Renal aminopeptidase activities in animal models of hypertension

Aminopeptidase activity (AP) has been implicated in the metabolism of renal and circulating vasoactive peptides. This activity is involved in the pathogenia of hypertension, essentially in spontaneously hypertensive rats. However, no other animal models, which develop hypertension by other different ways, have been used to study the possible role of aminopeptidase activity. To investigate the role of this activity in the pathogenesis of hypertension, angiotensinase A activity (glutamyl-AP and aspartyl-AP), aminopeptidase M activity (alanyl-AP), aminopeptidase B activity (arginyl-AP), pyroglutamyl-AP, and cystinyl-AP were measured in the serum and kidney of two experimental animal models of renovascular hypertension: Goldblatt two-kidney one clip (G2K-1C) and low renal mass rats (LRM). No differences were found in serum levels of AP in LRM or G2K-1C in comparison with their respective controls. In LRM rats there was a significant decrease in membrane-bound angiotensinase A (glutamyl-AP), arginyl-AP and alanyl-AP activities. In G2K-1C rats there was a significant decrease in soluble and membrane-bound angiotensinase A activity (aspartyl-AP). Our results suggest that AP activities play a role in the regulation of renal vasoactive peptides, and respond differently depending on the cause of hypertension.

Attenuation in rat brain nitric oxide synthase activity in the coarctation model of hypertension

The correlation of brain nitric oxide synthase (NOS) activity with renal hypertension has been investigated in rats. NOS activity was measured by oxyhaemoglobin and by conversion of radioactive arginine to citrulline. There was significant elevation of blood pressure (54% increase) along with left ventricular hypertrophy (26% greater than the control) 8 weeks after coarctation. The brain NOS activity was also significantly reduced in coarctated animals (45% of the control value). Treatment with captopril (angiotensin converting enzyme inhibitor) or centhaquin (centrally acting antihypertensive agent) led to significant reduction of left ventricular hypertrophy and a marked recovery in the brain NOS activity (to 92% and 135% of the control, respectively). Nifedipine (a calcium channel blocker) also brought about normalization of blood pressure but the left ventricular hypertrophy was not prevented. The brain NOS activity in the nifedipine treated group also showed a significant trend of recovery (to 73% of the control NOS activity). The results suggested that there is an inverse correlation between brain NOS activity and blood pressure level.

Extracellular signal-regulated kinase and c-Jun NH2-terminal kinase activities are continuously and differentially increased in aorta of hypertensive rats

We first examined the activities of extracellular signal-regulated kinases (ERKs) and c-Jun NH2-terminal kinases (JNKs) in the aorta of hypertensive rats. In Dahl salt-sensitive (DS) rats, chronic hypertension caused by a high-salt diet was followed by sustained activation of aortic p42ERK and p44ERK. p46JNK and p55JNK activities were also increased in hypertensive DS rats, but returned to control levels earlier than ERKs, suggesting that ERKs and JNKs may be independently activated in hypertensive rats. In stroke-prone spontaneously hypertensive rats (SHRSP) which spontaneously develop hypertension under a low salt-diet, aortic p42ERK and p44ERK activities were progressively increased with the development of hypertension, compared with control normotensive rats. p46JNK and p55JNK activities in SHRSP were increased, with a different time course from ERKs. Thus, we first demonstrated that ERKs and JNKs activities are chronically and differentially increased in the aorta of hypertensive rats, suggesting the involvement of these kinases in hypertensive vascular diseases.

Role of platelet-activating factor in two-kidney, one-clip hypertension

BACKGROUND

Platelet-activating factor (PAF) is a bioactive phospholipid which is a potent hypotensive agent. To investigate the role of PAF in renovascular hypertension, we determined the PAF concentration and its production level assessed by the activity of cholinephosphotransferase (CPT) in renal tissue and examined the effect of a PAF antagonist on the mean arterial pressure (MAP) in control and two-kidney with one clipped (2K1C) hypertensive rats.

MATERIALS AND METHODS

The concentration of PAF and CPT in the renal medulla and cortex were determined by radioassay. Also, the effect of a PAF antagonist, CV-6209, on MAP was also examined in both 2K1C hypertensive and normal control rats.

