Increased angiotensin-converting enzyme activities in diabetes mellitus: analysis of diabetes type, state of metabolic control and occurrence of diabetic vascular disease

Relationships among protein tyrosine phosphatase 1B, angiotensin II, and insulin-mediated aortic responses in type 2 diabetic Goto-Kakizaki rats

OBJECTIVE

We investigated the relationships among protein tyrosine phosphatase 1B (PTP1B), angiotensin II (Ang II), and insulin signaling in the presence of endothelial dysfunction in type 2 diabetic Goto-Kakizaki (GK) rat aortas.

METHODS AND RESULTS

Aortas isolated from GK or control Wistar rats were examined in the presence or absence of Ang II with or without a selective antagonist of the Ang II type 1 (AT1) receptor or a PTP1B inhibitor to evaluate vascular functional and molecular mechanisms, such as insulin-induced relaxation, nitric oxide (NO) production, phosphorylation of insulin receptor substrate (IRS)-1, endothelial NO synthase (eNOS), and phosphorylation, and the subcellular localization of PTP1B. GK aortas exhibited reductions of: 1) insulin-induced relaxation, 2) NO production, 3) Ser(1177)-p-eNOS, and 4) Tyr(612)-p-IRS-1. Pre-incubation with a PTP1B inhibitor normalized these reductions. In Wistar aortas, the four above-mentioned parameters were reduced by Ang II, but were completely inhibited by co-treatment with the PTP1B inhibitor. The membrane expression of PTP1B was greater in GK than in Wistar aortas, and it was increased by Ang II in Wistar rats. The membrane PTP1B expression in the presence of insulin + Ang II was reduced by the PTP1B inhibitor or AT1-receptor antagonist.

CONCLUSIONS

These results suggest that the membrane PTP1B suppressed insulin-mediated aortic relaxation, and this was due to the Ang II-AT1-receptor signaling pathway. The inhibition of PTP1B warrants further investigation as a potential therapeutic target for endothelial dysfunction in type 2 diabetes.

The effect of lycopene treatment on ACE activity in rats with experimental diabetes

In this study, the anti-inflammatory and antioxidant known as lycopene was applied to rats with experimental diabetes with the aim of investigating the detection of diabetes-related complications, and to determine the possible role of lycopene in diabetes complications regarding the effects of ACE activity. In order to induce diabetes in rats in the diabetes (D) and diabetes+lycopene (DL) groups, rats were given 45 mg/kg single-dose streptozotocin (STZ) intraperitoneally (i.p.); lycopene (10 mg/kg/day dissolved in sunflower oil) was administered to the rats in the lycopene-only (L) and DL groups. Blood glucose levels and HbA1c% in diabetes+lycopene group and diabetes group increased (p <0.05) compared to control and only lycopene treated group. The highest level of ACE activity was observed in the (D) group ( p < 0.05). Activity in the (L) group was also significantly greater than in the control group ( p < 0.05). The (DL) group had lower ( p < 0.05). ACE activity than the (D) group. Lycopene implementation was found to be effective in the inhibition of ACE activity, an important indicator of diabetes-related complications.

Losartan improves aortic endothelium-dependent relaxation via proline-rich tyrosine kinase 2/Src/Akt pathway in type 2 diabetic Goto-Kakizaki rats

In diabetic states, endothelial dysfunction is related to vascular complications. We hypothesized that insulin-induced relaxation and the associated proline-rich tyrosine kinase 2 (Pyk2)/Src/Akt pathway would be abnormal in aortas from the Goto-Kakizaki (GK) type 2 diabetic rat, which exhibits hyperglycemia/insulin resistance, and that losartan treatment of such rats (25 mg·kg−1·day−1 for 2 wk) would correct these abnormalities. Endothelium-dependent relaxation was by measuring isometric force in helical strips of aortas from four groups, each of 30 rats: normal Wistar (control), GK (diabetic), losartan-treated normal, and losartan-treated GK. Pyk2, Src, and Akt/endothelial nitric oxide synthase (eNOS) signaling-pathway protein levels and activities were assayed mainly by Western blotting and partly by immunohistochemistry. In GK (vs. age-matched control) aortas, various insulin-stimulated levels [nitric oxide production and the phosphorylations of eNOS at Ser1177, of Akt at Thr308, of phosphoinositide-dependent kinase-1 (PDK1) at Ser241, of Src at Tyr416, and of Pyk2 at Tyr579] were all significantly decreased and unaffected by either Src inhibitor (PP2) or Pyk2 inhibitor (AG17), while the insulin-stimulated levels of insulin receptor substrate (IRS)-1 phosphorylation at Ser307, total-eNOS, and total-Akt were significantly increased. Losartan treatment normalized these altered levels. The insulin-stimulated phosphorylation levels of Src/PDK1/Akt/eNOS, but not of Pyk2, were decreased by PP2 in control and losartan-treated GK, but not in GK, aortas. These results suggest that in the GK diabetic aorta increased phospho-IRS-1 (at Ser307) and decreased Pyk2/Src activity inhibit insulin-induced stimulation of the PDK/Akt/eNOS pathway. The observed increase in phospho-IRS-1 (at Ser307) may result from increased angiotensin II activity.

