Biomedical subjects

K Rakusan

Publications and source records attributed to K Rakusan.

136 records · Page 8Linked to original sources

PubMedDate not supplied

Cell size and capillary supply of the hypertensive rat heart: quantitative study.

Cardiac mass, cell size and capillary supply were studied in the hearts of spontaneously hypertensive rats (SHR) and compared to genetically similar non-hypertensive Wistar-Kyoto (WKY) of three adult ages: 5, 15 and 23 months. The left ventricular weight of SHR was not significantly greater than that of WKY at 5 months, but was by 15 months and became even more so by 23 months. This increase could be attributed to hypertrophy of the individual cardiac muscle cells and therefore, the estimated total number of myocytes per left ventricle was essentially the same in all experimental groups. Various indices of the myocardial capillary supply were also investigated. Cardiac hypertrophy in older hypertensive rats was characterized by greater and more variable intercapillary spacing, which may have importance in myocardial oxygen supply.

Age Factors↗

PubMedDate not supplied

The influence of potassium depletion on cardiac growth response to pressure overload.

Previous studies have reported that potassium depletion arrests both body and heart growth, and that aortic ligation can induce myocardial potassium loss. To examine the effects of potassium depletion on the cardiac growth response to an increase in pressure load, we induced severe potassium depletion in rats by dietary means for 3 weeks and then subjected them to aortic ligation. 3 weeks following ligation and after a total of 6 weeks of continued potassium deprivation, the animals were sacrificed. Our results show that after aortic ligation the left ventricular weight in potassium depleted rats significantly increased by an average of 155 mg, a value which was somewhat less than the 208-mg increase observed in normokalemic animals. The presence of focal myocardial necrosis in hypokalemic rats, accordingly, did not appear to prevent the increase in ventricular mass induced by augmented pressure load. Furthermore, despite marked reduction in skeletal muscle potassium content there was no decrease in the myocardial potassium content even after aortic ligation. We conclude that profound dietary potassium depletion for a prolonged period of 6 weeks does not impede the cardiac growth response to an increase in pressure load.

Animals↗

PubMedDate not supplied

Aorto-caval fistula in the rat. An experimental model of heart volume overloading.

Abdominal aorto-caval fistula was experimentally induced in rats, and animals were sacrificed 5 days, 1 month, and 6 months later. Cardiac weight almost doubled the normal weight during the first month. Cell length increased to the same extent as the cell width, indicating harmonious growth. Increase in cell volume, as well as the amount of degenerative changes, were more pronounced in subendocardium than in midwall and subepicardium. Cytological features of active cellular growth was found not only in the early stages (5 days and 1 month) but also 6 months after the operation. This finding is consonant with proteosynthesis stimulation not only in the early period of constitution of hypertrophy but also in the later stages.

Animals↗

PubMedDate not supplied

Isoproterenol induced rat endomyocardial damage in relationship to local capillary geometry.

Isoproterenol (2 mg/kg) injected subcutaneously into male Sprague-Dawley rats elicited morphological damage in the endomyocardium which was analyzed 16 h following injection. Our aim was to study the relationship between damaged individual myocytes and their capillary supply. Myocardial tissue sections were differentially stained in order to distinguish arteriolar (AC) and venular (VC) capillary portions. Tissue areas surrounding individual capillaries and the position of the capillaries with respect to the damaged individual myocytes were established by using the method of "capillary domains". In multicellular necrotic lesions 84% of the capillaries located within the necrotic foci and 77% of the capillaries in the surrounding tissue area were identified as the distal, venular portion with presumably low O2 content. The proportion of VCs related to necrotic lesions was significantly higher than in surviving endomyocardial regions. In the case of individual necrotic myocytes, we found 88% to be supplied by VCs, while the adjacent normal myocytes were supplied by 61% VCs. Both values were significantly higher when compared to control hearts (42%). These results strongly support the crucial role of a lack of oxygen delivery in the pathogenesis of isoproterenol-induced necrosis.

Animals↗

PubMedDate not supplied

Geometry of the capillary net in human hearts.

The geometry of the coronary capillary bed in human hearts was studied using samples obtained during cardiac surgery of children operated for tetralogy of Fallot and samples from fresh normal hearts used for valve harvesting. The results revealed a similar coronary capillary density and heterogeneity of capillary spacing in samples from both groups. A double-staining method was used to distinguish between capillary segments close to the feeding arteriole (proximal capillaries) and segments distant from the arteriole (distal capillaries). In both groups of hearts, capillary segment length was consistently shorter on the venular than the arteriolar portion of the capillary. Similarly, capillary domain areas were also smaller and the resulting capillary supply unit was smaller along venular portions compared to arteriolar regions of the capillary bed. This distinctive geometry would provide advantageous geometric conditions for tissue oxygen supply.

Adolescent↗

PubMedDate not supplied

A quantitative analysis of oxygen release due to changes in P50 and venous PO2.

