Should we aim at tissue renin-angiotensin systems?

Recent developments in our knowledge of the renin-angiotensin system (RAS) necessitate an update of the classical view on this system. These developments pertain to the pathways leading to formation of angiotensin II and other active metabolites, their receptors, biological functions and the presence of renin-angiotensin systems in tissues. The implications of the above new developments for the current interest in tissue renin-angiotensin systems as potential targets for drug therapy in cardiovascular disease are discussed in this review.

A novel method to examine the phenotype of chondrocytes.

Tissue engineering of articular cartilage in order to restore the function of degenerated, diarthrodial joints is currently widely under investigation. The results obtained thus far indicate that proper control of the differentiation of the cells used for this purpose is essential to produce and maintain a hyaline-like matrix. In this study, a procedure is described by which differentiation of chondrocytes in vitro and ex vivo can be studied. The method involves quantitative assessment of mRNA for different collagens, which are markers for differentiation of chondrocytes, by competitive PCR. In a culture system employing human osteoarthritic chondrocytes, mRNAs for the alpha1-chains of collagen types I, II and X are quantified. The procedure is fast, specific and sensitive. However, several controls should be included to ascertain the reliability of the assessment.

Expression and localization of renin and angiotensinogen in rat heart after myocardial infarction.

Wistar-Kyoto rats underwent myocardial infarction (MI) or sham surgery. At different time points after surgery (1-90 days), hearts were removed and divided into infarcted left ventricle (LV), noninfarcted septum, and right ventricle. The tissues were used for total RNA isolation or Formalin fixation for in situ hybridization (ISH). Renin and angiotensinogen mRNA contents were quantified by the competitive reverse transcriptase polymerase chain reaction. We found a 4-, 14-, and 8-fold increase (P < 0.05, n = 6) in renin mRNA in the infarcted LV at 2, 4, and 7 days after MI, respectively. No differences were observed between angiotensinogen mRNA levels in sham and infarcted hearts. ISH at 4 days after surgery revealed a dense renin mRNA labeling around the infarcted area, whereas ISH of angiotensinogen displayed an overall low density in the myocardium with somewhat higher levels in the epicardium of sham and MI animals. Atrial natriuretic factor mRNA, a marker for cardiac hypertrophy, was approximately twofold higher in all compartments of the hearts after MI. The low amounts of renin and angiotensinogen mRNA in the noninfarcted hypertrophied myocardium indicate that the intracardiac synthesis of these components does not play a dominant role in the development of cardiac hypertrophy in the rat heart after MI. In addition, the increased renin mRNA expression in the border zone of the infarcted LV suggests a role for intracardiac angiotensin II in infarct healing.

Does ACE inhibition limit structural changes in the heart following myocardial infarction?

A recent series of experiments in our laboratory were designed to elucidate the cellular changes that underlie the cardiac remodelling response following myocardial infarction (MI) in the rat as well as the potential role of the renin-angiotensin system (RAS) in this response. Inhibition of the RAS interferes with cardiomyocyte hypertrophy, interstitial cell DNA synthesis, and collagen deposition; these effects are mediated through the angiotensin II AT1 receptor subtype. Also, vascular outgrowth is functionally diminished, an effect that seems to depend on AT2 receptor activation. The intracardiac RAS may be involved in the wound healing response in the infarct area. However, we found no evidence for activation of the RAS in the remnant myocardium, which suggests that myocyte hypertrophy and interstitial fibrosis depend on activation of the systemic RAS. During the first weeks following MI, therapy of choice should thus inhibit the systemic RAS while allowing the wound-healing response of the intracardiac RAS, i.e. selective AT1 antagonists are appropriate early after MI. AT2 antagonists administered at that time can inhibit the cardiac vascularization response and cause a further decrease in level of cardiac function.

Activation of angiotensin-converting enzyme expression in infarct zone following myocardial infarction.

In the present study we quantified angiotensin-converting enzyme (ACE) mRNA and localized ACE mRNA and protein in the infarcted rat heart. Wistar rats underwent ligation of the left descending coronary artery, resulting in myocardial infarction (MI) or a sham operation. At different times (1-90 days) after surgery (n = 3 each), the heart was removed and divided into the right ventricle (RV), septum (Se) and left ventricle (LV). ACE mRNA was quantified by competitive reverse transcriptase-polymerase chain reaction (RT-PCR). At 4 and 7 days after MI, we found a 2.8-fold increase of ACE mRNA (n = 3; P < or = 0.05) in the infarcted LV compared with the LV of the sham group. No increases of ACE mRNA were found in the noninfarcted hypertrophied compartments. ACE activity increased 2.6- and 3.6-fold in the infarcted LV at 7 and 90 days after MI, respectively. In situ hybridization and immunohistochemistry showed increased ACE mRNA and protein density in the border zone of the infarcted area, predominantly in the endothelial cells lining capillaries. In the noninfarcted myocardium ACE mRNA and protein were confined to endothelial cells of the larger vessels. From these data we conclude that the intracardiac RAS is involved in the healing of the scar after MI in the rat, possibly giving rise to neovascularization. Furthermore, the data suggest that the intracardiac ACE is not necessarily associated with hypertrophy in the rat heart after MI.