Capillary neoformation in the rat heart--stereological studies on papillary muscles in hypertrophy and physiologic growth

AngiotensinII preconditioning promotes angiogenesis in vitro via ERKs phosphorylation

AngiotensinII (AngII) is involved in not only the formation of cardiac hypertrophy but also the development of cardiac remodeling both of which are associated with myocardial angiogenesis. This study was therefore performed to clarify the effects of AngII on the formation of vasculatures by cultured cardiac microvascular endothelial cells (CMVECs) after a long-period stimulation with or without the AngII preconditioning. Incubation with AngII for 18 hrs significantly impaired the formation of capillary-like tubes comparing to that without AngII. CMVECs with AngII pretreatment for 5 and 10 min formed more capillary-like tubes than those without AngII pretreatment, suggesting that preconditioning with AngII at a lower dose for a short period could prevent the further damage of CMVECs by a higher concentration of AngII. Moreover, AngII (10(-7) M) stimulation for 5 and 10 min significantly induced the increase in extracellular signal-regulated protein kinases (ERKs) phosphorylation, and an ERKs inhibitor, PD98059, abrogated the increase in the formation of capillary-like tubes induced by the AngII-pretreatment. In conclusion, preconditioning with a lower concentration of AngII for a short period prevents the subsequent impairment of CMVECs by a higher dose of AngII, at least in part, through the increase in ERKs phosphorylation.

Stereological characterization of left ventricular cardiomyocytes, capillaries, and innervation in the nondiabetic, obese mouse

BACKGROUND

Obesity is associated with left ventricular hypertrophy and dysfunction, but little is known about the structural remodeling of cardiomyocytes, capillaries, and nerve fibers in this state. We hypothesized that all three compartments should show quantitative structural alterations.

METHODS

Ten C57Bl6 mice were randomly assigned to a control or obesity group. Lean mice received standard chow, whereas obese mice received a high-fat Western diet. After 28 weeks, the mice were sacrificed, and the hearts were prepared for design-based stereology using light and electron microscopy.

RESULTS

Body mass and left ventricular mass were significantly elevated in obese vs. control mice. The left ventricular hypertrophy was accompanied by a significant increase in cardiomyocyte lipid droplets and total myocyte volume. The volume fractions of myofibrils, free sarcoplasm, and mitochondria did not differ between the groups. The total length of capillaries was significantly enhanced in obese vs. control mice, whereas the total length of axons ramifying between cardiomyocytes was not different.

CONCLUSIONS

Obesity is associated with significant structural alterations in cardiomyocytes and capillaries, whereas no structural changes in the myocardial innervation were observed. The structural characteristics in obese mice do not provide a clear basis for functional changes observed in obesity-related cardiac hypertrophy.

The application of stereological methods for estimating structural parameters in the human heart

This study describes and exemplifies generally applicable design-based stereological methods for obtaining quantitative estimates of the numbers and sizes of capillaries, cardiomyocytes, and cardiomyocyte nuclei in immersion-fixed human left ventricles (N = 6). The design-based stereological methods are valid in all cardiac investigations onto quantifying changes in structure and function as seen under various conditions such as during development, aging, hypertrophy, and following ischemia/reperfusion. The applied principles of unbiased stereology were as follows: 1) uniform random sampling was taken at all levels, also in respect to orientations, for estimates of length and mean sizes. 2) All global structural quantities were estimated as total quantity = density x volume of the left ventricle. As an example, the left ventricle contains 1.5 x 10(9) capillaries with a total length of just below 200 km. 3) Stereological methods were used for estimating the volume density, surface area density, and length density of capillaries and cardiomyocytes. The numerical density of cardiomyocyte nuclei and capillaries was estimated, using the optical and physical disector, respectively. 4) In all local quantities, "size" was estimated either directly, using unbiased estimators to obtain the average individual size and size distribution parameters, or indirectly, using the relationship that: average size = total quantity/total number. In the six hearts constituting this study, we observed the anticipated correlation between left ventricular volume and global estimates such as total number of capillaries. There were no correlation between local quantities and total left ventricular volume (e.g., average star volume of individual cardiomyocytes).

Beneficial effects of physical exercise on hypertension and cardiovascular adverse remodeling of diet-induced obese rats

BACKGROUND AND AIMS

Obesity is present among all age groups and in all socioeconomic groups. This study on obese rats aims to quantify the beneficial effects of physical exercise on blood pressure (BP), the heart, the elasticity and resistance of arteries.