RESULTS

The PAF concentration and CPT activity were significantly higher in the medulla than in the cortex in both 2K1C hypertensive and normal control rats, and both values in the medulla were also significantly higher in the clipped kidney than in the contralateral unclipped kidney or in control rat kidneys. We also observed a significant negative correlation between the PAF concentration in the medulla, and the medulla weight in the clipped kidney of 2K1C hypertensive rats. Infusion of the PAF antagonist, CV-6209, did not affect MAP in 2K1C hypertensive rats, but was significantly increased (P < 0.05) in control rats.

CONCLUSIONS

These findings suggest that PAF, whose production is induced by renal ischemia due to renal artery stenosis, plays an important role in the renomedullary vasodepressor system, but the effect of PAF as a vasodilator in the peripheral vessels is limited in 2K1C hypertension.

Immunoreactivity for nitric oxide synthase and endothelin in the coronary and basilar arteries of renal hypertensive rats

The ultrastructural localization of immunoreactivity to nitric oxide synthase (type-III and type-II) and endothelin-1 was examined by using pre-embedding peroxidase-antiperoxidase techniques in the coronary and cerebral basilar arteries in renal hypertensive rats. Renal hypertension was produced by excision of the right kidney and clipping of the left renal artery. Controls were normotensive sham-operated rats (right surgical nephrectomy; a clip inserted near the left renal artery). Both in controls and hypertensive rats, immunoreactivities for nitric oxide synthase-III and endothelin-1 were localized within subpopulations of endothelial cells. In addition, signs of translocation of nitric oxide synthase-III were noted from the cytoplasm to the Golgi complex in endothelial cells of the basilar artery of hypertensive animals. Neither controls nor hypertensive rats showed immunoreactivity for nitric oxide synthase-II. Preparations of the right coronary artery from hypertensive rats displayed fewer endothelial cells positive to nitric oxide synthase-III than in controls, although there were no significant changes in the distribution of endothelin-1-positive endothelial cells in the coronary artery of hypertensive rats. In contrast, the basilar artery from hypertensive rats displayed no changes in the percentage of endothelial cells immuno-positive either for nitric oxide synthase-III or for endothelin-1. In consequence, the ratio of nitric oxide synthase-III:endothelin-1 was reduced in the coronary but not in the basilar artery. Therefore, the nitric oxide/endothelin-1 system appears to play different roles in the coronary and cerebral circulations during renal hypertension.

New insights into the pathophysiology of renovascular hypertension

In recent years, the pathophysiology of renovascular hypertension has been reviewed, and the classic concept that activation of the renin-angiotensin system is solely responsible for the development and maintenance of renovascular hypertension has been challenged. In fact, experimental evidence indicates that other systems, such as the lipoxygenase pathway, may have a more critical role in the long-term maintenance of high blood pressure after renal artery stenosis. Herein we discuss the intrarenal mechanisms that control pressure-induced natriuresis under physiologic conditions and the role of the kidney in the pathophysiology of renovascular hypertension.

Inflammatory cells and myocardial fibrosis: spatial and temporal distribution in renovascular hypertensive rats

OBJECTIVE

The fibroblasts producing collagen are co-localized with inflammatory cells in myocardial fibrosis areas of spontaneously hypertensive rats, suggesting that collagen overproduction in this model may be modulated by inflammatory cells. The present study extends these observations to the Goldblatt model of hypertension in which the renin-angiotensin system is activated.

METHODS

Inflammatory cells were identified with monoclonal antibodies directed against macrophages (ED1+), T helper (CD4+) and cytotoxic lymphocytes (CD8+), and MHC class II-expressing cells (Ia+). The alkaline phosphatase-anti-alkaline phosphatase (APAAP) immuno-staining technique was used. A new computer-assisted morphometric method was utilized to quantify the inflammatory infiltrate in each cardiac compartment with polarized-light microscopy. Cells responsible for the collagen synthesis were identified by in situ hybridization. The collagen content was estimated by morphometry on left ventricle sections stained with Sirius red, and by biochemical quantification of the hydroxyproline concentration.

RESULTS

Computer-assisted morphometry under polarized light was well suited to quantify inflammatory cells labeled by the APAAP technique. Inflammatory cells were co-localized with collagen-synthesizing fibroblasts. The main inflammatory cells were CD4+ lymphocytes > Ia+ > ED1+ > CD8+ cells. These cell densities were increased in hypertensive rats in all cardiac areas compared to control rats except for IA+ cells which were concentrated in microscars. Macrophage density was correlated with plasma renin activity. The inflammatory cell density which best correlated with fibrosis was macrophage density, and which best correlated with systolic blood pressure was macrophage and T helper lymphocyte densities.