Altered cardiac bradykinin metabolism in experimental diabetes caused by the variations of angiotensin-converting enzyme and other peptidases

The peptidases angiotensin-converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP) mediate most of the kinin catabolism in normal cardiac tissue and are the molecular targets of inhibitory drugs that favorably influence diabetic complications. We studied the variations of those kininases in the myocardium of rats in experimental diabetes. ACE and NEP activities were significantly decreased in heart membranes 4-8weeks post-streptozotocin (STZ) injection. However, insulin-dependent diabetes did not modify significantly bradykinin (BK) half-life (t(1/2)) while the effect of both ACE (enalaprilat) and ACE and NEP (omapatrilat) inhibitors on BK degradation progressively decreased, which may be explained by the upregulation of other unidentified metallopeptidase(s). In vivo insulin treatment restored the activities of both ACE and NEP. ACE and NEP activities were significantly higher in hearts of young Zucker rats than in those of Sprague-Dawley rats. BK t(1/2) and the effects of peptidase inhibitors on t(1/2) varied accordingly. It is concluded that kininase activities are subjected to large and opposite variations in rat cardiac tissue in type I and II diabetes models. A number of tissue or molecular factors may determine these variations, such as remodeling of cardiac tissue, ectoenzyme shedding to the extracellular fluid and the pathologic regulation of peptidase gene expression.

Losartan improves impaired nitric oxide synthase-dependent dilatation of cerebral arterioles in type 1 diabetic rats

We examined whether activation of angiotensin-1 receptors (AT1R) could account for impaired responses of cerebral arterioles during type 1 diabetes (T1D). First, we measured responses of cerebral arterioles in nondiabetic rats to eNOS-dependent (acetylcholine and adenosine diphosphate (ADP)) and -independent (nitroglycerin) agonists before and during application of angiotensin II. Next, we examined whether losartan could improve impaired responses of cerebral arterioles during T1D. In addition, we harvested cerebral microvessels for Western blot analysis of AT1R protein and measured production of superoxide anion by brain tissue under basal conditions and in response to angiotensin II in the absence or presence of losartan. We found that angiotensin II specifically impaired eNOS-dependent reactivity of cerebral arterioles. In addition, while losartan did not alter responses in nondiabetics, losartan restored impaired eNOS-dependent vasodilatation in diabetics. Further, AT1R protein was higher in diabetics compared to nondiabetics. Finally, superoxide production was higher in brain tissue from diabetics compared to nondiabetics under basal conditions, angiotensin II increased superoxide production in nondiabetics and diabetics, and losartan decreased basal (diabetics) and angiotensin II-induced production of superoxide (nondiabetics and diabetics). We suggest that activation of AT1R during T1D plays a critical role in impaired eNOS-dependent dilatation of cerebral arterioles.

Inhibition of NAD(P)H oxidase alleviates impaired NOS-dependent responses of pial arterioles in type 1 diabetes mellitus

OBJECTIVE

The goal was to identify the role of NAD(P)H oxidase in cerebrovascular dysfunction in type 1 diabetes mellitus (T1D).

METHODS

In a first series of studies, rats were assigned to nondiabetic, diabetic (streptozotocin; 50 mg/kg IP), nondiabetic-apocynin (40 mg/kg/day in drinking water)-treated and diabetic-apocynin-treated groups. Two to three months later, the authors examined in vivo responses of pial arterioles to nitric oxide synthase (NOS)-dependent (acetylcholine and adenosine diphosphate (ADP)) and -independent (nitroglycerin) agonists. Next, they used Western blot analysis to examine protein levels for subunits of NAD(P)H oxidase in cerebral microvessels and parietal cortex tissue of nondiabetic and diabetic rats. Finally, they measured superoxide production by parietal cortex tissue in nondiabetic and diabetic rats.

RESULTS

Acetylcholine- and ADP-induced dilatation of pial arterioles was impaired in diabetic compared to nondiabetic rats. In addition, while apocynin did not alter responses in nondiabetic rats, apocynin alleviated T1D-induced impairment of NOS-dependent vasodilatation. In addition, p47phox and gp91phox proteins were elevated in cerebral microvessels and parietal cortex tissue, respectively, of diabetic compared to nondiabetic rats. Further, basal production of superoxide was increased in diabetic compared to nondiabetic rats and apocynin decreased this basal production.