METHODS AND RESULTS

Obese male Wistar rats, (obesity due to a high fat diet with 30% fat), and non-obese rats, were assigned to four groups (n=5): sedentary obese; exercise-practice obese; sedentary control; and exercise-practice control (motor treadmill for 13 weeks). Their organs were studied through light microscopy and stereology. The diet-induced obesity caused mild hypertension with adverse cardiovascular changes. Physical exercise diminished the alterations associated with BP elevation and obesity. The pressure-lowering effect observed in obese rats submitted to physical exercise improved the myocardial vascularization and the aortic and the carotid wall structure by reducing the thickness and normalizing both the elastic lamellae and the smooth muscle cells. The adaptive response of the gluteus superficialis muscle to physical exercise also improved the peripheral resistance arteries of obese rats.

CONCLUSION

Current research supports the notion of physical exercise as a potential non-pharmacological antihypertensive treatment for diet-induced obesity hypertension.

Impaired myocardial capillarogenesis and increased adaptive capillary growth in FGF2-deficient mice

Basic fibroblast growth factor (FGF2) plays a major role in angiogenesis and capillary growth. In contrast to vascular endothelial growth factor, which is required for proliferation and survival of endothelial cells, FGF2 does not seem to be essential since the Fgf2 knockout is not lethal. Therefore, the precise genetic and physiological roles of FGF2 for capillary development and adaptation remain to be determined. Here we show that myocardial capillary supply is normal at birth, but significantly reduced by approximately 25% in adult Fgf2+/- and Fgf2-/- mice as compared with wild-type littermates. In contrast, after induction of myocardial hypertrophy by continuous infusion of angiotensin II (ANG II) for 6 days marked capillary growth was seen in both Fgf2+/- and Fgf2-/- mice, but not in wild-type littermates. These data demonstrate that two intact Fgf2 genes are necessary for normal capillary development after birth, whereas FGF2 seems to be dispensable for adaptive myocardial capillary growth in the adult mouse.

Angiogenesis in ischaemic and hypertrophic hearts induced by long-term bradycardia

Angiogenesis and improved left ventricular function as a consequence of long-term bradycardia were first demonstrated in normal hearts, either electrically paced (rabbits, pigs) or treated with a selective sinus blocking drug alinidine (rats). Here we review the evidence that chronic heart rate reduction can have similar effects in the heart with compromised vascular supply, due to either hypertensive or haemodynamic overload hypertrophy (rats, rabbits) or ischaemic damage (rats, rabbits, pigs). Bradycardia induced over several weeks increased capillarity in all hypertrophied hearts, and in border and remote left ventricular myocardium of infarcted hearts. In some, but not all cases, coronary blood flow was improved by heart rate reduction, suggesting enlargement of the resistance vasculature in some circumstances. Cardiac or left ventricular function indices, which were depressed by hypertrophy or ischaemic damage, were preserved or even enhanced by chronic heart rate reduction. The expansion of the capillary bed in the vascularly compromised heart induced by bradycardia may be stimulated by mechanical stretch of the endothelium and/or VEGF activated by chamber dilation and myocyte stretch. The increased number of capillaries and more homogeneous distribution of capillary perfusion would support the better pump function, even in the absence of higher coronary flow. The beneficial impact of chronic heart rate reduction on myocardial angiogenesis and function in cardiac hypertrophy and infarction may be major factor in the success of beta-blockers in treatment of human heart failure.

DITPA stimulates arteriolar growth and modifies myocardial postinfarction remodeling

Myocardial infarction (MI) is characterized by ventricular remodeling, hypertrophy of the surviving myocardium, and an insufficient angiogenic response. Thyroxine is a powerful stimulus for myocardial angiogenesis. Male rats that underwent coronary artery ligation and subsequent MI were given 3,5-diiodothyropropionic acid (DITPA; MI+DITPA group) during a 3-wk period. We evaluated ventricular remodeling using echocardiography and histology and myocardial vessel growth using image analysis. Protein expression was assessed using Western blotting and immunohistochemistry. This study tested the hypothesis that the thyroxine analog DITPA facilitates angiogenesis and influences postinfarction remodeling in the surviving hypertrophic myocardium. The increase in the region of akinesis (infarct expansion) was blunted in the MI+DITPA rats compared with the MI group (3 vs. 21%); the treated rats had smaller percent increases in the left ventricular (LV) volume (64 +/- 14 vs. 95 +/- 12) and the LV volume-to-mass ratio (47 +/- 13 vs. 84 +/- 10) as well as a blunted decrease in ejection fraction (-9 +/- 8 vs. -30 +/- 7%). Arteriolar length density was higher after treatment in the largest (>50% of the free wall) infarcts (64 +/- 3 vs. 43 +/- 7). Angiogenic growth factors [vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF)] and the angiopoietin receptor tyrosine kinase with immunoglobulin and epidermal growth factor homology domains (Tie-2) values were elevated during the first week after infarction. DITPA did not cause additional increases in VEGF or Tie-2 values but did induce an increase in bFGF value after 3 days of treatment. This study provides the first evidence for an anatomical basis, i.e., attenuated ventricular remodeling and arteriolar growth, for improved function attributed to DITPA therapy of the infarcted heart. The favorable influences of DITPA on LV remodeling after large infarction are principally due to border zone preservation.

