Maternal/fetal dehydration: prolonged effects and responses to oral rehydration

Abstract

Dehydration induces marked alterations in maternal-fetal fluid homeostasis and accompanying fetal endocrine responses. We sought to determine if the increase in fetal plasma arginine vasopressin (AVP) levels during maternal dehydration is mediated by fetal plasma hypovolemia in addition to hyperosmolality and to examine maternal and fetal plasma atrial natriuretic factor (ANF) responses to maternal dehydration and oral rehydration. Seven pregnant ewes (127 +/- 1 day) were water deprived for 72-96 h, and five of these were orally rehydrated. Dehydration induced significant increases in maternal plasma osmolality (pOSM) (300 +/- 2 to 325 +/- 8 mosmol/kg) and AVP (3.0 +/- 0.4 to 18.9 +/- 4.0 pg/ml), and decreases in plasma ANF levels (28.1 +/- 3.1 to 19.7 +/- 3.1 pg/ml). Fetal pOSM (293 +/- 3 to 314 +/- 4 mosmol/kg), AVP (2.5 +/- 0.6 to 8.1 +/- 4.8 pg/ml), and urinary fractional sodium excretion increased significantly, whereas plasma ANF and fetal blood volume did not change. After maternal water access maternal plasma AVP decreased rapidly in comparison to the gradual decrease in maternal pOSM. Fetal plasma AVP levels did not change significantly and fetal pOSM decreased more slowly than maternal pOSM. Fetal plasma ANF increased in association with increased urine flow and glomerular filtration rate after maternal rehydration. These data indicate marked differences in fetal and maternal plasma ANF and AVP responses with dehydration-induced increases in fetal plasma AVP being secondary to plasma hyperosmolality, rather than hypovolemia. Rapid suppression of maternal plasma AVP may contribute to the slower equilibration of fetal pOSM during oral, as compared with intravenous, maternal rehydration.

Behavioral effects of centrally administered arginine vasopressin in the rat fetus.

“…The behavioral effects produced by central administration of AVP are unusual in this context: Injection of AVP into the cisterna magna of the E20 rat fetus resulted in modest increases in forelimb and head movements and decreases in rearlimb movements, but it also promoted very high rates of ordinarily rare categories of fetal behavior, notably, licking and facial wiping. The expression of perioral behavior after central administration of AVP is consistent with reports that human fetuses exhibit elevated serum levels of AVP associated with swallowing and other ingestivelike behavior in utero (Agnew et al, 1993; Ross et al, 1992). the ability to block the behavioral effects of AVP by central administration of [β-mercapto-β,β-cyclopentamethylene- propionyl 1 , O-Me-Tyr 2 , Arg 8 ] indicates that changes in fetal behavior induced by AVP are mediated by the V 1 subclass of receptor.…”

“…Elevated levels of AVP have been reported in the fetal sheep in response to intracarotid injection of sodium chloride solutions (Ross, Agnew, Fujino, Ervin, & Day, 1992), which stimulates fetal swallowing of amniotic fluid (Ross, Sherman, Ervin, Day, & Humme, 1989). Similarly, maternal dehydration, which is associated with increased thirst and drinking in adults, results in increased AVP levels in the fetus (Agnew, Ross, Fujino, Ervin, Day, & Kullama, 1993). The association of AVP with drinking and swallowing generally has been interpreted as the result of AVP's effects on osmoregulation, which indirectly affects thirst (Ramsay & Thrasher, 1990; Ross et al, 1992).…”

Prenatal programming of hypernatremia and hypertension in neonatal lambs

“…In the present study, maternal water restriction during pregnancy significantly increased maternal plasma osmolality and sodium concentration, and these increases were maintained for the duration of pregnancy. Maternal dehydration induces fetusto-mother water transfer, resulting in fetal plasma hyperosmolality in direct proportion to maternal hypertonicity and increased fetal plasma AVP (1,29,31). Although chronic hypertonicity maintains increased fetal plasma AVP for at least 96 h (1), it is unknown whether fetal plasma AVP remained continually elevated throughout the Ն35-day period of plasma hypertonicity.…”

Pregnancy and the Tropics: Physiology, Environment and Infectious Disease

“…Biochemical changes also mean that diarrhea will result more quickly in acidemia. The combination of this and dehydration may then lead to premature labor, hypovolemic shock and even fetal death [13].…”