CONCLUSIONS

One can speculate that the correlation between macrophage density and blood pressure as well as with plasma renin activity may indicate that angiotensins and/or elevation of blood pressure could participate in the initial signalling which may mobilize inflammatory cells. These inflammatory cells could promote fibrosis by releasing mediators such as growth factors or cytokines which act upon fibroblasts.

Coordinate changes of renin and brain-type nitric-oxide-synthase (b-NOS) mRNA levels in rat kidneys

In our study we have examined the mRNA levels of nitric-oxide-(NO-)synthases in rat kidneys during states of stimulated and reduced renin gene expression, to find out whether renal mRNA levels of NO-synthases are correlated with the activity of the renin system. Stimulation of the renin system was achieved by unilateral renal artery clipping (2-kidney/1-clip rats), treatment with the angiotensin II (ANG II) antagonist losartan (40 mg/kg), application of furosemide (12 mg x kg-1 x day-1) and a low-sodium diet (0.02% w/w Na+), which increased renin mRNA levels to 464%, 495%, 309% and 219% of those of control animals, respectively. Inhibition of the renin system was achieved in the nonclipped (contralateral) kidneys of 2-kidney/1-clip rats and in the kidneys of rats which were fed a high-sodium diet (4% w/w Na+); in both cases renin mRNA levels decreased to about 50% of the control values. First screening of the gene expression of brain-type NO-synthase (b-NOS), endothelial NOS (e-NOS) and inducible NOS (i-NOS) during all these alterations of the renin system was done using the reverse transcriptase-polymerase chain reaction (RT-PCR) technique. Results from such noncompetitive PCR experiments indicated that only b-NOS mRNA levels change concordantly with the levels of renin. These changes in b-NOS mRNA levels were checked by the more reliable method of RNase protection assay. Results of the RNase protection assay proved that the renal levels of b-NOS mRNA were significantly increased by about 50% after a low-sodium diet and hypoperfusion of the kidney. Given a stimulatory role of endothelium-derived relaxing factor (EDRF)/NO on the renin system our findings may provide the first evidence that increases of renal levels of b-NOS mRNA and, as a consequence, of renal EDRF/NO formation could be important mediators of the well-known effect of salt intake and hypoperfusion on the renin system.

Transcriptional induction of the human renin gene by cyclic AMP requires cyclic AMP response element-binding protein (CREB) and a factor binding a pituitary-specific trans-acting factor (Pit-1) motif

To delineate the cis-acting elements of the proximal promoter responsible for cyclic AMP (cAMP)-induced human renin gene transcription, 5'-flanking regions of the human renin gene were fused to a luciferase reporter gene and transfected in chorionic cells. Forskolin treatment induced the expression of luciferase by 2.4-fold when the reporter plasmid contained the promoter region (-582 to + 16). Mutation or deletion of the cAMP response element (CRE) diminished (1.7-fold) but did not abolish cAMP-induced transcription, demonstrating that the (-582 to -145) region containing the CRE and the region (-145 to -38) containing a Pit-1 (pituitary-specific trans-acting factor) site were both necessary for cAMP maximal induction. To study the molecular events mediating the cAMP induction, DNase I footprinting and electromobility shift assays (EMSAs) were performed with renin-producing chorionic cell and kidney cortex cell nuclear extracts, showing that the CRE-binding protein (CREB) interacts with the CRE and that tissue-specific factors, distinct from Pit-1, specifically bind the renin Pit-1 motif. Taken together, these results demonstrate that the cAMP response of the human renin gene may involve CREB binding the CRE and tissue-specific factors, different from Pit-1, that interact with the Pit-1 response DNA elements.

Cardiac angiotensin converting enzyme overproduction indicates interstitial activation in renovascular hypertension

OBJECTIVES

Angiotensin converting enzyme (ACE) activity in the plasma does not change significantly with hypertension in two-kidney, one-clip hypertensive (2K-1C) rats. However, heart ACE activity and mRNA increase with hypertension. We measured the ACE activity and mRNA in hypertrophied hearts at different times after clipping, and determined the cellular distribution of its increase in the left ventricle of 2K-1C hypertensive rats.