Kallikrein gene delivery attenuates cardiac remodeling and promotes neovascularization in spontaneously hypertensive rats

Hypertension that results in left ventricular (LV) hypertrophy and/or fibrosis can lead to cardiac dysfunction. Spontaneously hypertensive rats (SHR) develop high blood pressure and LV hypertrophy at an early age and are a popular model of human essential hypertension. To investigate the role of the tissue kallikrein-kinin system in cardiac remodeling, an adenovirus containing the human tissue kallikrein gene was injected intravenously into adult SHR and normotensive Wistar-Kyoto (WKY) rats. The blood pressure of WKY rats remained unchanged throughout the experiment. Alternatively, kallikrein gene transfer reduced blood pressure in SHR for the first 2 wk, but had no effect from 3 to 5 wk. Five weeks after kallikrein gene delivery, SHR showed significant reductions in LV-to-heart weight ratio, LV long axis, and cardiomyocyte size; however, these parameters were unaffected in WKY rats. Interestingly, cardiac collagen density was decreased in both SHR and WKY rats receiving the kallikrein gene. Kallikrein gene transfer also increased cardiac capillary density in SHR, but not in WKY rats. The morphological changes after kallikrein gene transfer were associated with decreases in JNK activation as well as transforming growth factor (TGF)-beta 1 and plasminogen activator inhibitor-1 levels in the heart. In addition, kallikrein gene delivery elevated LV nitric oxide and cGMP levels in both rat strains. These results indicate that kallikrein-kinin attenuates cardiac hypertrophy and fibrosis and enhances capillary growth in SHR through the suppression of JNK, TGF-beta 1, and plasminogen activator inhibitor-1 via the nitric oxide-cGMP pathway.

DITPA stimulates bFGF, VEGF, angiopoietin, and Tie-2 and facilitates coronary arteriolar growth

Previous studies from our laboratory and those of others have shown thyroxine to be a stimulator of coronary microvascular growth. The present study tested the hypothesis that 3,5-diiodothyropropionic acid (DITPA), a thyroid hormone analog with inotropic but not chronotopic characteristics, is angiogenic in the nonischemic heart. Daily injections (3.75 mg/kg sc) of DITPA to Sprague-Dawley rats affected protein increases in vascular endothelial growth factor (VEGF)(164), VEGF(188,) basic fibroblast growth factor (bFGF) (FGF-2), angiopoietin-1, and Tie-2 during the first few days of treatment. After 3 wk of treatment, arteriolar length density and the relative number of terminal arterioles (<10 microm diameter) increased in the left ventricle as determined by image analysis of perfuse-fixed hearts. These findings occurred in hearts that did not undergo changes in mass nor in increases in capillary length density. We conclude that DITPA, which is known to improve ventricular function after infarction, is angiogenic in normal nonischemic hearts.

Testosterone-propionate impairs the response of the cardiac capillary bed to exercise

OBJECTIVE

Experimental application of anabolic-androgenic steroids and exercise training induce cardiac hypertrophy. This study quantifies for the first time, on microscopical level, the adaptation of the cardiac capillaries and myocytes to the concomitant application of testosterone-propionate and exercise training.

METHODS

Female SPF-NMRI mice were studied over 3 and 6 wk. Experimental groups: (i) sedentary control (C); (ii) exercise (treadmill running, E); (iii) testosterone-propionate (TP); and (iv) testosterone-propionate+exercise (TPE). Morphometric parameters: 1) papillary muscles: capillary density, intercapillary distance, number of capillaries around a myocyte, and minimal myocyte diameter; and 2) left ventricular wall: capillary density and intercapillary distance.

RESULTS

Papillary muscle: A striking suppression of the exercise-induced improvement in capillary supply occurs in the testosterone-propionate+exercise groups over 3 and 6 wk. Exercise without drugs increases significantly (P < 0.05) the capillary density, shortens significantly (P < 0.05) the intercapillary distance, whereas it increases the number of capillaries around a myocyte. These alterations are not observed in the testosterone-propionate treated sedentary animals; e.g., capillary density after 6 wk (mean values +/- standard deviation, capillaries x mm(-2)): C: 4272 +/- 287, E: 5411 +/- 758, TP: 4221 +/- 364, and TPE: 3997 +/- 397. Moreover, only in the testosterone-propionate+exercise groups occurs a mild myocyte hypertrophy after both time periods: there is a trend toward hypertrophy (P < 0.1) in comparison with the C groups and a significant hypertrophy (P < 0.05) in comparison with the E groups.

