Cellular distribution of somatogenic receptors and insulin-like growth factor-I mRNA in the rat liver.

Abstract

Parenchymal and non-parenchymal cell fractions isolated from rat liver were analysed for the distribution of somatogenic receptors and for insulin-like growth factor-I (IGF-I) mRNA. The effect of hypophysectomy either alone or in combination with a single injection of human GH (hGH) on the levels of IGF-I mRNA was also studied in the two cell fractions. The contamination of parenchymal cells in the non-parenchymal cell fraction was in the range of 2-3%. Somatogenic receptors were found only in the parenchymal cell fraction. IGF-I mRNA was detected in both cell fractions, although the level of this mRNA was about fivefold higher in parenchymal cells. When RNA was studied by Northern gel analysis no major differences were observed in the size distribution of IGF-I transcripts in the two cell fractions. In hypophysectomized animals, the IGF-I mRNA level was decreased to 10 and 30% of control values in the parenchymal and non-parenchymal cell fractions respectively. Treatment of hypophysectomized animals with a single dose of hGH restored IGF-I mRNA in parenchymal and in non-parenchymal cells to the extent found in intact animals. In conclusion, our data indicate that somatogenic receptors are exclusively, and IGF-I mRNA predominantly, expressed in liver parenchymal cells compared with a total non-parenchymal cell fraction. The most marked effect of GH, correlating with the presence of somatogenic receptors, was seen in the parenchymal cells. The minor non-GH dependent expression of IGF-I mRNA suggests that this peptide may elicit effects in addition to the well-established GH-dependent activity.