Recent pathogenic aspects in essential hypertension and hypertension associated with diabetes mellitus

Hypertension in diabetic nephropathy: prevention and treatment

Hypertension is the major determinant of morbidity and mortality in diabetic patients. In type I diabetes hypertension develops in parallel with the evolution of nephropathy, whereas in type II diabetes hypertension precedes the onset of manifest diabetes mellitus by years or decades. Nephropathy is equally common in types I and II diabetes. Strong genetic determinants for nephropathy have been recognized, but it is unclear whether a genetic predisposition to hypertension and elevated sodium-lithium countertransport are involved. In epidemiologic studies hypertension is related to the risk and rate of evolution of diabetic nephropathy, retinopathy, and cardiovascular complications. The relationship appears to be causal, because antihypertensive treatment attenuates the rate of loss of glomerular filtration. In this respect angiotensin-converting enzyme inhibitors appear to be superior (renal protective action). Calcium channel blockers have been promising in experimental studies, but clinical information is currently incomplete.

Coexistence of diabetes and hypertension results in unique structural alterations in the renal artery in rats beyond that found with diabetes alone

Numerous investigators have presented evidence of increased mortality in patients with diabetes mellitus due to cardiovascular disease. It is still unclear as to the reasons why there is a predisposition to vascular pathology that in the advanced state leads to atherosclerosis. Our hypotheses were: (1) The condition of diabetes mellitus in a streptozocin animal model may show vascular changes similar to early pathology in macrovessels and (2) since the model is normotensive, inducing hypertension will result in early atherogenic pathology. We carried out a quantitative analysis of the renal artery using light and electron microscopy to test the hypotheses. Male Wistar rats had diabetes mellitus induced using streptozocin and 1 week later half of the diabetic animals had hypertension induced with deoxycorticosterone acetate (DOCA). Samples were taken following 7 weeks of diabetes, or 7 weeks of diabetes with DOCA administration during the final 6 weeks. The renal artery from the diabetic group did not have any differences in wall or luminal dimensions from control, but did have proportionately more extracellular matrix than smooth muscle in the tunica media. This is evidence of structural change, in a large supply artery, as a manifestation of diabetes mellitus, similar to that seen in vascular disease. Vessels from the control/hypertensive had a significantly thickened tunica media as did the diabetic/hypertensive over control values. The latter also had proportionately even greater significant elevation of the extracellular matrix compared with either the diabetic or control/hypertensive. In addition, only the diabetic/hypertensive group showed marked subendothelial invasion of macrophage type cells and deposits of various shapes and densities. We have, therefore, demonstrated significant vascular alteration due to the diabetic condition in this animal models and also shown that with hypertension and diabetes combined, the early vascular pathology is exacerbated.

A single-blind study of doxazosin in the treatment of mild-to-moderate essential hypertensive patients with concomitant noninsulin-dependent diabetes mellitus

Doxazosin, a selective alpha 1-inhibitor, was assessed for antihypertensive efficacy, effect on lipid parameters, and safety profile in 21 hypertensive patients with noninsulin-dependent diabetes mellitus. The study involved a 2- to 4-week baseline period, a 10-week period in which patients received doxazosin, 1 to 8 mg, once daily, and a 4-week maintenance period. All 16 of the efficacy evaluable patients (100%) had their blood pressure controlled (sitting diastolic blood pressure less than or equal to 90 mm Hg) at a mean dose of 3.6 mg once daily. For efficacy evaluable patients mean sitting blood pressure was significantly (p less than 0.05) reduced by 26/17 mm Hg at the final visit. Five patients each reported a single side effect and none was severe. No patients required dose reduction or discontinuation of therapy because of side effects. No clinically significant laboratory changes were apparent, and no trends were observed with regard to organ systems or correlations with dose or duration of treatment. The investigators' global assessment of efficacy of once-daily doxazosin therapy was excellent or good for 15 patients and fair for six patients. The overall assessment of patient toleration was excellent or good for 19 patients, fair for one, and not reported for one. High-density lipoprotein cholesterol was significantly increased (p = 0.03). From baseline to final visit, there was a highly significant reduction of 30% (p less than 0.005) in calculated coronary heart disease risk score on the basis of the Framingham equation.

