Right Ventricle Of Rats Research Articles

Expression of neural cell adhesion molecule immunoreactivity in hypertrophic myocardium

Myocardial neural cell adhesion molecule (N-CAM) is temporally regulated, being expressed during cardiac morphogenesis and innervation and suppressed in the adult heart. We have investigated the plasticity of N-CAM expression in hypertrophic muscle using the rat model of chronic hypoxia to selectively induce right ventricular hypertrophy over a 14 day time course. Sarcolemmal and intercalated disc N-CAM immunostaining was more extensive in the ventricular myocardium of hypoxic rats compared to normoxic controls. Quantitative assessment of the immunoreactivity in tissue extracts demonstrated a selective increase in the amount of N-CAM immunoreactivity in the hypertrophic myocardium of the right ventricle of rats exposed to hypoxia and this was associated with an increase of the 125 kDa isoform. We conclude that myocardial hypertrophy may be a factor influencing N-CAM expression in the heart and adhesion molecules may have a role in cardiac remodelling.

Differences in load dependence of relaxation between the left and right ventricular myocardium as a function of age in rats.

To determine whether the variation in the magnitude of work load sustained by the left and right ventricles during adulthood and senescence affects the load-dependent aspect of relaxation, posterior papillary muscles from the left and right ventricles of rats at 4, 10, and 20 months of age were studied under variably loaded conditions in vitro. Because of differences between the life spans of Fischer and Sprague-Dawley rats, the functional characteristics of relaxation were investigated to evaluate the possibility of a differential age-associated response in these two strains of animals. The kinetic performance of the diastolic phase of myocardial contraction was measured by assessing the relative time during which load bearing occurred in a series of afterloaded isotonic twitches. This measurement was expressed as the ratio of the duration of afterloaded isotonic shortening and relengthening to the time required for isometric force to decline to the same level during isometric relaxation. A ratio of less than unity identified a load-dependent state whereas a value greater than one reflected a load-independent condition. Results showed that the right myocardium was completely load independent whereas the left myocardium was fully load dependent at all physiological afterloads. Aging reduced the load independence of the right ventricle and the load dependence of the left ventricle in Fischer rats. In contrast, no aging effect on the properties of afterloaded isotonic relaxation was seen in Sprague-Dawley rats. In conclusion, distinct differences exist in the mechanical dynamics of inactivation between the left and right ventricular myocardium. Aging reduced these variations in Fischer rats but had no apparent influence in Sprague-Dawley animals up to 20 months after birth.

Changes in the transmural distribution of glucose-metabolizing enzymes across the left and right ventricular wall of rat heart during growth and ageing

The age-related changes in the activities of five glucose-metabolizing enzymes (hexokinase, HK; glucose-6-phosphate dehydrogenase, G6P-DH; aldolase, ALD; phosphofructokinase, PFK; and lactate dehydrogenase, LDH) were investigated in the walls of left and right ventricles of rats of various age-groups (1–24 months). Age-related changes were found in the activities of all of the enzymes in both ventricles during growth (with significant decreases between 2 and 6 months of age) and in the levels of PFK and LDH in the left ventricle during ageing (with a significant increase between 12 and 24 months of age). The distribution of the enzyme activities across the wall of both ventricles was quite uniform in young, adult and mature rats (the distribution of G6P-DH activity in the left ventricle wall at 2 months of age was the only notable exception) but became non-uniform in the old rats with regard to G6P-DH, PFK, LDH and probably HK in the left ventricle and G6P-DH and HK in the right ventricle. These data support the hypothesis that alterations connected with ageing do not lead to a generalized decline of cardiac metabolic capacity, and that they are also the result of specific adaptive modifications, perhaps related to alteration in the distribution of the work load and/or of nutrition across the ventricular wall.

Sarcomere length 'orders' relaxation in cardiac muscle.

Some microscopic aspects of relaxation were studied in thin, intact heart muscles isolated from the right ventricles of rats. Mean sarcomere length (SL) was observed, and changes in SL distribution inferred by light diffraction from 100 to 300 μm regions of the muscle. Direct feedback or programmed stretch and release allowed suitable control of regional SL. When the muscle was isometric, regional sarcomere shortening and lengthening appeared uniform and synchronous throughout a preparation's undamaged, fully striated 1 to 2 mm midlength. When a preparation's cross-sectional area varied, asynchronies in regional relaxation behavior were seen. However, direct control of regional SL produced contractions similar in shape and duration but varying in strength with the amount of muscle in any region. Uniformity during shortening and its enhancement during late relaxation agreed well with the observed SL force-velocity behavior. There was most often no direct evidence of increased dispersion when the SL was controlled directly, and contractile tension often fell completely without slowing. Whether measured as (1) the fall of tension at constant SL, or (2) the decrease of sarcomere shortening after a load release, the relative speed of relaxation always slowed at longer SL (2.0<SL<2.4 μm). The length-induced slowing of relaxation sometimes revealed a late, abrupt fall in tension followed by an exponential decay. Neither SL nor activation substantially influenced the shape of the rising phase of contraction when SL was held constant. These results indicate a specific well ordered influence of SL on relaxation dynamics. Like the increment of developed tension, the slowing of relaxation at longer SL may reflect an intrinsic property of the contractile lattice, and this feature may promote contractile uniformity in living heart muscle.

