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...