Inhibitory effect of fentanyl on phenylephrine-induced contraction of the rat aorta

In Vitro Effects of Fentanyl on Aortic Viscoelasticity in a Rat Model of Melatonin Deficiency

Melatonin influences arterial biomechanics, and its absence could cause remodeling of the arterial wall, leading to increased stiffness. Direct effects of fentanyl on the aortic wall have also been observed previously. This study aimed to evaluate in vitro the effects of fentanyl on aortic viscoelasticity in a rat model of melatonin deficiency and to test the hypothesis that melatonin deficiency leads to increased arterial wall stiffness. The viscoelasticity was estimated in strip preparations from pinealectomized (pin, melatonin deficiency) and sham-operated (sham, normal melatonin) adult rats using the forced oscillations method. In the untreated aortic wall pin, the viscoelasticity was not significantly altered. However, combined with 10-9 M fentanyl, the pin increased the natural frequency (f0) and modulus of elasticity (E') compared to the sham-operated. Independently, fentanyl treatment decreased f0 and E' compared separately to untreated sham and pin preparations. The effects of fentanyl were neither dose-dependent nor affected by naloxone, suggesting a non-opioid mechanism. Furthermore, an independent effect of naloxone was also detected in the normal rat aortic wall, resulting in reduced E'. Additional studies are needed that may improve the clinical decisions for pain management and anesthesia for certain patients with co-occurring chronic low levels of blood plasma melatonin and some diseases.

Atomistic Molecular Dynamics Simulations of Propofol and Fentanyl in Phosphatidylcholine Lipid Bilayers

Atomistic molecular dynamics (MD) and steered MD simulations in combination with umbrella sampling methodology were utilized to study the general anesthetic propofol and the opioid analgesic fentanyl and their interaction with lipid bilayers, which is not yet fully understood. These molecules were inserted into two different fully hydrated phospholipid bilayers, namely, dioleoylphosphatidylcholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC), to investigate the effects that these drugs have on the bilayer. We determined the role of the lipid chain length and saturation on the behavior of the two drugs. Pure, fully hydrated DOPC and DPPC bilayers were also simulated, and the results were in excellent agreement with the experimental values. Various structural and mechanical properties of each system, such as the area per lipid, area compressibility modulus, order parameter, lateral lipid diffusion, hydrogen bonds, and radial distribution functions, have been calculated to assess how the drug molecules affect the different bilayers. From the calculated results, we show that fentanyl and propofol generally follow similar trends in each bilayer but adopt different favorable positions close to the headgroup/chain interface at the carbonyl groups. Propofol was shown to selectively form hydrogen bonds at the carbonyl carbon in each bilayer, whereas fentanyl interacts with water molecules at the headgroup interface. From the calculated free-energy profiles, we determined that both molecules show a preference for the low-density, low-order acyl chain region of the bilayers and both significantly preferred the DOPC bilayer with propofol and fentanyl having energy minima at -6.66 and -43.07 kcal mol^-1, respectively. This study suggests that different chain lengths and levels of saturation directly affect the properties of these two important molecules, which are seen to work together to control anesthesia in surgical applications.

Intravital investigation of rat mesenteric small artery tone and blood flow

KEY POINTS

Substantial information on rat mesenteric small artery physiology and pharmacology based on in vitro experiments is available. Little is known about the relevance of this for artery function in vivo. We here present an intravital model where rat mesenteric small artery diameters are studied under isolated and controlled conditions in situ with simultaneous measurement of blood flow. The responses of the isolated arteries vary with the anaesthetic used, and they are quantitatively but not qualitatively different from the responses seen in vitro.

ABSTRACT

Functional characteristics of rat mesenteric small arteries (internal diameter ∼150-200 μm) have been extensively studied in vitro using isometric and isobaric myographs. In vivo, precapillary arterioles (internal diameter < 50 μm) have been studied, but only a few studies have investigated the function of mesenteric small arteries. We here present a novel approach for intravital studies of rat mesenteric small artery segments (∼5 mm long) isolated in a chamber. The agonist-induced changes in arterial diameter and blood flow were studied using video imaging and laser speckle analysis in rats anaesthetized by isoflurane, pentobarbital, ketamine-xylazine, or by a combination of fentanyl, fluanison and midazolam (rodent mixture). The arteries had spontaneous tone. Noradrenaline added to the chamber constricted the artery in the chamber but not the downstream arteries in the intestinal wall. The constriction was smaller when rats were anaesthetized by rodent mixture in comparison with other anaesthetics, where responses were qualitatively similar to those reported in vitro. The contraction was associated with reduction of blood flow, but no flow reduction was seen in the downstream arteries in the intestinal wall. The magnitude of different endothelium-dependent relaxation pathways was dependent on the anaesthesia. Vasomotion was present under all forms of anaesthesia with characteristics similar to in vitro. We have established an intravital method for studying the tone and flow in rat mesenteric arteries. The reactivity of the arteries was qualitatively similar to the responses previously obtained under in vitro conditions, but the choice of anaesthetic affects the magnitude of responses.

