Increased plasma renin activity in type 1 diabetes with microvascular disease

The effect of palm oil-derived tocotrienol-rich fraction in preserving normal retinal vascular diameter in streptozotocin-induced diabetic rats

PURPOSE

Angiogenesis in diabetic retinopathy (DR) is associated with increased retinal expression of angiopoietin-2 (Ang-2) and protein kinase C (PKC). Tocotrienol-rich fraction (TRF) has been shown to reduce the expression vascular endothelial growth factor (VEGF) in several experimental models. However, its effect against other angiogenic markers such as Ang-2 and PKC in rat model of diabetes remains unknown. Therefore, we investigated the effect of TRF on the retinal vascular changes and Ang-2 and PKC expressions in rats with streptozotocin (STZ)-induced DR.

METHODS

Sprague-Dawley rats were divided into normal control rats (N) which received vehicle, and diabetic rats which either received vehicle (DV) or 100 mg/kg of TRF (DT). Diabetes was induced with intraperitoneal injection of STZ (60 mg/kg body weight). Treatments were given orally, once daily, for 12 weeks after confirmation of hyperglycaemia. Fundus photographs were captured at baseline, 6- and 12-week post-STZ injection and average diameter of retinal veins and arteries were measured. At 12-week post-STZ injection, rats were euthanised, and retinae were collected for measurement of Ang-2 and PKC gene and protein expressions.

RESULTS

Retinal venous and arterial diameters were significantly greater in DV compared to DT at week 12 post-STZ injection (p < 0.001 and < 0.05, respectively). The vessel diameter measurements in DT were comparable to N and this effect of TRF was associated with significantly lower Ang-2 and PKC gene and protein expressions compared to DV.

CONCLUSION

Oral TRF reduces the expression of retinal angiogenic markers and preserves the retinal vascular diameter of rats with STZ-induced DR.

Serum prorenin levels and diabetic retinopathy in type 2 diabetes: new method to measure serum level of prorenin using antibody activating direct kinetic assay

AIM

To investigate the serum levels of prorenin and its correlation with the severity of diabetic retinopathy (DR).

METHODS

248 patients with diabetes and 108 control subjects were divided into four groups: no-DR (n = 146), no proliferative diabetic retinopathy (no-PDR) (n = 78), PDR (n = 24), and controls (n = 108). Serum levels of prorenin from all subjects were measured using the new antibody activating direct kinetic (AAD-PR) assay. The serum prorenin levels were compared among the groups.

RESULTS

The serum levels of prorenin in the control, no-DR, no-PDR, and PDR groups, respectively, were 109.1 (66.1), 194.6 (160.4), 271.5 (220.3), and 428.4 (358.4) pg/ml (mean (SD)). Prorenin in the PDR group was remarkably high compared with the control and no-DR groups (p<0.0001) and with the no-PDR group (p = 0.002). Serum levels of prorenin increased with increasingly severe retinopathy. No correlation was found between the prorenin level and the duration of disease or HbA(1c).

CONCLUSIONS

The serum levels of prorenin in patients with PDR were found to be markedly high using the AAD-PR assay. Increased levels of prorenin in diabetes may have an important role in the pathogenesis of DR.

The renin-angiotensin-aldosterone system and the eye in diabetes

Diabetic retinopathy is the leading cause of blindness in the under 65s, and with the burden of disease case load expected to exceed 200 million worldwide within 10 years, much effort is being spent on prophylactic interventions. Early work focused on improving glycaemic control; however, with the publication of EURODIAB Controlled trial of Lisinopril in Insulin-dependent Diabetes (EUCLID) and United Kingdom Prospective Diabetes Study (UKPDS), the focus has recently moved to control of blood pressure and specifically the renin-angiotensin system (RAS). There is a large body of evidence for a local RAS within the eye that is activated in diabetes. This appears to be directly responsible, as well as indirectly through other mediators, for an increase in concentration of vascular endothelial growth factor (VEGF), a selective angiogenic and vasopermeability factor that is implicated in the pathogenesis of diabetic retinopathy. Inhibition of angiotensin-converting enzyme appears to reduce concentrations of VEGF, with a concurrent anti-proliferative effect independent of systemic VEGF levels or blood pressure. Angiotensin II (Ang II) Type 1 (AT(1)) receptor blockade has been shown to reduce neovascularisation independent of VEGF levels in animal models. This may be due to antagonism of activation of mitogen-activated protein kinase, which is a potent cellular proliferation stimulator, by Ang II, although this needs further evaluation.

