99 INSULIN-LIKE GROWTH FACTORS (IGF), PLACENTAL LACTOGEN QQ (PL), INSULIN (Ins) AND SUBSTRATES IN THE PREGNANT EWE AND NEWBORN LAMB

Abstract

The regulation of IGF secretion in pregnancy and in the fetus is poorly understood. 10 triplet bearing ewes were fed maintainance plus control abomasal infusion (n=3), plus glucose infusion (n=3), plus casein (n=2), plus glucose and casein (n=2) through the last 42 days of gestation to provide a range of substrate availability. Birth weight (BW) was not affected. 18-27 days before birth, multiple maternal plasma samples were taken at fixed times relative to meals. Maternal PL levels were decreased by casein (p < 0.05) but not by glucose infusion. A negative correlation (p < 0.05) was seen between PL and IGF-1 (by RIA)(r=-0.72). There was a positive correlation between PL and IGF-2 (by rat placental RRA) (r=0.64). There was a strong inverse correlation between maternal IGF-1 and IGF-2 (r=-0.94). The correlation between nonesterified free fatty acids and the IGF-2/IGF-1 ratio was 0.81. A similar correlation to PL was 0.66. There was a correlation (p < 0.05) between cord IGF-1 levels and BW. Multiple linear regression showed an interaction between cord IGF-1, Ins and BW (p < 0.001) which explained 63% of the variation in BW. These findings suggest an interaction in the late gestation ewe between the relative secretion of IGF-1 and IGF-2, metabolic status and PL secretion. IGF-2 may be the mediator of the lipolytic action of PL. The neonatal observations support the concept that fetal IGF-1 and Ins are important detirminants of fetal growth.

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