CONCLUSIONS

The findings suggest that T1D impairs NOS-dependent reactivity of cerebral arterioles by a mechanism related to the formation of superoxide via activation of NAD(P)H oxidase.

Diabetes-induced cerebrovascular dysfunction: role of poly(ADP-ribose) polymerase

Our goal was to identify the role of poly(ADP-ribose) polymerase (PARP) in cerebrovascular dysfunction in Type 1 diabetes mellitus (T1D). In a first series of studies, rats were assigned to nondiabetic and diabetic (streptozotocin; 50 mg/kg IP) groups. Two to three months after injection of streptozotocin, we examine in vivo responses of pial arterioles to nitric oxide synthase (NOS)-dependent (adenosine diphosphate (ADP), acetylcholine and histamine) and -independent (nitroglycerin) agonists. After the initial examination of reactivity to the agonists, we treated pial arterioles acutely with an inhibitor of PARP (PJ-34; 1 microM), and then we again examined responses to the agonists. In a second series of studies, we examine superoxide production (lucigenin chemiluminescence) by parietal cortex tissue in nondiabetic and diabetic rats. We found that dilation of pial arterioles in response to ADP, acetylcholine and histamine, but not to nitroglycerin, was impaired in diabetic compared to nondiabetic rats. In addition, although PJ-34 did not alter responses in nondiabetic rats, PJ-34 alleviated T1D-induced impairment of NOS-dependent vasodilation. We also found that basal production of superoxide was increased in diabetic compared to nondiabetic rats and that PJ-34 decreased this basal production of superoxide. Our findings suggest that T1D impairs NOS-dependent reactivity of cerebral arterioles by a mechanism that appears to be related to the formation of superoxide via activation of PARP.

ANG II enhances contractile responses via PI3-kinase p110 delta pathway in aortas from diabetic rats with systemic hyperinsulinemia

We investigated the involvement of ANG II and phosphatidylinositol 3-kinase (PI3-K) in the enhanced aortic contractile responses induced by hyperinsulinemia in chronic insulin-treated Type 1 diabetic rats. Plasma ANG II levels were elevated in untreated compared with control diabetic rats and further increased in insulin-treated diabetic rats. Aortic contractile responses and systolic blood pressure were significantly enhanced in chronic insulin-treated diabetic rats compared with the other groups. These insulin-induced increases were largely prevented by cotreatment with losartan (an ANG II type 1 receptor antagonist) or enalapril (an angiotensin-converting enzyme inhibitor). LY-294002 (a PI3-K inhibitor) diminished the increases in contractile responses in ANG II-incubated aortas and aortas from chronic insulin-treated diabetic rats. The norepinephrine (NE)-stimulated levels of p110 delta-associated PI3-K activity and p110 delta protein expression were increased in aortas from insulin-treated diabetic compared with control and untreated diabetic rats, and chronic administration of losartan blunted these increases. Contractions were significantly larger in aortas from diabetic rats incubated with a low concentration (inducing approximately 10% of the maximum contraction) of ANG II or with NE or isotonic K+ than in aortas from nonincubated diabetic rats. NE-stimulated p110 PI3-K activity was elevated in aortas from diabetic rats coincubated with a noncontractile dose of ANG II. These results suggest that, in insulin-treated Type 1 diabetic rats with hyperinsulinemia, chronic ANG II type 1 receptor blockade blunts the increases in vascular contractility and blood pressure via a decrease in p110 delta-associated PI3-K activity.

Diabetes mellitus and heart failure: basic mechanisms, clinical features, and therapeutic considerations

Diabetic cardiomyopathy encompasses the spectrum from subclinical disease to the full-blown syndrome of congestive heart failure. The prevalence of type 2 diabetes mellitus is increasing at an alarming rate in the western world. and with it, the frequency of diabetes-related heart failure. There is at least early suggestion that target-driven, long-term, intensified intervention that is aimed at multiple risk factors in patients who have type 2 diabetes and microalbuminuria may reduce the risk of macrovascular (cardiovascular) and micro-vascular complications by approximately 50%. Thus, it is imperative that patients, particularly those who are at risk for the cardiovascular dysmetabolic syndrome, be screened aggressively for the presence of glucose intolerance and diabetes. When detected, all metabolic and cardio-vascular parameters should be evaluated and treated aggressively to reach currently recommended clinical targets. Such action will result in great benefit for patients by reducing morbidity and mortality and improving quality of life and will reduce the financial burden that is associated with this epidemic disease.

