Autoradiographic localization and characterization of angiotensin II receptor subtypes in the rat thymus

Angiotensin Receptor Blockers Are Not Just for Hypertension Anymore

Beyond blood pressure control, angiotensin receptor blockers reduce common injury mechanisms, decreasing excessive inflammation and protecting endothelial and mitochondrial function, insulin sensitivity, the coagulation cascade, immune responses, cerebrovascular flow, and cognition, properties useful to treat inflammatory, age-related, neurodegenerative, and metabolic disorders of many organs including brain and lung.

Physiology of Local Renin-Angiotensin Systems

Since the first identification of renin by Tigerstedt and Bergmann in 1898, the renin-angiotensin system (RAS) has been extensively studied. The current view of the system is characterized by an increased complexity, as evidenced by the discovery of new functional components and pathways of the RAS. In recent years, the pathophysiological implications of the system have been the main focus of attention, and inhibitors of the RAS such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin (ANG) II receptor blockers have become important clinical tools in the treatment of cardiovascular and renal diseases such as hypertension, heart failure, and diabetic nephropathy. Nevertheless, the tissue RAS also plays an important role in mediating diverse physiological functions. These focus not only on the classical actions of ANG on the cardiovascular system, namely, the maintenance of cardiovascular homeostasis, but also on other functions. Recently, the research efforts studying these noncardiovascular effects of the RAS have intensified, and a large body of data are now available to support the existence of numerous organ-based RAS exerting diverse physiological effects. ANG II has direct effects at the cellular level and can influence, for example, cell growth and differentiation, but also may play a role as a mediator of apoptosis. These universal paracrine and autocrine actions may be important in many organ systems and can mediate important physiological stimuli. Transgenic overexpression and knock-out strategies of RAS genes in animals have also shown a central functional role of the RAS in prenatal development. Taken together, these findings may become increasingly important in the study of organ physiology but also for a fresh look at the implications of these findings for organ pathophysiology.

Characterisation of a thymic renin-angiotensin system in the transgenic m(Ren-2)27 rat

We previously showed the rat thymus contains and secretes active renin. However, the cellular location of the thymic renin-angiotensin system (RAS) is unknown. To more easily study the thymic RAS we used the hypertensive transgenic (mRen-2)27 rat which overexpresses renin and angiotensin in extra-renal tissues. Comparisons were made with normotensive Sprague Dawley (SD) rats. All rats exhibited intense immunolabeling for renin protein and angiotensin in macrophages and thymic epithelial cells, however renin prosequence was not detected. In each rat strain, thymic renin was predominately active and highest in Ren-2 rats (Ren-2, 22.6+/-4.2, SD 0.8+/-0.1 mGoldblatt Units/g, mean+/-SEM). Renin mRNA was identified in Ren-2 and SD rat thymus by RT-PCR. Thymic angiotensin II concentrations/wet weight in Ren-2 (20.1+/-1.1 fmol/g) and SD (15.8+/-2.3 fmol/g) rats were similar to plasma. In conclusion, macrophages and epithelial cells are the source of active renin in the rat thymus. The thymic RAS may have actions systemically and may also influence local processes such as blood flow and cell growth.