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Biomedical subjects

K Takeya

Publications and source records attributed to K Takeya.

At least 109 records · Page 6Linked to original sources
PubMed1987

Mode of cardiotonic action of helenalin, a sesquiterpene lactone, on guinea pig ventricular myocardium.

We investigated the mechanisms of the direct positive inotropic effect (PIE) of helenalin, a sesquiterpene lactone isolated from the plant genus Helenium of the family Compositae in guinea pig ventricular myocardium. Helenalin (3 X 10(-4) M) produced biphasic PIEs (first and second PIE phases) on normal nonreserpinized papillary muscles, driven at 1 Hz in Krebs-Henseleit solution at 30 degrees C. The first PIE phase was abolished by reserpine treatment. Helenalin increased the force of "rested-state contraction" in a manner similar to that of other cyclic AMP-elevating substances, such as norepinephrine and IBMX (3-isobutyl-1-methylxanthine). In isometric contraction curves of the papillary muscle stimulated at 0.2 Hz, helenalin showed two clear peaks of an early and a late component. Carbachol preferentially suppressed the late component of contraction, a component that is clearly apparent in the presence of intracellular cyclic AMP-increasing substances. Helenalin potentiated the PIEs of isoproterenol and histamine but not that of dihydroouabain. In the presence of a phosphodiesterase (PDE) inhibitor (IBMX 10(-3) M), helenalin did not produce any PIE. In electrophysiological studies, helenalin prolonged the duration of transmembrane action potentials of papillary muscle. In partially depolarized muscles (external K+ = 30 mM), helenalin increased the overshoot and the duration of the slow action potential. These results led to the conclusion that helenalin produces an elevation of cyclic AMP through PDE inhibition, thereby increasing Ca2+ influx which enhances the contractility of the myocardium by increasing Ca2+ release from the SR.

Action Potentials↗
PubMed1987

[Studies on cardiac ingredients of plants (IV). Effect of reduced proscillaridins on guinea-pig hearts].

Five hydrogenated proscillaridins (bufa-4,20-dienolide (PH21), bufa-4,20 (22)-dienolide (PH22), 20R-bufa-4-enolide (PH4-R), 20S-bufa-4-enolide (PH4-S), chola-4-enoate (PH4-E) ) were prepared semi-synthetically, and their pharmacological effect was studied using guinea pigs. The positive inotropic effect (PIE) was examined in papillary muscles isolated from guinea-pig hearts. These compounds produced PIE, dose-dependently; the Dose-PIE curve was characterized by a faster PIE development than that by the parent compound proscillaridin (PS). The concentrations at which half maximum PIE just developed (pD2) were as follows: PS, 7.4; PH22, 6.2; PH21, 5.8; PH4-R, 5.3; PH4-E, 5.0; and PH4-S, 4.9. The time required to the half maximum effect (T50) at a given concentration of pD2 was measured in min: PS, 33; PH4-E, 22; PH22, 15; PH21, 7; PH4-S, 7; and PH4-R, 2. The speeds of inotropy of these compounds depended on the position of lactone ring reduction, though they have the same lipophilicity (Rm). Concentration-PIE curves of reduced PS-compounds were characterized by a decrease in potency and an increase in efficacy. PH21 and PH4-R produced PIE over wider range of concentrations than those of the other compounds. When PH21 at the dose of 11.9 mg/kg, an equivalent dose of 4.4 times the pD2 values, was administrated intravenously by bolus injection into guinea pigs, no arrhythmias were observed on the ECG.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Cardiovascular effects of NPK-1886, a new dihydropyridine compound with calcium entry blocking activity.