Reduced plasma aldosterone concentrations in randomly selected patients with insulin-dependent diabetes mellitus

Abnormalities of the renin-angiotensin system have been reported in patients with diabetes mellitus and with diabetic complications. In this study, plasma concentrations of prorenin, renin, and aldosterone were measured in a stratified random sample of 110 insulin-dependent (Type 1) diabetic patients attending our outpatient clinic. Fifty-four age- and sex-matched control subjects were also examined. Plasma prorenin concentration was higher in patients without complications than in control subjects when upright (geometric mean (95% confidence intervals (CI): 75.9 (55.0-105.6) vs 45.1 (31.6-64.3) mU I-1, p < 0.05). There was no difference in plasma prorenin concentration between patients without and with microalbuminuria and between patients without and with background retinopathy. Plasma renin concentration, both when supine and upright, was similar in control subjects, in patients without complications, and in patients with varying degrees of diabetic microangiopathy. Plasma aldosterone was suppressed in patients without complications in comparison to control subjects (74 (58-95) vs 167 (140-199) ng I-1, p < 0.001) and was also suppressed in patients with microvascular disease. Plasma potassium was significantly higher in patients than in control subjects (mean +/- standard deviation: 4.10 +/- 0.36 vs 3.89 +/- 0.26 mmol I-1; p < 0.001) and plasma sodium was significantly lower (138 +/- 4 vs 140 +/- 2 mmol I-1; p < 0.001). We conclude that plasma prorenin is not a useful early marker for diabetic microvascular disease. Despite apparently normal plasma renin concentrations, plasma aldosterone is suppressed in insulin-dependent diabetic patients.

Angiotensin II receptor blockade improves nerve function, modulates nerve blood flow and stimulates endoneurial angiogenesis in streptozotocin-diabetic rats and nerve function

We examined the effect of the angiotensin II receptor blocker, ZD 8731, on nerve function, capillary density, and blood flow in streptozotocin-diabetic rats. Deficits in sciatic motor and saphenous sensory nerve conduction velocity of 21% and 15%, respectively, were observed after 1 month of diabetes mellitus (p < 0.001). These were completely ameliorated by a further month of ZD 8731 treatment (p < 0.001). Treatment of non-diabetic rats for 1 month with ZD 8731 had no effect on motor or sensory conduction velocity. Sciatic nerve capillary density was not significantly affected by 1- or 2-month untreated diabetes, however, there was a 15% increase in density with ZD 8731 treatment (p < 0.001). Treatment of non-diabetic rats for 1 month had no effect on capillary density. Diabetes prolonged the time taken for 80% conduction failure by 19% (p < 0.05) and 49% (p < 0.001) for 1 and 2 months of diabetes, respectively, when sciatic nerve was exposed to hypoxia in vitro. ZD 8731 treatment during the second month of diabetes limited the prolongation to 22%, not significantly different from 1 month of untreated diabetes but less than for the 2-month diabetic group (p < 0.001). Concentrations of sciatic nerve polyol pathway metabolites were elevated six-fold and myo-inositol was reduced 40% by diabetes; ZD 8731 treatment was without effect. Acute experiments examined the effect of ZD 8731 on sciatic nerve blood flow using laser-Doppler flowmetry. In non-diabetic rats, blood flow changes followed the dose-dependent reductions in systemic arterial pressure and there were no significant variations in sciatic vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships between renin, aldosterone, blood pressure and renal function in hypertensive insulin-dependent diabetes mellitus

