We have established a transgenic rat model for the expression of the human endothelin-2 (ET-2). These animals exhibit overexpression of the transgene in tissues as well as in plasma. Despite these changes, blood pressure remains normal. To understand the regulatory mechanisms for normotension in the presence of increased ET-2 levels, we have investigated the ET system in more detail. We used competitive reverse transcription-polymerase chain reaction (RT-PCR) to evaluate possible overexpression or downregulation of endothelin A and B receptors at the mRNA level. PCR analyses revealed no significant differences of ETA and ETB receptor expression. In conclusion, the expression of human ET-2 in transgenic rats does not result in hypertension. Normotension in the transgenic animals is independent of ET receptor regulation. The reason for this may be counterregulation by other vasoactive systems, such as the NO system. Future studies will take this into account and will also concentrate on possible histomorphologic alterations caused by mitogenic properties of the endothelins.