"Picking winners": assessing new health technology

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Up regulation of AT4 receptor levels in carotid arteries following balloon injury

Angiotensin IV, (V-Y-I-H-P-F), binds to AT4 receptors in blood vessels to induce vasodilatation and proliferation of cultured bovine endothelial cells. This latter effect may be important not only in developing tissues but also in injured vessels undergoing remodelling. In the present study, using normal rabbit carotid arteries, we detected AT4 receptors in vascular smooth muscle cells and in the vasa vasorum of the adventitia. Very low receptor levels were observed in the endothelial cells. In keeping with the described binding specificity of AT4 receptors, unlabelled angiotensin IV competed for [125I]angiotensin IV binding in the arteries, with an IC50 of 1.4 nM, whereas angiotensin II and angiotensin III were weaker competitors. Within the first week following endothelial denudation of the carotid artery by balloon catheter, AT4 receptor binding in the media increased to approximately 150% of control tissue. AT4 receptor binding further increased in the media, large neointima and re-endothelialized cell layer to 223% at 20 weeks after injury. In view of the known trophic effects of angiotensin IV, the elevated expression of AT4 receptors, in both the neointima and media of arteries, following balloon injury to the endothelium, suggests a role for the peptide in the adaptive response and remodelling of the vascular wall following damage.

Upregulation of renin-angiotensin system during differentiation of monocytes to macrophages

BACKGROUND

We have demonstrated that accumulated macrophages in human coronary arteries strongly express angiotensin converting enzyme in accordance with the development of atheromatous plaques. However, there are few reports on the regulation of the renin-angiotensin system in macrophages and in monocytes as their source.

OBJECTIVE

To examine whether the renin-angiotensin system is upregulated during the differentiation of monocytes to macrophages, and whether it is further regulated by angiotensin II and cytokines.

MATERIALS AND METHODS

We used a human leukemia cell line, THP-1, for monocytes. Differentiated THP-1, induced by adding phorbol 12-myristate 13-acetate for 24 h, were used as macrophages. Expression of messenger RNA of the renin-angiotensin system components was measured by quantitative reverse-transcriptase polymerase chain reaction. Angiotensin converting enzyme activity and subtype-specific angiotensin-binding sites of cultured cells, and angiotensin II production in the culture medium were measured.

RESULTS

Macrophages expressed all components of the renin-angiotensin system except chymase. Cellular angiotensin converting enzyme activity and angiotensin II in the medium were increased 3.2- and 4.5-fold during differentiation, respectively. Expression of angiotensin II type 1 (AT1) and type 2 (AT2) receptors was increased 6.2-and 6.4-fold during differentiation, and was sustained for 7 days. Incubation with angiotensin II for 24 h caused downregulation of both AT1 and AT2 receptor messenger RNA, but the expression levels were still more than threefold higher compared with monocytes. The density of binding sites of AT1 and AT2 receptors in macrophages was 0.26 +/- 0.02 and 0.15 +/- 0.01 fmol/10(6) cells, respectively.

CONCLUSION

The renin-angiotensin system is markedly activated during monocyte/macrophage differentiation, and may participate in the development of atherosclerosis.

Short-term and long-term cardiovascular actions of different doses of perindopril in the rabbit

Short-term (one week) and chronic (six week) cardiovascular effects of orally administered perindopril were examined in the rabbit to demonstrate if short-term results can predict chronic outcomes. In short-term treatment, five doses of perindopril were examined in random order separated by a one week recovery period in each of six rabbits. Two doses of perindopril which resulted in a moderate hypotensive effect (-14 mmHg) and no hypotensive effect, respectively, were then selected for long-term treatment. Each rabbit in the short-term study received perindopril in doses of 0.01, 0.06, 0.32, 1.8 and 10 mg kg-1 day-1 for a week at a time. Rabbits on long-term treatment received either 0.3 or 0.01 mg kg-1 day-1 perindopril for six weeks. All rabbits had their mean arterial blood pressure (MAP) and heart rate recorded throughout treatment. Plasma angiotensin I (AngI), perindoprilat, angiotensin converting enzyme (ACE) inhibition were also assayed. Perindopril treatment for one week produced a dose-dependent hypotensive effect with the threshold dose, 0.06 mg kg-1 day-1, producing a 6.5 +/- 1.8 mmHg fall in MAP. The highest dose (10.0 mg kg-1 day-1) produced a large fall in blood pressure of -29.6 +/- 4.2 mmHg. The 0.01 and 0.06 mg kg-1 day-1 doses of perindopril produced an average 2.65 fold increase in plasma AngI levels compared to the initial control. The three higher doses (0.32-10.0 mg kg-1 day-1) of perindopril produced an equivalent 5.7 fold increase in plasma AngI levels compared to the initial controls. However, over six weeks 0.01 mg kg-1 day-1 perindopril induced a similar decrease in MAP as the 30 fold higher dose (-9.3 mmHg compared to -11.7 mmHg,). This was in spite of a 3 fold difference in plasma perindoprilat concentrations between the high and low dose perindopril groups. Plasma ACE inhibition was > 80% with both doses of perindopril. The results indicate that while perindopril decreases MAP in a dose-dependent manner in short-term (one week) periods, over longer treatment times (six weeks) low concentrations of perindopril, non-hypotensive with short-term treatment, may be as anti-hypertensive as considerably higher doses.

