The Insulin-Like Growth Factor-Binding Proteins of Porcine Serum: Endocrine and Nutritional Regulation*

Abstract

Several studies have shown that insulin-like growth factor-binding proteins (IGF-BPs) modify IGF activity. To investigate their role in regulating growth, the number and size of IGF-BPs in porcine serum and the role of nutritional and endocrine factors in controlling their relative abundance were determined. IGF-BPs were analyzed by ligand blotting; sera were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, then the separated proteins were transferred to nitrocellulose filters and probed with [125I]IGF-I or -II. The band intensities of various forms of IGF-BPs were quantified by scanning densitometry. Fetal and postnatal sera contained six IGF-BPs of 220,000, 43,000, 39,000, 34,000, 29,000, and 24,000 mol wt (Mr). The band intensity of all forms of IGF-BPs increased with advancing gestational age. Specifically, the intensities of the 43,000, 39,000, 34,000, 29,000, and 24,000 Mr IGF-BP bands were 2.8-, 2.7-, 4.3-, 4.4-, and 3.1-fold higher, respectively, in fetal plasma at 110 than at 45 days gestation. In fetal plasma the 34,000 and 29,000 Mr forms predominated, whereas postnatally, the 43,000 and 39,000 Mr IGF-BPs predominated. Fasting of newborn pigs for 24 h reduced the intensity of the 43,000, 39,000, 34,000, and 24,000 Mr forms to 11.5%, 7.2%, 69.8%, and 5.2% of control levels, respectively. However, the 29,000 Mr IGF-BP was 1.8-fold higher in fasted pig serum than in that of fed controls. The band intensities of the 34,000 and 29,000 Mr forms were increased in postnatal animals after hypophysectomy. In contrast, fetal decapitation resulted in a preferential decrease in only the 34,000 Mr form, which was reduced by 30% compared to that in age-matched controls. These studies indicate that porcine serum contains six IGF-BPs that can be detected by ligand blotting. The level of each of these proteins increases with advancing gestational age, although the increases are not uniform, suggesting that the proteins may be regulated differentially. In the postnatal animal both endocrine and nutritional factors modulate the levels of IGF-BPs by distinct controlling mechanisms.

GH and IGF-I binding sites in adipose tissue, liver, skeletal muscle and ovaries of feed-restricted gilts

“…Reduction of circulating IGF-I during malnutrition has been shown to be associated with changes in the plasma IGFBP profile in growing pigs [8,19]. However, the present study failed to show a significant difference in IGFBP levels between restricted and well-fed gilts.…”

Intestinal effects of milkborne growth factors in neonates of agricultural importance.

“…The amino acid sequences and gene structures of the IGFBP of production species have been less well characterized, with most work focusing on IGFBP-3 (Walton et al, 1989;Shimasaki et al, 1990;Spratt et al, 1991) and IGFBP-2 (Szabo et al, 1988;Walton et al, 1990). However, based on the porcine (McCusker et al, 1985), bovine (McGuire et al, 1992), and ovine (Hodgkinson et al, 1989) serum IGFBP profiles and the presence of IGFBP-1 (Walton et al, 1990), IGFBP-4 (Walton et al, 1990;, and IGFBP-6 in porcine and ovine body fluids, the IGFBP seem to be well conserved across species.…”

Effect of Excess Dietary Fat during the Third Trimester of Pregnancy on Maternal, Placental, and Fetal Metabolism in the Pig

“…Such alterations in fetal growth could be due to dietary-induced changes in maternal or fetal levels of serum insulin-like growth factors (IGF). These hor mones have been shown to be influenced by nutritional manipulations such as fasting [36][37][38] and caloric [39] or protein restric tion [38. 40.…”