METHODS

Cardiac ACE activity was quantified in left and right ventricles using a radiolabeled synthetic ACE substrate, and ACE mRNA steady-state level was quantified by ribonuclease protection assay. Tissue localization of ACE in normal and hypertrophied hearts was determined by measuring ACE activity in isolated ventricular cells. In situ hybridization with a rat ACE cDNA and immunohistochemistry with a monoclonal anti-ACE antibody were used to identify tissue compartments producing ACE mRNA and protein.

RESULTS

The left ventricle was hypertrophied 2 weeks after clipping and remained hypertrophied at 12 weeks. Left ventricular ACE activity was significantly increased 2 and 4 weeks (3.2 +/- 0.3 in 2K-1C vs. 1.7 +/- 0.1 pmol/mg prot/min in sham-operated rat) after renal artery clipping, but not at 12 weeks. The right ventricle was slightly hypertrophied 4 weeks after clipping and remained hypertrophied at 12 weeks. Right ventricular ACE activity was significantly increased at 4 (6.7 +/- 0.6 in 2K-1C vs. 3.1 +/- 0.3 pmol/mg prot/min in sham-operated rat) and 12 weeks. ACE activity was not detectable in cardiomyocytes isolated by Percoll gradient. Neither was ACE mRNA detected in isolated cardiomyocytes, even after ACE mRNA amplification by RT-PCR. In contrast, ACE activity and mRNA were detected in pooled non-cardiomyocytic cells. Thus the increase in cardiac ACE activity associated with hypertension must be due to an increase in ACE expression by non-cardiomyocytic cells. In situ hybridization showed an autoradiographic signal for ACE mRNA over the endothelial cells of coronary arteries and over the interstitial spaces including pericoronary and fibrosis areas. Immunohistochemistry confirmed these data, showing ACE on endothelial cells and in pericoronary spaces with an increased signal in pericoronary and fibrosed areas in hypertensive hypertrophied left ventricle.

CONCLUSION

Besides its usual endothelial expression, ACE is absent from cardiomyocytes and present in interstitial tissue, in the pericoronary spaces in normal tissue and more markedly in hypertrophied ventricles.

Chronic nitric oxide synthase inhibition and carotid artery distensibility in renal hypertensive rats

The goal of the present study was to examine the viscoelastic properties of the carotid artery in genetically identical rats exposed to similar levels of blood pressure sustained by different mechanisms. Eight-week old male Wistar rats were examined 2 weeks after renal artery clipping (two-kidney, one clip [2K1C] Goldblatt rats, n = 53) or sham operation (n = 49). One half of the 2K1C and sham rats received the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 1.48 mmol/L) in their drinking water for 2 weeks after the surgical procedure. Mean blood pressure increased significantly in the 2K1C-water (182 mm Hg), 2K1C-L-NAME (197 mm Hg), and sham-L-NAME (170 mm Hg) rats compared with the sham-water rats (127 mm Hg). Plasma renin activity was not altered by L-NAME but significantly enhanced after renal artery clipping. A significant and similar increase in the cross-sectional area of the carotid artery was observed in L-NAME and vehicle-treated 2K1C rats. L-NAME per se did not modify cross-sectional area in the sham rats. There was a significant upward shift of the distensibility-pressure curve in the L-NAME- and vehicle-treated 2K1C rats compared with the sham-L-NAME rats. L-NAME treatment did not alter the distensibility-pressure curve in the 2K1C rats. These results demonstrate that the mechanisms responsible for artery wall hypertrophy in renovascular hypertension are accompanied by an increase in arterial distensibility that is not dependent on the synthesis of nitric oxide.

