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Biomedical subjects

H Usui

Publications and source records attributed to H Usui.

241 records · Page 14Linked to original sources
PubMedDate not supplied

Relaxations of isolated rabbit coronary artery by purine derivatives: A2-adenosine receptors.

The pharmacological nature of purinoceptors in the rabbit coronary artery was investigated by comparing the extent of vasorelaxation induced by various purine derivatives, with or without amino group at C6 and with or without ribose at N9 in the purine structure. These derivatives were grouped according to structure--adenosine, inosine, adenine, and hypoxanthine analogs. The vasorelaxations produced by adenosine analogs were inhibited by aminophylline, while relaxations produced by the other three groups were unaffected. In the case of adenosine analogs, modification of amino group at C6 to secondary amine resulted in reduction of the potency of the vasorelaxing effect. The order of potency was as follows: adenosine greater than N6-(L)-phenylisopropyladenosine greater than N6-(D)-phenylisopropyladenosine greater than N6-cyclohexyl-adenosine greater than N6-(2,5-dioxo-3-pyrrolidinyl)-adenosine greater than kinetine riboside greater than N6-methyladenosine. On the other hand, the aminophylline-resistant relaxations of adenine analogs were augmented by modification of amino group at C6 to secondary or to tertiary amine. The order of potency was as follows: 6-cyclohexylaminopurine greater than 6-dimethylaminopurine greater than kinetine greater than 6-methylaminopurine adenine. Of adenosine, N6-cyclohexyladenosine, adenine, C6-cyclohexylaminopurine, and inosine, N6-cyclohexylaminopurine was the most potent phosphodiesterase inhibitor of crude enzyme prepared from rabbit aorta. From the order of potency of relaxations produced by adenosine analogs, adenosine receptors in the rabbit coronary artery seem to be of the A2-subtype. The relaxation induced by aminophylline-resistant adenine analogs may be due to activation of an unknown but specific site, since there is a structure-activity relationship in the relaxations produced by this group. Such relaxations may be linked to inhibition of phosphodiesterase in the rabbit coronary artery.

Adenine↗
PubMedDate not supplied

Vasodilation produced by forskolin compared with that produced by adenosine in rabbit coronary artery.

We compared the relaxing action of forskolin with that of adenosine in rabbit coronary artery and analyzed the pharmacological properties of this effect of forskolin. In preparations of this artery precontracted by 10-16 mM KCl, the addition of forskolin (10(-9)-10(-5) M) and adenosine (10(-9)-10(-4) M) to the organ bath produced dose-dependent relaxations. The mean EC50 for the relaxing action of forskolin was 4.5 X 10(-8) M and that of adenosine was 3.6 X 10(-7) M, forskolin being 10 times more potent than adenosine. Relaxation produced by forskolin was not affected by treatment with propranolol (10(-5) M), atropine (10(-6) M), or 8-phenyltheophylline (10(-6) M), but was competitively inhibited by ouabain (10(-6) M). The relaxation produced by adenosine was inhibited by 8-phenyltheophylline (10(-6) M) competitively and by ouabain (10(-6) M) noncompetitively. In preparations precontracted by a higher concentration of KCl, 40 mM, forskolin produced full relaxation with a shift of the dose-response curve to the right; adenosine did not produce full relaxation. Both forskolin and adenosine attenuated the maximum contraction produced by Ca2+. These findings indicate that the vasorelaxing effect of forskolin was not due to activation of beta-adrenoceptors, muscarinic receptors, or adenosine receptors, whereas that of adenosine was due to activation of adenosine receptors. Increased availability of intracellular Ca2+ competitively inhibited the relaxation induced by forskolin and noncompetitively inhibited the relaxation induced by adenosine. Both forskolin and adenosine noncompetitively inhibited contraction induced by Ca2+.

Adenosine↗
PubMedDate not supplied

Characterization of muscarinic cholinergic receptors in human and dog cerebral arteries.

Various concentrations of acetylcholine (ACh) produced dose dependent relaxations of isolated, helical preparations of human cerebral arteries and these responses were blocked by atropine. The median effective concentration (EC50) of ACh was 6.1 +/- 0.2 X 10(-6)M. ACh produced dual responses in isolated dog cerebral arteries. ACh in low concentrations produced relaxation, and contraction occurred when the concentration was raised to 1 X 10(-5)M. The EC50 of ACh which produced relaxation, in dog cerebral arteries was 7.2 +/- 0.2 X 10(-7)M. Muscarinic cholinergic receptors in these arteries were analyzed directly using 3H-QNB as the ligand. The specific 3H-QNB binding to the arteries was saturable and of KD = 1.5 nM and Bmax = 93 fmol/mg protein in human cerebral arteries and KD = 0.59 nM, Bmax = 340 fmol/mg protein in dog cerebral arteries. Specific binding of 3H-QNB was displaced by muscarinic cholinergic agents. Ki values and Hill coefficients were as follows: QNB, 1.0 X 10(-9)M, 0.89; atropine, 1.1 X 10(-8)M, 0.95; ACh, 0.8 X 10(-8)M and 2.1 X 10(-6)M, 0.54; carbachol, 1.2 X 10(-7)M and 4.3 X 10(-5)M, 0.33 in human cerebral arteries and QNB, 0.55 X 10(-9)M, 0.85; atropine 0.9 X 10(-9)M, 1.00; ACh, 0.9 X 10(-9)M and 1.1 X 10(-6)M, 0.43; carbachol 6.3 X 10(-8)M and 1.1 X 10(-5)M, 0.36 in dog cerebral arteries. Endogenous choline acetyltransferase (ChAT) activity was 1.6 +/- 0.4 nmol/mg protein/hr in human cerebral arteries and 3.7 +/- 0.1 nmol/mg protein/hr in dog cerebral arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMedDate not supplied

Percutaneous ethanol injection therapy for hepatocellular carcinoma: validity of MR imaging in the evaluation of treatment effect.

To evaluate the validity of magnetic resonance imaging for the follow-up of percutaneous ethanol injection therapy, 14 patients with a single hepatocellular carcinoma lesion smaller than 2.5 cm in diameter underwent MR imaging at 0.5 Tesla before and after treatment. Posttreatment follow-up examination included ultrasonography, contrast-enhanced computed tomography, and fine-needle biopsy in all cases. Only one patient showed recurrence within the 12-month follow-up period. After treatment, HCC lesions showed hypointensity on T1-, and T2-weighted images that lasted 12 months after treatment. In three cases, wedge-shaped hyperintense regions peripheral to the HCC nodule were observed after treatment on T2-weighted images. Obstructive vasculitis of the portal vein was considered to occur as a result of the drainage of ethanol injected in the tumor. These MR imaging findings may be helpful in clinical practice.

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