Continuous axial contraction wave in the free wall of the guinea pig left ventricle

We studied the variation from the simultaneous contraction of the normal left ventricle (LV). The pattern of the contraction along the LV long axes was assessed on the LV free wall on seven guinea pig hearts in situ with ultra fast video system and epicardial markers by means of the latitude and the size of the areas defined by markers. We found that the contraction occurs as a continuous contraction wave from the apex towards the base, which might yield functional adaptation of these two regions to diastolic and systolic function, respectively.     

实验性急性心肌缺血的早期形态学指标探讨

对犬和兔的冠状动脉分别形成不同程度的机械性狭窄和药物性痉挛1小时,观察冠状动脉狭窄后急性心肌缺血的早期形态学改变,探讨其形态学诊断标准。结果表明:光镜下急性早期缺血性改变为心肌细胞嗜伊红增强和较具特征性的心肌纤维波浪状变和收缩带形成。轻度波浪状变电镜下仅见轻度线粒体肿胀;重度波浪状变线粒体肿胀明显,嵴断裂、溶解消失、空泡变,肌原纤维肿胀、变性或断裂。波浪状变和收缩带并存时,Z线增宽,肌节呈节段性疑聚,形成典型之“竹根样”或“竹节样”改变。作者认为,轻度心肌纤维波浪状变不足以说明为心肌缺血性改变;重度波浪状变可作为早期心肌缺血的形态学指标;若波浪状变同时伴有收缩带形成时,表明心肌缺血程度严重。     

A review on static splinting therapy to prevent burn scar contracture: Do clinical and experimental data warrant its clinical application?

Background

Static splinting therapy is widely considered an essential part in burn rehabilitation to prevent scar contractures in the early phase of wound healing. However, scar contractures are still a common complication. In this article we review the information concerning the incidence of scar contracture, the effectiveness of static splinting therapy in preventing scar contractures, and specifically focus on the – possible – working mechanism of static-splinting, i.e. mechanical load, at the cellular and molecular level of the healing burn wound.

Method

A literature search was done including Pubmed, Cochrane library, CINAHL and PEDRO.

Results

Incidence of scar contracture in patients with burns varied from 5% to 40%. No strong evidence for the effectiveness of static splinting therapy in preventing scar contracture was found, whereas in vitro and animal studies demonstrated that mechanical tension will stimulate the myofibroblast activity, resulting in the synthesis of new extracellular matrix and the maintenance of their contractile activity.

Conclusion

The effect of mechanical tension on the wound healing process suggests that static splinting therapy may counteract its own purpose. This review stresses the need for randomised controlled clinical trials to establish if static splinting to prevent contractures is a well-considered intervention or just wishful thinking.     

Nitric oxide induces acetylcholine-mediated contractions in the guinea-pig small intestine

In longitudinal muscle/myenteric plexus preparations of the guinea-pig ileum, exogenous nitric oxide (NO) induced concentration-dependent relaxations. In tissues at basal tone, NO (3 × 10^–6 M) induced a moderate relaxation followed by a pronounced contraction, consisting of a quick and sustained component. Tetrodotoxin (5 × 10^–7 M) abolished both phases of the contraction. Atropine (5 × 10^–7 M) abolished the quick component and reduced the sustained component of the contraction; the latter was further suppressed by the selective NK₁ receptor antagonist CP 96,345. Hexamethonium (5 × 10^–5 M) failed to affect the contractile response to NO. It is concluded that administration of exogenous NO in the guinea-pig ileum can lead to activation cholinergic and to a lesser degree tachykininergic neurones. Correspondence to: L. Barthó at the above address     

The reactivity of isolated venous preparations to electrical stimulation

Summary The reactivity of spiral strips and isolated segments of the lateral saphenal vein of the dog was investigated. In a first series of experiments the influence of progressively increasing distension on the isotonic or isometric reactions of both preparations to a constant electrical stimulation was examined. It appeared that in every case the reaction first increases with progressive distension. Whenever the venous wall becomes overstretched, the amplitude of the reaction diminishes gradually. In a second series of experiments, spiral strips and isolated segments were prepared from the same veins and their sensitivity to increasing stimulation frequencies tested at the optimal point of their distension-reaction relation, both in isotonic and isometric conditions. From these experiments it appeared that the isotonic preparations are more sensitive than the isometric, and that the sensitivity of the isolated segment is also greater than that of the spiral strip.     

