Role of L-type calcium channels in altered microvascular responses to propofol in hypertension

5-Aminolevulinic acid hydrochloride enhances bupivacaine-induced hypotension in spontaneously hypertensive rats

PURPOSE

Oral administration of 5-aminolevulinic acid hydrochloride (5-ALA-HCl) has been reported to enhance the hypotensive effects associated with anesthetics, especially in elderly hypertensive patients treated with antihypertensive agents. The present study aimed to clarify the effects of antihypertensive-agent- and anesthesia-induced hypotension by 5-ALA-HCl in spontaneously hypertensive rats (SHRs).

METHODS

We measured blood pressure (BP) of SHRs and normotensive Wistar Kyoto (WKY) rats treated with amlodipine or candesartan before and after administration of 5-ALA-HCl. We also investigated the change in BP following intravenous infusion of propofol and intrathecal injection of bupivacaine in relation to 5-ALA-HCl administration.

FINDINGS

Oral administration of 5-ALA-HCl significantly reduced BP in SHRs and WKY rats with amlodipine and candesartan. Infusion of propofol significantly reduced BP in SHRs treated with 5-ALA-HCl. Intrathecal injection of bupivacaine significantly declined SBP and DBP in both SHRs and WKY rats treated with 5-ALA-HCl. The bupivacaine-induced decline in SBP was significantly larger in SHRs compared with WKY rats.

CONCLUSION

These findings suggest that 5-ALA-HCl does not affect the antihypertensive agents-induced hypotensive effect, but enhances the bupivacaine-induced hypotensive effect, especially in SHRs, indicating that 5-ALA may contribute to anesthesia-induced hypotension via suppression of sympathetic nerve activity in patients with hypertension.

Amlodipine Improves Vessel Function and Remodeling in the Lewis Polycystic Kidney Rat Mesenteric Artery

BACKGROUND

Hypertension is a common comorbidity associated with chronic kidney disease (CKD). Treatment in these patients often involves L-type Ca2+ channel (LTCC) blockers. The effect of chronic LTCC-blockade treatment on resistance vasculature was investigated in a genetic hypertensive rat model of CKD, the Lewis Polycystic Kidney (LPK) rat.

METHODS

Mixed-sex LPK and Lewis control rats (total n = 38) were allocated to treated (amlodipine 20 mg/kg/day p.o. from 4 to 18 weeks) and vehicle groups. Following systolic blood pressure and renal function assessment, animals were euthanized and mesenteric vasculature was collected for functional and structural assessment using pressure myography and histology.

RESULTS

Amlodipine treatment reduced LPK rat blood pressure (untreated vs. treated: 185 ± 5 vs. 165 ± 9 mm Hg; P = 0.019), reduced plasma creatinine (untreated vs. treated: 197 ± 17 vs. 140 ± 16 µmol/l; P = 0.002), and improved some vascular structural parameters (internal and external diameters and wall-lumen ratios); however wall thickness was still increased in LPK relative to Lewis despite treatment (Lewis vs. LPK: 31 ± 2 vs. 41 ± 2 µm, P = 0.047). Treatment improved LPK rats' endothelium dysfunction, and nitric oxide-dependent and endothelium-derived hyperpolarization vasorelaxation components, and downregulated prostanoid contributions. LTCC blockade had no effect on biomechanical properties of compliance and intrinsic stiffness, nor artery wall composition.

CONCLUSIONS

Our results indicate that blockade of LTCCs with amlodipine is effective in improving, to a certain extent, detrimental structural and functional vascular features of resistance arteries in CKD.

Propofol induces the elevation of intracellular calcium via morphological changes in intracellular organelles, including the endoplasmic reticulum and mitochondria

Propofol, most frequently used as a general anesthetic due to its versatility and short-acting characteristics, is thought to exert its anesthetic actions via GABA_A receptors; however, the precise mechanisms of its adverse action including angialgia remain unclear. We examined the propofol-induced elevation of intracellular calcium and morphological changes in intracellular organelles using SHSY-5Y neuroblastoma cells, COS-7 cells, HEK293 cells, and HUVECs loaded with fluorescent dyes for live imaging. Although propofol (>50 μM) increased intracellular calcium in a dose-dependent manner in these cells, it was not influenced by the elimination of extracellular calcium. The calcium elevation was abolished when intracellular or intraendoplasmic reticulum (ER) calcium was depleted by BAPTA-AM or thapsigargin, respectively, suggesting that calcium was mobilized from the ER. Studies using U-73122, xestospongin C, and dantrolene revealed that propofol-induced calcium elevation was not mediated by G-protein coupled receptors, IP3 receptors, or ryanodine receptors. We performed live imaging of the ER, mitochondria and Golgi apparatus during propofol stimulation using fluorescent dyes. Concomitant with the calcium elevation, the structure of the ER and mitochondria was fragmented and aggregated, and these changes were not reversed during the observation period, suggesting that propofol-induced calcium elevation occurs due to calcium leakage from these organelles. Although the concentration of propofol used in this experiment was greater than that used clinically (30 μM), it is possible that the concentration exceeds 30 μM at the site where propofol is injected, leading the idea that these phenomena might relate to the various propofol-induced adverse effects including angialgia.