Immunohistochemical localization of renin in end-stage kidneys

Hypertension in chronic renal failure is usually due to excessive accumulation of salt and water. In some cases, sodium and volume depletion by dialysis fail to reduce the high BP, and plasma renin activity tends to be higher. We performed a semiquantitative analysis of the immunohistochemical distribution of renin in the kidneys of ten patients with end-stage renal disease and hypertension using a specific antihuman renin antibody and a peroxidase-antiperoxidase technique on paraffin sections of nephrectomy and/or autopsy specimens. In five cases with severe, dialysis-resistant hypertension, the degree of immunoreactivity was most striking, exceeding that found in renovascular hypertension and present in arterioles at a distance from the glomeruli. Three cases of advanced diabetic glomerulosclerosis consistently showed minimal immunoreactivity. We conclude that renin often can be detected immunologically in the kidney of patients with chronic renal failure and hypertension, but its pathophysiological role will require further study.

Norepinephrine-related mechanism in hypertension accompanying renal failure

Various blood pressure (BP)-regulating factors were assessed before and after 4 weeks of selective norepinephrine (NE) inhibition with the sympathetic neurone blocker, debrisoquine, in nine hypertensive, nine normotensive hemodialysis patients (HDP), and 11 normal subjects. On placebo, hypertensive HDP had an increased total blood volume (P less than 0.05) and exchangeable sodium (P less than 0.001), while both HDP groups had increased (P less than 0.05) plasma clearances of NE and angiotensin II (AII), and tended to have higher basal plasma NE, renin, and AII levels, and lower BP responses to NE or AII than normal subjects. Plasma epinephrine and the chronotropic dose of isoproterenol (CDI) did not differ significantly among groups. Debrisoquine lowered supine BP markedly in hypertensive HDP (on average from 181/107 to 148/88 mm Hg) and slightly in normotensive HDP (143/78 to 131/76 mm Hg), but not in normal subjects (116/74 to 120/79 mm Hg). In all groups, plasma NE, CDI, and NE pressor dose were reduced in parallel (by 35 to 75%; P less than 0.05 to less than 0.001), and the relation between stepwise increasing plasma NE and BP changes during NE infusion was commensurably displaced to the left (P less than 0.01). The remaining parameters were not changed consistently.

CONCLUSION

HDP, as normal subjects, respond to decreased sympathetic outflow with increased alpha- and beta-receptor sensitivity. Hypertension in HDP depends strongly on a NE-related mechanism. The latter seems to complement renin-angiotensin, sodium and fluid volume in the pathogenesis of high BP.

Survival of diabetic hypertensive patients

Seventy-nine of 673 patients attending a hypertensive outpatient clinic were classified as diabetics at the first examination. These patients were age- and sex-matched to two control groups: nondiabetic hypertensives and the background population. Nondiabetic hypertensive patients had a significantly poorer survival than expected during a 10-year observation period; the survival of diabetic hypertensives was even poorer, although not significantly. No sex difference was observed in the survival rates of hypertensive diabetics, neither was a difference seen between insulin-dependent and non-insulin-dependent patients. Acute myocardial infarction was the most frequent cause of death in both diabetic (40%) and nondiabetic (42%) hypertensive persons.

Basement membrane of hypothalamus and cortex capillaries from normotensive and spontaneously hypertensive rats with streptozotocin-induced diabetes

Basement membrane (BM) thickness of hypothalamic arcuate nucleus capillaries was measured in normotensive (WKY) and hypertensive (SHR) rats 4 and 8 months after streptozotocin or saline injection. Three groups were studied: controls (C), diabetics (D), and animals with impaired glucose tolerance (L). For comparison, BM thickness of cortical capillaries of an occipital and a frontal area was measured in three different layers starting from the pial surface. Independently from strain, hypothalamic capillary BM was thicker in older than in younger animals. At both 4 and 8 months, BM thickness was lowest in C, highest in D, and intermediate (between C and D) in L. Hypertension combined with diabetes did not further increase BM thickness. In both C and D no difference was found between the two cortical areas. The BM thickness of C increased from the superficial to the deep layer. In C hypertension induced BM thickening in the superficial frontal and the deep occipital layer. In the intermediate and the deep layer of the frontal area BM was thicker in WKY-D than in WKY-C. In every layer BM was thicker in SHR-D than in corresponding controls. Hypertension combined with diabetes enhanced BM thickening in the intermediate and the deep layer of the frontal and in the intermediate layer of the occipital area. Degenerative changes occurred in hypothalamic and cortical pericytes. These changes were more frequent in hypertensive than in normotensive animals. In conclusion, a microangiopathy characterized by BM thickening and pericytic degeneration occurs in the brain of diabetic animals. Its intensity and enhancement by a concomitant hypertension vary from hypothalamus to cortex.