CONCLUSIONS

Testosterone-propionate profoundly inhibits the exercise-induced augmented capillarization, whereas (under training conditions) it leads to a mild myocyte hypertrophy. The microvascular impairment could trigger an imbalance between the myocardial oxygen supply and demand, especially during physical exercise.

Coordinated capillary and myocardial growth in response to thyroxine treatment

BACKGROUND

Thyroid hormone-induced cardiac hypertrophy is a model of enhanced physiological growth and angiogenesis. This study addressed the growth and geometry of the capillary bed in relation to the development of cardiac hypertrophy.

METHODS

Thyroxine was administered daily (0.2 mg/kg, s.c.) for 5 or 10 days to Fischer 344 rats. After obtaining ventricular function and hemodynamic data, the hearts were perfuse fixed, and specimens from the left ventricle (LV) were subjected to image analysis to determine indices of capillary growth.

RESULTS

After 5 days of treatment, prior to cardiac enlargement, capillary length density was significantly greater in the epimyocardium of the thyroxine rats than in the controls (saline injected). Most of the increase could be attributed to an increase in capillary numerical density, but some enhancement in capillary profile axial ratio suggests that enhanced tortuosity or formation of oblique channels also occurred. After 10 days of treatment, all capillary parameters (length, volume, and surface densities) were similar to the controls despite a 30% enlargement of the LV. We estimate that total LV capillary length increased by 14% during the first 5 days and by 9% during the next 5 days of treatment.

CONCLUSIONS

These findings indicate that capillary angiogenesis precedes the development of ventricular enlargement due to thyroxine administration. Therefore, angiogenesis in this model is not stimulated by the presence of hypertrophy.

Early coronary angiogenesis in response to thyroxine: growth characteristics and upregulation of basic fibroblast growth factor

Although a substantial coronary angiogenesis occurs after thyroid hormone treatment, its regulation and relationship to cardiac hypertrophy are not understood. This study was designed to determine (1) the onset of capillary proliferation, (2) the sites of capillary proliferation, and (3) whether basic fibroblast growth factor (bFGF) upregulation occurs in response to thyroxine administration. Male Sprague-Dawley rats were injected daily with L-thyroxine (T4, 0.2 mg/kg s.c.). Bromodeoxyuridine labeling of capillary endothelial cells increased during the first 24 hours of treatment and peaked after 2 days of treatment. Northern blot analysis revealed a slight increase in bFGF mRNA during this period, followed by a doubling of expression by 48 hours, at which time bFGF protein was also increased. In situ hybridization, used to localize bFGF mRNA, showed an increase in transcripts within 24 hours after T4. This enhancement was uniform in the epimyocardium and endomyocardium. Histochemical analysis (double staining for alkaline phosphatase and dipeptidyl peptidase) of frozen sections, used to discriminate capillary profiles as arteriolar and venular, respectively, showed that growth occurred in the latter, since the percentage of capillary profiles positive for dipeptidyl peptidase was higher than the control value after 4 days of T4 administration. These data indicate that in the thyroxine model of cardiac hypertrophy (1) capillary DNA synthesis occurs after a single injection of thyroxine, (2) capillary growth coincides with an upregulation in bFGF mRNA and increase in bFGF protein, and (3) proliferation occurs in the venular capillaries.

Contribution of bradykinin to the cardioprotective action of angiotensin converting enzyme inhibition in hypertension and after myocardial infarction

Angiotensin converting enzyme (ACE) is identical with kininase II. Besides reducing the production of angiotensin II, inhibition of ACE potentiates the biological actions of endogenous kinins. In hypertension-induced left ventricular hypertrophy, potentiation of endogenous kinins contributes to the improvement of cardiac function and energy metabolism and to capillary proliferation effected by ACE inhibitors. In myocardial infarction (MI), the potentiation of kinins has been shown to be involved in the reduction of infarct size and improvement of cardiac function by ACE inhibition. The cardioprotective actions of ACE inhibition in MI seem to be, in part, mediated by the augmentation of myocardial blood flow, especially in the ischemic region of the heart.

