Modulation of cyclothiazide on the glutamate receptor/NO/cyclic GMP pathway in the hippocampus of freely-moving rats

通过活体微透析的方法研究了环噻嗪对大鼠海马谷氨酸受体／ＮＯ／ｃＧＭＰ通路的影响．局部灌流α－氨基羟甲基异唑丙酸（ＡＭＰＡ）受体脱敏阻断剂环噻嗪能引起细胞外ｃＧＭＰ水平的提高．环噻嗪的这种作用能够被ＮＯ合酶抑制剂Ｎ－硝基－Ｌ－精氨酸（Ｌ－ＮＮＡ）或选择性的可溶性鸟苷酸环化酶抑制剂１Ｈ－［１，２，４］二唑［４，３－ａ］喹喔啉－１－酮（ＯＤＱ）所阻断．在环噻嗪灌流过程中，大鼠呈现明显的痉挛前的行为变化湿狗样反应（ＷＤＳ）．由环噻嗪引起的ｃＧＭＰ增加和ＷＤＳ反应能够被Ｎ－甲基－Ｄ－天冬氨酸（ＮＭＤＡ）受体通道阻断剂甲基二苯并环庚烯亚胺（ＭＫ－８０１）或镁离子所阻断．ＡＭＰＡ受体拮抗剂６，７－二硝基喹喔啉－２，３－二酮（ＤＮＱＸ）和２，３－二羟基－６－硝基－７－氨磺酰基－苯并（ｆ）－喹喔啉（ＮＢＱＸ）可拮抗ＷＤＳ反应，但不能阻断环噻嗪引起的ｃＧＭＰ反应．这种结果表明：（１）在海马内与ＮＯ－ｃＧＭＰ通路有关的ＡＭＰＡ受体由于内源性谷氨酸的存在保持部分脱敏状态．（２）环噻嗪对ＡＭＰＡ受体脱敏的阻断作用可导致内源性ＮＭＤＡ受体的激活．     

环噻嗪对大鼠海马谷氨酸受体/NO/cGMP通路的调节

通过活体微透析的方法研究了环噻嗪对大鼠海马谷氨酸受体/NO/cGMP通路的影响. 局部灌流α- 氨基羟甲基异噁唑丙酸(AMPA)受体脱敏阻断剂环噻嗪能引起细胞外cGMP水平的提高. 环噻嗪的这种作用能够被NO合酶抑制剂N-硝基-L-精氨酸(L-NNA)或选择性的可溶性鸟苷酸环化酶抑制剂1H-［1，2，4］噁二唑［4，3-a］喹喔啉-1-酮(ODQ)所阻断. 在环噻嗪灌流过程中，大鼠呈现明显的痉挛前的行为变化--湿狗样反应(WDS). 由环噻嗪引起的cGMP增加和WDS反应能够被N-甲基-D-天冬氨酸(NMDA)受体通道阻断剂甲基二苯并环庚烯亚胺(MK-801)或镁离子所阻断. AMPA受体拮抗剂6，7-二硝基喹喔啉-2，3-二酮(DNQX)和2，3-二羟基-6-硝基-7-氨磺酰基 苯并(f)- 喹喔啉(NBQX)可拮抗WDS反应，但不能阻断环噻嗪引起的cGMP反应. 这种结果表明：（1）在海马内与NO-cGMP通路有关的AMPA受体由于内源性谷氨酸的存在保持部分脱敏状态.（2）环噻嗪对AMPA受体脱敏的阻断作用可导致内源性NMDA受体的激活.     

