GH and IGF-I binding in adipose tissue, liver, and skeletal muscle in response to milk intake level in piglets

Two experiments were undertaken to get a better understanding of the regulation of the GH/IGF-I axis by nutritional status in suckling piglets. In experiment 1, 18 newborn unsuckled pi-lets were bottle-fed low (L), intermediate (I). or high (H) levels of sow colostrum and milk from birth to 7 days of age. L and H levels corresponded to maintenance requirement and ad libitum intake, respectively. Plasma IGF-I and 43-39 kDa IGFBP levels decreased (P < 0.05) with the reduction of milk intake. Specific binding of I-125-bGH in liver decreased (P < 0.01) with decreasing milk intake. It did not differ (P > 0.1) between the groups in skeletal muscle. Specific binding of I-125-IGF-I increased (P < 0.05) with decreasing milk intake in skeletal muscle but did not differ (P > 0.1) between the three groups in liver. In experiment 2, variation in milk intake was induced by litter size manipulation. In the 24h following birth, the litter sizes of six litters were normalized to 6 (L6) or 12 piglets (L12). Animals were killed at 21 days of age. Plasma IGF-I concentrations (P < 0.001) and 43-39 kDa IGFBP levels (P < 0.05) were lower in L12 than in L6. Specific binding of I-125-bGH in adipose tissue, liver, and skeletal muscle did not differ (P > 0.1) between the two groups. Specific binding of I-125-IGF-I in liver was lower (P < 0.001) in L12 than in L6, whereas it did not differ ( P > 0.05) between groups in other tissues. In conclusion, the present report shows that undernutrition consistently decreases plasma IGF-I and 43-39 kDa IGFBP levels but produces variable responses at the GH and IGF-I binding levels in piglets. (C) 2002 Elsevier Science (USA). All rights reserved.