IGF-I AND IGF-BINDING PROTEIN GENE EXPRESSIONS IN SPONTANEOUS DWARF RAT

Effects of growth hormone (GH) and fasting on hepatic expressions of i nsulin-like growth factor I (IGF-I) and IGF-I-binding protein (IGFBP)- 1, -2, -3, and -4 were examined in spontaneous dwarf rats (SDR), which completely and specifically lack GH among pituitary hormones. The hep atic expressions of mRNA encoding IGF-I and IGFBP-3 were reduced and I GFBP-1 mRNA was elevated in the SDR. Both chronic and acute administra tion of GH restored these changes, indicating the association of GH bu t not other pituitary hormones with hepatic expressions of these genes . In addition, the present examination revealed that mRNA level of IGF BP-2 was elevated in SDR, which could not be attenuated by exogenous G H, and that GH may not be directly relevant to the regulation of hepat ic IGFBP-4 expression. Fasting for 2 days reduced IGF-I mRNA level and increased IGFBP-2 mRNA level in the SDR, as well as in the normal rat , suggesting the presence of factors other than reduced serum GH respo nsible for fasting-induced alteration in the expression of these mRNAs . On the other hand, fasting resulted in little change or even a reduc tion of IGFBP-1 mRNA level in the SDR.