Heart prolyl endopeptidase activity in one-kidney, one clip hypertensive rats

1. Heart mass, prolyl endopeptidase activity and fractionated proteins from heart tissue were studied in one-kidney, one clip hypertensive rats (N = 6) and compared to sham-operated rats (N = 6). 2. Body weight, arterial pressure and tissue mass were measured 4 weeks after artery clipping. Z-Gly-Pro-p-nitroaniline hydrolysis was used to measure tissue prolyl endopeptidase activity in the homogenate. Protein was fractionated into the soluble and myofibrillar fractions. 3. In the normotensive rats, prolyl endopeptidase activity expressed in terms of protein specific activity (microM substrate hydrolyzed h-1 mg supernatant protein-1) occurred in atria and was 2.5-fold higher than in the ventricles (3.79 +/- 0.20 vs 1.44 +/- 0.02, P < 0.05). In the one-kidney, one clip hypertensive rats, the left ventricle tissue increased 1.7-fold (2.27 +/- 0.11 vs 3.72 +/- 0.11 mg wet weight tissue/g body weight, P < 0.001), the soluble protein fraction (54.86 +/- 3.60 vs 57.38 +/- 6.64 mg/g wet weight tissue) was unchanged, while the myofibrillar fraction increased 1.9-fold (118.9 +/- 9.09 vs 229.8 +/- 8.47 mg/g wet weight tissue, P < 0.001). 4. The specific activity of the atrial and ventricular prolyl endopeptidase decreased in atria and increased in ventricles as the result of hypertension (3.79 +/- 0.2 vs 2.84 +/- 0.13 and 1.44 +/- 0.02 vs 1.87 +/- 0.13; respectively). These regional differences in prolyl endopeptidase enzyme content caused by one-kidney, one clip hypertension in neurosecretory and non-neurosecretory heart areas suggest that this enzyme plays a local role in the turnover of specific polypeptides.

ACE in three tunicae of rat aorta: expression in smooth muscle and effect of renovascular hypertension

Angiotensin I-converting enzyme (ACE) is known to be present at the surface of endothelial cells and also in the adventitia in large vessels. The presence of ACE in the vascular smooth muscle remains controversial. We microdissected segments of adventitia and media with or without endothelium from a region devoid of collateral arteries. The membrane-bound ACE activity in the media averaged 41% (pmol [glycine-1-14C]hippuryl-L-histidyl-L-leucine hydrolyzed.g tissue-1.min-1) of the values found in the whole aorta, whereas the adventitia contained only 6%. Immunoreactive ACE in media was characterized by Western blotting. ACE mRNAs were detected and characterized after polymerase chain amplification in isolated media. Angiotensin I and angiotensin II were equally able to contract medial rings, and the response to angiotensin I was blocked by enalaprilat. In aortas of two-kidney, one-clip hypertensive rats, there was an increase in ACE mRNA estimated by ribonuclease protection assay (P = 0.02) and in ACE activity at 15 days and 1 and 3 mo after clipping. This corresponded to a 1.5- to 2-fold increase in the ACE activity of both the media and the adventitia compared with sham-operated rats (P < or = 0.02). Thus ACE gene expression occurs in smooth muscle of rat aorta, which contains roughly the same amount of enzyme as the endothelium and readily converts angiotensin I to angiotensin II. ACE in the medial layer and the adventitia is upregulated in renovascular hypertension.

Role of glomerular proteinases in the evolution of glomerulosclerosis

Recent studies suggest that proteolytic enzymes located within the glomerulus are involved in the degradation of extracellular matrix components. In the present investigation glomerular proteinase activities were followed in a variety of non-immune-mediated renal diseases as well as during different dietary manipulations. Azocaseinolysis was significantly reduced in the obese Zucker rat compared with lean littermates (pH 5.4:8.9 +/- 0.4 vs 11.4 +/- 0.7; pH 7.4:5.8 +/- 0.7 vs 9.3 +/- 0.6 arb. U/mg protein). When the glomerular proteolytic capacity was measured in old rats, again a significant decline in proteolysis was observed (pH 5.4:9.8 +/- 0.8 vs 17.7 +/- 0.8; pH 7.4:6.4 +/- 0.7 vs 11.7 +/- 0.5 arb. U/mg protein). In Goldblatt hypertensive rats the unclipped kidney, which is exposed to high blood pressure, revealed lower glomerular azocaseinolytic activity compared with the contralateral clipped kidney (pH 5.4:8.1 +/- 0.4 vs 12.9 +/- 0.5 arb. U/mg protein). In parallel, the cathepsin B content was also diminished in glomeruli from kidneys exposed to hypertension. When proteinases were followed in glomeruli from intact kidneys of rats fed protein-modified diets (fraction of casein 0.05, 0.20 or 0.60) a significant fall in the activities of cysteine proteinases, e.g. cathepsin B (casein 0.05:1,498 +/- 110 vs casein 0.60:914 +/- 84 microU/micrograms DNA), as well as metalloproteinases, e.g. collagenase (casein 0.05:233 +/- 14 vs casein 0.60:137 +/- 11 microU/micrograms DNA), occurred. These data indicate that in both early and late stages of glomerulosclerosis, proteolytic activities within the glomerulus tend to be reduced, which could allow extracellular matrix accumulation. Moreover, changes in dietary protein intake resulted in profound alterations of glomerular proteinases.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo and in vitro effects of atrial natriuretic peptide on renin release