A cross-sectional analysis of associations between total plasma renin (TPR) and aldosterone, blood pressure, renal haemodynamics, autonomic function and electrolyte balance was carried out in 35 hypertensive non-azotaemic insulin-dependent diabetics. Supine TPR was increased in 10 subjects and reduced in one, although erect TPR was increased in nine but reduced in 18 subjects. The supine to erect TPR gradient was greater than 40% in all cases. Supine and erect TPR correlated closely (r = 0.99, P less than 0.001). No correlation was found between TPR and age or blood pressure and multiple regression analysis failed to reveal independent predictors for TPR. Supine aldosterone was reduced in two subjects and increased in three, and erect aldosterone levels were reduced in three but increased in eight subjects. However, the postural aldosterone gradient was greater than 40% in only 20 cases. Supine and erect aldosterone correlated with each other (rs = 0.64, P = 0.001) but not with TPR. Aldosterone levels were most strongly related inversely to duration of diabetes, diabetic retinopathy, parasympathetic neuropathy and directly to diastolic blood pressure and glomerular filtration rate. Aldosterone levels correlated negatively with age. This was corrected for in multiple regression analysis which revealed an inverse relationship between supine aldosterone and serum potassium (P less than 0.05) and a direct one with renal plasma flow (P less than 0.007). Erect aldosterone was independently associated with duration of diabetes (P less than 0.005), systolic postural gradient (P less than 0.02), and the postural aldosterone gradient with the presence of parasympathetic neuropathy (P less than 0.004). The observation of elevated TPR in 10 subjects and the lack of relationship between TPR and other variables may reflect the overproduction of inactive relative to active renin in insulin-dependent hypertensive diabetics with autonomic dysfunction. The association between aldosterone and blood pressure, renal haemodynamics and electrolyte balance suggests that mineralocorticoids may be relevant to the natural history of hypertensive diabetic renal disease.

Hormonal response to blood volume expansion in diabetic subjects with and without autonomic neuropathy

The hormonal and renal response to volume expansion, produced by water immersion for 4 h, was studied in 14 insulin-dependent diabetic subjects (seven without complications, seven with autonomic neuropathy) and in 14 age-and-sex-matched normal control subjects. The diabetic subjects showed an impaired natriuretic response to volume expansion (total amount of sodium excreted 21 mmol compared to 39 mmol in normals, P less than 0.01) but the response did not differ in those with and without autonomic neuropathy. There was no significant difference in the suppression of plasma renin or aldosterone during immersion in either group. Plasma catecholamines suppressed on immersion in all groups. Basal values were lowest in the group with autonomic involvement. Atrial natriuretic peptide levels showed a twofold rise (from 4.8 to 9.6 pmol/l, P less than 0.01) on immersion. There was no significant difference in the levels of this hormone between diabetic patients and normal subjects or between those diabetics with and those without autonomic neuropathy. The present study confirms that diabetic subjects retain sodium avidly during volume expansion. This enhancement cannot be ascribed to any measurable difference in the levels of circulating hormones known to be involved in natriuresis and is not influenced by the presence of autonomic neuropathy.

Central role for sodium in the pathogenesis of blood pressure changes independent of angiotensin, aldosterone and catecholamines in type 1 (insulin-dependent) diabetes mellitus

