Studies on the mechanism of action of the bipyridine milrinone on the heart

Summary Milrinone is a positive inotropic and vasodilator agent when tested in experimental animals and in human heart-failure patients. It is generally believed that milrinone acts by inhibiting phosphodiesterase IV, thus increasing cyclic AMP, [Ca^{+ +}]_i and cardiac contractile force and relaxation. Maximal force produced by milrinone is greater when single-dose response curves are compared to cumulative dose-response curves. In vitro, milrinone produces a tachyphylaxis, the extent of which is both dose- and time-dependent. Recovery of tachyphylaxis is both dose- and time-dependent and is not influenced by inhibitors of protein or RNA synthesis. There is a specific cross-tachyphylaxis between milrinone and amrinone, theophylline, papaverine, and Bay K8644. This tachyphylaxis may explain the low maximal contractile response of the cumulative dose-response observed in isolated tissues. Milrinone increased cyclic AMP in dog and guinea pig cardiac muscle. As previously shown by Endoh et al. [17], milrinone in low doses produced a biphasic effect on cyclic AMP. The early increase (first 60–70 s) in cyclic AMP shows a good correlation with contractile force changes. If cyclic AMP is determined at maximal contractile force this correlation was poor. Here we also present instances where the increase in cyclic AMP after milrinone (determined at maximal effect) does not correlate with the contractile response. The cross-tachyphylaxis of milrinone with Bay K8644 suggests that milrinone has an action on the sarcolemmal Ca⁺⁺ channels. Bay K8644 suppresses the positive inotropic effect of catecholamines by 50%, but not the cyclic AMP response. The inotropic effect of milrinone, in contrast to norepinephrine is highly sensitive to [Ca⁺⁺]₀, stimulation rate, and [K⁺]₀. In this respect milrinone behaves more like Bay K8644. We postulate that the main inotropic action of milrinone is due to a sarcolemmal effect. The early cyclic AMP production described could be in the sarcolemmal compartment and this may explain some of the similarities of milrinone’s actions with those of Bay K8644. The tachyphylaxis observed with the inotropic effect of milrinone does not extend to the decreases in relaxation time. This and other findings to be discussed suggest that the positive inotropic and reduction in relaxation time by milrinone depend on different mechanisms, possibly through differential compartmentalization of cyclic AMP.     

锌对心肌保护作用机理的探讨

应用电镜、电子示踪技术和立体计量测试法，从形态学上观察异丙基肾上腺素对心肌膜系统的影响及锌的保护作用，同时应用标准玻璃微电极技术和微机实时分析方法，研究异丙基肾上腺素致心肌损伤及锌对心肌保护作用的机理。实验结果表明：异丙基肾上腺素可引起心肌细胞膜系统损伤，此时心肌细胞的去极化和复极化过程均发生改变；经锌前处理后，心肌损伤程度明显减轻，心肌细胞的复极化过程得到明显改善。锌对心肌的保护作用，主要是通过阻断心肌细胞膜慢通道、减少平台期钙离子内流、防止细胞内钙超载来实现。     

Study on the Compression Effect of Clothing on the Physiological Response of the Athlete

The study aimed to analyze whether the high compression of unique, tight-fitting sportswear influences the clothing physiology comfort of the athlete. Three specific sportswear with different compression were tested on four subjects while they were running on a treadmill with increasing intensity. The compression effect of the sportswear on the body of the test persons, the temperature distribution of the subjects, and the intensity of their perspiration during running were determined. The results indicate that the compression effect exerted by the garments significantly influences the clothing physiology comfort of the athlete; a higher compression load leads to more intense sweating and higher skin temperature.     

Data on the spread of Culex pipiens on the territory of the USSR]

A map of Culex pipiens molestus distribution over the USSR was made using data of sanitary epidemiological stations of various regions of the country, literature and the authors' own data. It was shown that during the last decades (1978-1990) the Cx. p. molestus breeding occurring predominantly in flooded basements of comfortable houses, especially in new built towns and cities, was recorded throughout the European part of the USSR including some subarctic regions. Cx. p. molestus is also widespread in the Asiatic part of the country including Western and Eastern Siberia, southern regions of Far East and the Sakhalin Island and Kamchatka. In the permafrost areas, most of new houses are built on piles without basements and cellars, and it prevents Cx. p. molestus breeding. The dates of appearance of these mosquitos in various parts of the country due to the development of transportation are discussed.     

丙硫咪唑对囊尾蚴糖原作用的观察

猪囊尾蚴于体外经驱虫药丙硫味唑在0,20,50,100μg/ml和96小时作用后,进行了组织化学观察。对照组囊尾蚴的糖原分布在头颈部和外囊壁上,颈部区糖原分布较均匀,外囊壁糖原较多。实验各组头颈部糖原均有减少,而外囊壁糖原无显著变化。     

Comments on the effect of variations in the size of the heart on the magnitude of ECG potentials

Utilizing a mathematical model of the inhomogeneous torso, the effect of variations in the size of the heart on the amplitude of the surface potential is studied. The results show that incases of congestive heart failure, low potentials may result in spite of the cardiomegaly. This can be explained by the increased lung conductivity due to edema.