Effects of angiotensin II receptor blockers on renal handling of uric acid in rats

Elevated serum uric acid level has been associated with increased cardiovascular risk in hypertensive patients. Several angiotensin II receptor blockers exhibit differential effects on regulation of serum uric acid level in humans. We have demonstrated that some angiotensin II receptor blockers trans-stimulate the uptake of uric acid by human URAT1 and others inhibit the transport of uric acid mediated by human URAT1, OAT1, OAT3 and MRP4 in vitro. This study investigated the effects of candesartan, pratosartan and telmisartan on renal handling of uric acid in rats in vivo and in vitro. Candesartan (0.1 mg/kg) significantly decreased the urinary excretion of uric acid and increased the plasma uric acid concentration. The kidney candesartan level after low-dose treatment is close to that required to trans-stimulate uric acid uptake in vitro. Pratosartan exhibited dose-dependent hypouricemic and uricosuric effects, while telmisartan showed no effects on plasma uric acid level. Furthermore, we confirmed the effects of the tested drugs on uric acid transport by rat renal brush border membrane transporter(s) and basolateral Oat1 and Oat3. Effects of angiotensin II receptor blockers in rats may be mainly determined by their intrinsic effects (cis-inhibition and trans-stimulation) on uric acid reabsorption transporter(s) and their pharmacokinetic properties in rats.     

Adrenomedullin inhibits the pressor effects and decrease in renal blood flow induced by norepinephrine or angiotensin II in anesthetized rats.

Adrenomedullin (AM), a hypotensive peptide originally isolated from human pheochromocytoma, has been reported to regulate renal functions. In patients with glomerulonephritis, the serum levels of AM are elevated as well as hypertensive agents norepinephrine (NE) and angiotensin II (AII). The effects of AM on the NE- or AII-induced pressor effects and renal blood flow responses, however, are not well clarified. We examined the effects of AM on blood pressure and renal blood flow induced by NE or AII in anesthetized rats. Arterial blood pressure and renal blood flow were measured using a calibrated pressure transducer and a laser Doppler flowmeter, respectively. Drugs were injected into the tail vein with a syringe. Intravenous administration of AM (1-3 nmol/kg) decreased the arterial blood pressure in anesthetized rats in a dose-dependent manner, whereas it did not affect the renal blood flow. NE or AII administration in anesthetized rats caused both increases in blood pressure and decreases in renal blood flow. Simultaneous administration of AM with NE or All prevented the increasing effects of blood pressure and inhibited the decreases in renal blood flow caused by NE or AII. These findings suggest that AM may have a protective role against the pressor effects and decrease in renal blood flow caused by NE or AII.     

A newly found angiotensin II receptor subtype mediates cyclic GMP formation in differentiated Neuro-2A cells.

In search of the functional role of the newly found angiotensin II (Ang II) binding site which is expressed in differentiated Neuro-2A cells, we found that Ang II causes a marked stimulation of cGMP formation dose-dependently. The stimulation was blocked by the nonselective Ang II receptor antagonist [Sar1,Ile8]Ang II but not by the AT1 antagonist DuP 753 or the AT2 antagonist PD 123319. These results suggest that Ang II increased cGMP level via a new Ang II receptor subtype in differentiated Neuro-2A cells.     

Effects of endothelin on renal function and renin secretion in anesthetized rats

The infusion of endothelin into the renal artery of anesthetized rats at 1 ng/kg per min, a dose with no influence on renal function, had no effect on the basal levels of plasma renin activity (PRA) and renin secretory rate (RSR), but significantly inhibited the isoproterenol-induced increases in PRA and RSR. Endothelin, 2 ng/kg per min, elicited significant decreases in renal hemodynamics and in urine formation but the mean arterial pressure was not affected. The possibility that endothelin may participate in controlling renal function and renin secretion in vivo warrants further attention.     

