Fig. 4. Effect of Trolox (Tr), Lipoic acid (LA) and SB203580 (SB) on atrial natriuretic peptide (ANP) mRNA levels in samples from CoCl₂-perfused amphibian hearts. (A) RT-PCR analysis of RNA isolated from the ventricles of cardiac muscle perfused with 500 µmol l^-1 CoCl₂ in the presence or absence of Tr (10 µmol l^-1), LA (10 µmol l^-1) and SB203580 (1 µmol l^-1). Amplification of ANP (top) and ß-actin (bottom) cDNA in identical samples was performed. (B) After densitometric analysis of the PCR products the results were normalized for ß-actin and presented as fold stimulation, expressed as ANP/ß-actin ratio. Results are means ± s.e.m. for at least three independent experiments. ^*P<0.001 vs control (untreated) hearts; P<0.001 vs CoCl₂-treated hearts. The PCR products of ANP (375 bp) and ß-actin (900 bp) were analysed in 1.2% and 1% (w/v) agarose gel electrophoresis, respectively.