Influence of age and fetal hypophysectomy on porcine preadipocytes: insulin-like growth factor-I (IGF-I) response, receptor binding and IGF binding proteins secretion.

The effects of fetal hypophysectomy (hypox) and age on insulin-like growth factor-I (IGF-I) response, receptor binding and IGF-I & IGF binding protein secretion by porcine preadipocytes was examined. Primary cultures of stromal vascular (S-V) cells derived from fetal and postnatal adipose tissue were established and exposed to test media (different concentrations of pig serum with or without IGF-I) for morphological study or to serum-free media for measuring IGF-I receptor binding and IGF-I & IGFBPs secretion. Conditioned media were collected and subjected to IGF-I RIA and ligand blot and immunoblot analysis. IGF-I significantly stimulated total cell growth (determined by DNA levels) and increased fat cell cluster number and lipid deposition in porcine S-V cultures (determined by image analysis). Although the pattern of response to IGF-I was similar in fetal and postnatal cultures, the response was greater in fetal cultures. The mitogenic and adipogenic response of fetal preadipocytes to IGF-I was impaired by fetal hypox. Specific IGF-I binding sites on fetal preadipocytes had a higher binding affinity for IGF-I (Kd = 2.82 +/- 0.28 nM) than did postnatal preadipocytes (Kd = 7.28 +/- 1.52 nM, P < 0.05). Preadipocytes secreted IGF-I and four IGF-BPs (BP-1, -2, -3, and -4) in a developmentally regulated manner. For example, IGFBP-2, and -3 were predominant binding proteins secreted by fetal preadipocytes which represented 47% and 30% of the total, respectively. IGFBP-1 was the major binding protein secreted by postnatal preadipocytes. Furthermore, fetal cells secreted greater amounts of IGF-I in cultures than did postnatal cells (2428 +/- 205 pg/ml vs. 870 +/- 31 pg/ml, P < 0.05). Fetal hypox caused a decrease from 47% to 68% of control values in all four IGFBPs secreted by preadipocytes. The changes in IGF-I receptor binding and IGF-I and IGFBP secretion by preadipocytes may account for altered response of preadipocytes to IGF-I. Thus, secretion of IGF-I and IGFBPs, IGF-I binding and response of porcine preadipocytes were affected by age and fetal hypox. The results indicated that locally produced IGF-I and IGFBPs may play a critical paracrine/autocrine role during fetal adipose development.