The stimulation of human neutrophil migration by angiotensin II: its dependence on Ca2+ and the involvement of cyclic GMP

1. Angiotensin II had a bimodal effect on human neutrophil migration. Low concentrations of angiotensin II stimulated random migration. At a concentration of 10⁻¹⁰ M it caused a maximal increase of migration; migration increased from 47.2±2.1 μm in the absence of angiotensin II, to 73.1±2.2 μm with 10⁻¹⁰ M angiotensin II present in the lower compartment of the Boyden chamber (n=5, P<0.001). Stimulation of migration by angiotensin II was partly chemotactic and partly chemokinetic. Angiotensin II concentrations of 10⁻⁸ M and higher inhibited chemotactic peptide-stimulated chemotaxis.
2. The stimulant effect of angiotensin II on migration was completely dependent on extracellular Ca²⁺. In the presence of 1 mM Ca²⁺, angiotensin II stimulated migration to 76.1±1.7 μm, while migration in the absence of Ca²⁺ was 42.2±1.9 μm (n=4, P<0.001). Different types of calcium channel blockers either moderately or strongly inhibited angiotensin II-activated migration. Stimulation of migration by angiotensin II in intact cells required higher concentrations of Ca²⁺ than in electroporated cells. This supports the view that there is an influx of Ca²⁺ through the plasma membrane, and a requirement of calcium for an intracellular target.
3. Angiotensin II-stimulated migration was inhibited by pertussis toxin; from 71.6±2.0 μm in the absence, to 43.6±1.5 μm in the presence of pertussis toxin (n=4, P<0.001). Migration of electroporated neutrophils stimulated by angiotensin II was synergistically enhanced by GTPγS. This suggests that one or more G-proteins are involved in the activating effect of angiotensin II.
4. Inhibitors of soluble guanylate cyclase and antagonists of cyclic GMP-dependent kinase strongly inhibited the activating effect of angiotensin II. The results suggest that the activating effect of angiotensin II is mediated by cyclic GMP and by cyclic GMP-dependent kinase.

     

Imbalance between the endothelial cell-derived contracting factors prostacyclin and angiotensin II and nitric oxide/cyclic GMP in human primary varicosis

1. The role of the endothelium in the vasomotor control of human veins in the lower extremity is little understood. We tested the hypothesis that the production of relaxing and contracting factors is altered in endothelial cells from varicose saphenous veins which may predispose to the decreased vessel tone observed in primary varicosis.
2. We determined the intracellular accumulation of guanosine 3′:5′-cyclic monophosphate cyclic GMP; a measure of nitric oxide production) and the release of endothelin and prostacyclin (measured as its stable metabolite 6-keto-prostaglandin F_1α) from cultured cells derived from the long saphenous veins of patients with primary varicosis (Varicose saphena group, n=27) or from patients undergoing coronary artery bypass surgery (Healthy saphena group, n=22). In addition, levels of endothelin, angiotensin II, bradykinin, cyclic GMP and cyclic AMP in plasma from patients with primary varicosis and healthy volunteers (n=8–11 in each group) were determined.
3. Although basal cyclic GMP levels were similar, more cyclic GMP accumulated in response to histamine (1–100 μmol l⁻¹) in cells from varicose saphenous veins (0.75±0.1 pmol per well) than in cells from veins without varicosis (0.27±0.05 pmol per well). Furthermore, the relaxant potency of nitroprusside (1 nmol l⁻¹–300 μmol l⁻¹) in vitro was higher for varicose veins (mean EC₅₀=5.9 μmol l⁻¹; n=8) than healthy veins (mean EC₅₀=20.0 μmol l⁻¹; n=7).
4. The production of prostacyclin was significantly less in cells from varicose than healthy saphenous veins (66±8.7 and 121±20.1 nmol g⁻¹ protein), but the production of endothelin was similar in both groups. Prostacyclin (3 nmol l⁻¹–30 μmol l⁻¹) consistently contracted rings of varicose saphenous vein in vitro with a mean EC₅₀ value of 10–20 μmol l⁻¹ (n=7); the maximum tension generated was ∼50% of that of a completely depolarizing solution of K⁺ (120 mmol l⁻¹).
5. In plasma from patients with varicose veins, levels of cyclic GMP were higher than in healthy controls (9.2±0.03 and 7.2±0.02 nmol l⁻¹), levels of angiotensin II were lower (81±11.5 and 147±21.7 pmol l⁻¹), and levels of endothelin, cyclic AMP, and bradykinin were not different.
6. It is concluded that endothelial cells from diseased saphenous veins secrete less constrictor mediators than cells from healthy veins and that in diseased veins the nitric oxide/cyclic GMP system is up-regulated which may shift the balance of vasoactive factors towards vasodilatation and contribute to the development of primary varicosis.

