Nitric Oxide Donor NOR 3 Inhibits Ketogenesis from Oleate in Isolated Rat Hepatocytes by a Cyclic GMP-Independent Mechanism

Abstract: Studies were conducted to clarify the effects of nitric oxide donors NOR 3 (±)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide, FK409), S1N-1 (3-morpholinosydnonimine) and SNAP (S-nitroso-N-acetylpenieillarnine) on the accumulation of cGMP and cAMP and Ca²⁺ mobilization as well as ketogenesis from oleate in isolated rat hepatocytes. NOR 3 caused inhibition of ketogenesis from oleate along with stimulation of cGMP accumulation in rat hepatocytes, whereas SIN-1 and SNAP exerted no effect on ketogenesis despite their marked stimulation of cGMP accumulation. Although the nitric oxide trapping agent, carboxy-PTIO (2-phenyl-4,4,5,5-tetramethylimidazoline-l-oxyl 3-oxide), antagonized the stimulation by NOR 3 of cGMP accumulation, it failed to modulate the anti-ketogenic action of NOR 3. Furthermore, neither 8-bromoguanosine-3′,5′-cyclic monophosphate nor N²,2′-O-dibutyrylguanosine-3′,5′-cyclic monophosphate mimicked the anti-ketogenic action of NOR 3. It is concluded in the present study that NOR 3-induced inhibition of ketogenesis in rat hepatocytes is not mediated by cGMP. The present study revealed that the remaining structure of NOR 3 from which nitric oxide had been spontaneously released had no anti-ketogenic action. We first and clearly demonstrated that nitrite production was dramatically enhanced when NOR 3 was incubated in the presence of rat hepatocytes. The mechanism whereby NOR 3 inhibits ketogenesis in rat hepatocytes will be discussed.