Effect of lactation, pregnancy and somatotropin treatment on plasma IGF‐1 concentrations, IGF‐1 partition between binding protein groups and binding protein pattern in goats

Abstract

To elucidate the role of IGF‐1 in the galactopoietic effect of somatotropin, the partition of plasma IGF‐1 between groups of binding proteins (BP) was studied in goats at different stages of pregnancy, lactation and somatotropin treatment.

By size‐exclusion chromatography, total plasma IGF‐1 was divided into a 150 kDa class and a 35 kDa class. Lactation was associated with marked reduction in plasma concentrations of IGF‐1, specifically of the 150 kDa class. During lactation, BP3 concentrations were also low and BP3 circulated mainly in a “free”; or non‐complex bound form. Somatotropin treatment changed IGF‐1 concentration and distribution towards that seen in pregnancy.

It is concluded that the change in distribution of IGF‐1 and its binding protein at the start of lactaion means increased turnover of IGF‐1 and probably increased availability of IGF‐1 to mammary cells and other target tissues. The observed changes may be important aspects of the homeorhetic adaptation to lactation.

Key words:

• BP3
• galactopoietic
• homeorhetic
• insulin
• ligand blot
• mammary
• target