     

NO/cyclic GMP pathway mediates the relaxation of feline lower oesophageal sphincter

1. We examined the role of the NO/cyclic GMP (cyclic GMP) pathway in nitric oxide (NO)- and vasoactive intestinal peptide (VIP)-induced relaxation of feline lower oesophageal sphincter (LES). Furthermore, it was studied whether methylene blue, LY83583 and ODQ, which are soluble guanylate cyclase (sGC) inhibitors, could inhibit NO-induced relaxation. 2. The nitric oxide synthase (NOS) inhibitor, N omega-nitro-L-arginine (L-NNA) had no effect in sodium nitropruside (SNP)-induced relaxation, but 3-morpholinosydnonimine-N-ethylcarbamide (SIN-1)-induced relaxation was decreased by the pretreatment of L-NNA, which showed that SIN-1, not SNP, could activate NOS to cause relaxation. Methylene blue and LY83583 did not inhibit the relaxation by SNP and SIN-1. However, the more specific sGC inhibitor ODQ blocked the relaxation induced by NO donors. 3. To identify the relationship of NOS, sGC and adenylate cyclase in VIP-induced relaxation, tissue were pretreated with L-NNA and ODQ and SQ22536. These inhibitors produced significant inhibition of this response to VIP. The adenylyl cyclase inhibitor SQ 22536 also inhibited relaxation by VIP. 4. In conclusion, our data showed that SNP- and SIN-1-induced relaxation was mediated by sGC. Of sGC inhibitors, methylene blue and LY83583 were not adequate for the examination of NO donor-induced feline LES smooth muscle relaxation. VIP also caused relaxation by the pathway involving NO and cGMP and cAMP.     

Effects of NKH477 on renal functions and cyclic AMP production in anesthetized dogs.

The present study was undertaken to evaluate the effects of an adenylate cyclase activator N,N-dimethyl-beta-alanine[3R-(3alpha, 4alphabeta, 5beta, 6beta, 6aalpha, 10alpha, 10abeta, 10balpha)]-5(acetyloxy)-3-ethenyldodecahydro-10, 10b-dihydroxy-3, 4a, 7, 7, 10a-pentamethyl-1-oxo-1H-naphtho [2,1-b] pyran-6-yl ester hydrochloride (NKH477) on renal functions and cyclic AMP production in the dog kidney. The intrarenal arterial infusion of NKH477 (30, 100 and 300 ng kg(-1) min(-1)) increased renal blood flow, glomerular filtration rate, urine flow rate, urinary Na+ and cyclic AMP excretion, fractional Na+ excretion and arterial and renal venous plasma cyclic AMP concentrations in a dose-dependent manner. The intrarenal arterial infusion of rolipram (0.3 microg kg(-1) min(-1)), a cyclic AMP-specific phosphodiesterase inhibitor, also caused the same renal responses as NKH477. The increasing effects of NKH477 on renal blood flow, fractional Na+ excretion and renal venous plasma cyclic AMP concentration were facilitated in the presence of rolipram. NKH477 reduced glomerular filtration rate and filtration fraction in the presence of rolipram. The increasing effects of NKH477 on urine flow rate and urinary Na+ excretion were not affected by rolipram. The present results suggest that NKH477 increases glomerular filtration and suppresses tubular sodium reabsorption through activation of cyclic AMP production, and thereby induces natriuresis. The results also demonstrate that renal cyclic AMP level during the activation of adenylate cyclase is regulated by phosphodiesterase IV in both the vascular and tubular sites.     

