Lipofundin MCT/LCT Inhibits Levcromakalim-Induced Vasodilation by Inhibiting Endothelial Nitric Oxide Release

Abstract

The goal of this study was to examine the effect of lipid emulsion on the vasodilation induced by ATP-sensitive potassium (KATP) channels in isolated rat aortae and the underlying mechanism. The effects of Intralipid, containing 100% long-chain fatty acids, and Lipofundin MCT/LCT, containing 50% long-chain fatty acids plus 50% medium-chain fatty acids, on the vasodilation induced by levcromakalim in endothelium-intact aorta with or without NW-nitro-L-arginine methyl ester (L-NAME) and in endothelium-denuded aorta were examined. The effects of L-arginine, L-NAME, glibenclamide, and Lipofundin MCT/LCT, alone or combined, on the levcromakalim-induced vasodilation were examined. Lipofundin MCT/LCT inhibited the levcromakalim-induced vasodilation of isolated endothelium-intact aortae, whereas Intralipid did not. In addition, Lipofundin MCT/LCT had no effect on the levcromakalim-induced vasodilation of endothelium-denuded rat aortae and endothelium-intact aortae with L-NAME. L-arginine and Lipofundin MCT/LCT produced more levcromakalim-induced vasodilation than Lipofundin MCT/LCT alone. Glibenclamide inhibited levcromakalim-induced vasodilation. Levcromakalim did not significantly alter endothelial nitric oxide synthase phosphorylation, whereas Lipofundin MCT/LCT decreased cyclic guanosine monophosphate. Lipofundin MCT/LCT did not significantly alter levcromakalim-induced membrane hyperpolarization. Taken together, these results suggest that Lipofundin MCT/LCT inhibits the vasodilation induced by levcromakalim by inhibiting basally released endothelial nitric oxide, which seems to occur through medium-chain fatty acids.

Lipid Emulsion Enhances Vasoconstriction Induced by Dexmedetomidine in the Isolated Endothelium-Intact Aorta

“…Similar to the findings of previous reports, LE (1%) enhanced the DMT-induced maximal contraction of the endothelium-intact aorta ( Figure 2 A), whereas L-NAME pretreatment abolished LE (1%)-mediated enhancement of the DMT-induced contraction of the endothelium-intact aorta ( Figure 3 A), suggesting that LE (1%)-mediated enhancement of the DMT-induced contraction was caused by inhibition of NO synthesis, which seemed to be associated with the decreased concentration of DMT caused by LE [ 17 , 20 ]. As LE alone reduces NO synthesis, the complete separation of indirect (reduction of DMT concentration) and direct effect (direct inhibition of DMT-induced eNOS phosphorylation) of LE contributing to the inhibition of NO synthesis induced by DMT, was very difficult to achieve in our study ( Figure 10 ) [ 17 , 21 ]. The high concentration of LE (3%) decreased DMT-induced contraction of the endothelium-denuded aorta and endothelium-intact aorta pretreated with L-NAME ( Figure 2 B and Figure 3 A,B).…”

“…Additionally, similar to the LE-mediated enhancement of the DMT-induced contraction in the endothelium-intact aorta ( Figure 2 A and Figure 3 A) via inhibition of NO synthesis, LE reverses both the increased stimulatory eNOS (Ser1177) phosphorylation and the decreased inhibitory eNOS (Thr495) phosphorylation induced by DMT ( Figure 6 A,B), leading to decreased NO release and cGMP formation ( Figure 5 ). This effect seems to be mainly associated with the absorption of DMT by LE and partially caused by direct inhibition of NO release ( Figure 10 ) because LE alone decreases cGMP formation [ 21 ]. Src kinase inhibitor PP2 attenuated the increased stimulatory eNOS (Ser1177) phosphorylation and the decreased inhibitory eNOS (Thr495) phosphorylation induced by DMT ( Figure 8 A,B), suggesting that DMT-induced eNOS (Ser1177 and Thr495) phosphorylation is mediated by Src kinase.…”

Nitric oxide-dependent vasodilation induced by minoxidil in isolated rat aorta

“…However, other in vitro studies have suggested that minoxidil-induced vasodilation is endothelium independent (Spokas et al 1983;Meisheri et al 1988). Hence, the role of endothelial NO on minoxidil-induced vasodilation seems controversial (Spokas et al 1983;Meisheri et al 1988;Kontos and Wei 1996;Kinoshita et al 1999;Lee et al 2020). Therefore, we investigated whether minoxidil-induced vasodilation is mediated by endothelial NO.…”

“…Male Sprague-Dawley rats (body weight: 250-300 g) were anesthetized with 100% carbon dioxide, administered via a small hole in the rat cage. Isolated rat aorta was used for measuring isometric tension; it was prepared as described previously (Lee et al 2020). The rat thoracic cavity was exposed and the descending thoracic rat aorta of each rat was removed from the thoracic cavity and immersed in Krebs solution, composed of NaCl (118 mM), NaHCO 3 (25 mM), glucose (11 mM), KCl (4.7 mM), CaCl 2 (2.4 mM), MgSO 4 (1.2 mM), and KH 2 PO 4 (1.2 mM).…”

“…Levcromakalim induces vasodilation via the activation of K ATP channels of vascular smooth muscle and partially by endogenous nitric oxide (NO)-induced activation of K ATP channels. This suggests that endothelial NO additively contributes to vasodilation mediated by levcromakalim, an K ATP channel agonist (Kinoshita et al 1999;Flagg et al 2010;Lee et al 2020). In an in vivo study, nitro-L-arginine, a nitric oxide synthase (NOS) inhibitor, inhibited minoxidil-induced vasodilation of cerebral arterioles (Kontos and Wei 1996).…”