L-arginine-induced vasodilation of the renal vasculature is preserved in uremic type 1 diabetic patients after kidney and pancreas but not after kidney-alone transplantation

OBJECTIVE

In uremic type 1 diabetic patients, kidney and pancreas transplantation (KP) and kidney-alone transplantation (KD) provide full restoration of normal renal function; however, only KP, i.e., curing diabetes, is expected to prevent endothelial damages. Our aim was to study L-arginine-induced vasodilation of the renal vasculature in uremic type 1 diabetic patients after KP or KD using magnetic resonance (MR).

RESEARCH DESIGN AND METHODS

MR quantitative flow measurements were performed in 15 KP patients (mean age 39.0 +/- 1.7 years, 10 men and 5 women), in 11 KD patients (mean age 47.3 +/- 1.9 years, 7 men and 4 women), and in 8 nondiabetic kidney transplant patients (mean age 44.0 +/- 4.8 years, 7 men and 1 woman), who were used as control subjects, to measure renal blood flow and velocity and renal vascular resistance before and immediately after infusion of L-arginine.

RESULTS

Renal blood flow and velocity were not different at baseline in KP, KD, and control subjects. In contrast, during L-arginine administration renal blood flow increased significantly in KP subjects (basal 8.4 +/- 0.6 vs. post 9.6 +/- 0.8 ml/s, Delta 14.3 +/- 4.4%, P < 0.05) and in control subjects (basal 9.3 +/- 0.8 vs. post 9.1 +/- 0.8 ml/s, Delta 17.3 +/- 6.2%, P < 0.01), while it remained unchanged in KD subjects (basal 10.0 +/- 0.8 vs. post 11.6 +/- 0.9 ml/s, Delta -1.36 +/- 6.9%, NS). Parallel results have been achieved for renal blood velocity (KP subjects: 20.1 +/- 4.9%, P < 0.01; control subjects: 23.0 +/- 7.99%, P < 0.01; and KD subjects: -0.3 +/- 6.5%; NS). A reduction in renal vascular resistance in response to L-arginine was evident in KP and control subjects but not in KD patients.

CONCLUSIONS

L-Arginine vasodilatory response was successfully assessed with MR quantitative flow measurements. KP patients and control subjects, but not those with KD, showed a preserved L-arginine-induced vasodilation of the renal vasculature.

Enalapril prevents impaired nitric oxide synthase-dependent dilatation of cerebral arterioles in diabetic rats

BACKGROUND AND PURPOSE

Our goal was to identify the effects of chronic treatment with enalapril on cerebrovascular dysfunction and endothelial nitric oxide synthase (eNOS) protein in diabetic rats.

METHODS

Rats were assigned to 1 of 4 groups: nondiabetic, diabetic, nondiabetic/enalapril-treated, and diabetic/enalapril-treated groups. Rats assigned to the nondiabetic groups were injected with vehicle (sodium citrate buffer), and rats assigned to the diabetic groups were injected with streptozotocin (50 mg/kg IP). Enalapril (10 mg/kg per day) was administered in the drinking water and coincided with the injection of vehicle or streptozotocin. Two to 3 months later, we examined responses of pial arterioles to nitric oxide synthase (NOS)-dependent agonists (acetylcholine and ADP) and a NOS-independent agonist (nitroglycerin). After these functional studies, we harvested cerebral microvessels for Western blot analysis of eNOS protein.

RESULTS

We found that acetylcholine- and ADP-induced dilatation of pial arterioles was impaired in diabetic compared with nondiabetic rats. In addition, while enalapril did not alter responses in nondiabetic rats, enalapril prevented diabetes-induced impairment of NOS-dependent vasodilatation. Furthermore, eNOS protein was higher in diabetic than in nondiabetic rats, and enalapril did not produce a further increase in eNOS protein in enalapril-treated diabetic rats compared with untreated diabetic rats.

CONCLUSIONS

These results suggest that enalapril prevents cerebrovascular dysfunction in diabetic rats. We speculate that the protective role of enalapril may be independent of an alteration in eNOS protein in cerebral microvessels.

Cysteinyl leukotrienes modulate angiotensin II constrictor effects on aortas from streptozotocin-induced diabetic rats