Effects of the Na ionophore monensin on the contractile response and the movements of monovalent cations in the vascular smooth muscle of rabbit aorta

Summary The effects of monensin, a Na ionophore, on the muscle contraction and the movements of monovalent cations were investigated in rabbit aorta. Experiments were conducted in the presence of phentolamine (10^–6 M) to avoid the vasoactive effect of monensin due to the release of endogenous catecholamine. Both monensin (2×10^–5 M) and ouabain (2×10^–5 M), added separately, produced a small and slowly developing contraction, whereas simultaneous application of these agents produced more rapid and greater contraction. Verapamil (10^–6 M) decreased the contraction by 75%. Ouabain gradually increased cellular Na content. Monensin augmented the ouabain-induced Na increase. Further, the loss of cellular Na into Na deficient solution was enhanced by monensin. Low temperature (0.5°C) inhibited the monensin-induced increase in Na permeability. The relaxation of noradrenaline-contraction induced by a K-readmission was inhibited by ouabain but not by monensin. These results suggest that monensin increases Na movement down its electrochemical gradient, augments cellular Na accumulation when the Na pump is inhibited by ouabain, and induces muscle contraction, and that the contraction induced by monensin and ouabain is mainly due to an increased Ca influx through voltage sensitive Ca channels.     

Raised uterine resting tone in patients with abruptio placentae

Uterine contractions were studied in 21 patients with abruptio placentae and intrauterine death. Contractions were examined in four 10-minute windows taken immediately prior to delivery, 30 and 60 minutes before delivery and at the beginning of the recording. Mean resting tone values for the 4 periods fluctuated between 23 and 25 mmHg. The mean contraction frequency for all the windows was 8 per 10 minutes. It is postulated that the high resting tone and frequent uterine contractions contribute to the high perinatal mortality associated with abruptio placentae.     

Electrophysiologic correlates of the inotropic effects of Isoproterenol in canine myocardium

The action of l-isoproterenol was studied in isolated canine papillary muscles. The simultaneous action potential and contraction traces were first recorded in digital form on magnetic tape and later measured and analyzed by a computer program. The data were controlled and grouped to permit a three-way analysis of variance in order to test significant effects and correlations. Complete dose-response curves were performed both before and after beta-adrenergic blockade with (±)propranolol. It was demonstrated that isoproterenol produced and increase in the peak potential, the height and duration of the plateau (phase 3), and the rate of repolarization of the action potential (phase 4). Corresponding increases in peak tension, time to peak tension, rate of tension development, and rate of relaxation of the contraction were noted. At the highest isoproterenol concentrations, occasional after-potentials and after-contractions occurred. The changes in the action potential were explained by changes in the inward calcium current, while the inotropic effect on the contraction was attributed to the resulting increase in intracellular calcium concentration. These effects were all blocked by the addition of propranolol, but the blockade could be overcome by increasing the isoproterenol concentration of the perfusate.     

Effects of chronic diabetes mellitus on the electrical and contractile activities,45Ca2+ transport,fatty acid profiles and ultrastructure of isolated rat ventricular myocytes

The effects of chronic experimental diabetes on electrophysiological properties, contractile behavior,⁴⁵Ca²⁺ transport, fatty acid profiles and ultrastructural characteristics were studied in enzymatically dissociated ventricular myocytes. Diabetes was induced in rats by streptozotocin administration and animals were killed 8–10 weeks later. Myocytes from diabetic rats exhibited electrical behavior similar to that of myocytes from control rats, but their contractile properties were altered. Their sensitivity of the twitch contractions to various positive and negative inotropic agents (isoproterenol, norepinephrine, phenylephrine, acetylcholine, ouabain and veratridine) was greatly diminished. However, a part of the contractile response (the tonic, sustained contractions) were increased in the diabetic myocytes, indicating that the changes are not caused by a decreased sensitivity of myofilaments. Furthermore, the diabetic myocytes exhibited also significant decrease in total Ca²⁺ content. The fatty acid profile in the diabetic group was changed mainly in that there were slightly elevated levels of docosahexaenoic acid and diminished levels of palmitic acid. The ultrastructure of the diabetic myocytes was affected only slightly. These investigations offer for the first time a comprehensive picture of changes related to diabetic cardiomyopathy as they occur at the level of cardiomyocytes.     

The effects of isoprenaline and tyramine on the 45calcium uptake,the total calcium content and the contraction force of isolated guinea-pig atria in dependence on different extracellular hydrogen ion concentrations

Summary Isolated, electrically stimulated left guinea-pig atria were incubated at 30° C in a Tyrode solution, the hydrogen ion concentration of which was varied by altering the percentage of the aerating CO₂/O₂-mixture. The increase of the extracellular hydrogen ion concentration from pH 8.0 to pH 7.0 caused a reduction of the ⁴⁵calcium uptake and of the contraction force. The positive inotropic effect and the concomitantly occuring increased ⁴⁵calcium uptake induced by isoprenaline and tyramine were markedly diminished at the lower pH, the response to tyramine being more affected by increased hydrogen ion concentration than that of isoprenaline. This is possibly due to a decrease in noradrenaline available at pH 7.0 for release by tyramine. Isoprenaline and tyramine enhanced the relative specific ⁴⁵calcium activity (RSA) without altering the total tissue calcium content. On the contrary, the increase of the extracellular calcium concentration caused an augmentation of the relative specific ⁴⁵calcium activity and the total tissue calcium content.A preliminary report of this paper was presented at the 12^th meeting of the Deutsche Pharmakologische Gesellschaft: Noack et al., 1971.Supported by the Deutsche Forschungsgemeinschaft.