Stimulation by N6,O2?-dibutyryl adenosine 3?,5?-cyclic monophosphate of RNA and DNA synthesis and of cell proliferation of rat hepatocytes in primary tissue culture

Abstract

The effects of DBcAMP in doses from 1.5 × 10⁻⁸ to 1.5 × 10⁻³ M on the compartmental apparent surface area (ASA) and (5-³H)uridine radioactivity concentration (URC), (methyl-³H)thymidine labelling index per 1 hour ([Me-³H]Tdr LI/h) and per cent mitotic index (MI%) and colchicine metaphase index (CMI%) of young rat differentiated hepatocytes in primary tissue culture were investigated by morphometric and radioautographic methods. In these cells DBcAMP was found to elicit: (1) progressive increments in the ASA of nucleoli, karyoplasm and cytoplasm; (2) peak increases in nucleolar URC at 1.5 × 10⁻⁸ and 10⁻⁵ M, but a slight decrease at 1.5 × 10⁻³ M; (3) significant increments in karyoplasmic and total nuclear URC at all doses, except at 1.5 × 10⁻⁶ and 10⁻⁴ M, when such parameters remained at control levels; (4) steady and progressive increases in cytoplasmic and total cell URC values; (5) marked increments in (Me-³H)Tdr LI/h, MI% and CMI% up to the dose of 1.5 × 10⁻⁴ M, but at 1.5 × 10⁻³ M these parameters were found to be either much less enhanced or to approach closely to control values. cAMP in doses from 1.5 × 10⁻⁸ to 10⁻⁴ M also markedly incremented the in vitro hepatocyte CMI%, while having a lesser stimulatory effect at 1.5 × 10⁻³ M. Finally of the various possible metabolites of DBcAMP administered at 1.5 × 10⁻⁸ M to liver cultures, N⁶- and O^2′-MBcAMP and, again, cAMP significantly increased the CMI% of cultured hepatocytes, whereas 5′-AMP, adenosine and allantoin had no significant effect and Na-butyrate slightly decreased it. The present observations strengthen the hypothesis that cAMP and its butyrated derivatives, by possibly amplifying the template activity of the liver chromatin, accelerate the flow of differentiated primary young rat hepatocytes into the various stages of the mitotic cell cycle.