| Summary: | 碩士 === 高雄醫學大學 === 醫學研究所 === 89 === During the past decade, various vanilloid-base b-adrenoceptor blockers have been investigated in our laboratory. Among them, labedipinedilol-A, displaying long acting antihypertensive and vasodilatory effects, was suggested to possesses a/b-adrenoceptor and calcium entry blocking activities in one molecule. In our previous study, we found that KMUP 880708, a b-adrenoceptor blocker, with a-adrenoceptors blocking associated vasorelaxant and partial b2-agonist activity associated tracheal relaxant activities.
The phorbol esters, such as phorbol 12-myristate 13-acetate (PMA), are known to be powerful tumor promoters and activators of protein kinase C (PKC). In fact that it represents the direct receptor protein of phorbol esters, substances known to interfere dramatically with proliferative and differentiation events by promoting oncogenic transformation of cells in vivo and in situ. Previous report indicated that labedipinedilol-A was a new generation calcium entry blocker with a/b-adrenoceptor blocking and long-acting antihypertensive properties.
In the present study, we further described the intracellular protein kinase and calcium signalling associated blocking activities of labedipinedilol-A on adrenoceptor and calcium channel. Phorbol 12-myristate 13-acetate (PMA) induced a slow and progressive increase in tension of rat thoracic strips and human saphenous veins. Labedipinedilol-A significantly inhibited PMA induced slowly developing vascular contractility in isolated human umbilical vein and isolated rat thoracic aorta strips and thus indicated these action are related with protein kinase C (PKC) inhibition. PMA-induced intracellular calcium changes of cultured human umbilical vein endothelial cells (HUVEC cells), determined by laser cytometry, was also decreased after administration of labedipinedilol-A (10-8, 10-7, 10-6 M). Cytotoxicity of labedipinedilol-A was evaluated using a growth rate assay quantifying cell number by tetrazolium dye reduction. PMA-induced cell growth of the HUVEC cells was inhibited by labedipinedilol-A. The expression of PKC activities in cytosol and membrane extracts of A7r5 (rat aorta smooth muscle of thoracic aorta) cells and HUVEC cells were also compared. The results indicated that treatment of HUVEC cells with PMA for 30 min leading to translocation of specific PKC isozymes from the cytosol to the membrane. Pretreatment of these cells with and labedipinedilol-A (10-6, 10-7, 10-8 M) affect above changes.
KMUP 880708, newly synthesized from a series of vanilloid, is a antihypertensive agent with a- and b-adrenoceptor blocking activities. The autonomic and antihypertensive activities of KMUP 880708 were studied in conscious rats. Single oral administration of KMUP 880708 (10, 25, 50 mg/kg) in conscious spontaneously hypertensive rats and deoxycorticosterone acetate (DOCA) hypertension rats, produced a dose-dependent hypotensive and bradycardia responses. In sodium pentobarbitol-anesthetized spontaneously hypertensive rats, KMUP 880708 (0.1, 0.5, 1.0, 2.0 mg/kg, i.v.) produced dose-dependent hypotensive and bradycardia responses. Respectively, these finding clearly indicated that the compound inhibits both b- and a-adrenoceptors to almost the same extent in agreement with previously reported results in normotensive rats.
In conclusion, our results suggested that labedipinedilol-A appeared to cause inhibition of PKC translocation induced by PMA; its actions on cardiovascular system may be regulated by cellular cytosol and membrane PKC activities. KMUP 880708 may inhibit cell growth by regulating cytosolic PKC and preventing its membrane translocation and activation.
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