Daily changes in amniotic and allantoic fluid during the last three months of pregnancy in conscious, unstressed ewes, with catheters in their foetal fluid sacs

Abstract

SUMMARY1. Catheters were inserted into the maternal and foetal vasculatures of ten ewes, 100-139 days pregnant, and daily samples ofuterine and umbilical blood and maternal jugular vein blood were taken for periods of 5-27 days after operation.2. Catheters were inserted into the fluid sacs of nineteen foetuses, 60-97 days post-conception, and daily samples were withdrawn for up to 90 days from amniotic sacs (eleven foetuses) and for up to 70 days from allantoic sacs (eight foetuses). Maternal jugular plasma was obtained 3 times weekly and an approximation from its composition to that of uterine and umbilical plasma was made using results from the ewes and foetuses with vascular catheters.3. The pH, osmolality, [Na+] 6. Changes during recovery from operation were followed and indicated that maternal and foetal plasma required about 3 days and the foetal fluids up to 7 days before stability of composition was achieved.7. After recovery from operation, daily changes in the composition of each foetal fluid showed the same general pattern in all foetuses, but the absolute values of constituents sometimes showed large differences. D. J. MELLOR AND J. S. SLATER 8. It is suggested that flow of foetal urine into the amniotic sac increased from 80 days gestational age, that urine flow into the allantoic sac decreased until about 100 days but did not cease thereafter, and that relative to foetal urine the influence of foetal pulmonary fluid on amniotic fluid composition was not great.9. A relative impermeability of the amnion appeared to be a major factor influencing amniotic fluid composition, whereas pumping mechanisms in the chorioallantois seem to have been responsible largely for changes in the composition of allantoic fluid.10. The quantity of solute relative to that of water within each sac appears to be a major determinant of changes in foetal fluid volumes.11. Changes in the [Na+] and [K+] of allantoic fluid during the normal course of pregnancy were consistent with an increasing action of mineralocorticoids on pumping mechanisms in the chorioallantois. Similar but more rapid changes seemed to be associated with acute and chronic episodes of maternal hypoglyeaemia. Under these circumstances foetal hypoglycaemia may effect a relative increase in the secretion of foetal corticosteroids having an action on the chorioallantois.12. The results from this study demonstrate clearly the value of using chronically catheterized animals, and it is suggested that their use in physiological studies on the conceptus must eventually supersede that of acute, anaesthetized preparations.

The influence of intra-uterine surgery and of fetal intravenous nutritional supplements ‘in utero’ on plasma free amino acid homeostasis in the pregnant ewe

“…The marked but temporary fall in the concentration of branched chain amino acids during the operative procedure was an expected response to the infusion of glucose and was probably due to the release of insulin, äs in other species (MUNRO [20]). The post-operative fall in blood urea of the control fetuses and that of the mothers in both groups confirm MELLOR and SLATER'S [18] observations in the ewe and those for the fetus, implied by the falling urea concentrations found in the allantoic fluid in the days following surgery. The results suggest an Inhibition of urea synthesis in both the mother and fetus following the hysterotomy; this is apparently in contrast to the findings of O'KEEFE et al [21] that moderate surgery reduces protein synthesis rate, but has little influence on protein bfeakdown.…”

Origin and developmental patterns of lactase and other glycosidases in sheep amniotic and allantoic fluid

“…Such patterns would be consistent with the suggestion that fetal urine is a source of agalactosidase and /Y-acetyl-ß-hexosaminidase activities and that sheep fetal urine is first accumulated in the allantoic sac via the urachus up to a gestational age of 86-90 days and thereafter passes more and more into the amniotic sac. This is thought to be due to the occlusion of the urachus and increasing potency of the urethra (Smith et al, 1966;Mellor & Slater, 1971. The protein concentration also followed a similar pattern being about 6-fold more elevated in allantoic than in amniotic fluid at 49-65 days and reaching approximately equal concentrations in both sacs at 106-132 days.…”

“…Evidence has been found that the human fetus releases its intestinal content into the amniotic cavity: Benzie & Doran (1975), using a special endoscope, observed fetal defaecation in utero in an 18-week fetus, and the presence of intestinal disaccharidases (Potier et al, 1975(Potier et al, , 1976 and biliary salts (Délèze, Sidiropoulos & Paumgartner, 1977) has been reported in amniotic fluid. The pregnant ewe is particularly useful for study of the origin of amniotic fluid enzymes because the fetal urine is apparently accumulated in the allantoic cavity early in gestation (Smith, Adams, Borden & Hilburn, 1966;Mellor & Slater, 1971 while intestinal enzymes are extruded in the amniotic cavity.…”

The gustatory sense in foetal sheep during the last third of gestation

“…There are also progressive changes in amniotic fluid composition over gestation (Mellor & Slater, 1971 Jacobson (1970) has suggested that whereas the connexions of some neurones are genetically established, the specific connexions of others are dependent on sensory stimulation during early development. The taste experiences of the foetus may, then, determine the taste sensitivities and preferences of the adult.…”