INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEINS IN THE RAT UTERUS AND THEIR REGULATION BY ESTRADIOL AND GROWTH-HORMONE

The rat uterus has previously been shown to be a site of insulin-like growth factor I (IGF-I) production and reception. The purpose of this study was to explore the possibility that the rat uterus can also horm onally regulate elaboration of IGF-binding proteins (IGFBPs). Uteri fr om adult ovariectomized rats were perfused, rinsed thoroughly and extr acted. Western ligand blotting of SDS-polyacrylamide-fractionated uter ine extracts revealed several bands of IGFBPs with molecular masses of 24, 28, 30-32 and 38-42 kDa; the 28 kDa protein was not detected in t he serum. Hypophysectomy caused a marked decrease in 38-42 and 30-32 k Da proteins which was reversed by systematic treatment with growth hor mone (2 x 120 mug per rat per day for 3 days). The 28 and 24 kDa prote ins, however, were not altered by growth hormone. Oestradiol (1 mug pe r rat per day for 3 days) induced more than a 50% decrease in both 38- 42 and 28 kDa proteins, irrespective of the growth hormone status in o variectomized rats. These studies disclose the multiplicity of uterine IGFBPs and show the ability of growth hormone and, more importantly, oestradiol to regulate these proteins. The ability of oestradiol to at tenuate the IGFBPs in the uterus may enhance the access of endogenousl y produced IGFs to its cognate cell receptors and hence its cellular h ormone action.