Angiotensin II (Ang II) is a vasopressor peptide involved in the pathogenesis of cardiovascular diseases associated with diabetes mellitus. We have previously reported that the 5-lipoxygenase-derived products, particularly the cysteinyl leukotrienes (CysLTs), are involved in Ang II-induced contraction. In this study, we demonstrated that CysLTs contribute to the contraction elicited by Ang II in isolated aortas from streptozotocin-induced diabetic (SS) rats but not from insulin-treated diabetic rats, fructose-fed rats, or control rats. In an organ bath, pretreatment with the 5-lipoxygenase inhibitor (AA861, 10 micromol/L) reduced by 37.6+/-8.2% and 30.1+/-10.9% the Ang II-induced contractions in intact and endothelium-denuded aortic rings, respectively, from SS rats. In contrast, the CysLT(1) receptor antagonist (MK571, 1 micromol/L) or the dual CysLT(1)/CysLT(2) receptor antagonist (BAY-u9773, 0.1 micromol/L) did not affect Ang II-induced contraction. In addition, Ang II induced a 6.2+/-1.5-fold increase in CysLT release through the stimulation of the Ang II type 1 receptor. Furthermore, the urinary excretion of leukotriene E(4) was increased in SS rats (leukotriene E(4), 13.7+/-2.9 ng/24 h [SS rats, n=10] versus 1.5+/-0.5 ng/24 h [control rats, n=6]; P<0.0004). These data suggest the activation of the 5-lipoxygenase pathway in SS rats and the involvement of 5-lipoxygenase-derived products, particularly the CysLTs, in Ang II-induced contraction in aortas from SS rats through stimulation of CysLT receptors different from the well-characterized CysLT(1) or CysLT(2) receptor.

Should the use of short acting angiotensin-converting enzyme inhibitors be abandoned?

BACKGROUND

Angiotensin-converting enzyme inhibitors (ACE-I) have different modes of action and different durations of inhibition. The effects of ACE-I on the various components of the renin-angiotensin system (RAS) at trough hours were studied in patients with diabetes mellitus receiving long-term ACE-I treatment.

METHODS

Out of 86 Type 1 and 2 diabetic patients, 49 were untreated, 25 received captopril and 12 received enalapril as chronic treatment. Blood for the determination of plasma renin activity (PRA), serum ACE activity and plasma angiotensin II (Ang II) was drawn in the morning (0700-0900 hours) after an overnight fast, about 12 hours after the last dose. PRA and Ang II were measured by RIA and serum ACE activity was assayed by a radiometric assay using (3)H-hippuryl-glycyl-glycine as a substrate.

RESULTS

Mean age was significantly greater in the enalapril-treated patients. Systolic and diastolic blood pressures were not different between the captopril-treated and untreated groups. Serum ACE activity in the captopril-treated diabetic patients was 101.5+/-42.5 nmol/mL/min, values obtained in untreated diabetic patients (101.4+/-25.2 nmol/mL/min). In contrast, ACE activity in the enalapril-treated patients was significantly reduced (5.5+/-7.5 nmol/mL/min) compared with untreated and captopril-treated patients (p<0.00001). PRA values in the ACE-I treated patients were significantly increased. Plasma Ang II levels were significantly increased in the captopril-treated vs. untreated patients (65.1+/-50.2 vs. 36.2+/-31.7 pg/mL, p=0.006), whereas the values in the enalapril-treated patient were slightly, but not significantly, reduced (23.8+/-21.4 pg/mL). CONCLUSIONS Trough serum ACE activity is not suppressed in diabetic patients receiving captopril, compared with those receiving enalapril and we thus question the use of short acting ACE-I in these patients.

The study of renin-angiotensin-aldosterone in experimental diabetes mellitus

It is generally accepted that hypertension and other vascular pathologies increase in diabetes mellitus (DM) patients as a result of the renin-angiotensin-aldosterone (RAA) system. In this study, changes in the renin-angiotensin-aldosterone (RAA) system level was determined in Streptozotocin (STZ)-injected rats. A total of 46 female Wistar albino rats (180-220 g body weight) was utilized in these experiments. STZ was given intraperitoneally to induce diabetes in rats. Streptozotocin (60 mg kg(-1) body weight) was dissolved in 0.1 m citrate--phosphate buffer (pH 4-5). The non-diabetic rats were injected with sterilized buffer alone to act as a control group. Blood glucose levels were 398+/-8.2 mg dl(-1), 488+/-11.75 mg dl(-1) and 658+/-29.6 mg dl(-1) at days 3, 12 and 30 respectively. The level of plasma renin activity (PRA) was measured as 7.69+/-1.07 ng ml(-1) h(-1); 1.82+/-0.22 ng ml(-1) h(-1) and 0. 67+/-0.12 ng ml(-1) h(-1) at days 3, 12 and 30, respectively. These values showed that the PRA levels are decreased with increased time period. Serum angiotensin converting enzyme (ACE, E.C. 3.4.15.1) levels were increased at days 12 and 30 (p<0.05 and p<0.005), whereas serum aldosterone levels were increased at days 3 and 12 (p<0.05). The level of urea and creatinine increased at days 12 and 30 (p<0.05 and p<0.005, respectively) when compared to the control group. The data from these experiments indicate that the PRA level decreased whereas ACE activity level increased in diabetic rats compared with the control. Aldosterone levels increased at the first stage of the experiment, but then decreased by the end of the experiment as a result of changes in renin and ACE levels.

Angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists in the treatment of heart failure caused by left ventricular systolic dysfunction

Activation of the renin-angiotensin-aldosterone system (RAAS) in left ventricular systolic dysfunction is a critically important determinant in the pathophysiologic processes that lead to progression of heart failure and sudden death. Angiotensin II, acting at the specific angiotensin receptor (AT1-R), activates a series of intracellular signaling sequences which are ultimately expressed within the cardiovascular system as vasoconstriction and associated vascular hypertrophy and remodeling. Angiotensin converting enzyme (ACE) inhibition leads to increases in the vasodilatory peptides bradykinin and substance P and at least an initial reduction in angiotensin II concentrations. AT1-R blocking drugs prevent access of angiotensin II to the AT1-R and thus prevent cellular activation. ACE inhibitors have clearly been demonstrated through a large number of clinical trials to increase survival in congestive heart failure, primarily by reducing the rate of progression of left ventricular dilatation and decompensation. However, this beneficial effect diminishes over time. Preliminary short-term clinical studies evaluating the efficacy of AT1-R blocking drugs in the treatment of heart failure have suggested that they elicit similar hemodynamic and neuroendocrine effects as do the ACE inhibitors. The combination ACE inhibitors and AT1-R blocking drugs offer the theoretical advantage of increasing bradykinin while blocking the actions of angiotensin II, and thus possibly show a synergistic effect. Again, preliminary studies have yielded encouraging results that are difficult to interpret because neither ACE inhibitor nor the AT1-R blocking drug doses were titrated to tolerance. Pharmacological manipulation of the RAAS has led to better understanding of its role in heart failure and improved clinical outcomes.

The role of angiotensin II in diabetic nephropathy: emphasis on nonhemodynamic mechanisms

Several systemic or intrarenal networks of cytokines and growth factors can be modulated by the diabetic state. We summarize the status of the renin-angiotensin system in diabetes mellitus and review the evidence of its involvement in the pathogenesis of diabetic nephropathy. Particular emphasis is placed on the nonhemodynamic properties of this vasoactive agent as both a renal growth factor and a profibrogenic peptide. Antagonizing the effects of angiotensin II with converting enzyme inhibitors is an established protective strategy in the management of diabetic nephropathy even in the absence of systemic hypertension. This and other indirect evidence from experimental animal studies suggest that the intrarenal concentration of angiotensin II may be increased as a result of increased synthesis and despite enhanced breakdown, that this peptide participates in the progression of diabetic nephropathy. However, down-regulation of angiotensin type 1 (AT1)-receptors is one of the abnormalities of both tubules and glomeruli in diabetic renal disease. A heightened bioactivation of the intrarenal angiotensin II system is therefore likely but not certain. Studies in cultured proximal tubular and glomerular mesangial cells have disclosed striking similarities between the effects of high glucose-containing medium and of treatment with angiotensin II on the growth properties and the induction of cytokines in these cells. There may also exist additive effects of angiotensin II and high glucose on signal-transduction pathways, such as activation of protein kinase C, although the contractile response to angiotensin II may be blunted by high glucose in mesangial cells. An important downstream mediator of the effects of both angiotensin II and high glucose is the activation of transforming growth factor-beta that can mediate at least some of the hypertrophic and profibrotic effects of either angiotensin II or high glucose in the diabetic kidney.

Urinary angiotensin-converting enzyme activity in type 2 diabetes mellitus: its relationship to diabetic nephropathy

Urinary angiotensin-converting enzyme (ACE) and urinary N-acetyl-beta-D-glucosaminidase (NAG) were measured after a 5-year interval in 38 non-azotemic type 2 diabetic patients. Of these patients at baseline, 16 had nil nephropathy, 15 had incipient nephropathy, and 7 had overt nephropathy. During the follow-up, 6 and 1 of the 16 patients with nil nephropathy developed incipient and overt nephropathy, respectively. Four of the 15 patients with incipient nephropathy progressed to overt nephropathy. The 7 patients with overt nephropathy continued to have overt nephropathy, with slight azotemia in one. Urinary ACE and NAG levels were normal at baseline and showed no significant elevations at follow-up in the patients with nil nephropathy, no significant changes in baseline and modest elevations at follow-up in the patients with incipient nephropathy, and high at baseline and marked elevations at follow-up in the patients with overt nephropathy. In all patients, urinary ACE during the follow-up was positively correlated with urinary albumin or NAG, but not with glomerular filtration rate. Urinary ACE may be of poor prognostic value for the follow-up of diabetic patients, which is at variance with urinary albumin.

The role of platelets in essential hypertension

Recent research is helping us understand the complex interactions that occur between platelets and their environment. The several intracellular events that occur during platelet activation are being identified as ar their effects on other platelets, the endothelium and coagulation factors. Heightened platelet activation is seen early in essential hypertension and probably plays an important role in the initiation and progression of atherosclerosis and the disorders associated with it. This review identifies some of the changes in platelet structure and function in essential hypertension and their role in the pathogenesis of hypertensive vascular disease.