We studied 73 Type 1 (insulin-dependent) diabetic patients, 18 to 50 years of age, with a diabetes duration of more than five years. Group 1: normal urinary albumin excretion below 30 mg per 24 h (n = 19); group 2: microalbuminuria, 30-300 mg per 24 h (n = 36); and group 3: diabetic nephropathy, above 300 mg per 24 h (n = 18). Fifteen nondiabetic persons matched for sex and age served as control subjects. The sodium intake evaluated on the basis of 24-h urine sodium excretion was similar in patients and control subjects. Blood pressure in groups 1 and 2 and control subjects was below 160/95 mmHg. The blood pressure was increased in group 3 as compared with the other groups (systolic/diastolic 161 +/- 22/101 +/- 9 mmHg vs 131 +/- 13/84 +/- 10, mean +/- SD, p less than 0.0001). Exchangeable sodium was increased in patients (p less than 0.01) and correlated to the mean blood pressure (n = 70, r = 0.41, p less than 0.01). Extracellular volume was increased in patients (p less than 0.05), whereas plasma volume was normal. Supine serum angiotensin II was suppressed in the patients (p less than 0.001). A negative correlation was found between mean blood pressure and supine serum aldosterone (n = 68, r = -0.24, p less than 0.05), and exchangeable sodium and aldosterone (n = 66, r = -0.36, p less than 0.002) in all patients. The catecholamine levels were also suppressed or normal in the patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of hypertension on serum concentration of type IV collagen antigens in streptozotocin-diabetic and non-diabetic rats

The serum concentration of 7S collagen was measured radioimmunologically as a marker of basement membrane type IV collagen synthesis in diabetic and nondiabetic rats with Goldblatt hypertension. In non-diabetic rats the 7S collagen level was significantly raised after induction of hypertension (51%; p less than 0.001), and showed a positive correlation with relative heart weight as an integral parameter of hypertension (r = 0.63; p less than 0.01). In diabetic rats, which displayed a 7S collagen concentration roughly 2.5 times as high as the metabolically normal animals, the 7S collagen level was 27% higher in the hypertensive animals (p less than 0.01). There was no correlation with blood pressure or heart weight, but only a positive correlation with blood glucose (r = 0.51; p less than 0.05). The results indicate that haemodynamic alterations may alter basement membrane collagen metabolism. However, type IV collagen metabolism in diabetes is influenced to a greater extent by metabolic than by haemodynamic factors.

The relationship of the renin-angiotensin system in type I diabetes to microvascular disease

There are conflicting data on the relationship between diabetes mellitus and its complications and the renin-angiotensin-aldosterone system. Much of this relates to the patient populations studied (those with types I and II diabetes) and the definitions of diabetic complications. We studied plasma renin activity and concentration, and factors involved in their control (age, blood pressure, and sodium excretion) in 40 healthy subjects (group 1), 18 patients with type I diabetes without complications (group 2), and 31 with type I diabetes with proliferative retinopathy (group 3). The groups were well matched for age, sex, and body weight, but patients in group 3 had higher supine blood pressures than those in the other two groups (133/78 mm Hg vs 118/74 group 1, p less than 0.01; 120/72 group 2, p less than 0.05). Median plasma renin activity, both supine and erect, was 60 to 120% higher in group 3 than in group 1 (p less than 0.001) and 55 to 75% higher than in group 2 (p less than 0.05). There was good evidence of a fall in both values with increasing age in all three groups. Patients in groups 1 and 2 showed evidence of inverse relationships of both blood pressure and urinary sodium with plasma renin activity/concentration ratio, but these relationships were not apparent in subjects in group 3. There is thus evidence of impaired regulation of renin secretion in persons with type I diabetes with proliferative retinopathy, the commonest form of microvascular disease. This may contribute to the relative hypertension and progression of complications.

Plasma renin activity in insulin-dependent diabetics with raised glomerular filtration rate

Basal and ambulant plasma renin activity (PRA) were measured in 12 insulin-dependent diabetics (IDDS) with elevated glomerular filtration rate (GFR), 12 IDDs with normal GFR matched for age, sex and duration of diabetes and 12 age and sex matched non-diabetic control subjects. The two diabetic groups did not differ with respect to extracellular fluid volume, urinary sodium excretion, arterial blood pressure, mean plasma glucose concentration or urinary glucose excretion. Basal PRA did not differ significantly between the three groups. Ambulant PRA was significantly higher (P less than 0.02) in the group of IDDs with elevated GFR than in the control group. Our data suggest that, in IDDs with high GFR, haemodynamic alterations may stimulate a rise in PRA and thus angiotensin, a potent vasoconstrictor. Whether this represents an attempt of the renin-angiotensin system to normalise GFR or is the result of insensitivity of the renal vasculature to circulating angiotensin remains to be established.

