B. Ošťádal

Differences in weight parameters, myosin-ATPase activity and the enzyme pattern of energy supplying metabolism between the compact and spongious cardiac musculature of carp (Cyprinus Carpio) and turtle (Testudo Horsfieldi)

Summary1.The compact and spongious musculature of the carp and turtle heart were separated quantitatively. In both parts weight parameters, Ca++-ATPase activity of myosin and an enzyme activity pattern of the energy-supplying metabolism were estimated.2.In the carp, the compact musculature comprises 37% of the total cardiac weight, in the turtle 55%. In both species the weight of the compact layer increases with increasing heart weight.3.The myosin ATPase activity (Ca++-activated) of the compact layer of the carp heart is significantly higher than that of the spongious musculature. No such difference was found in the turtle.4.In the carp heart the activities of enzymes connected with aerobic oxidation (eitrate synthase and malate dehydrogenase) are higher in the spongious musculature as compared with the compact layer. Similar differences were observed for hexokinase representing the capacity of glucose phosphorylation. No such differences were found in the activities of enzymes connected with glycolysis (triosephosphate dehydrogenase, glycerolphosphate dehydrogenase and lactate dehydrogenase).5.In the turtle heart the activities of citrate synthase and hexokinase are also higher in the spongious musculature. However, the percentual difference between the two layers of cardiac musculature for citrate synthase is significantly less in the heart of the turtle than in that of the carp.6.These facts suggest that the compact musculature of the reptilian heart not only plays an increased role in the maintenance of blood pressure balance, but probably also in the more developed cardiac function.

Isoproterenol-induced acute experimental cardiac necrosis in the turtle (Testudo Horsfieldi)

Abstract 1. 1. Administration of isoproterenol to the turtle (Testudo Horsfieldi) in 2 equal doses during 48 hours causes acute necrotic and inflammatory changes in the myocardium. 2. 2. Necroses are mainly localized in the internal spongylike musculature of the heart, which is supplied by diffusion from the ventricular lumen. Necroses are found only exceptionally in the compact musculature supplied by coronary arteries. The changes are morphologically similar to those found in homoiotherms. 3. 3. The incidence of necroses was independent on the seasonal activity of the animals. 4. 4. The fact that necroses are localized in the part of the turtle heart where coronary supply is lacking supports the opinion that the necrogenic action of isoproterenol seems not to be caused solely by vascular mechanism.

Thyroid control of contractile function and calcium handling in neonatal rat heart.

Newborn rats were rendered hyperthyroid (daily subcutaneous injections of L-triiodothyronine, 10 μg 100 g−1 body weight) or hypothyroid (0.05% 6-n-propyl-2-thiouracil in drinking water to nursing mothers) during the first 3 weeks of postnatal life. Compared with the euthyroid group, hyperthyroidism resulted in: (1) cardiac enlargement with right ventricular preponderance, (2) increased cardiac contractile function, (3) increased Ca2+ uptake by the sarcoplasmic reticulum (SR), (4) decreased sensitivity to the negative inotropic effect of verapamil and (5) greater inhibition of contractile function by ryanodine. Hypothyroidism generally resulted in opposite changes. The data suggest that the development of the heart and its contractile function during early postnatal life depends on the plasma level of thyroid hormones. In particular, the relative contribution of the SR and sarcolemmal Ca2+ transport to the control of cardiac contractility seems to be markedly affected by altered thyroid states. The postnatal maturation of the SR function is accelerated in hyperthyroidism but retarded in hypothyroidism. Consequently, hyperthyroid hearts appear to be less dependent and hypothyroid ones more dependent on trans-sarcolemmal Ca2+ fluxes when compared with age-matched euthyroid animals.

Effect of hypoxaemia on enzymes supplying myocardial energy in children with congenital heart disease

The differences in energy metabolism of the myocardium in children with congenital cardiac malformations producing hypoxaemia (arterial oxygen saturation 77 +/- 2%) or normoxaemia (arterial oxygen saturation 94 +/- 2%) were analysed by measuring the activity of the representative energy-supplying enzymes. Right atrial and ventricular tissue samples were obtained during surgical interventions. We demonstrated that myocardial metabolism was significantly influenced by hypoxaemia: the aerobic capacity of the energetic metabolism was reduced both in the atriums and ventricles. Atrial myocardium was more affected: in addition to citrate synthase, the activity of enzymes connected with lactate uptake and carbohydrate catabolism was also significantly decreased. These results demonstrate that the human heart is able to adapt to hypoxaemia by changing its energetic metabolism.

Relative organ blood flow in rats exposed to intermittent high altitude hypoxia.

SummaryCirculating blood volume, cardiac output and relative organ perfusion changes were studied, using the Sapirstein method of86Rb tissue uptake, in male 75-day-old rats exposed to intermittent high altitude hypoxia (gradually up to 7000 m, 4 h daily, 5 days a week; the total number of exposures was 24).Intermittent hypobaric exposure caused a significant rise of the erythrocyte volume, whereas the plasma volume remained unchanged. The relative perfusion of the left and particularly of the right ventricular myocardium, as well as of the spleen, liver, lung, small intestine and skeletal muscle, was significantly higher. The cardiac output determined in other experimental animals similarly treated was significantly higher after 24 exposures to the intermittent high altitude hypoxia. We suggest that these changes are triggered by tissue hypoxia and a greater blood flow demand.

