Search PubMed⌕ Search

Biomedical subjects

K Rakusan

Publications and source records attributed to K Rakusan.

At least 37 records · Page 2Linked to original sources
PubMed1995

Coronary angiogenesis. From morphometry to molecular biology and back.

We have reviewed briefly the current state of knowledge relating to the regulation of angiogenesis, including the role of angiogenic growth factors, and we have described the major structural components of the vascular wall and their changes during formation of new channels. Finally, we have described quantitative evaluations of vascular growth in cardiac muscle. Examples of substantial angiogenesis during the early postnatal stages of normal development were used together with examples depicting a more moderate stimulation of capillary growth in adult rat hearts treated with nifedipine or thyroxine. Adequate capillary supply is a precondition for tissue survival and proper function. This is probably why vascular growth is so tightly regulated by several systems which may alternately stimulate or inhibit the formation of new vessels. Recent advances in molecular biology have enabled us to study the mechanisms of angiogenesis under both in vitro and in vivo conditions, but the final assessment of vascular growth should be accomplished through morphometric analysis.

Aging↗
PubMed1995

Proliferating cell nuclear antigen (PCNA) detection of cellular proliferation in hypothyroid and hyperthyroid rat hearts.

Immunocytochemical techniques examining the expression of cell proliferation-related markers such as proliferating cell nuclear antigen (PCNA), may be employed to provide visual and quantitative evidence of cell proliferation. The efficacy of this method in frozen samples was tested on sections of 2-day-old rat heart. Mouse monoclonal anti-PCNA and goat anti-mouse IgG2a peroxidase-conjugated antibodies were applied to tissue cross-sections. PCNA positive (PCNA+) cells were evident in these sections as intensely stained, dark brown nuclei. This method was then applied to the hearts of four groups of adult rats (1) 1 month hyperthyroid, (2) 1 month hypothyroid, (3) 6 days hyperthyroid following 1 month hypothyroidism, or (4) euthyroid, in order to assess the ability of identifying and quantifying PCNA+cell types (myocyte, endothelial, or remaining, "other" cells). Serial cross-sections were prepared, half of the sections processed using the PCNA technique, while corresponding sections were stained with hematoxylin and eosin. Identification of PCNA+cell types was made by comparison of PCNA with H&E sections. PCNA labeling indices for a given cell type were expressed as the proportion of PCNA+nuclei per 1000 nuclei. No PCNA+myocyte nuclei were observed in any of the adult hearts. Only hypothyroid/hyperthyroid demonstrated significantly higher PCNA labeling of endothelial and "other" nuclei compared to euthyroid. This finding agrees with previous morphometric data which suggested capillary growth in these hearts. Results demonstrate that quantitation of PCNA expression on frozen heart tissue is possible, and can be used to provide direct, discernible evidence for cell proliferation.

Animals↗
PubMed1994

Morphometry of arterioles and capillaries in hearts of senescent mice.

OBJECTIVE: The aim was to characterise quantitative changes in the coronary arterioles and capillaries with aging in mice. METHODS: Morphometric analysis of the coronary resistance vessels was carried out in 12 "young" mice (63 days) and 11 "old" mice (650 days). RESULTS: Compared to hearts from young mice, those from senescent mice were heavier, contained less water, and differed in several variables characterising terminal vessels. The main changes were a decreased capillary and arteriolar density, increased heterogeneity of capillary spacing, and larger arterioles with thicker walls. CONCLUSIONS: Aging of the murine myocardium is characterised by important changes at the level of the terminal vascular bed, the most prominent being a decrease in capillary and arteriolar density. The decrease in arteriolar density is most prominent in the classes of smallest vessels. All these changes represent an impairment of geometrical conditions for the oxygen supply to the myocardial tissue.

Aging↗
PubMed1994

Geometry of coronary capillaries in hyperthyroid and hypothyroid rat heart.