Effects of angiotensin-converting enzyme inhibition and angiotensin II AT1 receptor antagonism on cardiac parameters in left ventricular hypertrophy

Left ventricular hypertrophy (LVH) is considered to be an independent risk factor giving rise to ischemia, arrhythmia, and left ventricular dysfunction. In this article, we summarize recent studies performed in our laboratory to investigate (1) the contribution of the renin-angiotensin system to the cardiac remodeling process, which is triggered by myocardial infarction (MI) or hypertension-induced cardiac hypertrophy; (2) the effects of angiotensin-converting enzyme (ACE) inhibition and angiotensin AT1 receptor antagonism on cardiac parameters, such as myocardial infarct size, cardiac hypertrophy, heart function, and myocardial metabolism; (3) the mechanism of an ACE inhibitor-induced increase in cardiac capillary density in spontaneously hypertensive rats (SHR) and stroke prone SHR (SHR-SP). We observed that AT1 receptor gene expression in rat vascular smooth muscle cells (but not in rat coronary endothelial cells) was markedly enhanced after an ischemic insult in vitro. In a rat model in which MI was induced by coronary artery ligation, the AT1 receptor mRNA levels were transiently increased after MI and reached a peak level 24 hours post-MI. The AT2 receptor gene expression increased in a pattern similar to that of the AT1 receptor. ACE expression at the protein level in the repairing scar, which was demonstrated by monoclonal antibody staining, started to increase 2 weeks after MI and reached a peak level 3 weeks post-MI. Furthermore, long-term treatment with an ACE inhibitor limited infarct size, prevented cardiac hypertrophy, and improved heart function in the rat MI model. In SHR-SP, long-term treatment with either an ACE inhibitor or an AT1 receptor antagonist improved cardiac function and metabolism. Cardiac metabolism was even improved after low-dose ACE inhibitor treatment, which did not prevent hypertension and cardiac hypertrophy. In both SHR and SHR-SP, we found that the ACE inhibitor ramipril significantly increased capillary length density independently of its antihypertensive and antihypertrophic actions. Most of the cardiac effects of the ACE inhibitor could be abolished by a bradykinin B2 receptor antagonist. Thus, these cardiac effects of ACE inhibitors can be ascribed, at least under our experimental conditions, to ACE inhibitor-induced bradykinin potentiation.

Blockade of bradykinin B2 receptors prevents the increase in capillary density induced by chronic angiotensin-converting enzyme inhibitor treatment in stroke-prone spontaneously hypertensive rats

We investigated the mechanism of action of the ACE inhibitor-induced increase in cardiac capillary length density. Stroke-prone spontaneously hypertensive rats were treated prenatally and up to the age of 20 weeks with the ACE inhibitor ramipril (0.01 and 1 mg/kg per day PO) and the AT1 receptor antagonist losartan (30 mg/kg per day PO). The contribution of endogenous bradykinin potentiation to the ACE inhibitor actions was assessed by cotreatment with the bradykinin B2-receptor antagonist Icatibant (0.5 mg/kg per day, SC via osmotic minipumps) from 6 to 20 weeks of age. At the end of the treatment period, cardiac capillary length density was measured stereologically using the orientator method. The development of hypertension and left ventricular hypertrophy was prevented by high- but not low-dose ramipril and was not affected by chronic bradykinin B2-receptor blockade. Low- and high-dose ramipril significantly increased cardiac capillary length density (3577 +/- 279, n = 11 and 3988 +/- 300 mm/mm3; n = 10; P < .05) compared with vehicle-treated animals (2935 +/- 137 mm/mm3; n = 13). These effects were abolished by chronic bradykinin B2-receptor blockade. The bradykinin antagonist alone was without effect on cardiac capillary length density. Losartan prevented hypertension and left ventricular hypertrophy but did not significantly alter cardiac capillary length density (3429 +/- 309 mm/mm3; n = 7). Our results demonstrate that chronic ACE inhibitor treatment can increase cardiac capillary length density in stroke-prone spontaneously hypertensive rats independently of a reduction in blood pressure or left ventricular hypertrophy. This effect is related to the ACE inhibitor-induced potentiation of endogenous bradykinin since it was prevented by chronic bradykinin B2-receptor blockade and was not observed following antihypertensive treatment with the AT1-receptor antagonist losartan.

Time-related normalization of maximal coronary flow in isolated perfused hearts of rats with myocardial infarction

BACKGROUND

In the present study, we investigated the time dependency and regional differences of the vascular adaptation of the myocardium after myocardial infarction (MI) in rats.