Arterial blood gases, muscle fiber diameter and intercapillary distance in cardiac hypertrophy of rats with an old myocardial infarction.

In rats with a myocardial infarction due to ligation of the left coronary artery a marked right ventricular hypertrophy developed after 41/2 weeks. At this time no difference against control animals was observed in arterial\(P_{{\text{O}}_2 }\),\(P_{{\text{CO}}_2 }\), pH, ideal alveolar\(P_{{\text{O}}_2 }\), and alveolar-arterial O2 pressure difference, as measured in unanesthetized animals at normoxia. In histological sections of the heart stained by PAS reaction capillaries and muscle fibers were counted, and the mean intercapillary distance and muscle fiber diameter were estimated. In the right ventricle of the rats with myocardial infarction both increased when compared with control animals or with sham-operated rats. Fibercapillary ratio was the same in all three groups. Similar results were obtained in the remaining undamaged tissue of the left ventricle of rats with a myocardial infarction when compared with the left ventricle of control or sham-operated rats. Findings concerning intercapillary distance suggest that also in the myocardium which remains intact during the development of the infarction and later hypertrophies, tissue oxygen transport might be impaired, particularly during a stress situation. Results in the right ventricle of rats with myocardial infarction show an opposite trend against rats exposed chronically to simulated high altitude, where in the hypertrophied right ventricle a shorter intercapillary distance occurs and therefore an improvement of tissue oxygen transport might be expected.

In vitro contractility of the hypertrophied right ventricle of rats with pulmonary hypertension due to confinement in "hypoxic cages".

Four weeks' confinement of rats in individual airtight cages with walls of defined permeability for respiratory gases induced hypoxic pulmonary hypertension and right ventricular hypertrophy. Parameters of isometric contractility of strips of hypertrophied right myocardium did not show significant changes when compared with the parameters of the inotropic state of slices of normal right ventricle.

Cardiac hypertrophy in the first generation of rats native to simulated high altitude. Muscle fiber diameter and diffusion distance in the right and left ventricle.

In rats born and staying their whole life at a simulated altitude of 3500 m a severe cardiac hypertrophy develops which is most pronounced in the right ventricle. On histological sections muscle fiber and capillary densities were counted and the surfaces occupied by muscle fibers and capillaries in the slides were estimated. Mean muscle fiber diameter and half mean distance between capillaries (diffusion distance) were obtained in the heart ventricles and were compared with those of control animals. In both ventricles an increase of the mean muscle fiber diameter occurred (true hypertrophy), being more pronounced in the right ventricle. We cannot tell whether also hyperplasia of muscle fibers occurred or not. The diffusion distance in the left ventricle of rats exposed to hypoxia was about the same as in control animals but was shorter in the right ventricle. This indicates that the total number of capillaries is higher in both ventricles of rats born in the low pressure chamber (hyperplasia of the capillaries). The shortening of the diffusion distance in the right ventricle of rats born and living their whole life at simulated high altitude was on the average smaller than that of rats exposed to simulated high altitude later in life. The physiological importance of this observation is discussed.

The influence of histone fraction F1 and ATP on the amplitude of contractions of the isolated right ventricle of rats.

L'action de la fraction F1 des histones et de l'ATP sur l'amplitude des contractions a ete examinee sur le ventricule droit des rats blancs. On a constate que l'ATP applique apres l'arret des contractions du a l'histone F1 provoquait la reprise de celles-ci. La presence de l'ATP avant l'application des histones F1 abaisse seulement l'amplitude, mais les contractions persistent jusqu'a la fin de l'experience. L'application simultanee de l'ATP et des histones F1 provoque une inhibition irreversible des contractions ventriculaires.

Technique of permanent cannulation of the right ventricle in rats and ground squirrels.

SummaryRecently a technique for permanent cannulation of the aorta and vena cava was described which permits simultaneous blood sampling and circulatory studies in unanesthetized and undisturbed small animals. To make this technique usable for cardiac output determinations (Fick principle), the venous cannula is now permanently implanted in the right ventricle where mixing of the venous blood is adequate. Two hundred forty-one adult male rats and 61 adult ground squirrels of both sexes were cannulated in this way. Postoperative survival was 100%. The animals regained preoperative body weight after 3.9 days and continued afterwards to grow normally. Except for a few animals in which the cannula slipped from the ventricle into the atrium, the patency of the cannulas seemed to be limited only by the life span of the animal.