Restriction of placental growth in sheep enhances placental metabolism of fetal beta-endorphin-like immunoreactivity.
The opioid polypeptide beta-endorphin is present in fetal blood but it is not clear whether its source is the fetus or the placenta. We therefore measured beta-endorphin in extracts of fetal femoral arterial and umbilical venous blood plasma in sheep by radioimmunoassay to determine whether the fetus or the placenta is the major source of beta-endorphin in the fetal circulation. Chromatographic analysis of extracts of fetal arterial plasma showed that beta-lipotropin and other precursors of beta-endorphin made only a minor contribution to the immunoreactivity detected. Concentrations of immunoreactive beta-endorphin were higher in the femoral artery than in the umbilical vein in fetal sheep between 113 and 128 days of pregnancy. Therefore the placenta removes beta-endorphin or a closely related polypeptide of fetal origin from the umbilical circulation in sheep at this stage of gestation. Acute hypoxaemia and hypoglycaemia increase the concentrations of immunoassayable beta-endorphin in blood plasma of adult and fetal sheep, but little is known about the effects of chronic hypoxaemia or hypoglycaemia on the circulating levels of beta-endorphin and related polypeptides in the fetus. Therefore we also measured immunoreactive beta-endorphin in blood plasma from fetal sheep in which growth retardation in association with restricted placental growth was produced by removal of endometrial caruncles before mating. Intra-uterine growth retardation was accompanied by chronic hypoglycaemia and chronic hypoxaemia in the fetuses. This was not associated with higher concentrations of beta-endorphin-like immunoreactivity in fetal arterial or umbilical venous plasma, but was accompanied by significantly increased placental extraction of fetal immunoreactive beta-endorphin from the umbilical circulation.(ABSTRACT TRUNCATED AT 250 WORDS)
Owens
P C
PC
Faculty of Medicine, University of Newcastle, Shortland, New South Wales, Australia.
Owens
J A
JA
Lovelock
M
M
Chan
E C
EC
Falconer
J
J
Robinson
J S
JS
Smith
R
R
D000818:Animals; D001835:Body Weight; D002850:Chromatography, Gel; D005260:Female; D005263:Femoral Artery / Q000032:analysis; D005312:Fetal Blood / Q000032:analysis; D005317:Fetal Growth Retardation; D009929:Organ Size; D010920:Placenta / Q000502:physiology*; D011247:Pregnancy; D011270:Pregnancy, Animal; D011863:Radioimmunoassay; D012756:Sheep; D014471:Umbilical Veins; D001615:beta-Endorphin / Q000378:metabolism*
D001615:beta-Endorphin