Coronary capillary geometry was studied in male rats treated with 3,3',5-triiodo-L-thyronine (T3; Hyper), 6-N-propyl-2-thiouracil (PTU; Hypo), or a sequence of PTU and T3 (Hypo/Hyper). Ventricular mass and heart-to-body mass ratios revealed myocardial hypertrophy in Hyper, atrophy in Hypo, and a return of ventricular mass to control (Con) values in Hypo/Hyper rats. From cross-sectional analysis, capillary densities for Hyper and Hypo/Hyper were comparable with Con, despite increased left ventricular mass. Hypo rats demonstrated increased capillary density. In Hyper and Hypo rats, tissue area surrounding individual capillaries (capillary domain) decreased, compared with Con, for capillaries close to the feeding arteriole. In Hyper and Hypo/Hyper, capillaries distal to the feeding arteriole had similar domain areas as Con; in Hypo, this area was smaller. From longitudinal analysis, capillary segment lengths were significantly shorter in all groups compared with Con. Our data suggest that while hypothyroidism induced myocardial atrophy and hyperthyroidism induced myocardial hypertrophy, both thyroid states stimulated capillary proliferation.

Alkaline Phosphatase↗
PubMed1994

Effect of nifedipine on coronary capillary geometry in normotensive and hypertensive rats.

The aim of this study was to describe quantitatively changes in the coronary capillary network resulting from hypertrophy in spontaneously hypertensive rats (SHR) and a potential effect of long-term treatment of these animals with nifedipine. Age-matched male SHR and Wistar-Kyoto (WKY) rats were treated for 27 weeks. Four experimental groups were analyzed: (1) untreated SHR, (2) nifedipine-treated SHR, (3) untreated control WKY rats, and (4) nifedipine-treated WKY rats. Treatment significantly decreased systolic blood pressure in SHR, although normotensive pressures were not reached. SHR had significantly higher cardiac weight, which decreased in nifedipine-treated rats, but values remained above those in control animals. Morphometric evaluation revealed lower capillary density and larger capillary domain area in hearts from SHR, which were partially attenuated by treatment with nifedipine. Capillary domain area was also significantly larger at arteriolar portions compared with domains supplied at venular portions. Capillary segment length was consistently shorter on the venular than arteriolar portion of the capillary, whereas no differences were observed between hearts from WKY rats and SHR. Treatment with nifedipine resulted in a prolongation of segment length. Reconstruction of the three-dimensional capillary supply unit (capillary domain area times capillary segment length) revealed significant differences between the amount of tissue supplied by a capillary at its arteriolar portion than more distally, which was detectable in all experimental groups. In hypertrophic hearts from SHR this tissue volume is increased mainly because of longer intercapillary distances and larger domains, especially on arteriolar portions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Changes in the microvascular network during cardiac growth, development, and aging.

Quantitative changes in the terminal vascular bed of the mammalian heart were assessed during postnatal development and aging. The most striking feature is a considerable formation of new capillaries in the early postnatal period, accompanied by a moderate formation of new arterioles. On the other hand, coronary arterioles seem to disappear at a higher rate than capillaries in the senescent heart. We proposed a three-dimensional structural model of tissue capillary supply, defined as capillary domain area times capillary segment length. This so called capillary supply unit increases as a function of age and body growth. It is very similar in size and shape (length to width ratio) to cardiac myocytes.

Adult↗
PubMed1994

The effect of hypoxia on capillary flow direction in the isolated perfused rat heart.

