Saralasin

Abstract: Recently, angiotensin II (Ang II) has been shown to cause hypertrophy of cultured quiescent rat aortic smooth muscle (RASM) cells. This observation along with the demonstration of angiotensinogen mRNA in the vessel wall has led us to postulate a role for vascular angiotensin in hypertensive blood vessel hypertrophy. To investigate further the possible molecular mechanisms, we examined the effect of Ang II on the expression of two genes known to be involved with cellular growth response. Near-confluent RASM cells were made quiescent by 48-h exposure to a defined serum-free medium. Ang II (10(-6) to 10(-11) M) resulted in an induction of the protooncogene c-myc mRNA within 30 min which persisted for 6 h. Interestingly, 6 h after the addition of Ang II, platelet-derived growth factor (PDGF) A-chain mRNA expression was elevated, peaked in 9 h, and persisted for 11 h. This was accompanied with a 15-20-fold increase in PDGF concentration in the culture medium. These effects were dose-dependent and were blocked by saralasin. Whereas the inhibition of protein synthesis by cycloheximide resulted in a stabilization of c-myc mRNA, cycloheximide abolished the elevation of the PDGF A-chain mRNA. Taken together, our data show that exposure of RASM cells to Ang II results in the sequential activation of c-myc and PDGF A-chain mRNA expressions. This sequential activation of protooncogene and growth factor gene may be an important mechanism in angiotensin-induced smooth muscle growth and hypertrophy.

Abstract: In the 1970s, a series of observations demonstrated that angiotensin II has deleterious effects on the heart and kidney and that patients with high levels of plasma renin activity are at a higher risk of developing stroke or myocardial infarction than those with low plasma renin activity.1 2 Thereafter, the development of pharmacological probes that block the renin-angiotensin system helped define the contribution of this system to blood pressure control and to the pathogenesis of diseases such as hypertension, congestive heart failure, and chronic renal failure. Thus, the concept of treating hypertension and congestive heart failure by a specific blockade of the renin-angiotensin system was first established with the use of saralasin, a nonselective peptidic antagonist of angiotensin II receptors.3 4 5 6 7 8 9 With saralasin, it became possible to demonstrate that angiotensin II receptor blockade, alone or in combination with salt depletion, lowers blood pressure in hypertensive patients and improves systemic hemodynamics in patients with congestive heart failure.3 4 5 6 7 8 9 10 However, saralasin had many drawbacks. Because it is a peptide, it had to be administered intravenously. This characteristic limited its use to hours or a few days at maximum. In addition, at higher doses, saralasin had some partial agonist, angiotensin II–like effects. The next major breakthrough in the understanding of the renin-angiotensin system was triggered by the development of orally active angiotensin-converting enzyme (ACE) inhibitors.10 11 12 13 14 15 Studies performed with these agents rapidly confirmed and reinforced the seminal clinical observations made with saralasin. ACE inhibitors are now recognized as an important therapeutic step to control blood pressure in hypertensive patients and to reduce morbidity and mortality in patients with congestive heart failure.16 In addition, because of their ability to lower proteinuria, ACE inhibitors have …

Abstract: Numerous previous studies have proposed a role for angiotensin II (AII) in the renal regulation of salt balance. At least one nephron site, the proximal convoluted segment, has been implicated in this role. We used in vitro microperfusion of rabbit proximal convoluted tubules to further examine this question. To insure use of appropriate in vivo concentrations as well as potency of the hormone in vitro, we measured plasma AII levels by radioimmunoassay in normal, sodium-depleted, and adrenalectomized rabbits, and measured AII activity by bioassay after incubation in various microperfusion baths. Plasma levels ranged from approximately 2 X 10(-11) to 5 X 10(-11) M. AII activity was stable in Ringer's solution plus albumin, but not in rabbit serum or Ringer's solution plus fetal calf serum. In Ringer's solution plus albumin, physiologic concentrations of AII stimulated volume reabsorption (Jv). 10(-11) M AII increased Jv by 16% (P less than 0.01). 10(-10) M AII produced a lesser increase, 7.5% (P less than 0.05). At a frequently studied, but probably pharmacologic dose, 10(-7) M AII inhibited Jv by 24% (P less than 0.001). AII at 10(-11) M did not stimulate Jv in the presence of 10(-7) M saralasin. Though previous studies have suggested agonistic effects of saralasin alone in epithelia, we found no significant effect of 10(-7) M saralasin on Jv. None of the AII doses measurably changed transepithelial voltage. We conclude that AII in physiologic doses directly stimulates Jv in proximal convoluted tubules and this effect is probably receptor mediated and, within the limits of detection, electroneutral.

Abstract: Rodents are the unique species carrying duplicated angiotensin (Ang) type 1 (AT1) receptor genes, Agtr1a and Agtr1b. After separately generating Agtr1a and Agtr1b null mutant mice by gene targeting, we produced double mutant mice homozygous for both Agtr1a and Agtr1b null mutation (Agtr1a-/-; Agtr1b-/-) by mating the single gene mutants. Agtr1a-/-, Agtr1b-/- mice are characterized by normal in utero survival but decreased ex utero survival rate. After birth they are characterized by low body weight gain, marked hypotension, and abnormal kidney morphology including delayed maturity in glomerular growth, hypoplastic papilla, and renal arterial hypertrophy. These abnormal phenotypes are quantitatively similar to those found in mutant mice homozygous for the angiotensinogen gene (Agt-/-), indicating that major biological functions of endogenous Ang elucidated by the abnormal phenotypes of Agt-/- are mediated by the AT1 receptors. Infusion of Ang II, AT1 blockers, or an AT2 blocker was without effect on blood pressure in Agtr1a-/-; Agtr1b-/- mice, indicating that AT2 receptor does not exert acute depressor effects in these mice lacking AT1 receptors. Also, unlike Agt-/- mice, some Agtr1a-/-; Agtr1b-/- mice have a large ventricular septum defect, suggesting that another receptor such as AT2 is functionally activated in Agtr1a-/-, Agtr1b-/- mice.