It is almost impossible to estimate the amount of oxygen released from hemoglobin on the basis of the P50 values without calculation, because of the shape of the oxygen dissociation curve. For this reason, we prepared two tables : one indicating the saturation of hemoglobin with oxygen in the venous blood as influenced by venous Po2 and P50 (Table I) and the other, the oxygen release from the arterial blood as influenced by venous Po2 and P50 (Table II). Both tables are based o- the Hill's equation and normal entry data. Values of P50 vary from 20 to 45 torr, while the range for venous Po2 is 5-50 torr. The discussion on possible use of the tables follows.

Arteries↗

PubMedDate not supplied

Regression of cardiomegaly induced in newborn rats.

Pressure overload was induced by banding the abdominal aorta in newborn male rats on day 5. Half of the animals were killed on day 30 while in the remaining animals the aortic band was removed and the rats were killed four weeks later. The banded rats had 2.5 x greater left ventricular mass than their sham-operated controls. This was due to both increased number of myocytes (hyperplasia) and of their increased size (hypertrophy). In the hearts of banded rats, significantly higher concentrations of RNA and hydroxyproline were found together with decreased concentrations of DNA. However, the total DNA content increased as well as the amount of DNA contributed by muscle cell nuclei. In the debanded rats, the mass of the left ventricle remained moderately elevated and contained more myocytes as compared to their age-controls. Similarly, myocardial RNA concentration, total DNA, and the amount of DNA contributed by muscle nuclei remained elevated in contrast to the concentrations of DNA and hydroxyproline which returned to control values. In addition, the percentage of polynucleated myocytes was higher in the hearts from experimental animals.

Animals↗

PubMedDate not supplied

A new look into the microscope: proliferation and regression of myocardial capillaries.

The key to understanding the mechanics of capillary proliferation probably lies in comprehension of the normal capillary growth during the early postnatal period when most of the terminal vessels in mammalian hearts are being formed. Similarly, stimulated cardiac growth is accompanied mainly, but not exclusively, by capillary proliferation if it takes place in the young, growing organism. The opposite situation, decreased capillarization of the heart, is commonly found in several experimental and clinical situations. The cause of lower capillary density is more often due to the growth of capillaries which is slower than the rate of growth of the remaining tissue, rather than to a disappearance of the existing capillaries. This brief review is followed by the discussion of how to evaluate the myocardial capillary supply based on the theoretical analysis of the effect of alterations in capillary surface density on myocardial PO2. The final part deals with confusing teminology in the field, with the following terms discussed in depth: diffusion distance, maximal diffusion distance and hexagonal array.

Animals↗

PubMedDate not supplied

Myocardial capillaries and tissue oxygenation.

The classical tissue model of August Krogh remains the cornerstone in the modeling of tissue PO2. However, heterogeneities of O2 determinants can profoundly affect the calculated oxygen fields. One of them is the heterogeneity in capillary spacing. At the present time there are two methods available for the estimation of capillary spacing: the method of capillary domains and the closest-individual method. The former estimates the distribution of the surface areas surrounding each capillary while the latter derives the distribution of distances of tissue points to the nearest capillary. Both can be transformed into the distribution of the radii of tissue cylinders according to the model of Krogh. Their distribution is approximately lognormal and is characterized by the mean (or median) value and the logarithmic standard deviation (log SD), which serves as the heterogeneity index. When applied to the same photomicrographs, both methods give similar values of the mean but the domain method yields a smaller log SD than does the closest-individual method. Subsequently, the calculated tissue PO2 histograms are also more uniform with the domain method. This difference is caused by the asymmetry of the domains. The shape of the domains is not circular and the capillary is not situated in the center as suggested by the model of Krogh. The method of capillary domains, however, is more direct and less time-consuming and thus more suitable for routine work. Nevertheless, the goal of future research is to develop a method that would characterize not only the distribution of the surface area of the domains but also their asymmetry.

Animals↗

PubMedDate not supplied

Effects of age and isoproterenol on the cardiac output and regional blood flow in the rat.

Heart rate, stroke volume, cardiac output, its distribution and organ blood flows were measured, using the microsphere technique (15 micron in diameter microspheres), in 5, 12 and 24 months old conscious male rats. Each rat was then infused with isoproterenol (0.2 microgram/kg.min) and the measurements were repeated. It was found that resting cardiovascular values do not change within the age range studied, with the exception of the renal blood flow. After infusion of isoproterenol, the heart rate and cardiac output increased in the youngest group while only smaller increase in heart rate and no significant changes in cardiac output were found in the oldest group. Similarly, organ blood flow increased after isoproterenol in all organs studied in the 5 months group, with significance levels reached in the case of blood supply to the right and left ventricles, total heart, skin and carcass. In contrast, infusion of the same dose of isoproterenol in the 24 months old animals did not elicit any significant changes in the regional blood flow. Thus, the response to beta-adrenergic stimulation is depressed with advancing age. This finding of decreased in vivo response to beta-adrenergic stimulation may be a mechanism for the altered cardiovascular performance during stress seen in aged animals and man.

Aging↗