1. This study investigated the effect of atrial natriuretic peptide on renin release from the kidney. The in vitro direct effect was examined in the animal experiment using renal cortical slices of rat, and the in vivo effect was observed in the human infusion study. 2. In the in vitro experiments, alpha-human atrial natriuretic peptide (alpha-hANP) ranging 10(-9) to 10(-6) mol/L did not change the basal renin release rate from the renal cortical slices (-9% at 10(-6) mol/L, NS). Isoproterenol (10(-6) mol/L) increased renin release by 40% (P < 0.001), whereas angiotensin II (10(-6) mol/L) suppressed it by 48% (P < 0.001). However, alpha-hANP did not affect the stimulative effect of isoproterenol or the inhibitory effect of angiotensin II. 3. Also in the human study, infusion of 25 ng/kg per min alpha-hANP failed to change the plasma renin activity in normotensive subjects (-4%) or patients with essential hypertension (+5%), or even in patients with raised renin levels such as renovascular hypertension (+10%) or congestive heart failure (-13%). 4. These results put forth negative views on the direct involvement of atrial natriuretic peptide in renin release from the juxtaglomerular apparatus.

[Effect of brain serotonin on the arterial pressure and plasma renin in normal and hypertensive rats]

The effects of changes in brain serotonin content after injections of p-chlorophenylalanine (p-CPA), L-5-hydroxytryptophan (L-5HTP) and 5-6-dihydroxytryptamine (5-6DHT) on the mean arterial pressure (MAP), plasma renin activity (PRA) and peripheral levels of atrial natriuretic peptide (ANP) have been studied in normal and hypertensive (2K:1C model) male Wistar rats. The p-CPA (250 mg/kg) and L-5HTP (200 mg/kg) were injected i.p., while 5-6 DHT (15 micrograms/animal in 10 mu/animal vehicle) was injected into lateral brain ventricles. The effects were studied 24 h after the p-CPA injection, 2 h after L-5HTP and 10 or 20 days after 5-6DHT administration. The fall in brain serotonin produced by p-CPA and 5-6DHT did not modify the MAP values in the normal and hypertensive rat model, whereas the increase induced after L-5HTP injection only caused a slight decrease in arterial pressure in normotensive animals. The ARP experimented remarkable rises in the normal and hypertensive rats, these values increasing after L-5HTP and falling after p-CPA and 5-6 DHT injections. Similar changes are detected in the normal group after administration of these substances related to serotoninergic brain activity. The ANP levels rose after renal artery constriction, and they are not affected by the above mentioned substances. Only p-CPA and 5-6DHT reduced a low decrease in the ANP levels 10 days after their administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of experimentally-induced hypertension on angiotensin converting enzyme activity in the aortic endothelium and smooth muscle cum adventitia of the Sprague Dawley rat

The effect of experimentally-induced hypertension on the angiotensin converting enzyme (ACE) activity in the endothelium and smooth muscle cum adventitia of the Sprague Dawley rats was investigated. The ACE activity in both tissues of the 1-clip 2-kidney renovascular hypertensive rats and the deoxycorticosterone acetate/salt hypertensive rats were significantly higher than those of the normotensive control. These findings (i) support the suggestion that the 1-clip 2-kidney renovascular hypertensive rat represents a model of renin- and angiotensin-dependent hypertension and that the increased vascular ACE activity could play a role in the maintenance of hypertension (ii) provide new information regarding the association of increased vascular ACE activity and hypertension in the mineralocorticoid/salt treated hypertensive rats which may account for the finding by others that captopril is effective in preventing the development of hypertension in this low renin model of hypertension. On the other hand, the data also bring forth the possibility that the observed increase in vascular ACE activity could be the result of hypertension.