OBJECTIVE: To characterize regional capillary flow direction in the isolated perfused heart subjected to acute hypoxia. DESIGN: A technique incorporating sequential infusion of differently coloured 10 microns microspheres into hearts of adult male Sprague-Dawley rats was employed in two series of experiments. In series A, a control group (n = 10) received three infusions of coloured microspheres (each distinctly coloured) in sequence during normoxic perfusion. A 'hypoxic' group (n = 12) received the initial two infusions under identical conditions, with the third infusion under conditions of experimental hypoxia. Hearts in series B (n = 5) received two differently coloured infusions, the initial under normoxic conditions and the second during hypoxia. Subsequent histological examination of 40 microns sections obtained from midmyocardial (MID) and subendocardial (SUB-E) regions of the heart revealed flow vectors based on the sequence of colours trapped within neighbouring capillaries. RESULTS: Series A-A prevalence in concurrent flow was observed among neighbouring capillaries, with significantly lower percentages in SUB-E than in MID (P < 0.01). A higher percentage of countercurrent flow was revealed subsequent to the hypoxic intervention than during the earlier normoxic period, as well as in comparison with normally perfused controls (P < 0.01). Flow vector observations from series B depicted lower proportions of concurrent flow compared with the two-colour normoxic interval in 'hypoxic' hearts from series A (P < 0.05). CONCLUSION: Reversals in capillary flow direction, suggested by the reorientation of final injected microspheres relative to the positions of earlier injected microspheres, were interpreted as a response to sustain myocyte oxygenation due to severe reductions in arterial oxygen tension.

Animals↗
PubMed1993

Cardiac structural remodelling after treatment of spontaneously hypertensive rats with nifedipine or nisoldipine.

OBJECTIVE: The aim was to determine if long term treatment with nifedipine or nisoldipine affects structural remodelling of cardiac myocytes and is effective in attenuating or preventing reparative and reactive myocardial fibrosis in essential hypertension. METHODS: Five and a half month old male spontaneously hypertensive rats and Wistar Kyoto (WKY) rats received either 1000 ppm nifedipine or nisoldipine or no treatment (controls) for 22 weeks. Haemodynamic variables were measured and hearts recovered from animals of each group. Cardiac myocytes were isolated by retrograde coronary perfusion with collagenase. Cell volume was determined by Coulter analysis, cell length by direct measurement, and cross sectional area by volume/length. Cardiac myocyte number was calculated for both ventricles. Tissue sections from perfusion fixed hearts were stained with picrosirius red and myocardial collagen was analysed. Reparative fibrosis was assessed by the presence of microscopic scarring and reactive (interstitial and perivascular) fibrosis was quantified. RESULTS: Nifedipine and nisoldipine significantly decreased systolic and diastolic blood pressure in spontaneously hypertensive rats, although normotensive pressures did not result. Left ventricular weight relative to body weight was significantly decreased in nifedipine and nisoldipine treated compared with untreated spontaneously hypertensive rats, although values remained significantly greater than WKY controls. Cardiac myocyte volume was slightly decreased with attenuation of blood pressure in spontaneously hypertensive rats, but no significant differences were found. Cardiac myocyte number for each ventricle was similar between groups. Microscopic scarring was significantly decreased in nifedipine and nisoldipine treated compared with untreated spontaneously hypertensive rats and interstitial and perivascular fibrosis were substantially reduced. CONCLUSIONS: Nifedipine and nisoldipine: (a) attenuate hypertension and decrease left ventricular mass in spontaneously hypertensive rats, but the associated decrease in myocyte size was not significant; (b) are cardioprotective as indicated by a significant decrease in the incidence of microscopic scarring; and (c) decrease the extent of reactive, both interstitial and perivascular, fibrosis normally found in untreated spontaneously hypertensive rats. Nifedipine and nisoldipine have the potential to positively alter myocardial pathology in essential hypertension.

Animals↗
PubMed1993

Effects of hypertension and aging on coronary arteriolar density.

Coronary reserve has been shown repeatedly to be depressed in hypertension and aging. The underlying mechanisms remain elusive, but structural alterations of the coronary vasculature have been implicated. In this study, we measured maximal coronary dilator capacity and structural characteristics relevant to coronary resistance in aging normotensive (Wistar-Kyoto, n = 22) and spontaneously hypertensive rat (SHR) strains (n = 25) at 1.5, 4, 11, 16, and 22 months of age. Coronary flow measurements, using radiolabeled microspheres, demonstrated a significant (p < 0.01) hypertension- and age-related decline in maximal coronary dilator capacity. After flow measurements, vascular dimensions and arteriolar density were obtained from 1-micron sections prepared from perfusion-fixed hearts. A total of 10,012 arterioles were analyzed, 4,820 in hypertensive and 5,192 in normotensive rats. There was an 18-28% reduction in arteriolar density in hypertensive rats that specifically affected the terminal arteriolar bed at 1.5-11 months. However, the decrement in arteriolar density stabilized at 10% and 6% in 16- and 22-month-old hypertensive rats, respectively. Arteriolar density was not affected by aging. In both strains, there was a significant (p < 0.01) age-related decrease in the ratio of lumen diameter to wall thickness in arterioles > 50 microns. In addition, there was an overall 30% decrease (p < 0.01) in the ratio of lumen diameter to wall thickness in hypertensive compared with normotensive rats. These data indicate that both hypertension and aging are accompanied by structural alterations of the coronary resistance vasculature. These structural alterations may contribute to the depression in coronary reserve that complicates hypertension and aging.

