RAPID ACTIVATION OF THE TYPE-B VERSUS TYPE-A NATRIURETIC FACTOR GENE BY AORTOCAVAL SHUNT INDUCED CARDIAC VOLUME OVERLOAD

Objective: The aim was to compare activities of the type A and type B natriuretic factor genes during development of cardiac hypertrophy by use of a non-radioactive method designed for assessment of stable atri al and brain natriuretic factor (ANF, BNF) transcript levels in biopsy sized tissue samples. Methods: At 1 and 7 days after aortocaval shunt or sham surgery in rats, quantitative reverse transcriptase mediated polymerase chain reaction (Q-RT-PCR) was used to determine mRNA levels in cardiac tissues. Phosphoglycerate kinase-1 (PGK-1) mRNA levels ser ved as an external standard for Q-RT-CR. Results: The shunt increased left ventricular end diastolic pressure at days 1 and 7, and cardiac w eight was increased by day 7. By day 1, left ventricular BNF mRNA leve ls were twice those of controls, whereas ANF mRNA levels were not chan ged. By day 7, left ventricular BNF mRNA levels were increased 15-fold , and those for ANF were increased fivefold; the BNF mRNAs were also i ncreased in right atria and right ventricle, about fivefold in both ca ses. Conclusions: Both natriuretic factor genes were activated by card iac volume overload, and the increase in the level of left ventricular BNF transcripts - observed for the first time - was in fact more rapi d and exceeded that of ANF. The Q-RT-PCR assay will be of value to inv estigate the response to increased work load of cardiac msucle in vivo .