METHODS AND RESULTS

MI was induced by total occlusion of the left anterior descending coronary artery. Time-dependent adaptation of the coronary vasculature was determined by histological staining of endothelial cells and measurement of basal and maximal coronary flow at days 0, 4, 7, 21, 35, and 90 after surgery in isolated retrogradely perfused hearts of sham-operated and infarcted rats. Cardiac function was determined during anterograde perfusion. In a separate group of experiments, regional myocardial flow was measured with radiolabeled microspheres in sham-operated and infarcted hearts to determine local differences in adaptation. Basal coronary flow was completely normalized within 7 days, whereas maximal coronary flow was not normalized until 35 days after MI. Normal growth, as observed in sham-operated hearts, resulted in a parallel increase in coronary flow and tissue mass from day 7 to 35 after surgery. In contrast, the increase in coronary flow was lower than the hypertrophic response in the right ventricles and septa of infarcted hearts, whereas a parallel increase in tissue mass and coronary flow was observed in the left ventricles of these hearts. These functional data were supported by structural data that showed the presence of numerous and dilated vessels, especially in the border zone of the infarcted and noninfarcted tissue.

CONCLUSIONS

These observations demonstrate that vessel growth, predominantly in the region adjacent to the infarcted zone, results in complete normalization of coronary vasodilatory capacity within 35 days after MI.

Angiotensin converting enzyme inhibitors, left ventricular hypertrophy and fibrosis

From pharmacological investigations and clinical studies, it is known that angiotensin converting enzyme (ACE) inhibitors exhibit additional local actions, which are not related to hemodynamic changes and which cannot be explained only by interference with the renin angiotensin system (RAS) by means of an inhibition of angiotensin II (ANG II) formation. Since ACE is identical to kininase II, which inactivates the nonapeptide bradykinin (BK) and related kinins, potentiation of kinins might be responsible for these additional effects of ACE inhibitors. a) In rats made hypertensive by aortic banding, the effect of ramipril in left ventricular hypertrophy (LVH) was investigated. Ramipril in the antihypertensive dose of 1 mg/kg/day for 6 weeks prevented the increase in blood pressure and the development of LVH. The low dose of ramipril (10 micrograms/kg/day for 6 weeks) had no effect on the increase in blood pressure or on plasma ACE activity but also prevented LVH after aortic banding. The antihypertrophic effect of the higher and lower doses of ramipril, as well as the antihypertensive action of the higher dose of ramipril, was abolished by coadministration of the kinin receptor antagonist icatibant. In the regression study the antihypertrophic actions of ramipril were not blocked by the kinin receptor antagonist. Chronic administration of BK had similar beneficial effects in a prevention study which were abolished by icatibant and NG-nitro-L-arginine (L-NNA). In a one year study the high and low dose of ramipril prevented LVH and fibrosis. Ramipril had an early direct effect in hypertensive rats on the mRNA expression for myocardial collagen I and III, unrelated to its blood pressure lowering effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of capillary length density in skeletal muscle by unbiased stereological methods: I. Use of vertical slices of known thickness

BACKGROUND

The unbiased estimation of the capillary length density in skeletal muscle tissue Lv(cap/mus) has been performed in this study applying a new stereological methodology based on the use of vertical slices and the intersections of cycloid test curves with capillaries in a three-dimensional space defined by systematically chosen fields of vision and the thickness of the sections.

METHODS

The following simple requirements must be fulfilled: selection of a fixed vertical axis in skeletal muscle, adequate systematic muscle sampling, obtention of vertical slices of constant and known thickness but indifferent in magnitude, superposition of a cycloid test system with the minor axis of cycloid curves positioned perpendicularly to the vertical axis, and counting the intersections between cycloid curves and capillaries. In our study, the vertical axis was defined as that which is parallel to the natural, major axis of the muscle where fibres and capillaries are arranged parallel to this axis. The muscle sampling was performed using the fractionator method, and 25 microns thick sections were chosen.

RESULTS

The application of the equation for estimation of Lv(cap/mus) permits determination of an average of 1,480 mm of capillaries per mm3 of muscle tissue, knowing the number of intersections, section thickness, and the points hitting the muscle with a known ratio between cycloid test curve length to a test point.

CONCLUSIONS

The estimation of Lv(cap/mus) is efficient, unbiasedly obtained, and no assumptions on the degree of capillary anisotropy are required.

Blood flow rate and total blood flow related to length density and total length of blood vessels in mini-pig urinary bladder after chronic outflow obstruction and after recovery from obstruction

Chronic partial bladder outlet obstruction was created in mini-pigs by implanting a 6-7 mm ring around the proximal urethra. After a median obstruction period of 63 days the ring was removed, and after a median recovery period of 60 days the animals were sacrificed. At each study occasion the blood flow rate (ml per 100 g per min) was measured by washout of locally injected 133Xe in the bladder wall and the washout curves analyzed by the corrected initial slope method. Stereological estimation of length density and total length of blood vessels in the bladder were performed. The results can be summarized as follows: (1) no differences in the blood flow rate at the time of ring implantation, obstruction, or recovery, (2) no decrease in the blood flow rate in normal bladders after bladder distension, (3) a significant decrease in blood flow rate in obstructed bladders after distension, (4) a 6-fold increase in total bladder blood flow after obstruction, (5) an unchanged blood flow per length of blood vessels per min during the study, (6) no changes in length densities of blood vessels during the study, and (7) a 7-fold increase in total length of blood vessels after obstruction and reversion to control level after recovery. The unchanged blood flow per length of vessels implies that capillary proliferation matched the increased bladder mass during the study.

