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Effects of phorbol esters, A23187 and vasopressin on oleate metabolism in isolated rat hepatocytes
Author(s) -
Nomura Takahide,
Tachibana Masakatsu,
Nomura Hiroko,
Chihara Masaru,
Hagino Yasumichi
Publication year - 1987
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02540362
Subject(s) - vasopressin , ketogenesis , chemistry , extracellular , metabolism , medicine , calcium , endocrinology , clinical chemistry , phorbol , biochemistry , biology , protein kinase c , enzyme , ketone bodies , organic chemistry
Studies were conducted to compare the metabolic effects of vasopressin, 4β‐phorbol‐12‐myristate‐13‐acetate (PMA) and A23187 on ketogenesis and oleate metabolism in isolated hepatocytes from fed rats. Vasopressin inhibited the formation of acid‐soluble products from [1‐ 14 C]oleate (0.25 mM, 0.5 mM and 1 mM), the inhibition being most marked at low (0.25 mM) concentration of oleate. Conversion of [1‐ 14 C]oleate into 14 CO 2 and esterified products was stimulated by vasopressin. The stimulatory effect of this hormone on 14 CO 2 production was most marked at high (1 mM) concentration of oleate, whereas that on [1‐ 14 C]‐oleate esterification was most marked at low (0.25 mM) concentration of oleate. These vasopressin actions were abolished when hepatocytes were incubated in the absence of calcium in the medium. Our results strongly suggest that both increase in esterification and increase in oxidation to CO 2 contribute to the anti‐ketogenic action of vasopressin when oleate is added as substrate, although the relative extent of their contribution varies according to the oleate concentration. The anti‐ketogenic action of vasopressin was mimicked by PMA but not by A23187. PMA also caused a stimulation of [1‐ 14 C]oleate esterification although the effect was diminished at 1 mM [1‐ 14 C]oleate. A23187 failed to affect [1‐ 14 C]oleate esterification. The metabolic effects of PMA were elicited in the absence of extracellular calcium, too. Conversion of [1‐ 14 C]oleate into 14 CO 2 was only slightly increased by both PMA and A23187 when 1 mM [1‐ 14 C]oleate was added as substrate. The marked stimulatory effect of vasopressin on 14 CO 2 production from [1‐ 14 C]oleate was not reproduced even by the combination of PMA and A23187. The possible involvement of protein kinase C and calcium mobilization in the regulation of oleate metabolism is discussed.