Constriction of Retinal Venules to Endothelin-1: Obligatory Roles of ETA Receptors, Extracellular Calcium Entry, and Rho Kinase

Purpose

Endothelin-1 (ET-1) is a potent vasoconstrictor peptide implicated in retinal venous pathologies such as diabetic retinopathy and retinal vein occlusion. However, underlying mechanisms contributing to venular constriction remain unknown. Thus, we examined the roles of ET-1 receptors, extracellular calcium (Ca²⁺), L-type voltage-operated calcium channels (L-VOCCs), Rho kinase (ROCK), and protein kinase C (PKC) in ET-1-induced constriction of retinal venules.

Methods

Porcine retinal venules were isolated and pressurized for vasoreactivity study using videomicroscopic techniques. Protein and mRNA were analyzed using molecular tools.

Results

Retinal venules developed basal tone and constricted concentration-dependently to ET-1. The ET_A receptor (ET_AR) antagonist BQ123 abolished venular constriction to ET-1, but ET_B receptor (ET_BR) antagonist BQ788 had no effect on vasoconstriction. The ET_BR agonist sarafotoxin S6c did not elicit vasomotor activity. In the absence of extracellular Ca²⁺, venules lost basal tone and ET-1–induced constriction was nearly abolished. Although L-VOCC inhibitor nifedipine also reduced basal tone and blocked vasoconstriction to L-VOCC activator Bay K8644, constriction of venules to ET-1 remained. The ROCK inhibitor H-1152 but not PKC inhibitor Gö 6983 prevented ET-1-induced vasoconstriction. Protein and mRNA expressions of ET_ARs and ET_BRs, along with ROCK1 and ROCK2 isoforms, were detected in retinal venules.

Conclusions

Extracellular Ca²⁺ entry via L-VOCCs is essential for developing and maintaining basal tone of porcine retinal venules. ET-1 causes significant constriction of retinal venules by activating ET_ARs and extracellular Ca²⁺ entry independent of L-VOCCs. Activation of ROCK signaling, without involvement of PKC, appears to mediate venular constriction to ET-1 in the porcine retina.

Sevoflurane may be more beneficial than propofol in patients receiving endoscopic variceal ligation and endoscopic variceal sclerotherapy: A randomized, double-blind study

The aim of the present study was to evaluate the safety and efficacy of various general anesthesia regimens during endoscopic variceal ligation (EVL) and endoscopic variceal sclerotherapy (EVS). A total of 123 patients with American Society of Anesthesiologists physical status III and IV, aged 40-70 years, undergoing general anesthesia for EVL and EVS were randomly divided into two groups: Sevoflurane anesthesia (group S; n=60) and propofol anesthesia (group P; n=60). Vital signs, particularly heart rate (HR) and mean arterial pressure (MAP), were monitored. The designated time points were as follows: 5 min before induction (T0), and 1, 5, 10, 15, 20, 25 and 30 min after intubation (T1, T2, T3, T4, T5, T6 and T7, respectively). Time intervals were recorded, including recovery time and extubation time. Following surgery, the observer recorded the Ramsay sedation scale (RSS) score and the visual analogue scale (VAS) score. Adverse reactions were noted. Results demonstrated that there were significant differences in MAP between the two groups at T2, T3, T5, T6 and T7 (P<0.05). There was a significant difference in HR between the two groups at T2, T3 and T4 (P<0.05). Recovery time and extubation time in group P were significantly longer than those in group S (P<0.05; 18.38±2.25 min vs. 14.57±1.04 min and 21.70±2.70 min vs. 15.83±0.88 min, respectively). The rate of ephedrine injected was 58.3% (35/60 patients) in group P vs. 28.3% (17/60 patients) in group S (P<0.05). There was a significant difference in the RSS score between the two groups 5 min after extubation (P<0.05). VRS scores demonstrated that anesthetists and patients were significantly more satisfied with the procedure in group S than in group P (P<0.01). In conclusion, the superiority and special clinical value of inhalational anesthesia has been demonstrated during EVL and EVS attributed to stable hemodynamics and high quality of anesthesia recovery in the present study.