Aging↗
PubMed1992

Microvascular flow vectors in normal and hypertrophic myocardium as determined by the method of colored microspheres.

Sequential in vivo infusion of two differently colored microsphere suspensions into the left atrium of normal and hypertrophic rat myocardium revealed that certain coronary capillaries contained microsphere aggregates of both colors. A capillary flow vector was established based on the sequence of colors embolized within each aggregate. Critical examination of flow vectors among neighboring capillaries enabled the characterization of capillary flow direction. Results indicated a predominance in concurrent flow direction, which decreased significantly (P less than 0.001) with capillaries further removed from an individual reference capillary. The percentage of concurrent flow was also found to be significantly lower in subendocardium (P less than 0.001) than in midmyocardium. Cardiac hypertrophy was not a contributing factor to the above findings. This study provides previously unattainable data regarding transmural capillary flow direction and suggests regional adaptations in coronary microvascular flow.

Animals↗
PubMed1992

Capillary network geometry during postnatal growth in rat hearts.

To determine the effects of postnatal growth on the coronary microcirculation, the geometry of capillary nets was studied in male rats at 21, 28, 60, and 240 days of age. Tissue sections were exposed to a histochemical technique that distinguished arteriolar (AC) and venular (VC) capillary regions by color. The tissue area (capillary domain) surrounding individual capillaries progressively increased with growth of the heart (P less than 0.01). In all groups, AC domain area was larger than VC domain area (P less than 0.01). The heterogeneity of capillary spacing, which is another important determinant of oxygen supply, demonstrated significant increases with age for AC regions (P less than 0.01). With increasing left ventricular mass, there was a lateral expansion of the arteriovenous capillary set, which was displayed by an increase in the number of and distance between adjacent capillaries that traversed the distance from arteriole to venule (P less than 0.01). Our data indicate that differences in the geometry of arteriolar and VC regions are present by 21 days of age. During postnatal growth, the results from both cross and longitudinal sections suggest that the geometrical conditions for oxygen supply are notably reduced.

Aging↗
PubMed1992

Capillary length, tortuosity, and spacing in rat myocardium during cardiac cycle.

Microvascular geometry was evaluated in rat left ventricular midmyocardium (male Sprague-Dawley, n = 14), arrested in systole (S) or diastole (D), by bolus injections of CaCl2 or KCl, respectively. The histological method employed in this study allowed for the visualization of capillary pathways from arteriole to venule. Capillary length, as directly measured from terminal arteriole to collecting venule, was not significantly different between S and D groups, averaging 606 +/- 15 microns (pooled mean +/- SE). The capillary length tortuosity, defined as the ratio of the capillary length to the direct arteriovenous distance, was significantly increased in systolic-arrested hearts (S = 1.31 +/- 0.03; D = 1.18 +/- 0.02, P < 0.01). At the level of individual capillary segments, however, there was no increase in tortuosity in systolic-arrested hearts (S = 1.17 +/- 0.03; D = 1.16 +/- 0.02). Intercapillary spacing was significantly more uniform in systolic-arrested hearts. These data suggest that in systole, capillary length and tortuosity are generally preserved, and capillary spacing is more uniform, serving to maintain geometric conditions for oxygen supply during the cardiac cycle.

Animals↗