Angiotensin-converting enzyme inhibitors and atherosclerosis: relevance of animal models to human disease

1. Most studies examining the effect of angiotensin-converting enzyme (ACE) inhibitors on atherosclerosis in experimental animals have used doses well in excess of those given clinically. 2. Using a rabbit model of cholesterol-induced atherosclerosis characterized by subendothelial lipid accumulations ('juvenile fatty streaks') in the aorta and atheromatous lesions in the pre-injured carotid artery, we examined the effect of perindopril (at doses approaching clinical relevance) on the development, progression and regression of atherosclerosis. 3. Administration of perindopril during the 6 weeks of cholesterol feeding reduced lipid accumulation in developing atheromatous plaques of the carotid artery and in fatty streaks of the aorta. In animals with pre-existing fat-filled lesions, perindopril inhibited progression of the disease in both vessels and aided lesion regression following return to a normal diet for up to 10 months. The protective effect of perindopril was not related to a decrease in blood pressure nor to an influence on serum cholesterol levels. 4. The bradykinin B2 receptor antagonist Hoe140 did not alter the effectiveness of perindopril in inhibiting either the development of atherosclerosis or vessel wall ACE activity, indicating that the anti-atherogenic effect of perindopril is not mediated through the B2 receptor. 5. The angiotensin II (AngII) receptor antagonist losartan had no effect on the development of atherosclerotic plaques in this rabbit model, indicating that inhibition of AngII production is not the mechanism by which perindopril exerts its antiatherogenic effects.

An angiotensin converting enzyme inhibitor, perindopril, prevents progression of preformed atherosclerotic lesions in the cholesterol-fed rabbit

1. The aim was to determine whether the angiotensin converting enzyme inhibitor perindopril, at a concentration approaching that used in human antihypertensive therapy, influences progression of preformed atherosclerotic plaques. 2. Rabbits had their right carotid artery deendothelialized with a balloon catheter, which resulted in the formation of a myointimal thickening. 3. At 14 weeks post surgery groups I, II and III (n = 6 per group) were fed a 1% cholesterol-enriched diet for 6 weeks, then group I rabbits were sacrificed. Groups II and III were placed on a normolipidaemic diet for a further 6 weeks with group III rabbits also receiving 0.3 mg day-1 kg-1 perindopril. Groups IV and V were treated the same as groups II and III, respectively, except that they received a normal diet throughout. 4. Group I rabbits fed a 1% cholesterol-enriched diet for 6 weeks developed lipid-filled lesions covering 26.3 +/- 14.3% of the surface area of the descending thoracic aorta. This was exacerbated in rabbits fed a 1% cholesterol diet for 6 weeks followed by 6 weeks on a normal diet (61.2 +/- 27.3%). In rabbits fed a 1% cholesterol diet for 6 weeks than a normal diet for a further 6 weeks plus 0.3 mg day-1 kg-1 perindopril, the percentage surface area covered by lesions was 21.8 +/- 15.8%. No lesions developed in the aortas of rabbits fed a normal diet. In the right coronary artery the resulting neointima in rabbits fed a 1% cholesterol diet for 6 weeks only was 42.4 +/- 5.7% of the cross-sectional area of the vessel wall, 57.4 +/- 8.0% in rabbits receiving 6 weeks' cholesterol diet than 6 weeks' normal diet, 36.0 +/- 6.6% in rabbits fed a 6-week cholesterol diet than 6 weeks' normal diet with 0.3 mg day-1 kg-1 perindopril and 33.2 +/- 4.9% and 31.8 +/- 3.1% in rabbits on a normal diet throughout with 0 and 0.3 mg day-1 kg-1 perindopril respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Perindopril inhibits both the development of atherosclerosis in the cholesterol-fed rabbit and lipoprotein binding to smooth muscle cells in culture