Propofol induces excessive vasodilation of aortic rings by inhibiting protein kinase Cβ2 and θ in spontaneously hypertensive rats

BACKGROUND AND PURPOSE

Exaggerated hypotension following administration of propofol is strongly predicted in patients with hypertension. Increased PKCs play a crucial role in regulating vascular tone. We studied whether propofol induces vasodilation by inhibiting increased PKC activity in spontaneously hypertensive rats (SHRs) and, if so, whether contractile Ca²⁺ sensitization pathways and filamentous-globular (F/G) actin dynamics were involved.

EXPERIMENTAL APPROACH

Rings of thoracic aorta, denuded of endothelium, from normotensive Wistar-Kyoto (WKY) rats and SHR were prepared for functional studies. Expression and activity of PKCs in vascular smooth muscle (VSM) cells were determined by Western blot analysis and elisa respectively. Phosphorylation of the key proteins in PKC Ca²⁺ sensitization pathways was also examined. Actin polymerization was evaluated by differential centrifugation to probe G- and F-actin content.

KEY RESULTS

Basal expression and activity of PKCβ2 and PKCθ were increased in aortic VSMs of SHR, compared with those from WKY rats. Vasorelaxation of SHR aortas by propofol was markedly attenuated by LY333531 (a specific PKCβ inhibitor) or the PKCθ pseudo-substrate inhibitor. Furthermore, noradrenaline-enhanced phosphorylation, and the translocation of PKCβ2 and PKCθ, was inhibited by propofol, with decreased actin polymerization and PKCβ2-mediated Ca²⁺ sensitization pathway in SHR aortas.

CONCLUSION AND IMPLICATIONS

Propofol suppressed increased PKCβ2 and PKCθ activity, which was partly responsible for exaggerated vasodilation in SHR. This suppression results in inhibition of actin polymerization, as well as that of the PKCβ2- but not PKCθ-mediated, Ca²⁺ sensitization pathway. These data provide a novel explanation for the unwanted side effects of propofol.

Quinapril decreases antifibrinolytic and prooxidative potential of propofol in arterial thrombosis in hypertensive rats

Angiotensin converting enzyme inhibitors and propofol both exert hypotensive action and may affect hemostasis. We investigated the influence of quinapril and propofol on hemodynamics and hemostasis in renal-hypertensive rats with induced arterial thrombosis. Two-kidney, one clip hypertensive rats were treated with quinapril (3.0 mg/kg for 10 days), and then received propofol infusion (15 mg/kg/h) during ongoing arterial thrombosis. The hemodynamic and hemostatic parameters were assayed. Quinapril exerted a hypotensive effect increasing after propofol infusion. Quinapril showed an antithrombotic effect with the platelet adhesion reduction, fibrinolysis enhancement and oxidative stress reduction. Propofol did not influence thrombosis; however, it inhibited fibrinolysis and showed prooxidative action. The effect of propofol on fibrinolysis and oxidative stress was significantly lower in quinapril-pretreated rats. Mortality was increased among rats treated with both drugs together. Our study demonstrates that pretreatment with quinapril reduced the adverse effects of propofol on hemostasis. Unfortunately, co-administration of both drugs potentiated hypotension in rats, which corresponds to higher mortality.

Different effects of propofol and isoflurane on cochlear blood flow and hearing function in Guinea pigs

Objectives

To investigate the effects of isoflurane and propofol on mean arterial pressure (MAP), cochlear blood flow (CoBF), distortion-product otoacoustic emission (DPOAE), and the ultrastructure of outer hair cells (OHCs) in guinea pig cochleae.

Methods

Forty-eight male guinea pigs were randomly assigned to one of six treatment groups. Groups 1 to 3 were infused (i.v.) with a loading dose of propofol (5 mg/kg) for 5 min and three maintenance doses (10, 20, or 40 mg kg⁻¹·h⁻¹, respectively) for 115 min. Groups 4 to 6 were inhaled with isoflurane at concentrations of 1.15 vol%, 2.30 vol% or 3.45 vol% respectively for 120 min. CoBF and MAP were recorded prior to and at 5 min intervals during drug administration. DPOAE was measured before, immediately after, and 1 h after administration. Following the final DPOAE test, cochleae were examined using scanning electron microscopy.

Results

Propofol treatment reduced MAP in a dose-dependent manner. CoBF and DPOAE showed increases at propofol maintenance doses of 10 and 20 mg kg⁻¹·h⁻¹. Inhalation of isoflurane at concentrations of 2.30 vol% and 3.45 vol% reduced MAP and CoBF. DPOAE amplitude increased following inhalation of 1.15 vol% isoflurane, but decreased following inhalations of 2.30 vol% and 3.45 vol%. Cochlear structure was changed following inhalation of either 2.30 vol% or 3.45 vol% isoflurane.

Conclusions

Propofol could decrease MAP and increase both CoBF and DPOAE without affecting OHC structure. Inhalation of isoflurane at concentrations >2.30 vol% decreased CoBF and DPOAE, and produced injury to OHCs.