Dexmedetomidine Inhibits Phenylephrine-induced Contractions via Alpha-1 Adrenoceptor Blockade and Nitric Oxide Release in Isolated Rat Aortae

The goal of this in vitro study was to examine the effect of the alpha-2 adrenoceptor agonist dexmedetomidine on phenylephrine (alpha-1 adrenoceptor agonist)-induced contraction in isolated rat aortae and to elucidate the associated cellular mechanisms, with a particular focus on alpha-1 adrenoceptor antagonism. Dexmedetomidine dose-response curves were generated in isolated endothelium-intact and endothelium-denuded rat aortae precontracted with phenylephrine or 5-hydroxytryptamine. Endothelium-denuded aortic rings were pretreated with either dexmedetomidine or the reversible alpha-1 adrenoceptor antagonist phentolamine, followed by post-treatment with the irreversible alpha-1 adrenoceptor blocker phenoxybenzamine. Control rings were treated with phenoxybenzamine alone. All rings were repeatedly washed with Krebs solution to remove all pretreatment drugs, including phenoxybenzamine, phentolamine and dexmedetomidine. Phenylephrine dose-response curves were then generated. The effect of rauwolscine on the dexmedetomidine-mediated change in phenylephrine-induced endothelial nitric oxide synthase (eNOS) phosphorylation in human umbilical vein endothelial cells was examined using western blotting. The magnitude of the dexmedetomidine-mediated inhibition of phenylephrine-induced contraction was higher in endothelium-intact aortae than in endothelium-denuded aortae or endothelium-intact aortae treated with N^ω-nitro-L-arginine methyl ester. However, dexmedetomidine did not significantly alter 5-hydroxytryptamine-induced contraction. In further experiments, prazosin attenuated dexmedetomidine-induced contraction. Additionally, pretreatment with either dexmedetomidine plus phenoxybenzamine or phentolamine plus phenoxybenzamine produced greater phenylephrine-induced contraction than phenoxybenzamine alone, suggesting that dexmedetomidine protects aortae from the alpha-1 adrenoceptor blockade induced by phenoxybenzamine. Rauwolscine attenuated the dexmedetomidine-mediated enhancement of phenylephrine-induced eNOS phosphorylation. Taken together, these results suggest that dexmedetomidine attenuates phenylephrine-induced contractions via alpha-1 adrenoceptor blockade and endothelial nitric oxide release in the isolated rat aorta.

The impact of high fructose on cardiovascular system: Role of α-lipoic acid

The aim of this study was to evaluate the role of α-lipoic acid (α-LA) on oxidative damage and inflammation that occur in endothelium of aorta and heart while constant consumption of high-fructose corn syrup (HFCS). The rats were randomly divided into three groups with each group containing eight rats. The groups include HFCS, HFCS + α-LA treatment, and control. HFCS was given to the rats at a ratio of 30% of F30 corn syrup in drinking water for 10 weeks. α-LA treatment was given to the rats at a dose of 100 mg/kg/day orally for the last 6 weeks. At the end of the experiment, the rats were killed by cervical dislocation. The blood samples were collected for biochemical studies, and the aortic and cardiac tissues were collected for evaluation of oxidant-antioxidant system, tissue bath, and pathological examination. HFCS had increased the levels of malondialdehyde, creatine kinase MB, lactate dehydrogenase, and uric acid and showed significant structural changes in the heart of the rats by histopathology. Those changes were improved by α-LA treatment as it was found in this treatment group. Immunohistochemical expressions of tumor necrosis factor α and inducible nitric oxide synthase were increased in HFCS group, and these receptor levels were decreased by α-LA treatment. All the tissue bath studies supported these findings. Chronic consumption of HFCS caused several problems like cardiac and endothelial injury of aorta by hyperuricemia and induced oxidative stress and inflammation. α-LA treatment reduced uric acid levels, oxidative stress, and corrected vascular responses. α-LA can be added to cardiac drugs due to its cardiovascular protective effects against the cardiovascular diseases.