Pharmacodynamics and kinetics of etozolin/ozolinone in hypertensive patients with normal and impaired kidney function

The effect on urinary electrolyte excretion, renin release and plasma norepinephrine of single oral doses of 400 mg etozolin (E) and of 40 mg furosemide (F) were studied in hypertensive patients with normal (n = 6) and impaired kidney function (n = 6). E caused a marked saluresis up to 24 hours, showing its long duration of action. F, however, displayed a brief, brisk peak diuresis, followed by a rebound from the 4th to the 24th hours. The brisk peak diuresis induced by F was associated with pronounced release of renin, almost twice that induced by E. In chronic renal failure the renin release in relation to the magnitude of the diuresis was increased, i.e. the sensitivity of these patients to changes in water homeostasis was increased. E and F stimulated the sympathetic system to roughly the same extent. Patients with essential hypertension had higher plasma levels of norepinephrine than hypertensive patients with chronic renal failure. In addition, hypertensive patients with normal renal function (n = 4) and varying degrees of renal impairment (n = 11) were also given 400 mg daily for 2 weeks. Effects on blood pressure and electrolyte homeostasis were monitored, as well as the plasma kinetics of metabolite I, ozolinone. At the end of the 2 week treatment E had significantly lowered systolic (-12 mm Hg) and diastolic (-9 mm Hg) blood pressure, and had produced a significant loss of body weight, without altering plasma electrolytes or blood chemistry. There was no accumulation of the effective metabolite ozolinone under conditions of severe impairment of kidney function.(ABSTRACT TRUNCATED AT 250 WORDS)

Correction of altered noradrenaline reactivity in essential hypertension by indapamide

Fourteen patients with untreated mild to moderate essential hypertension had, on average, an abnormally high cardiovascular reactivity to exogenous noradrenaline and angiotensin II, while plasma noradrenaline, renin activity, exchangeable body sodium, and blood volume were normal. Treatment with a low dose of indapamide (2.5 mg/day) for 6 weeks decreased blood pressure by 10% in these hypertensive patients but not in 13 normal control subjects. Plasma or blood volume and exchangeable sodium were not changed significantly; nevertheless, the latter, and body weight, tended to be decreased slightly. Though a mild reduction in extracellular sodium in both normal and hypertensive subjects appears possible, it may not fully explain per se the blood pressure-lowering effect of indapamide in essential hypertension. Indapamide induced a mild decrease in angiotensin II pressor responsiveness in normal or hypertensive subjects, but a possible depressor influence from this change was probably antagonized by a concomitant pronounced increase in plasma renin activity. In hypertensive patients, the abnormally high noradrenaline reactivity was corrected by indapamide without an accompanying increase in endogenous plasma noradrenaline levels. Indapamide-induced changes in blood pressure correlated with those in noradrenaline pressor dose. It was concluded, therefore, that indapamide may decrease blood pressure in essential hypertension at least in part by lowering an abnormally high cardiovascular noradrenaline reactivity without causing an equivalent increase in adrenergic nervous activity.

