UP-REGULATED AND DOWN-REGULATED TRANSCRIPTION OF MYOCARDIAL GENES AFTER PULMONARY-ARTERY BANDING IN PIGS

Background. Acute or chronic pressure overload may occur during or aft er cardiac surgical procedures. Typical examples are aortic cross-clam ping and pulmonary artery banding. It is well known that mechanical st ress induces transcription of different myocardial genes. However, the se results were mainly obtained from in vitro studies and experiments with rodents. This experiment was carried out to investigate molecular alterations after pressure overload in porcine hearts. Methods. The s tudy was performed with 35 Landrace pigs with a mean weight of 32 +/- 1.2 kg. The five groups consisted of 7 pigs each, 3 sham-operated pigs and 4 banded pigs. The hearts were exised after different time interv als. We investigated messenger RNA expression of sarcoplasmic reticulu m adenosine triphosphatase, phospholamban, alpha-/beta-myosin heavy ch ain, and atrial natriuretic factor by Northern blot analysis. Results. The ratio of right ventricular weight to body weight increased signif icantly after 7 and 24 days in banded pigs (p < 0.05). Atrial natriure tic factor messenger RNA was significantly upregulated in banded pigs versus sham-operated pigs after 1 day (240% +/- 7% versus 100% +/- 6%; p < 0.01) and 3 days (520% +/- 8% versus 100% +/- 8%; p < 0.01). Ther e was insignificant downregulation of sarcoplasmic reticulum adenosine triphosphatase and phospholamban after 1, 3, and 7 days. Myosin heavy chain messenger RNA expression remained unchanged. Conclusions. Pulmo nary artery banding results in hypertrophic response of the porcine ri ght ventricle; however, the weight increase is not the result of myosi n heavy chain messenger RNA upregulation. Atrial natriuretic factor me ssenger RNA is locally expressed in mechanically stressed myocytes. Fu rthermore, pressure overload downregulates transcription of calcium-bi nding proteins that can influence ventricular contractility. These res ults may have an impact on cardiac surgical procedures. (C) 1998 by Th e Society of Thoracic Surgeons.