The renin-angiotensin system plays a pivotal role in blood pressure regulation. Recent molecular biological findings led to the new concept that in addition to the classic endocrine system, local tissue systems may also play an important role in cardiovascular diseases such as hypertension. In particular, the brain renin-angiotensin system was shown to influence the central control of blood pressure and is thought to contribute to the hypertensive phenotype of genetically hypertensive rat models. To identify the physiological role of these local systems, we established an antisense strategy to downregulate the expression of the precursor hormone angiotensinogen (AOGEN) in cell culture, which can also be used to establish transgenic rat lines. Plasmids encoding an RNA sequence complementary to the rat AOGEN mRNA under control of different viral and tissue-specific promoters were constructed and transfected into an AOGEN-expressing cell line. A competitive reverse transcription-polymerase chain reaction method was established for the quantification of AOGEN mRNA. Depending on the level of antisense RNA, the expression of the AOGEN gene was reduced down to 22% of control levels. Furthermore, the secretion of AOGEN protein was totally abolished. These results clearly demonstrate that the antisense constructs used are functional in reducing the AOGEN gene expression in vivo and can be used for the production of transgenic rats.