Enhanced cardiovascular pressor reactivity to norepinephrine in mild renal parenchymal disease

The cardiovascular pressor responsiveness to infused norepinephrine (NE) or angiotensin II (AII) as related to endogenous plasma NE or renin levels was assessed in 20 patients with mild parenchymal kidney disease (plasma creatinine 2.20 +/- 0.58 mg/dl, +/- SEM) and in 20 normal subjects approximately matched for sex and age. The two groups did not differ significantly in mean body weight, heart rate, blood volume, plasma electrolytes, exchangeable or urinary sodium, plasma aldosterone, epinephrine and renin levels, or AII threshold or pressor doses. Basal (including pre-infusion) plasma NE levels, the relationship between plasma NE measured during NE infusion and the corresponding NE infusion rate, as well as the total plasma clearance of NE (5.0 +/- 0.8 vs. 5.5 +/- 0.5 liter/min) also did not differ significantly between the two groups. In contrast, the threshold or pressor doses of infused NE decreased significantly in the patients with kidney disease (94 +/- 11 vs. 134 +/- 14 ng/kg/min and 21 +/- 3 vs. 40 +/- 7 ng/kg/min; P less than 0.05). Moreover, based on analysis of covariance, the individual pressor doses as related to basal plasma NE levels were distributed differently (P less than 0.01) between the patients and normal subjects. These findings suggest that the kinetics of plasma NE are unaltered largely in early stage kidney disease. However, such patients tend to develop an exaggerated pressor responsiveness to NE in the presence of normal plasma NE levels. This disturbance may favor the development of hypertension.

Pressor factors and cardiovascular pressor responsiveness in lean and overweight normal or hypertensive subjects

Several blood-pressure-regulating factors including exchangeable sodium, blood volume, plasma renin, aldosterone, norepinephrine (NE), and epinephrine (E) levels, urinary catecholamine excretion rates, and cardiovascular responsiveness to infused NE and angiotensin II (AII) were compared among age-matched subgroups of normal subjects (15 with normal weight, 15 with overweight) and patients with essential hypertension (15 with either normal weight, overweight, or obesity). Exchangeable sodium, blood volume, plasma and urinary sodium and potassium, plasma renin, aldosterone and epinephrine levels, and NE or E excretion rates did not differ significantly among the five subgroups. Minimal differences included a slightly higher heart rate in overweight patients than in overweight normal subjects (p less than 0.01) and a tendency for a higher plasma NE in overweight than in normal weight patients. Plasma NE obtained immediately before NE infusion as well as the plasma clearance of NE did not differ among the five subgroups except, however, for a somewhat low NE clearance in obese patients. The NE pressor dose tended to be lower in normal-weight hypertensive than in normal-weight normotensive subjects. No alteration was apparent in overweight or obese hypertensive patients. Pressor responses to AII were similar in the different subgroups. These findings suggest that overweight does not confer a unique aberration in the body sodium-volume state, circulating renin, aldosterone or catecholamines, or cardiovascular responses to NE or AII which result in hypertension.

Arachidonic acid metabolites, hypertension and arteriosclerosis

The level of arterial blood pressure is set by complete interactions of several mechanisms which influence both blood flow in and resistance of the vascular system. An imbalance favouring elevation of vascular resistance or extracellular volume will result in hypertension. Such alterations may include increased activity of the sympathetic nervous system, of the renin-angiotensin system, or excessive secretion of mineralocorticoids. Of equal importance may be a reduced activity of blood pressure-lowering factors such as prostaglandins and the kallikrein-kinin system. This paper describes the possible significance of prostaglandins in the pathophysiology of hypertension and in degenerative vascular disease, based on their involvement in the control of vascular resistance, renal regulation of extracellular volume and platelet-vessel wall interactions. An abnormality in the biosyn-thesis of certain prostaglandin endoperoxide metabolites may lead to hypertension even without an increase in the activity of the classic blood-pressure-elevating systems. The contribution of prostaglandins for the development of hypertension and degenerative vascular disease may be based on an inherent abnormality of the prostaglandin system, as well as on the effects of major risk factors such as dietary intake of sodium and fat on prostaglandin synthesis. Specific blockade or stimulation of distinct biosynthetic pathways leading to antagonistically acting prostaglandins and nutritional manipulation of precursor fatty acids should lead to a better understanding of the pathomechanisms involved and may offer new strategies for therapy or prevention of these cardiovascular disorders.