Response of serum angiotensin converting enzyme, plasma renin activity and plasma aldosterone to conventional dialysis in patients on chronic haemodialysis

The aim of this study was to examine serum angiotensin converting enzyme (SACE) activity and the renin-angiotensin-aldosterone system in patients on chronic haemodialysis during one routine dialysis session. Fourteen patients (8 men and 6 women; mean age 51.9 +/- 17 years) with end stage renal disease, receiving regular haemodialysis treatment for an average of 6 months, were studied. The patients were dialysed for 4 hours three times a week using cellulose membranes (cuprophan). After an overnight fast blood samples were taken from the patients before and after the haemodialysis session. Serum and plasma were separated and stored at -20 degrees C until assayed for SACE, plasma renin activity (PRA) and plasma aldosterone (PA). For comparison, SACE, PRA and PA were also measured in 8 patients after renal allotransplantation and on treatment with cyclosporin A (5 men, 3 women; mean age 38.9 +/- 12.3 years) and in 19 healthy subjects (13 men, 6 women; mean age 38.9 +/- 12.3 years). SACE levels in patients with chronic renal failure and on haemodialysis (17.55 +/- 9.03 nmol/ml/min) and in patients with renal transplantation (18.12 +/- 3.92) were significantly higher than those of the healthy subjects (9.27 +/- 1.67) (p < 0.0001, respectively). At the end of the dialysis session SACE levels in patients with chronic renal failure (14.9 +/- 7.19) did not increase in respect to pre-dialysis levels (17.55 +/- 9.03; p = 0.132). PRA and PA values increased after the dialysis session (p < 0.026 and p < 0.044, respectively). Correlation of SACE with PRA and PA was not demonstrated before or after the dialysis session. In patients with chronic renal failure and on haemodialysis our findings suggest that a disarrangement exists between the circulatory components of the reninangiotensin-aldosterone system before and after the dialysis session.

Increased serum angiotensin converting enzyme activity in type I insulin-dependent diabetes mellitus: its relation to metabolic control and diabetic complications

Serum angiotensin-converting enzyme (ACE) was measured in 150 insulin-dependent diabetes mellitus (IDDM) patients and 72 healthy subjects by radioassay, using [3H]-hippuryl-glycyl-glycine as a substrate. Mean (SD) serum ACE activity in diabetic patients was 120 +/- 33 nmol ml-1 min-1 (range 46-215) and was significantly increased by 56% compared to control values (77 +/- 23 nmol ml-1 min-1, range 46-125, P < 0.001). ACE activity > 125 nmol ml-1 min-1 was observed in 60 of 150 IDDM patients. 96 IDDM patients were normoalbuminuric (< 22 mg 24 h-1) and 49 patients were micro- or macroalbuminuric (range 22-6010 mg 24 h-1). Micro- and macroalbuminuric IDDM patients were found to have significantly greater ACE activity values than normoalbuminuric patients (128 +/- 36 vs. 115 +/- 30 nmol ml-1 min-1, P = 0.025). Metabolically well-controlled IDDM patients (glycosylated haemoglobin < or = 8%) had lower ACE activity values than the patients with glycosylated haemoglobin greater than 8% (109 +/- 20 vs. 127 +/- 32 nmol ml-1 min-1, P < 0.02). A significant correlation between degree of metabolic control and ACE activity was found (r = 0.435, P < 0.001) so that an increase in one glycosylated quartile unit is accompanied by an increase in ACE activity of 10.5 nmol ml-1 min-1. Thus ACE activity in the serum of IDDM patients was increased by 56% in 40% of the patients. It was increased in IDDM patients without complications and in patients with retinopathy or nephropathy.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathophysiology of erectile dysfunction

During the past decade, our knowledge of the hemodynamics, functional anatomy, neurophysiology, and neuropharmacology of erectile function has evolved substantially. The change of smooth muscle tone has emerged as a key factor in erection and detumescence. However, future studies are needed to elucidate the cellular and molecular basis of erectile physiology. With insight into normal physiology we will understand the pathologic process and be able to treat it.

Serum angiotensin converting enzyme in diabetic patients

Serum angiotensin converting enzyme (ACE) levels are higher in patients with diabetes mellitus than in many others. Techniques are available to grade different degrees of diabetic retinopathy, which can demonstrate a relationship between ACE and diabetic retinopathy. In this study, patients with diabetic retinopathy had higher serum ACE levels (6.3 +/- 0.2) than nondiabetic patients (4.3 +/- 0.5) (p < 0.001). In addition, the mean serum ACE level in diabetic patients with nonproliferative retinopathy (5.55 +/- 0.4) was less than that in diabetic patients with proliferative retinopathy (6.63 +/- 0.25) (p = 0.02). Due to the variability in individual serum ACE levels and the frequent use of ACE inhibitors by hypertensive diabetics, these techniques are not suitable for retinopathy screening programs. However, the graded relationship demonstrated by these data may have relevance for the pathophysiology of diabetic retinopathy.

