Pathogenic factors involved in renovascular hypertension. State of the art.

The complex hormonal action of angiotensin II in the long-term control of blood pressure or sodium metabolism, or in renal hypertension, is not completely understood. Structure-activity relations with analogues of angiotensin II gave information about the functions responsible for pressor and myotropic response in the molecule that led to the synthesis of competitive antagonists of this hormone. These antagonists, however, show variable agonist/antagonist ratios in different species or different tissues of the same species. This fact necessitates further work to induce tissue specificity. Although des-Asp1-angiotensin II ("angiotensin III") has been recognized as a hormone, its exact role in the biosynthesis of aldosterone is yet to be discovered. The antagonists such as des-Asp1-[Ile8]-angiotensin II or des-Asp1-[Thr8]-angiotensin II have provided important leads in this direction. Many of the biologic effects of angiotensin I have been attributed to its conversion to angiotensin II by the converting enzyme. Recent investigations indicate that angiotensin I itself may play a direct role; however, most of these studies were carried out by inhibiting the converting enzyme activity with peptides obtained from the venom of Bothrops jararaca. Since these peptides also potentiate bradykinin action, the observed biologic activities could be caused by either angiotensin I or bradykinin. Bsides, converting enzyme is no longer thought to be a single enzyme and its nature varies from species to species and from tissue to tissue in the same species. Renin inhibitors related to renin substrate or pepstatin are not freely soluble in plasma and are not effective under physiologic conditions. This points to the importance of renin inhibitors isolated from kidney or other natural sources. Thus, although the renin-angiotensin system appears to be an integral part of the problem of hypertension, characterization of various converting enzymes, roles of extrarenal renin, isorenin, tonin, and brain-renin, and the involvement of other humoral, neurogenic, and immunogenic factors should be pieced together to get a clear picture of the hypertension problem.