Suppression of renal vein renin profiles by mannitol prophylaxis: implications in the evaluation of renovascular hypertension

Renal arteriography with concomitant renal vein renin profiling remains the diagnostic standard for evaluating the anatomic and physiologic significance of stenotic renal artery lesions in hypertensive patients. False-negative renal vein renin profiles with failure of lateralization in patients with anatomically apparent high-grade stenosis complicate the diagnostic process. Mannitol is frequently administered prophylactically to minimize the risk of dye nephropathy in these patients. Yet, the potential effects of mannitol on renal vein renin profiling in man have not been previously reported. Seven patients with renovascular hypertension were studied prospectively to determine changes in renal vein renin profiles before and after mannitol prophylaxis. Despite captopril stimulation, all patients demonstrated significant renin suppression leading to the loss of renin lateralization in patients with unilateral renovascular hypertension. In 60% of the patients, renal vein renin ratios fell to below the standard 1.5 to 1 ratio after mannitol infusion. In patients with bilateral renovascular disease, the least stenotic side suppressed completely, while the more stenotic side suppressed partially. Percent suppression analysis showed a mean suppression of 56.8% on the stenotic side versus 8.2% on the noninvolved side (P less than 0.002). In every study, suppression equaled or exceeded 32% on the involved side and was less than this on the noninvolved side. Thus, the degree of renin suppression following mannitol infusion may prove to be an important tool in the diagnosis of clinically significant stenotic lesions. The mechanism of mannitol-induced suppression remains undefined, but appears independent of volume expansions or dilutional effects. The inhibitory effects of mannitol on renin profiles can obscure the diagnosis of underlying renovascular hypertension.

Proteinase activity in isolated glomeruli of Goldblatt hypertensive rats

In Goldblatt rats, the kidney exposed to high blood pressure reveals glomerulosclerosis. Moreover, in preexisting parenchymal renal disease, the development of glomerulosclerosis is accelerated in the unclipped kidney. Up to now, the pathogenetic mechanism underlying the development of glomerulosclerosis due to systemic hypertension has not completely been resolved. Traditionally, hemodynamic mechanisms have been discussed. This study was performed to investigate whether there might be a decreased activity of glomerular proteinases in the unclipped kidney of Goldblatt rats as a potential pathogenetic factor for glomerulosclerosis. 20 weeks after the surgical intervention, we found a reduced proteinase activity in ultrasonically destroyed isolated glomeruli obtained by differential sieving technique in comparison with the contralateral clipped kidney and the kidneys of sham-operated normotensive controls. This could be confirmed, when proteinase activity was related to DNA instead of protein. When investigating glomerular cathepsin B-content, a lysosomal enzyme, which is able to degrade glomerular structural as well as non-structural proteins, we found a decreased level in the kidney of Goldblatt rats exposed to systemic hypertension in comparison with normotensive control animals. Basing on these results we presume that glomerular protein accumulation and concomitant glomerulosclerosis due to systemic hypertension might be a result of a synergistical interaction between hemodynamic factors and biochemical ones; we suggest one of the latter to be a decreased glomerular proteinase activity.

A kallikrein-like enzyme in blood vessels of one-kidney, one clip hypertensive rats

Active and inactive kallikrein or a kallikrein-like enzyme are found in the aorta, vena cava, and tail artery and veins of the rat. We studied the concentration of vascular kininogenase in rats with one-kidney, one clip renovascular hypertension and in unilaterally nephrectomized normotensive rats. Six weeks after surgery, active and total vascular kininogenase activity (active plus trypsin-activated) was measured. Blood pressure was 212 +/- 4 mm Hg in the hypertensive rats (n = 33) and 120 +/- 1 mm Hg in the normotensive rats (n = 32) (p less than 0.001). Active kininogenase was lower in the hypertensive rats; although the difference was not significant in the thoracic aorta (56 +/- 8 versus 77 +/- 15), it was highly significant in the abdominal aorta (63 +/- 13 versus 167 +/- 17, p less than 0.001) and tail artery (48 +/- 8 versus 197 +/- 31, p less than 0.003). Total vascular kininogenase activity (active plus trypsin-activated) was lower in the hypertensive rats in all arteries examined: thoracic aorta (183 +/- 16 versus 380 +/- 38, p less than 0.003), abdominal aorta (565 +/- 61 versus 1,093 +/- 74, p less than 0.001), and tail artery (532 +/- 112 versus 1,243 +/- 135, p less than 0.003). Active kininogenase in the vena cava was higher in the hypertensive rats (213 +/- 56 versus 131 +/- 31); however, this difference was not statistically significant, whereas in the tail veins it was highly significant (1,803 +/- 221 versus 771 +/- 79, p less than 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)

