Lack of production and growth-modulating effects of 1a,25-dihydroxyvitamin D3 in cultured fetal rat hepatocytes.

1a,25-Dihydroxyvitamin D3 [1,25(OH)2D3], the hormonal form of vitamin D3, has been shown to play a role in the regulation of growth of the regenerating adult rat liver following partial hepatectomy. In addition, a recent study implicated the neonatal liver as a possible extrarenal site of 1,25(OH)2D3 synthesis. Therefore, in our present study we used rapidly growing fetal hepatocytes in culture as a model cell line for regenerating hepatocytes and tested the hypothesis that fetal hepatocytes locally produce 1,25(OH)2D3 which in turn regulates their growth. Hepatocytes isolated from 19-day rat fetuses were grown in culture for 24 h in minimal essential medium without added serum or mitogens. To identify 1,25(OH)2D3 production, we incubated fetal hepatocytes in culture with 3H-25-hydroxyvitamin D3 (3H-25-OH D3) for 2, 6 and 24 h. High-pressure liquid chromatographic analysis of the lipid extract of the medium and cells revealed no evidence of conversion of 3H-25-OH D3 into 3H-1,25(OH)2D3. Additionally, to investigate the effect of 1,25(OH)2D3 on DNA synthesis in fetal liver, we measured 3H-thymidine incorporation by the cultured fetal hepatocytes following 24 h of exposure to various concentrations of 1,25(OH)2D3. The results of DNA synthesis revealed no effect of 1,25(OH)2D3 on fetal hepatocyte growth. As alterations in growth regulation by 1,25(OH)2D3 in other cells are thought to be mediated by intracellular vitamin D receptors (VDR), the expression of the VDR message in the fetal and maternal tissues of a pregnant rat was studied. RNA was first isolated from fetal liver, fetal kidney, maternal liver and maternal kidney, and the corresponding cDNA was then generated by reverse transcription.(ABSTRACT TRUNCATED AT 250 WORDS)