Comparative effects of chronic angiotensin-converting enzyme inhibition and angiotensin II type 1 receptor blockade on cardiac remodeling after myocardial infarction in the rat

BACKGROUND

After myocardial infarction, the noninfarcted left ventricle develops reactive hypertrophy associated with a depressed coronary flow reserve, myocardial interstitial fibrosis, and reduced capillary density. The present study investigated the comparative cardiac effects of chronic angiotensin-converting enzyme (ACE) inhibition and selective angiotensin II type 1 receptor (AT1) blockade in the rat model of myocardial infarction and failure.

METHODS AND RESULTS

Seven days after coronary ligation (MI), rats were randomized to enalapril (n = 8; 500 micrograms.kg-1.d-1), losartan (n = 9; 3 mg.kg-1.d-1), or placebo (n = 8) and treated for 6 weeks. Sham-operated rats (n = 10) served as controls. Coronary blood flow was measured with radiolabeled microspheres during baseline and maximal coronary dilation induced by dipyridamole (2 mg.kg-1.min-1 over 10 minutes). Right and left ventricular (LV) weight was increased in infarcted rats compared with sham-operated animals and enalapril- and losartan-treated MI rats. Minimal LV and right ventricular coronary vascular resistance was increased in MI rats but normalized with enalapril and losartan (LV:sham, 8.9; MI-placebo, 12.7; MI-enalapril, 9.2; MI-losartan, 8.8 mm Hg.mL-1.min-1.g-1, all P < .05 versus MI-placebo). Interstitial fibrosis determined from perfusion-fixed hearts was increased in infarcted rats but reduced by both enalapril and losartan. Myocardial capillary density improved with enalapril and losartan. In separate groups treated as above, plasma and tissue ACE activity was determined and demonstrated significantly higher ACE activity in noninfarcted LV tissue of MI-placebo rats compared with sham (0.64 vs 0.27 nmol.mg protein-1.min-1, P < .05). Enalapril and losartan reduced LV ACE activity (0.39 and 0.29 nmol.mg protein-1.min-1, P < .05 versus MI-placebo).

CONCLUSIONS

The present study demonstrates that both chronic ACE inhibition and AT1 receptor blockade (1) reduces cardiac hypertrophy, (2) restores minimal coronary vascular resistance in postinfarction reactive hypertrophy, and (3) attenuates the development of myocardial interstitial fibrosis in the noninfarcted LV. These results suggest that inhibition of generation of angiotensin II and AT1 receptor blockade are equally effective in preventing important features of ventricular remodeling after myocardial infarction.

Angiotensin-converting enzyme inhibition improves cardiac function. Role of bradykinin

The effect of chronic low- and high-dose treatment with the angiotensin-converting enzyme (ACE) inhibitor ramipril (0.01 and 1 mg/kg per day) on the development of hypertension and left ventricular hypertrophy as well as on functional and biochemical alterations of the heart was studied in stroke-prone spontaneously hypertensive rats treated prenatally and subsequently up to the age of 20 weeks. The contribution of endogenous bradykinin potentiation to the ACE inhibitor actions was assessed by cotreatment of rats with the bradykinin B2-receptor antagonist Hoe 140 (500 micrograms/kg per day SC) from 6 to 20 weeks of age. High- but not low-dose ACE inhibitor treatment prevented the development of hypertension and left ventricular hypertrophy. Chronic bradykinin receptor blockade did not attenuate the antihypertensive and antihypertrophic actions of ramipril. High-dose ramipril treatment improved cardiac function, as demonstrated by an increase in left ventricular pressure (29.9%), dP/dtmax (34.9%), and coronary flow (22.1%), without a change in heart rate. The activities of lactate dehydrogenase and creatine kinase and lactate concentration in the coronary effluent were reduced by 39.3%, 55.5%, and 66.7%, respectively. Myocardial tissue concentrations of glycogen and the energy-rich phosphates ATP and creatine phosphate were increased by 31.3%, 39.9%, and 73.7%, respectively, whereas lactate was decreased by 20.8%. Chronic low-dose ACE inhibitor treatment led to a pattern of changes in cardiodynamics and cardiac metabolism similar to that observed with the high dose. All ACE inhibitor-induced effects on cardiac function and metabolism were abolished by chronic bradykinin receptor blockade.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of combined renovascular hypertension and diabetes mellitus on myocardial cells, non-vascular interstitium and capillaries: a stereological study on rat hearts

