Tissue converting enzyme activity is low in the kidney of spontaneously hypertensive rats

Developmental expression of ACE2 in the SHR kidney: a role in hypertension?

The abnormal development of the intrarenal renin-angiotensin system (RAS) is thought contribute to adult-onset hypertension in the spontaneously hypertensive rat (SHR). Angiotensin-converting enzyme 2 (ACE2) is a novel enzyme with complementary actions to that of ACE. Recent studies have shown that ACE2 expression is reduced in the adult SHR. However, its regulation in pre-hypertensive animals is unknown. In this study, we examine the developmental expression of ACE2 in the rodent kidney and its temporal expression, as it relates to the development of hypertension in the SHR model. Kidneys from SHR and normotensive Wistar Kyoto (WKY) rats (n=8-12/group) at birth, 6 weeks of age, and adulthood (80 days) were examined. Gene expression and activity of ACE2 were determined by real-time reverse transcription-polymerase chain reaction and quenched fluorescence assays, respectively. Renal expression was localized by in situ hybridization and immunohistochemistry. The expression and ACE2 activity are significantly increased in the SHR kidney at birth. With the onset of hypertension, the tubular expression of ACE2 falls in SHR compared to WKY and remains reduced in the adult SHR kidney. Glomerular expression is paradoxically increased in the SHR glomerulus. The overall developmental pattern of ACE2 expression in the SHR kidney is also modified, with declining expression over the course of renal development. The developmental pattern of ACE2 expression in the SHR kidney is altered before the onset of hypertension, consistent with the key role of the RAS in the pathogenesis of adult-onset hypertension. Further research is required to distinguish the contribution of these changes to the development and progression of hypertension in this model.

Kidney angiotensin II receptors and converting enzyme in neonatal and adult Wistar-Kyoto and spontaneously hypertensive rats

The aim of the present study was to correlate the development of the renin angiotensin system (RAS) in the kidney of the rat with the development of genetic hypertension. Immature (1-week-old) and adult (12-week-old) normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive kidney rats (SHR) were used for quantification of angiotensin II (ANG II) receptors and angiotensin converting enzyme (ACE) binding sites using quantitative autoradiography. In both neonatal and adult animals of either strain, ANG II receptors were of AT1 subtype. In all kidney areas of 1-week-old rats. ANG II receptor density was higher in SHR than WKY. Binding density increased with age in WKY rats; thus, in the glomeruli and the outer stripe of the outer medulla of 12-week-old WKY, binding was significantly higher than that present in age-matched SHR. [125I]351A binding to ACE was highest in the outer medulla and not detectable in glomeruli. In 1-week-old rats, binding to ACE was higher in WKY than in SHR strain. No differences in ACE binding were found between adult SHR and WKY rats, with the exception of the inner stripe of the outer medulla, where no binding was detected in SHR. Our results support the hypothesis that the RAS in kidney is developmentally regulated and is involved in the development and maintenance of genetic hypertension in SHR.

The effect of captopril treatment and its withdrawal on the gene expression of the renin-angiotensin system

The mRNA expression of renin, angiotensinogen and angiotensin converting enzyme (ACE) was determined in the kidneys and livers from spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) during chronic treatment with captopril and following its withdrawal. Chronic captopril treatment was associated with a dramatic rise in renin mRNA in the kidney and an elevation in mRNA for ACE in the liver. The release from captopril treatment was associated with a reversal of the increase in kidney renin mRNA but no reversal of the sustained elevation of ACE mRNA in the liver. In situ hybridisation revealed a localisation of renin to the area of the juxtaglomerular apparatus in the kidneys from untreated animals, but recruitment of vascular sites of renin expression in kidneys from captopril-treated animals. In kidneys from released animals, renin mRNA expression was once again confined to the juxtaglomerular apparatus. ACE mRNA was expressed in hepatocytes throughout the livers from animals in all treatment groups. The results highlight a differential effect of captopril withdrawal upon the gene expression of the components of the renin-angiotensin system in kidney and liver.

A comparison of the properties and enzymatic activities of three angiotensin processing enzymes: angiotensin converting enzyme, prolyl endopeptidase and neutral endopeptidase 24.11

The discovery of angiotensin-(1-7) [Ang-(1-7)] as a bioactive Ang II fragment of the renin-angiotensin system (RAS) alters the current understanding of the enzymatic components that comprise the RAS cascade. Two neutral endopeptidases, prolyl endopeptidase (E.C. 3.4.21.26) and neutral endopeptidase 24.11 (E.C. 3.4.24.11), are capable of forming Ang-(1-7) from Ang I and have been implicated in the in vivo processing of Ang I. This makes them putative Ang processing enzymes and part of the RAS cascade. This review summarizes the physical characteristics and distribution of angiotensin converting enzyme (E.C. 3.4.15.1), a known Ang I processing enzyme, and compares its features to what is known of prolyl endopeptidase and neutral endopeptidase 24.11.

Pathogenetic role of vascular angiotensin-converting enzyme in the spontaneously hypertensive rat

1. This study was undertaken to examine the possibility that the level of angiotensin-converting enzyme (ACE) increases in vascular tissue, and that this may participate in the pathogenesis of hypertension in spontaneously hypertensive rat (SHR). 2. In SHR, at the established hypertensive stage, the prolonged antihypertensive effect induced by a single oral dose of spirapril was closely correlated to the long-lasting inhibition of ACE in aortae and mesenteric arteries. In contrast, ACE in plasma, lung, heart and kidney recovered from inhibition faster than in vessels. 3. Prolonged daily oral treatment of SHR with spirapril, initiated at the age of 8 weeks and continued for 8 weeks, prevented the development of hypertension with concomitant decrease in aortic ACE activity. Blood pressure continued to be suppressed after the drug was withdrawn, as did the aortic ACE activity. 4. Spontaneously hypertensive rats developed hypertension with age as well as with the increase in aortic ACE activity which became higher with age than that of Wistar-Kyoto (WKY) normotensive control rats. On the contrary, ACE activity in plasma and lung of SHR was substantially lower than that of WKY at any age from 4 to 20 weeks old. Brain ACE activity of SHR did not differ from that of WKY at any age. Aged SHR showed the lower enzyme activity in the kidney compared with that of age-matched WKY. 5. Our results support the hypothesis that increased vascular ACE may play an essential role in the development and maintenance of hypertension in SHR.