70 NUTRITION-INDUCED CHANGES IN INSULIN-LIKE GROWTH FACTORS (IGF'S) AND BINDING PROTEINS IN NEONATAL RATS

Abstract

IGF's are potent hormones that may regulate perinatal growth and are found linked to high affinity binding proteins (BP's) in blood and tissues. To investigate the premise that caloric (cal) intake is a determinant of IGF/BP synthesis, 10d rats were milk deprived and given 24 hr infusions of saline (SAL), glucose (GLU), glucose/amino acids (GA), or glucose/amino acids (aa)/lipid (GAL). Acid chromatography was used to separate IGF's and BP in sera and liver cytosols. When compared to controls (CON), fasting (SAL) induced a marked decline (p<0.001) in serum IGF-1 and 2 concentrations [IGF-1,2] as well as liver [IGF-2]. In addition, serum [IGF-2] but not [IGF-1] was restored in GAL rats to near CON levels. BP activity, as measured in untreated specimens by radioreceptor assay (RRA-IGF-2), rose 2-4x above CON in SAL serum and liver. Infusion of aa suppressed the changes in liver BP activity and in pooled data, liver BP was inversely related to serum aa but not to cal intake. Increased liver BP activity appears due to a 40,000 MW BP. In serum, BP activity was inversely related to cal intake but not to [aa]. The fasting induced rise in serum BP activity appears due to a BP of 180,000 MW. Fasting induced changes in IGF & BP may be a protective mechanism to depress growth during cal restriction.