Spi-1: an hepatic serine protease inhibitor regulated by GH and other hormones

A sensitive RNAse protection method was used to show that serine protease inhibitor-1 (Spi-1) is expressed in rat liver and heart, but not in kidney or brain. Bovine somatotropin (bGH) and placental lactogen (bPL) induced rat hepatocyte cultures to express both Spi-1 and IGF-1 mRNA, with bPL approximately 100-fold more potent than bGH. Bovine prolactin (bPrL) did not induce hepatocyte Spi-1 mRNA, demonstrating lack of involvement of lactogenic receptors. Albumin mRNA levels were stable during hepatocyte culturing and were unaffected by growth hormone (GH) treatment, showing that neither culture conditions nor GH treatment affected cellular differentiation. Eliminating serum-free medium hormone supplements one at a time, estradiol, testosterone and T3 were shown to be unnecessary for GH induction of Spi-1, while dexamethasone removal decreased Spi-1 mRNA levels to 10% of GH-stimulated controls. bGH induction of Spi-1 mRNA in the presence of only dexamethasone and glucagon was 75% higher (p < 0.01) than levels seen with insulin also present.