Increased vasopressor responsiveness to angiotensin II in type 1 (insulin-dependent) diabetic patients without complications

The blood pressure response to infused angiotensin II (0.3 to 3 ng X kg-1 X min-1) was investigated in six normotensive patients with Type 1 (insulin-dependent) diabetes free of complications and in six healthy subjects matched for age, sex and weight. Basal blood pressures (111/68 and 114/72 mmHg) and basal plasma angiotensin II levels (18.0 +/- 5.2 and 14.1 +/- 2.4 pmol/l; mean + SD) were similar in the diabetic and control groups as were 24 h urinary excretions of sodium (157 +/- 88 and 154 +/- 84 mmol/24 h). Equal increments in plasma angiotensin II were produced during the infusions in the two groups. Increases in both diastolic and systolic blood pressure were significantly greater in the diabetic patients throughout the infusion. Mean diastolic increments were: 6.7 versus 1.3 mmHg (0.3 ng dose), 11.0 versus 6.9 mmHg (1 ng dose) and 16.7 versus 12.3 mmHg (3 ng dose) (p less than 0.001). Corresponding figures for systolic pressure were: 8.7 versus 1.3 mmHg, 10.3 versus 3.7 mmHg and 15.3 versus 8.7 mmHg (p less than 0.001). Vasopressor responsiveness to angiotensin II is thus increased in Type 1 diabetic patients without complications; it may, therefore, be a consequence of the diabetes rather than of the presence of microvascular disease or hypertension.

Factors in the control of plasma renin activity and concentration in Type 1 (insulin-dependent) diabetes

Possible factors involved in the control of plasma renin activity (PRA) and concentration (PRC) have been analysed in 49 patients with long-standing Type 1 diabetes and in 40 healthy controls matched for age and sex. Eighteen of the diabetic subjects were clinically free of all microvascular and macrovascular complications of their disease (Group A); 31 had proliferative retinopathy (Group B). Both lying and standing PRA and PRC were similar in Group A and healthy controls. Mean PRA was 50-115% higher in Group B diabetics than in controls (P less than 0.001 supine and erect) and 50-70% higher than in Group A diabetics (P less than 0.05 supine and erect); PRC also was 60% higher in Group B than in Group A (P less than 0.05 supine and erect). Control subjects showed significant falls in both PRA and PRC with increasing age, while Groups A and B showed significant falls in PRA or PRC with age. Group A showed a significant inverse correlation between systolic blood pressure and supine PRC (r = -0.57), but this was not significant in the controls and was completely absent in Group B. With correction for the effect of age there were significant relationships of PRA and PRC with sodium excretion in the controls and in Group A, but not in Group B. PRA and PRC are thus normal in uncomplicated long-standing Type 1 diabetes, but regulation of renin secretion appears to be impaired in patients with microvascular disease. Renin secretion inappropriate to their blood pressure and sodium status may contribute to maintenance of their relative hypertension.

Diabetes and arterial hypertension

The epidemiology, pathogenesis, significance and management of hypertension in diabetic subjects are discussed. In Type 1 diabetes the presence of diastolic hypertension is closely related to the presence of diabetic nephropathy, from the stage of persistent proteinuria onwards. There may also be some elevation of systolic pressure. The apparent increased prevalence of hypertension in Type 2 diabetes is largely explicable, directly or indirectly, by obesity but there may be an excess of systolic hypertension among elderly patients. Hypertension in the diabetic population is associated with an increased incidence of both microvascular and macrovascular complications, but whether the high blood pressure is causal is not clear. The possible roles of sodium and insulin, the renin-angiotensin system, catecholamines and physical factors are explored. All current antihypertensive agents have additional limitations and disadvantages when used in diabetic patients: diuretics and beta-blockers are probably the initial drugs of choice. Only in the case of diabetic nephropathy is there yet reasonable evidence of antihypertensive treatment reducing the rate of progression of the disease.