Influence of cyclic nucleotides, norepinephrine and calcium on 3H-uridine incorporation into RNA in thyroid slices.

The role of cyclic nucleotides and Ca2+ on RNA synthesis was investigated in beef thyroid slices. Both cyclic AMP and cyclic GMP caused a significant stimulation of 3H-uridine incorporation into total RNA (around 500%). No additive effect was observed when slices were incubated with cAMP plus cGMP. Another cyclic nucleotide, cyclic 3'5' cytidine monophosphate (cCMP) was also studied. At 0.2 mM cCMP the stimulatory action of cGMP was no longer evident (control 2183 +/- 311 cpm/mg RNA; 0.5 mM cGMP 3849 +/- 316; 0.2 mM cCMP 1885 +/- 238; cGMP + cCMP 1750 +/- 178), extending our previous observation on the blocking effect of cCMP on cAMP stimulation of RNA synthesis. The distribution of uridine nucleotides, precursors of RNA, was studied by paper chromatography in slices labeled with 3H-uridine. Both cAMP and cGMP caused a significant increase in labeled UTP (% UTP in chromatogram: control 2.4 +/- 0.4; 1 mM cAMP 4.9 +/- 1.3 and 1 mM cGMP 5.3 +/- 0.5). The influence of Ca2+ on RNA labeling was studied by incubating the slices under mild Ca2+ depletion (KRB without Ca2+) and severe Ca2+ depletion (KRB without Ca2+ + 2 mM EGTA). Basal RNA labeling was significantly affected only by severe depletion (control 1312 +/- 50; severe Ca2+ depletion 912 +/- 190). Under this latter condition, RNA synthesis failed to respond to TSH, cAMP and cGMP stimulation, and EM showed severe alterations in structure (e.g., nuclear swelling, mitochondrial condensation, etc.).(ABSTRACT TRUNCATED AT 250 WORDS)