Purification and characterization of porcine growth hormone-dependent insulin-like growth factor binding protei

The objectives of this thesis were (1) to evaluate molecular weight (M$sb{rm r}$) profiles of IGF-I and $sp{125}$I-IGF-I; binding activity in pig serum; (2) to determine whether exogenous IGF-I partitions to IGFBPs in the circulation in pigs; (3) to purify and characterize the GH-dependent IGFBP from pig serum; (4) to assess the effects of the IGFBP on IGF-I action in vitro; (5) to establish a radioimmunoassay for the IGFBP; and (6) to measure IGFBP concentrations in serum from GH- and IGF-I-treated pigs.;The majority (67-83%) of IGF-I in serum was bound to an IGFBP complex of 150 kDa, the remainder was bound to an IGFBP of 40 kDa; "free" IGF-Ik was not detected. Porcine GH (pGH) treatment increased total IGF-I and $sp{125}$I-IGF-I binding to the 150 kDa IGFBP, indicating that this larger M$sb{rm r}$ IGFBP is under pGH regulation.;Endogenous IGF-I distributed to fast (half-life, t$sb{1/2}$ = 5.7 min) and slow (t$sb{1/2}$ = 253 min) components in serum. The slow component comprised IGF-I bound to the 40 and 150 kDa IGFBPs, whereas the fast component comprised unbound IGF-I. Furthermore, endogenous IGF-I decreased serum glucose concentrations.;An acid-stable IGFBP was purified from pig serum. This IGFBP comprised two major binding species of 45 and 50 kDa, and inhibited the acute insulin-like effects of IGF-I in vitro. A radioimmunoassay for this IGFBP recognized a serum protein of 150 kDa; therefore, the purified IGFBP is probably a subunit of the 150 kDa IGFBP. The IGFBP was detected in porcine milk, colostrum, allantoic, amniotic and follicular fluids.;Acute treatment of pigs with pGH (10-1,000 ug/kg bw) or IGF-I (4, 8 mg) had no effect on serum IGFBP concentrations in pigs. In contrast, serum IGFBP was significantly increased (63%) in pigs chronically injected with pGH (70 ug/kg bw per d) for 17 d.;This is the first report of a specific radioimmunoassay for the porcine GH-dependent IGFBP. The results indicate that the IGFBP is found in a wide variety of biological fluids and is regulated by pGH.