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

To elucidate the role of IGF-1 in the galactopoietic effect of somatot ropin, the partition of plasma IGF-1 between groups of binding protein s (BP) was studied in goats at different stages of pregnancy, lactatio n and somatotropin treatment. By size-exclusion chromatography, total plasma IGF-1 was divided into a 150 kDa class and a 35 kDa class. Lact ation was associated with marked reduction in plasma concentrations of IGF-1, specifically of the 150 kDa class. During lactation, BP3 conce ntrations were also low and BP3 circulated mainly in a ''free'' or non -complex bound form. Somatotropin treatment changed IGF-1 concentratio n and distribution towards that seen in pregnancy. It is concluded tha t the change in distribution of IGF-1 and its binding protein at the s tart of lactaion means increased turnover of IGF-1 and probably increa sed availability of IGF-1 to mammary cells and other target tissues. T he observed changes may be important aspects of the homeorhetic adapta tion to lactation.