In pregnancy, dehydration produces marked effects on maternal and fetal body water homeostasis including an increase in fetal urinary sodium concentration and excretion. To examine the role of fetal plasma atrial natriuretic factor (ANF) and glomerular ANF receptors in dehydration-induced natriuresis, we compared plasma ANF levels and glomerular ANF binding characteristics in dehydrated and control maternal and fetal sheep. Mean (± SEM) maternal and fetal plasma ANF levels in control animals (n = 9) at 132–136 days gestation were 37 + 3 pg/ml and 138 ± 20 pg/ml, respectively. Although mean ANF receptor maximum binding capacities (Bmax) were significantly higher in maternal than in fetal glomeruli (83 ± 11 vs. 34 ± 12 fmol/mg protein, respectively), the dissociation constants (Kd) for ANF binding were not different (2.7 ± 0.6 and 3.7 ± 1.7 × 10^––10M, respectively). In an additional 9 animals studied after 63 ± 4 h of water deprivation, maternal plasma ANF levels were significantly lower than in the control group (14 ± 4 vs. 37 ± 3 pg/ml), maternal glomerular ANF receptor Bmax values were significantly higher (732 ± 203 vs. 83 ± 11 fmol/mg protein), and Kd values were six-fold higher (17.0 ± 7.1 vs. 2.7 ± 0.6 × 10^––10M), although this difference was only marginally significant (p = 0.06). In contrast to the adult, there was a small, nonsignificant decrease in plasma ANF levels and no difference in Bmax or Kd values between the dehydrated and euhydrated fetal animals. These results indicate that the maternal ewe, like the adult rat, responds to dehydration with decreased plasma ANF levels and up-regulation of renal ANF receptors. The fetal lamb by contrast has increased plasma ANF levels and decreased renal glomerular ANF binding relative to the ewe, and fetal renal ANF binding characteristics are not affected by maternal dehydration. Thus, while changes in maternal plasma ANF and renal ANF receptors may partially explain maternal dehydration-induced natriuresis, the role of ANF in fetal dehydration-induced natriuresis remains unclear.

Levels of a novel oxytocin (OT)- and arginine vasotocin (AVT)-like peptide detected by one antiserum to OT (Pitt Ab-1) and one antiserum to AVT (Tor AVT) were recently found to rise in human plasma in response to administration of estrogen. The novel peptide rose in parallel with the estrogen-stimulated neurophysin (ESN). The mean level (+/- SEM) of ESN in plasma of 11 individuals with altered renal function (nondialyzed) was significantly higher than the level in individuals with normal renal function (4.2 +/- 0.9 vs. 1.1 +/- 0.04 ng/ml; P less than 0.01). In patients treated with hemo- or peritoneal dialysis, mean (+/- SEM) levels of ESN were 18.1 +/- 3.2 and 16.8 +/- 3.7 ng/ml, respectively. Levels of estradiol and estrone were not elevated and did not correlate with high levels of ESN. Levels of OT Pitt Ab-1, AVT, and ESN immunoreactivity were measured in plasma form nine patients undergoing hemodialysis and eight patients undergoing peritoneal dialysis. Mean (+/- SEM) levels of all three peptides were elevated (12.9 +/- 1.5 microU/ml, 32.1 +/- 6.7 pg/ml, and 13.5 +/- 4.0 ng/ml, respectively). ESN was significantly correlated with OT Pitt Ab-1 and AVT (R2 = 0.80; P less than 0.001). Plasma samples from the same patients were pooled, treated, and separated by reverse phase HPLC. The plasma contained a peak of immunoreactivity detected by Pitt Ab-1 and Tor AVT Ab. The position of the material was distinct from that of synthetic OT, AVT, or AVP and corresponded to the position of the novel OT-like peptide found in plasma of individuals given estrogen. The findings support parallel secretion of the OT-like peptide with ESN and represent the first disease state characterized by high levels of this OT- and AVT-like peptide.

ABSTRACT. To examine the effect of prolactin (PRL) on transplacental water flow, we infused mannitol (500 ml; 20% solution) over 10 min into five chronically catheterized ewes (121-134 days' gestation), producing a peak maternal plasma osmolality by 10 min and fetal osmolality by 20 min. One day before or after, an identical amount of mannitol was infused into the same ewe during the 2nd h of a 2-h infusion of PRL (40 + 2.2 pg/h) into a fetal leg vein. Mean (2 SE) fetal plasma PRL levels were 6.9 + 3.2 ng/ml at baseline. Steady state fetal PRL levels were 17.7 2 7.4 ng/ml during PRL infusion. Maternal mannitol infused without administration of PRL to the fetus evoked a rise in fetal plasma osmolality similar to that following maternal mannitol during PRL administration to the fetus. Thus,.as shown previously, PRL affects water permeability across the membranous chorioamnion, whereas results of the present study indicate that the hormone does not affect water transfer across the ovine chorionic villi (placenta). 19: 986-988, 1985) Abbreviations AF, amniotic fluid PRL, prolactin AVP, arginine vasopressin (Pediatr ResThe importance of PRL in osmoregulation in fish and some mammals is well recognized. In these species PRL appears to act on several sites of hydromineral exchange including the fish gill, bladder, intestinal mucosa, and avian salt gland. Several recent studies also suggest that PRL plays a role in mammalian water homeostasis during pregnancy (1-1 1). PRL is found in high concentrations in human amniotic fluid (approximately 400 ng/ ml at term) although its function remains unclear. In pregnant women plasma PRL concentrations increase throughout gestation, with a return to basal levels by one week following delivery (I). PRL levels in human fetal plasma are relatively low before 25 wk but increase rapidly in the 3rd trimester; the mean value at term approximates 200 ng/ml (9). In comparison to human AF levels, PRL levels are low in ovine amniotic fluid throughout gestation (approximately 10 ng/ml). PRL is present in ovine fetal blood in increasing concentrations from 90 days gestation with a sharp increase after 1 10 days gestation; at term the mean value has been reported to approximate 35 ng/ml(8,9). Thus, although there are quantitative differences, the ontogenic pattern for ovine fetal plasma PRL is similar to that of the human fetus.PRL has been identified as one of the hormones affecting AF water dynamics. In vitro studies by Leontic and Tyson (6), Holt and Perks (2), and Manku et al. (3) have shown that PRL affects diffusional water transfer across the isolated amniotic membrane, although the direction of this hormonally influenced water transfer may differ from species to species. Additionally, we have shown in vivo that elevated ovine AF PRL levels diminish bulk flow of water across the chorioamnion from the amniotic fluid to maternal circulation in response to acute changes in maternal osmolality (1 1). Also we have shown that following maternal mannitol infusion, fetal to maternal water tr...