Effects of inhaled 1,1,1-trichloroethane on the regional brain cyclic GMP levels in mice and rats

As it is known that volatile organic compounds (VOCs) exhibit differential dispositions among anatomically discrete brain regions in rodents as well as in humans, potential toxicological consequences of this pharmacokinetic feature were evaluated using measurements of cyclic GMP (glucose monophosphate). With the knowledge of 1, 1, 1-trichloroethane (TRI) uptake and distribution in the various brain regions, cyclic GMP was evaluated due to (1) known susceptibility to the effects of organic solvents, (2) pivotal physiological role in perpetuating changes in neurochemical pathways, and (3) possible involvement with neurobehavioral functions, whose disruption is one of the primary health effects associated with solvent exposures. Male CD-1 mice and Sprague-Dawley rats inhaled 5000 ppm TRI for 40 and 100 min in dynamic inhalation exposure chambers, and the brain was procured from the animals immediately following termination by microwave irradiation. After 40 min of TRI inhalation, significant decreases in cyclic GMP levels were found in the cerebellum of both species, 55% and 58%, respectively, relative to the controls. There was a further decrease in both species after 100 min of TRI inhalation. Smaller decreases in cyclic GMP were seen in the cortex of both species at both time points of measurement. A decrease in cyclic GMP was observed in the medulla oblongata of mice but not in rats after 40 min of exposure. Due to its signal transduction functions, it might be expected that the effects of TRI on cyclic GMP levels could directly impact neurological function. Comparison of the results from this study with the regional brain distribution of TRI and its effects on behavioral performance seen in previous studies by this laboratory appeared to indicate that alterations in brain cyclic GMP levels are only involved with the neurobehavioral toxicity of TRI in an indirect fashion; consequently, behavioral effects and decreases in cyclic GMP do not appear to be directly related to regionally differential dispositions of TRI in rodent brain.     

Role of phosphodiesterases III and IV in the modulation of vascular cyclic AMP content by the NO/cyclic GMP pathway.

1. The effect on cyclic nucleotide contents of selective inhibitors of cyclic nucleotide phosphodiesterase (PDE) isoforms III and IV (respectively SK&F 94120 and rolipram) and their interactions with endothelium and NO have been studied in rat aorta in the presence of indomethacin (10 microM). The participation of NO was assessed by using either NG-nitro-L-arginine methyl ester (L-NAME) (NO synthase inhibitor: 30 microM) or 3-morpholinosydnonimine (SIN-1, NO donor: 10 microM with SOD 100 units ml-1). 2. The presence of endothelium significantly increased both adenosine 3':5'-cyclic monophosphate (cyclic AMP, 1.7 fold) and guanosine 3':5'-cyclic monophosphate (cyclic GMP, 2.2 fold) contents. Cyclic GMP was largely affected by L-NAME or SIN-1 treatment, this was not the case for cyclic AMP suggesting that the presence of endothelium modified cyclic AMP content in aorta independently of the NO production. 3. In the presence or absence of endothelium, neither SK&F 94120 nor rolipram, alone or combined, significantly modified cyclic GMP content. 4. The PDE III inhibitor significantly affected cyclic AMP content only in non treated aorta without endothelium. In contrast, the PDE IV inhibitor increased cyclic AMP in all conditions. These increases were generally about 2 fold but markedly higher in aorta treated with SIN-1 and superoxide dismutase (SOD, 6 fold). Association of a low concentration of the PDE III inhibitor (5 microM) with the PDE IV inhibitor (30 microM) potentiated the effect of the PDE IV inhibitor on cyclic AMP content, except for aorta without endothelium treated with SIN-1 plus SOD.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of adenosine receptor agonists on efferent renal nerve activity in anesthetized rats