Serum angiotensin converting enzyme activity and plasma renin activity in experimental models of rats

1. Serum angiotensin converting enzyme activity (ACEA) and plasma renin activity (PRA) were determined in rats under different experimental conditions such as: nephrotic syndrome (NS), bilateral nephrectomy (BN), renovascular hypertension (RH), dehydration (DEH), anaesthesia (AN), low sodium diet (LSD) and high sodium diet (HSD), and injection with propranolol (PRO) and isoprenaline (ISO). 2. PRA increased in LSD, AN, NS, RH, DEH and IPT groups, and decreased in HSD, BN, and PRO groups. Serum ACEA did not change in RH, HSD, IPT, DEH, AN, and PRO groups, increased in NS group, and decreased in LSD and BN groups. 3. Serum ACEA changed in the opposite direction to PRA only in the LSD group. This finding suggests that ACE may limit the full expression of the renin-angiotensin system in the LSD group, but not in the other groups.

Contrasting effects of norepinephrine and 5-hydroxytryptamine on contractility of abdominal aorta of two kidney-two clip hypertensive rats. Effects of inhibitors of arachidonic acid metabolic enzymes

This study intends to: 1) define reactivity in vessels of two kidney-two clip (2K2C) hypertensive rats (6-11 days after clipping); 2) determine the possible involvement of prostaglandins in modulating contractile vascular responses. Cumulative dose-response curves to norepinephrine (NE), 5-hydroxytryptamine (5-HT) and potassium chloride (KCl) were elicited on helical strips of abdominal aorta both in the absence and in the presence of prostacyclin synthetase (transylcypromine, TCP, 0.25mM) or cyclooxygenase (indomethacin, IND, 0.014 mM and acetylsalicylic acid, ASA, 0.20 mM) inhibitors Vessels of hypertensive animals developed significantly less tension to NE (n = 21) but higher tension and lower ED50 in response to 5-HT (n = 9) than sham control rat vessels. Force development to KCl (n = 9) was not statistically different between hypertensive and sham vessels. Vascular responses were decreased with the inhibitors, but the contrasting effects of NE and 5-HT on clip vessels were maintained. Threshold doses of PGE2 significantly reversed the effect of IND but not that of TCP on NE responses. Threshold doses of PGI2 had no significant effect on NE and 5-HT responses under TCP. The results would indicate: 1) different functional alterations for contractions to NE and 5-HT appear to have developed in vessels of 2K2C hypertensive rats; 2) PGE2 effectively contributes to modulation of NE responses in rat aorta strips; 3) these experiments suggest that prostaglandins do not play a significant role in the altered contractility of vessels in hypertensive rats.

A lack of coordination in the release of urinary lysosomal and brush border enzymes following renovascular surgery

The urinary secretion of two lysosomal enzymes, N-acetyl-D-glucosaminidase (NAG, EC 3.2.1.30) and beta-glucuronidase (GLR, EC 3.2.1.31), and two brush border enzymes, alanine aminopeptidase (AAP, EC 3.4.11.2) and gamma-glutamyltransferase (GGT, EC 2.3.2.2), was examined in apparently healthy individuals and in patients before and after renovascular surgery for treatment of hypertension. Eight out of nine patients had elevated levels of at least one enzyme before surgery. The ranking in their frequency of elevation was NAG greater than AAP greater than GLR greater than GGT. In comparing the release of any two enzymes in apparently healthy individuals, the release was coordinated except for GGT and GLR. In individual patients following surgery the excretion of the lysosomal enzymes was highly coordinated whereas the release of the brush border enzymes was less coordinated. Comparisons of lysosomal to brush border enzyme activities revealed dissimilar release patterns between these two classes of enzymes. Analysis of variance over the entire hospitalization period showed that NAG/GLR (p = 0.42) and AAP/GGT (p = 0.12) did not vary significantly whereas all comparisons of lysosomal to brush border enzymes varied significantly (p less than or equal to 0.03). These results indicate that enzymes derived from different subcellular organelles, lysosomes or brush borders, have similar release patterns. However, the lack of a significant correlation between lysosomal and brush border enzyme excretion implies that the two processes are not interdependent. These studies further suggest that the transient pathophysiological changes that occur within renal cells following renovascular surgery affect these cellular components in different ways.