation increases. These results suggest that the reset (lower) maternal plasma osmolality during human pregnancy may serve to minimize fetal ingestive and perhaps arginine vasopressin-mediated antidiuretic responses to acute maternal hypertonicity.
KW - Amniotic fluid
KW - Fetal swallowing
KW - Hypotonicity
KW - Sheep
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U2 - 10.3109/14767059809020435
DO - 10.3109/14767059809020435
M3 - Article
C2 - 9730481
AN - SCOPUS:0031927528
VL - 7
SP - 165
EP - 171
JO - Journal of Maternal-Fetal and Neonatal Medicine
JF - Journal of Maternal-Fetal and Neonatal Medicine
SN - 1476-7058
IS - 4
ER -