EFFECTS OF INSULIN-LIKE GROWTH FACTOR-I AND ITS ANALOGS ON BOVINE HYDROGEN-PEROXIDE RELEASE BY NEUTROPHILS AND BLASTOGENESIS BY MONONUCLEAR-CELLS

The biological potencies of recombinant human insulin-like growth fact or-I (IGF-I) and two of its analogues were examined for hydrogen perox ide release by neutrophils and blastogenesis by mononuclear cells. The binding affinities of these peptides for bovine serum IGF-binding pro teins (IGFBPs) and IGF-I receptors on bovine neutrophils and mononucle ar cells were also investigated. Relative to control treatment contain ing no IGF-I, preincubation of neutrophils with 12.5 mu g/l of IGF-I, des(l-3)IGF-I (an analogue of human IGF-I lacking the N-terminal tripe ptide Gly-Pro-Glu) and long R(3) IGF-I(an analogue of human IGF-I with arginine replacing glutamate at position 3 of human IGF-I and the N-t erminal extension t-Phe-Pro-Ala-Met-Pro-Leu-Ser-Ser-Leu-Phe-Val-Asn) i ncreased the release of H2O2 by 65%, 64% and 32% respectively. However , the difference in stimulating the release of H2O2 between long R(3) IGF-I and other two (IGF-I and des(1-3)IGF-I) was reduced at a dosage of 100 mu g/l. In the absence or presence of 2.5% fetal calf serum (FC S), 100 mu g/l of IGF-I, des(1-3)IGF-I but not long R(3) IGF-I signifi cantly stimulated thymidine incorporation into mononuclear cells. In a ddition, des(1-3)IGF-I was more potent than IGF-I in stimulating thymi dine incorporation into mononuclear cells in the presence of 2.5% FCS. IGF-I displaced I-125-labelled IGF-I binding to serum IGFBPs with hal f-maximal inhibitory concentrations of approximately 1.5 nmol/ l, whil e des(1-3)IGF-I and long R(3) IGF-I only inhibited binding by 20% and 6% respectively, even at a concentration of 35 nmol/l. Similar affinit ies for IGF-I receptors on neutrophils and mononuclear cells were show n for IGF-I and des(1-3)IGF-I. Conversely, much lower affinities for t hese receptors were demonstrated for long R(3) IGF-I. These results su ggest that the biological activities of IGF-I and its analogues in cel ls of the bovine immune system depend on their binding characteristics both to receptors and to binding proteins.