The effects of combined renovascular hypertension and diabetes mellitus on the rat heart were investigated in order to detect possible synergistic effects of the two conditions. Hypertensive diabetic and hypertensive non-diabetic animals were compared to diabetic and non-diabetic controls. Hypertension was established for 12 weeks by a surgical stenosis of the left renal artery; diabetes mellitus was maintained for 8 weeks by a single intraperitoneal injection of 60 mg/kg streptozotocin. Light microscopic stereology did not reveal significant divergences between diabetic hypertensives and non-diabetic hypertensives. Hypertension induced a focal perivascular and interstitial fibrosis with increased volume densities of non-vascular interstitium and fibrosis (P less than 0.001). Capillary density (QA) was decreased in transverse sections (P less than 0.01) and increased in longitudinal sections (P less than 0.01). This indicates a three-dimensional remodelling of the capillary bed with an increased number of obliquely running capillaries. At least the length density (LV) of capillaries (mm/mm3) tends to be normalized in long-term renovascular hypertension. At the ultrastructural level, a synergism of hypertension and diabetes mellitus was observed: the volume ratio of mitochondria to myofibrils was significantly decreased in hypertensive diabetics, but not in non-diabetic hypertensives or in diabetics. This may enhance the risk of cardiac deterioration. We conclude that the primary target of the synergistic damage in hypertensive diabetic heart muscle disease is the myocardial cell and not the cardiac interstitium.

Effect of early onset angiotensin converting enzyme inhibition on myocardial capillaries

We investigated the preventive effects of long-term treatment with the angiotensin converting enzyme inhibitor ramipril on myocardial left ventricular hypertrophy and capillary length density in spontaneously hypertensive rats. Rats were treated in utero and subsequently up to 20 weeks of age with a high dose (1 mg/kg per day) or with a low dose (0.01 mg/kg per day) of ramipril. Animals given a high dose of ramipril remained normotensive, whereas those given a low dose developed hypertension in parallel to vehicle-treated controls. At the end of the treatment period, converting enzyme activity in heart tissue was inhibited dose-dependently in the treated groups. Both groups revealed an increase in myocardial capillary length density together with increased myocardial glycogen and reduced citric acid concentrations. Left ventricular mass was reduced only in high dose- but not in low dose-treated animals. Our results demonstrate that early onset treatment with a converting enzyme inhibitor can induce myocardial capillary proliferation, even at doses too low to antagonize the development of hypertension or left ventricular hypertrophy. We hypothesize that potentiation of kinins is responsible for this effect, probably by augmenting myocardial blood flow, which is a well-known trigger mechanism of angiogenesis in the heart.

Functional and stereologic estimations of myocardial capillary exchange capacity in treated and untreated spontaneously hypertensive rats

Myocardial capillary exchange capacity was investigated by stereologic and functional techniques in parallel during pressure-overload cardiac hypertrophy and after long-term antihypertensive therapy with the vasodilator felodipine. In 26-week-old female spontaneously hypertensive rats (SHR) blood pressure increased by 25% and left ventricular weight (LVW/BW) increased by 18% compared to Wistar-Kyoto rats (WKY). Myocardial capillary surface and volume densities normalized for organ weight were similar in both ventricles for both strains. Moreover, capillary surface density was higher sub-epicardially (EPI) than in the subendocardium (ENDO) in the left ventricle of SHR. Thirteen weeks of felodipine-therapy (SHR-Felo) normalized blood pressure without affecting LVW/BW although a transition from concentric to eccentric hypertrophy is known to occur. Myocardial capillary surface and volume densities and the left ventricular ENDO-EPI-gradient in surface density were similar to untreated SHR. However, felodipine-treatment increased right ventricular weight and capillary volume density. Functional capillary exchange was estimated in terms of permeability surface area products (PS) for Cr-EDTA and vitamin B12 and normalized for organ weight. PSCr-EDTA, PSB12 and the ratio PSCr-EDTA/PSB12 (an index of capillary permeability) were similar in SHR and WKY. Furthermore, the relation between functional and stereological indices of exchange capacity was investigated in a multiple linear regression analysis. However, no significant correlation between PS and neither capillary surface nor volume density was found. In conclusion, myocardial capillary exchange capacity was well adapted to the pressure overload cardiac hypertrophy present in female SHR. Despite induction of right ventricular hypertrophy, felodipine-treatment did not affect capillary exchange capacity. Furthermore, when functional and stereologic estimates were performed in parallel, the importance of dynamic factors for myocardial capillary exchange capacity (e.g. heterogeneity) was illustrated.