| Research Abstract |
A : Zonal differences of DNA synthesis in hepatocytes induced by hepatocyte growth factor/scatter factor (HGF/SF)and epidermal growth factor (EGF) were investigated under fed or starved conditions. Under fed conditions, 5*10^<-10>M HGF/SF induced a 12-fold increase in DNA synthesis in cultured perivenous hepatocytes (PVH) compared with controls, while there was a 7-fold increase in periportal hepatocytes (PPH). In contrast, 10^<-8>M EGF inuced a 16-fold increase in PPH,but a 10.5-fold in PVH.Under starved conditions, HGF-SF induced a 7.1-fold increase in PVH at most and a 4.6-fold increase in PPH,and EGF induced a 9,2-fold increase in PVH,a'4.9-fold in PPH.Overall DNA synthesis was greater in fed rats than in starved rats. Sensitivity to EGF was reversed by a change in nutritional conditions, but that to HGF-SF was not influenced by nutritional conditions. [^<125>I] EGF and [^<125>I] HGF/SF-receptor binding studies, revealed no significant difference between PPH and PVH in starved and
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fed rats. Then, zonal differences seemd to be not due to receptor numbers, but might be related to postreceptor networks.
B : Change of DNA synthesis induced by HGF/SF and EGF in PPH and PVH isolated at different times after partial hepetectomy was investigated. Hepatocytes were isolated at 6,12,36,72,96 hours, 1, and 2 weeks after 70% partial hepatectomy. In experiment of cell cycles, there were no difference between PPH and PVH.However, the G_1-M phase entry of hepatocytes was different according to the preparation time. (At 6,12 hours after hepatectomy, the maximum DNA synthesis was observed from 24 to 48 hours. At 36,72,96 hours, 1, and 2 weeks, that was observed from 48 to 72 hours.) According to the results above, we investigated change of maximum DNA synthesis induced by HGF/SF and EGF in PPH and PVH isolated at different times after partial hepatectomy. That was most decreased in PPH isolated at 12 hours, and in PVH at 6 hours after hepatectomy. And that returned to the control level (without hepatectomy) in PPH isolated at 72 hours after hepatectomy, that returned in PVH at 96 hours. In [^<125>I] HGF/SF and [^<125>I] EGF binding study, the receptor number most decreased at 12-36 hours after heptectomy. and recover at 2 weeks-1 month. whereas there was no significant difference between PPH and PVH in Kd values. Differencies in change of DNA synthesis in PPH and PVH suggested that liver regeneration might occur unevenly according to spatial zone. Less
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