The aim of this study was to investigate the effects of A1 and A2 adenosine-receptor activation on the sympathetic nervous system. The effects on efferent renal nerve activity of selective A1 (CCPA; 2-chloro-N-6-cyclopentyladenosine) and A2 (2HE-NECA; 2-hexynyl-5'-N-ethylcarboxamidoadenosine) adenosine-receptor agonists were studied in anesthetized rats either with intact baroreflexes (intact rats) or with bilateral sinoaortic denervation and vagotomy (denervated rats). After a control period of 5 min, A1 or A2 agonist or vehicle were intravenously infused for 8 min in separate groups of intact or denervated rats, in which arterial pressure and heart rate were continuously recorded. CCPA (5.0 microg/kg/min) and 2HE-NECA (0.7 microg/kg/min) were selected to obtain comparable blood pressure changes over the period of observation. Arterial pressure significantly and equally decreased during the A1 (-41 +/- 8%), and A2 (-35 +/- 5%) agonist administration. Heart rate significantly decreased during A1 agonist infusion, but it did not change during A2 agonist administration. Bilateral sinoaortic denervation and vagotomy did not modify the hemodynamic responses to both drugs. The A1 and A2 administration caused a large and significant increase in efferent renal nerve activity (+66 +/- 22% and +76 +/- 15%, respectively), and this effect was entirely abolished in denervated rats. A linear relation with a significant negative slope between changes in arterial pressure and changes in neural discharge was observed for each treatment. The comparison of the regression slopes showed that the reflex increase of efferent sympathetic activity caused by the administration of both agonists was significantly smaller than the increment induced by equipotent hypotensive dose of sodium nitroprusside (10 microg/kg). These data show that the selective activation of A1 and A2 receptors elicits a reflex increase in efferent renal nerve activity. This neural activation is smaller as compared with the effect of equihypotensive doses of sodium nitroprusside, thus indicating a blunting effect of both adenosine agonists on baroreceptor sensitivity.     

Effects of angiotensin II receptor blocker on proteinuria in renal transplant recipients

INTRODUCTION: Therapeutic approaches directed at reducing proteinuria are under development. The aim of the present study was to prospectively elucidate the impact of losartan treatment in renal transplant recipients with persistent proteinuria. PATIENTS AND METHODS: Twenty-eight patients with persistent proteinuria or mild hypertension were assigned to receive losartan. Proteinuria was defined as a ratio of urinary protein to urinary creatinine (U(P)/U(Cr)) >0.5 in continual urinary tests in the outpatient setting. RESULTS: All patients with mild hypertension reached target blood pressure (BP) with losartan treatment, but the change was not significant. In twelve patients with proteinuria before initiation of the study, urinary protein excretion was significantly reduced with treatment. No correlation was observed between reductions in proteinuria and mean BP. A significant decrease was identified in the hemoglobin concentration of patients with serum creatinine concentrations >2.0 mg/dl before the study. DISCUSSION: Losartan efficiently reduces proteinuria in renal transplant recipients with adequate tolerance. Multicentric prospective studies are required to confirm its clinical effectiveness.     

1,25-二羟维生素D_3对单侧输尿管梗阻大鼠肾间质纤维化调节性T细胞的作用研究

目的:探讨1,25-二羟维生素D3[1,25(OH)2D3]对单侧输尿管梗阻(UUO)大鼠肾间质纤维化调节性T细胞(Treg)的作用。方法:54只健康雄性wistar大鼠随机分为假手术组(A组)、UUO组(B组)、1,25(OH)2D3治疗组(C组)。每组于术后第1天、第3天、第7天分批处死6只,留取肾脏组织。用HE染色观察肾脏病理变化,采用免疫组织化学染色法测定肾脏人叉头框蛋白P3(FOXP3)、平滑肌肌动蛋白(α-SMA)的表达。结果:与假手术组相比,UUO组FOXP3表达水平显著降低,α-SMA表达水平显著升高,差异有统计学意义(P<0.05);与UUO组相比,1,25(OH)2D3治疗组FOXP3表达水平显著升高,α-SMA表达水平显著降低,差异有统计学意义(P<0.05)。结论:调节性T细胞可能参与了肾间质纤维化的发生及发展;1,25(OH)2D3作为免疫调节剂可通过上调调节性T细胞减缓肾脏纤维化的进展。     