The aim of the study was to examine the effect of low doses of perindopril, approximating those used therapeutically and sub-therapeutically in human hypertensives, on the development of atherosclerosis in the cholesterol-fed rabbit. The right carotid artery of 12 week old rabbits was balloon de-endothelialized to induce the formation of a myointimal thickening. After 14 weeks rabbits were placed into 6 groups, 6 rabbits per group. Groups I, II and III were fed a 1% cholesterol diet for the following 6 week experimental period, while Groups IV, V and VI received a normolipemic diet. In addition, Groups II and V rabbits received in their drinking water 0.3 mg/kg per day perindopril, and Groups III and VI 0.01 mg/kg per day. At the end of 6 weeks' treatment, the mean arterial pressure (MAP) in Groups II and V decreased by about 12%, while that in Groups III and VI decreased by 13%. Plasma cholesterol levels of rabbits on a normolipemic diet (Groups IV, V, VI) averaged 1.3 mmol/l while those on a cholesterol-enriched diet (Groups I, II, III) averaged 10.5 mmol/l. Plasma perindoprilat concentrations and percentage of plasma angiotensin converting enzyme (ACE) inhibition in Groups II and V averaged 14 ng/ml and 92.1% respectively, while in Groups III and VI they were 5.7 ng/ml and 80.5%, respectively. The percentage luminal surface area of the thoracic aorta covered by lipid-filled plaques (as observed by en face staining with Oil-Red-O) averaged 26.3% in Group I, 4.7% in Group II and 20.0% in Group III. No lesions developed in Groups IV, V and VI. Microscopic examination of the right (manipulated) carotid arteries of Group I rabbits revealed lesions of large, lipid-filled cells radially oriented, overlying the pre-formed myointimal thickening. Both doses of perindopril in the cholesterol-fed rabbits (Groups II and III) decreased the amount of lipid-filled cells which were oriented circumferentially. More extracellular matrix was present in the lesions of Groups II and III than of Group I. No lesions were observed in the right carotid arteries of Groups IV, V and VI (normal diet) or in the unmanipulated left carotid arteries of all 6 groups. The sizes of the neointima plus lesion in Groups I, II and III were, however, not significantly different, being 42.4%, 48.5% and 46.9% of the cross-sectional area of the artery wall.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphometric analysis of the actions of angiotensin II on renal arterioles and glomeruli

To study the effects of angiotensin II on afferent and efferent arteriole diameters and on intraglomerular dimensions, angiotensin II (20 ng.kg-1.min-1) or saline vehicle was infused intravenously for 20 min into anesthetized rabbits pretreated with enalapril. Both kidneys were perfusion fixed (glutaraldehyde), and vascular casts were made of the right kidneys using methacrylate. Morphometric analysis of the left kidneys using transmission electron microscopy revealed no significant effects of angiotensin II within the glomerulus, including the degree of mesangial contraction. The diameters of the afferent and efferent arteriole casts from the right kidneys were measured at 20, 50, and 75 microns from the glomerulus by scanning electron microscopy. In the outer cortex the mean diameters of the afferent and efferent arterioles were 14.1 +/- 0.8 and 9.7 +/- 0.5 microns, respectively, in the angiotensin II-infused rabbits, significantly less than in the control (vehicle) rabbits, 17.0 +/- 0.7 microns (P less than 0.001) and 10.7 +/- 0.4 microns (P less than 0.005), respectively. Calculation of the relative changes in vascular resistance, however, indicated that the effects of angiotensin II on efferent arteriole resistance (average difference 2.4 +/- 1.2 units/microns) were significantly greater per unit length than the effects on afferent arteriole resistance (average difference 0.9 +/- 0.3 units/microns). Thus infused angiotensin II caused greater reduction in afferent arteriolar diameter than in efferent, but the calculated increase in vascular resistance per micron was greater in efferent vessels due to their smaller resting diameter.

Intravascular volume and tonicity as factors in the regulation of body temperature

The effect of alterations in intravascular volume and tonicity on thermoregulatory and cardiovascular responses to heat and exercise have been compared in four subjects. Core temperatures were found to be significantly higher during dehydration, and when dehydration was prevented by administration of 1% saline, than when dehydration was prevented by water administration. These higher temperatures were associated with elevated levels of plasma [Na] and osmolarity, but no consistent relationship between temperature and changes in intravascular volume could be demonstrated. Relationships observed between core temperature and plasma tonicity were consistent with the hypothesis that the adverse effects of dehydration on thermoregulation can be attributed to an inhibition of sweating mediated by an increase in either plasma osmotic pressure or plasma [Na]. In separate experiments the heart rate response to exercise was shown to be reduced by saline, compared with water and dehydration, and this may be explained by the smaller reduction in intravascular volume which occurs during exercise following administration of hypertonic saline. It is concluded that the effects of reduced intravascular volume, and increased intravascular tonicity on physical work capacity may be distinguished by the adverse effect on the cardiovascular system of the former, and on the thermoregulatory system of the latter.

Nitrogen exchange across the lungs in resting man

The relationship between the partial pressure of N2 in the inspired air (PIN2), and the nitrogen transfer across the lungs (VN2), has been examined in 8 resting subjects, and a study made of the effect of diet upon this relationship. Alterations in PIN2, over the range 60 mm Hg below, to 20 mm Hg above ambient PIN2, caused changes in VN2 which could be described by a linear equation. These changes agreed both in magnitude and direction with those predicted by a four-compartment electrical analogue of the body N2 stores. They were not affected by the protein content of a meal taken 3/4 hr before the start of measurements of VN2. The study has shown that any imbalance in N2 transfer across the lungs is very small and that the open-circuit method of measuring O2 consumption is valid.