Intermittent high altitude hypoxia — induced structural changes in the pulmonary myocardium in young mice

SummarySeven-day-old mice, strain H, were exposed to intermittent high altitude hypoxia (IHA) in a barochamber (7,000 m, 4 h/day, 5 days a week); a total number of exposures was 10. It has been shown that the layer of cardiac musculature in the adventitia of the pulmonary veins, the so-called pulmonary myocardium, reacts to IHA hypoxia by enlargement even sooner than the right ventricular myocardium. The average thickness of the layer of pulmonary myocardium was significantly greater in animals exposed to IHA hypoxia as compared with the controls. Furthermore, IHA hypoxia induces the extension of the pulmonary myocardium to the periphery of the pulmonary venous bed. Ultrastructural investigation of the pulmonary myocardium in hypoxic animals revealed the presence of unoriented myofïlaments in the peripheral myofïbril-free sarcoplasma, increase in the number of ribosomes and appearance of profiles of granular endoplasmic reticulum. Our data provide quantitative support for the hypothesis that it is not only the contraction of pulmonary arteries, but also venoconstriction which contribute to the hypoxic pressure response in mice.

Effect of Verapamil on Pulmonary Hypertension and Right Ventricular Hypertrophy Induced in Rats by Intermittent High Altitude Hypoxia

Adult male Wistar rats were used for studying the effect of Ca2+ antagonist verapamil on pulmonary hypertension, right ventricular hypertrophy and the medial thickness of pulmonary arterioles, induced by intermittent high altitude (IHA) hypoxia. This was simulated in a hypobaric chamber (7,000, 8 h daily, 5 days a week, 24 exposures). Verapamil was injected subcutaneously in a single dose of 8 mg/kg before each IHA exposure. Administration of verapamil to IHA-exposed animals significantly reduced right ventricular systolic pressure, right ventricular hypertrophy and pulmonary arteriolar medial thickness. Our results support the hypothesis that the transmembrane influx of extracellular calcium is an important component of the mechanisms of hypoxic pulmonary vasoconstriction.

Ontogenetic differences in cardiac sensitivity to verapamil in rats.

SummaryThe degree of a negative inotropic response of the isolated right ventricle to verapamil as well as the mortality rate were studied in rats during their postnatal development. Male Wistar rats aged 3, 15, 30, and 90 days were used. The isolated right ventricle was incubated in a glucose-free solution with a mixture of 95% O2 and 5% CO2 and electrically stimulated. The amplitude of isotonic contractions (AIC) was registered. In 90-day-old rats, AIC was 74.1±6.2% of initial amplitude 45 min after administration of verapamil; in 30-day-old, 41.1±6.4%; in 15-day-old, 38.2±4.1%; and in 3-day-old rats, only 2.6±1.5. The difference between the 3-day-old rats and all older groups was statistically highly significant. The mortality rate of verapamil-treated rats increased with decreasing age of animals. It is concluded that the sensitivity of the rat myocardium to verapamil is age dependent: the negative inotropic effect of this drug increases with decreasing age of the animal. This indicates a possible risk in the therapeutic use of verapamil when given to newborns and infants.

Structural and enzymatic properties of cardiac myosin in ischaemic and non-ischaemic regions of the rat myocardium.

SummaryIn rats with ligation of the left coronary artery changes in ATPase activity and structure of cardiac myosin in both ischaemic and non-ischaemic zones of the myocardium were followed. In control aninals. ATPase activity and the structure of the myosin molecule in right and left ventricles did not differ. Non-specific factors, such as anaesthesia and thoracotomy, can result in a decrease or an increase in ATPase activity respectively.One hour after ligation of the left coronary artery ATPase activity increased in the right, non-ischaemic myocardium and there was a significant right-to-left difference. Four hours after ligation, ATPase activity in both ventricles significantly decreased and the right-left difference disappeared. Within 48 h, normal values were found only in the non-ischaemic right ventricle.Ligation of the left coronary artery results after 48 h in the formation of structural alterations in cardiac myosin, primarily in the left, ischaemic myocardium. These changes are characterised by the formation of myosin aggregates, which have a significantly lower ATPase activity in comparison with monomeric myosin.

The effect of isoprenaline on the phospholipid content of the compact and spongious musculature of the carp ventricular myocardium

1. After a single injection of 40 mg kg-1 of isoprenaline to the carp, lysophospholipids appear in the tissue of the heart ventricle, ethanolamine plasmalogens increase and choline plasmalogens decrease; phosphatidylinositol is lowered in the spongious layer only. 2. Daily administration of 5 mg kg-1 of the drug leads, after 5 doses, to a dramatic decrease of the diphosphatidylglycerol content; during the subsequent 5 and 10 doses a return to normal values occurs. Shifts in plasmalogens are similar to those found after a single high dose. Some other phospholipids change significantly. 3. All changes reveal that the spongious musculature is more sensitive to the drug than the compact one.