AUTOCRINE PARACRINE DETERMINANTS OF STRAIN-ACTIVATED BRAIN NATRIURETIC PEPTIDE GENE-EXPRESSION IN CULTURED CARDIAC MYOCYTES/

The application of mechanical strain leads to activation of human brai n natriuretic peptide gene promoter activity, a marker of hypertrophy, in cultured neonatal rat ventricular myocytes. We have used a combina tion of transient transfection analysis and reverse transcriptase-poly merase chain reaction to examine the role of locally produced factors in contributing to this activation. Conditioned media from strained, b ut not static, cultures led to a dose-dependent increase in human brai n natriuretic peptide gene promoter activity. This increase was comple tely blocked by losartan or BQ-123, implying a role for angiotensin an d endothelin as autocrine/paracrine mediators of the response to strai n. Inclusion of the same antagonists in the cultures themselves led to only partial inhibition (similar to 60%), whereas inclusion of exogen ous endothelin or angiotensin II resulted in amplification of the stra in response. Angiotensin II and endothelin appear to be arrayed in ser ies in the regulatory circuitry; the angiotensin response was blocked by BQ-123, whereas the endothelin response was unaffected by losartan. Mechanical strain was also shown to stimulate expression of the endog enous angiotensinogen, angiotensin-converting enzyme, and endothelin g enes in this system. Collectively, these data indicate that locally ge nerated angiotensin II and endothelin, acting in series, play an impor tant autocrine/paracrine role in mediating strain-dependent activation of cardiac-specific gene expression.