三七总皂苷对腺嘌呤致肾间质纤维化的影响

目的研究三七总皂苷(PNS)对腺嘌呤致大鼠肾间质纤维化的防治作用。方法Wistar雄性大鼠50只,随机分为正常对照组(n=6)、模型组(n=22)和干预组(n=22)。2%腺嘌呤250mg·kg~(-1)·d~(-1)混悬液灌胃,连续21d,制作大鼠肾问质纤维化模型;干预组7d后同时腹腔注射三七总皂苷50mg·kg~(-1)·d~(-1)。磺柳酸比浊法测定量24h尿蛋白,酶联免疫吸附实验检测血清中血小板源性生长因子(PDGF)-BB,HE、Masson染色观察肾脏病理变化,免疫组织化学法观察肾小管间质α-平滑肌肌动蛋白(α-SMA)表达并行半定量分析。结果与对照组比较,在实验d7、14、21、28,模型组和干预组大鼠血清PDGF-BB、24h尿蛋白定量、肾间质纤维化程度及α-SMA均升高(P<0.05或P<0.01),干预组低于模型组(P<0.05或P<0.01)。结论在腺嘌呤致大鼠肾间质纤维化早期阶段给予三七总皂苷可降低其血清PDGF-BB水平、肾间质α-SMA表达,阻滞肾间质纤维化进展。     

Lithium ions have a potent and selective inhibitory effect on cyclic GMP formation stimulated by neurotensin, angiotensin II and bradykinin

The effect of lithium ion (Li+) on receptor-mediated synthesis of cyclic GMP, a putative second messenger, was examined using intact murine neuroblastoma cells (clone N1E-115). Lithium chloride potently inhibited cyclic GMP formation stimulated by the neuropeptides, neurotensin, angiotensin II and bradykinin in an identical concentration-dependent (IC50 s of around 12 mM), saturable and reversible manner. In the presence of veratridine, an alkaloid which by stimulating sodium channels can increase Li+ entry into the cells, Li+ inhibited neurotensin-stimulated cyclic GMP formation more potently (IC50 = 7 mM). No effect of Li+ was observed on phosphodiesterase (EC 3.1.4.17) activity. These results suggest that Li+ may interfere with the function of these receptors through its inhibitory effect at a common site in the pathway of receptor-mediated cyclic GMP formation.     

Determination of interstitial rocuronium concentrations in the muscle tissue of anesthetized dogs by microdialysis

INTRODUCTION: The objective was to establish and validate a microdialysis technique for the quantification of interstitial concentrations of the neuromuscular blocker, rocuronium, in the muscle tissue of dogs under steady-state conditions. METHODS: The standard and combined retrodialysis approaches were used for in vivo microdialysis probe calibration. After induction of anesthesia with pentobarbital (30 mg/kg), the left femoral vein was cannulated and blood drawn for protein binding determination. Microdialysis probes were inserted in the muscle and calibrated in vivo, using vecuronium as the calibrator. Each dog received a short 2-min infusion followed by a 120-min infusion of rocuronium via the right jugular vein and three microdialysis samples were collected at steady-state during a 2-h period. Samples were stored at -70 degrees C until HPLC analysis. RESULTS: Using combined retrodialysis, rocuronium unbound interstitial (C(ISFu)) and venous plasma (C(pssuv)) concentrations are in good agreement; with a ratio C(ISFu)/C(pssuv) of 100+/-11%. Using standard retrodialysis, this ratio was 47+/-7%. CONCLUSIONS: Combined retrodialysis is a more reliable and accurate technique for quantitative assessment of rocuronium interstitial concentrations especially for lengthy anesthetic procedures. These findings have potential implications, as drug concentrations in the site of action would be more relevant for concentration-effect relation of muscle relaxants.