The cardiovascular effect of NPK-1886 (NPK), a novel photostable dihydropyridine compound, was studied by comparing it with that of nifedipine (Nif). In normal Wistar rats (NWR), systolic blood pressure was only slightly depressed by NPK or Nif, while in three types of hypertensive rats (i.e., spontaneously hypertensive rats (SHR), renal hypertensive rats (RHR) and DOCA-saline-induced hypertensive rats (DOC-Na-R)), the hypotensive potency of NPK was more than or equal to that of Nif. The effectiveness of NPK on the normal and hypertensive models was in the following order: DOC-Na-R, RHR, SHR, NWR. Coronary perfusion flow in Langendorff's heart was increased almost the same extent by NPK and Nif. On isolated rabbit aortic strips, the antagonistic potencies of NPK, like those of Nif, were greater for calcium than for norepinephrine, serotonin and angiotensin II. The negative ino- and chronotropic potency of NPK in isolated guinea-pig right atria was less than that of Nif. The slow membrane action potentials of guinea-pig papillary muscle were suppressed by NPK, but less than by Nif, with manifestations of a reduction of Vmax and AP-duration. These results indicate that NPK has a potent hypotensive effect on hypertensive models and a weaker cardiac inhibition. The general toxicity of NPK was lower than that of Nif.

Action Potentials↗
PubMed1984

Lysogenicity and prophage type of the strains of Vibrio cholerae O-1 isolated mainly from the natural environment.

Attention has recently been given to the increasingly frequent detection of atypical Vibrio cholerae O-1 in the natural environments throughout the world. Lysogenicity of V. cholerae O-1, mainly isolated from environmental sources in nine areas, including the United States, was studied by electron microscopy and a cross-lysis test between bacteria and the culture supernatants. A total of 38 strains isolated in Texas in 1973 and in Louisiana in 1978 were lysogenic, whereas there were no lysogenic strains among those isolated in Louisiana in 1979. Because these phages were identical in terms of serology and host range, the phage in them was named T-L phage. T-L phage differed in host range from the k type phage in the epidemic strain of the seventh cholera pandemic. Although the T-L phage was neutralized by antiserum to the k type phage and vice versa, the two phage types were not serologically identical. By a prophage typing method, strains of V. cholerae O-1 isolated from the environment in Guam, Bangladesh, and Japan were classified as either of the Celebes type (epidemic strain) or the Classic-Ubon type. All strains isolated in Brazil, the Chesapeake Bay, and England were nonlysogenic and classified as Classic-Ubon type.

Bacteriophage Typing↗
PubMed1984

Relationship between the inotropy speeds in guinea-pig myocardium and lipophilic character of cardenolides and ericaceous toxins.

Interrelation between lipophilic characters and speeds of positive inotropic effect (PIE) of cardenolides and ericaceous toxins was studied by determining both parameters of lipophilicity and inotropy speeds. The lipophilic characters of 8 kinds of cardenolides, evaluated from Rm or log k' values by means of thin layer chromatography (Rf) or high performance liquid chromatography (retention time), increased in the order of ouabain, digoxin, digitoxigenin, digitoxigenin-monodigitoxoside, digitoxigenin-bis-digitoxoside, digitoxin, alpha-acetyl-digitoxin, triacetyl-digitoxin. Lipophilic character, evaluated from Rm values of 6 kinds of ericaceous toxins, was in decreasing order of 10S-grayanotoxin II, 6-acetyl grayanotoxin I, asebotoxin I, grayanotoxin I, asebotoxin III, asebotoxin X. The speed with which PIE developed was evaluated from the time to half maximum PIE (T50) of cardenolides and ericaceous toxins at a pD2 concentration. The speed of positive inotropy of cardenolides was independent of their concentration tested in the range from half to twice the concentration of pD2, while the speeds of PIE of ericaceous toxins depended on their concentration in the same range used in case of cardenolides. Inotropy speed of these two classes of cardiotoxins correlated well with the lipophilic character: a) In the case of cardenolides, a positive and close correlation (r = 0.98) was observed between T50 and Rm. The more lipophilic the cardenolides, the more time was required to reach the fully development of PIE. b) In contrast, a negative correlation (r = -0.82, between Rm and T50) was obtained in the case of ericaceous toxins; Toxins with more lipophilic nature caused faster development of PIE. The present results can be interpreted to mean that the PIE receptor for cardenolides in myocardial cells is located on the outer surface of the sarcolemma, while that for ericaceous toxins is located on the inside of the myocardial cell.

Animals↗