Mesenteric vascular angiotensin-converting enzyme is increased in experimental diabetes mellitus

1. Diabetes mellitus was induced by streptozotocin in male Wistar rats, and angiotensin-converting enzyme measured in plasma and mesenteric vessels 3 weeks later. 2. Diabetes was associated with increased mesenteric wet weight/bodyweight ratio (control 0.2 s.e.m. 0.02 mg/g, n = 21, vs diabetes 1.0 s.e.m. 0.3 mg/g, n = 27, P less than 0.01, ANOVA). 3. Plasma angiotensin-converting enzyme activity was increased in diabetic rats (98 s.e.m. 3 nmol HL/mL per min) compared with controls (64 s.e.m. 6 nmol HL/mL per min, P less than 0.01, ANOVA). 4. Mesenteric vessel angiotensin-converting enzyme was increased in diabetes mellitus estimated by radioligand binding site density (fmol/mg protein; 1407 s.e.m. 166 fmol/mg protein) compared with controls (890 s.e.m. 56 fmol/mg protein, P less than 0.05, ANOVA) and by enzyme kinetic assay (diabetes, 15.5 s.e.m. 1.5 nmol HL/mg protein per min, controls, 8.3 s.e.m. 0.7 nmol HL/mg protein per min, P less than 0.01, ANOVA). The equilibrium dissociation constant of ligand-angiotensin-converting enzyme interaction was unchanged. 5. Increased vascular angiotensin-converting enzyme concentration may contribute to vascular hypertrophy and diabetic vasculopathy by increased local synthesis of angiotensin II.

Diagnostic aspects of angiotensin converting enzyme in pulmonary sarcoidosis

Angiotensin converting enzyme (ACE) has been measured in 102 biopsy-proven sarcoid patients, 70 patients diagnosed by clinical and radiological methods and 74 nonsarcoid patients as controls. The distributions of the various groups have been examined, and the effects of stage of disease, disease activity and prednisone treatment have been evaluated. Receiver operating characteristic (ROC) curves have been established for ACE, and the appropriateness of various statistical procedures is discussed. We have not discerned any effect of stage of sarcoidosis or of extent of disease activity on ACE values. The ROC curves suggest an upper limit of normal of about 50 U/L for our assay, and a sensitivity of 63% and specificity of 93%, yielding predictive values of 93% for a positive result and 74% for a negative result, with a likelihood ratio of 3.6. The results are discussed in the context of other work on ACE and in relation to the more invasive procedures of bronchoalveolar lavage and Gallium scan.

Angiotensin-converting enzyme (ACE): relationship to insulin-dependent diabetes and microangiopathy

Angiotensin-converting enzyme (ACE) is secreted by the vascular endothelium and serum activity may reflect endothelial damage. A study of 48 insulin-dependent diabetics, 15 with and 33 without evidence of diabetic retinopathy and 41 non-diabetic controls was performed. ACE activity was significantly elevated in the diabetics compared with controls (mean +/- SD 46 +/- 14 vs 35 +/- 9 U/l, p less than 0.001) (units in micromoles substrate converted/min/l serum). This elevation was more marked in diabetics with such evidence of microangiopathy as retinopathy or raised albumin excretion rate (AER) (51 +/- 14 U/l, p less than 0.0001), and also in those with raised AER alone (47.2 +/- 15 U/l, p less than 0.002). Patients with both raised AER and retinopathy had significantly higher ACE activities than those with no complications (53 +/- 15 vs 41.2 +/- 15 U/l, p less than 0.05). No correlation was found with glycosylated haemoglobin or smoking habits. We conclude that mean serum angiotensin converting enzyme activity is increased in insulin-dependent diabetes, particularly in those with evidence of microangiopathy and this may reflect microvascular damage.

Serum angiotensin converting enzyme activity in cigarette smokers

Low activity of angiotensin converting enzyme (ACE) has been reported in patients with smoking related diseases, such as chronic bronchitis, emphysaema and carcinoma of the lung [1] but this has not been reported in healthy, chronic smokers. Serum ACE was measured in 40 healthy cigarette smokers and in 42 healthy non-smokers. The mean value was significantly lower in the smokers. Hence a non-smokers. The mean value was significantly lower in the smokers. Hence a patient's smoking habits should be taken into consideration when assessing the significance of his serum ACE levels.