Lipid transport and metabolism in the postterm rabbit

Abstract

Gonadotropin-injected pregnant rabbits were delivered by cesarean section near term (27 and 30 days after conception) (term, 31 days) and three and four days after term. Lipid metabolism of the postterm fetus, near-term fetus, and 3- and 4-day-old newborn rabbit was compared. Prenatal and postnatal body and organ weights as well as lipid concentrations in brain, liver, lung, brown adipose tissue, and placenta were determined. The half time (t½) of free fatty acids (FFA) in the mother and fetus was calculated following a single maternal injection of 1-14C-palmitate. Placental weight was unchanged after 30 days' gestation. A significant positive correlation existed between fetal body weight and placental weight. The weight of the brain increased proportional to body weight. Brain lipid concentration remained constant throughout the study period. Dramatic changes (a greater than 50 per cent drop) in fetal lipid concentration occurred in the liver when the postterm period extended beyond 34 days (between three and four days post term). The rate and time of peak appearance of radioactivity in fetal circulation indicated a peak shift at four days post term: Peak appearance was at about four minutes (30 days' gestation) increasing to eight minutes (four days post term). A slower rate of FFA entry at four days post term versus 30 days' gestation was also noted. These changes implied some breakdown in placental transport (placental insufficiency). The concentration and t½ of FFA in fetal plasma were maintained despite the significantly slower placental transfer of FFA. Maternal compensation included a diminished t½; this was evidently inadequate, requiring, in addition, dramatic increases in fetal liver lipid mobilization.