Antihypertensive mechanism of the diuretic muzolimine in mild renal failure. Roles of sodium and cardiovascular norepinephrine responsiveness

Eighteen patients with mild impairment of renal function (glomerular filtration rate 65 +/- 5 ml/min:m +/- SEM) and hypertension (168/105 +/- 6/3 mmHg) were shown on average to have abnormally increased cardiovascular pressor responsiveness to infused norepinephrine (NE; p less than 0.05), whereas plasma and urinary NE, exchangeable body sodium and blood-volume did not differ significantly from normal. A slightly increased pressor responsiveness to angiotensin II was associated with a tendency to low plasma renin activity (PRA). Compared to placebo conditions, treatment with the loop-diuretic muzolimine in a mean dose of 35 +/- 2 mg/day for six weeks decreased blood-pressure and exchangeable sodium (p less than 0.05), and NE pressor responsiveness was restored to normal values, whilst plasma and urinary NE were not significantly changed. This was consistent with improvement of the initially abnormal relationship between NE levels and NE responsiveness factors. In contrast, the pressor dose of angiotensin II and PRA were increased to an approximatively similar extent during muzolimine treatment. These observations suggest that removal of body sodium and a decrease in NE reactivity without an equivalent increase in sympathetic nervous activity may be important complementary factors in the antihypertensive mechanisms of diuretic treatment in patients with mild renal functional impairment.

Exaggerated pressor responsiveness to norepinephrine in nonazotemic diabetes mellitus

Pressor responses to norepinephrine (NE) or angiotensin II (AII) were studied in 27 diabetic patients without heart or renal failure and in 27 normal subjects. Mean plasma or 24-hour urinary sodium, blood volume and preinfusion plasma NE levels were similar in diabetic and normal subjects; exchangeable sodium was higher (p less than 0.02) and preinfusion plasma renin activity (PRA) was slightly lower in diabetic patients. The NE pressor and threshold doses were lower in diabetic patients than in normal subjects (76 versus 141 and 16 versus 41 ng/kg/min, respectively; p less than 0.05). The AII pressor dose also tended to be lower in diabetic patients (7.2 versus 11.9 ng/kg/min; p less than 0.05), but the AII threshold dose did not differ between the two groups (1.1 versus 1.6 ng/kg/min). These findings were similar in the diabetic subgroup without or with retinopathy (N = 13 and 14, respectively) and in those with normal or high blood pressure (N = 17 and 10, respectively). These observations suggest that in nonazotemic diabetes mellitus increases in AII pressor responsiveness are associated with a concomitant reduction in PRA. However, cardiovascular pressor responsiveness to NE tends to be exaggerated despite normal plasma NE levels and this alteration may occur already in the normotensive stage of diabetes mellitus. Cardiovascular hyperresponsiveness in diabetic subjects may be related to excess body sodium or structural alterations in the vasculature, or both.

Correction of altered noradrenaline reactivity in essential hypertension by indapamide

Fourteen patients with untreated mild to moderate essential hypertension had on average an abnormally high cardiovascular reactivity to exogenous noradrenaline and angiotension II, while plasma noradrenaline, renin activity, exchangeable body sodium, and blood volume were normal. Treatment with a low dose of indapamide (2.5 mg/day) for six weeks decreased blood pressure by 10% in these hypertensive patients but not in 13 normal control subjects. Plasma or blood volume and exchangeable sodium were not changed significantly; nevertheless, the latter, and body weight, tended to be decreased slightly. Though a mild reduction in extracellular sodium in both normal and hypertensive subjects appears possible, it may not per se fully explain indapamide's blood pressure-lowering effect in essential hypertension. Indapamide induced a mild decrease in angiotensin II pressor responsiveness in normal or hypertensive subjects, but a possible depressor influence from this change was probably antagonised by a concomitant pronounced increase in plasma renin activity. In hypertensive patients, the abnormally high noradrenaline reactivity was corrected by indapamide without an accompanying increase in endogenous plasma noradrenaline levels. Indapamide-induced changes in blood pressure correlated with those in noradrenaline pressor dose. It was concluded, therefore, that indapamide may decrease blood pressure in essential hypertension at least in part by lowering an abnormally high cardiovascular noradrenaline reactivity without causing an equivalent increase in adrenergic nervous activity.