Adenosine receptor mediates nicotine-induced antinociception in formalin test.

In this study, the effect of adenosine receptor agents on nicotine induced antinociception, in formalin test, has been investigated. Intraperitoneal (i.p.) administration of different doses of nicotine (0.1, 1, 10 and 100 microgkg(-1)) induced a dose-dependent antinociception in mice, in the both first and second phases of the test. Adenosine receptor antagonist, theophylline (5, 10, 20 and 80 mgkg(-1), i.p.) also induced antinociception in the both phases, while a dose of the drug (40 mgkg(-1), i.p.) did not induce any response. Theophylline reduced antinociception induced by nicotine in both phases of formalin test. The A(2) receptor agonist, 5'-N-ethylcarboxamide adenosine (NECA; 1 and 5 microgkg(-1), i.p.) also produced antinociception, which was reversed with different doses of theophylline (5, 10, 20 and 40 mgkg(-1), i.p.). But administration of the adenosine receptor agonist, NECA did not potentiate the response of nicotine. It is concluded that adenosine system may be involved in modulation of antinociception induced by nicotine.     

Protection by nitric oxide of morphine-induced inhibition of rat submandibular gland function.

The effects of morphine, l -arginine (nitric oxide precursor) and l -NAME (nitric oxide synthesis inhibitor ) and their concurrent therapy on rat submandibular secretory function were studied. Pure submandibular saliva was collected intraorally by micro polyethylene cannula from anaesthetized rats using pilocarpine as secretagogue. Single intraperitoneal injection of morphine (6 mg kg(-1)) to rats induced significant (P< 0.01) inhibition of salivary flow rate (28%), total protein (12%) and calcium concentrations (27%). Sodium output was increased (23%, P< 0.01). Single intraperitoneal administration of l -arginine (100 mg kg(-1)) and l -NAME (10 mg kg(-1)) affected salivary gland function. Saliva flow rate was reduced by l -NAME (23%, P< 0.01). The total protein concentration of saliva was increased by l -arginine (21%, P< 0.05) and decreased by l -NAME (19%, P< 0.01). Calcium concentration of saliva was increased by l -arginine (25%, P< 0.01) and reduced by l -NAME (21%, P< 0.01). In combination treatment, l -arginine prevented (P< 0.01) morphine-induced reduction of flow rate while l -NAME potentiated it (P< 0.01). The secretion of total protein and calcium were influenced in a similar trend by concurrent therapy. l -NAME potentiated morphine-induced decrease of total protein and calcium concentrations (P< 0.01) while l -arginine restored (P< 0.01) them to levels close to control and morphine groups respectively. It is concluded that morphine inhibits salivary gland function and nitric oxide (NO) plays a positive role in this system. Also it is confirmed that morphine inhibitory effects on submandibular function are somewhat restored by l -arginine and expanded by l -NAME. The modulatory effect of the l -arginine/NO system on salivary gland function is suggested.     

Possible compensation in epidermal growth factor production by saliva in rat

In the present work, the authors investigated the effect of both main vegetative transmitters and some regulatory peptides on epidermal growth factor (EGF) secretion into whole saliva. We studied how the salivary and glandular EGF levels depend on the functional activity of salivary glands in rats. Experimental groups comprised: (a) control, (b) bilateral ablation (AB) of submandibular and sublingual salivary glands, (c) 0.5% citric acid in drinking water treatment (Cit), and (d) ablation plus citric acid combination (AB+Cit). On the 7th day under narcosis, pilocarpine-stimulated saliva was collected and the amylase activity was measured along with concentrations of EGF and the protein, both in saliva and in salivary glands. In the first study, in conscious rats adrenergic activation of EGF secretion was observed. During noradrenaline stimulation, the curve showing EGF discharge was parallel to the amylase secretory curve. Salivary amylase secretion was stimulated by adrenergic, cholinergic and VIP-ergic actions. Other regulatory peptides, such as CCK, bombesin and somatostatin, did not seem to be involved in controlling EGF or amylase secretion. In the second study, 7 days after ablation, protein concentration of salivary glands decreased in control animals 30 min after pilocarpine stimulation. There was no significant change in protein concentration after this stimulation in the other groups. EGF concentration increased about 40% in submandibular tissues of the Cit group of animals, and decreased in the parotid tissues in all treated groups. The EGF concentration decreased after pilocarpine stimulation to a great extent in all salivary tissues. Protein concentration in saliva was significantly higher than the initial level in all treated groups (AB:+240%; Cit: +80%; AB+Cit: +350%). EGF concentration of saliva was slightly decreased in the ablation group (?10%), while it increased in the other treated animals (Cit: +20%, AB+Cit: +200%). Changes in the EGF level in saliva were lower than 10% in the control group. In conclusion:

1. EGF secretion is controlled by adrenergic pathways but not by cholinergic mechanisms or by VIP, CCK, bombesin or somatostatin,
2. The EGF level in saliva can be increased by enhanced activity of salivary glands,
3. EGF in saliva is not exclusively produced by one type of salivary glands,
4. Parotid glands can compensate the EGF secretion to saliva when functional activity of the other main gland is lost.

     

枸橼酸西地非尔对兔海绵体组织作用及其机制的离体研究

目的　研究枸橼酸西地非尔对兔海绵体组织舒张功能的影响及其作用机制。方法　 37℃温孵兔海绵体组织(RCC) ,用放射免疫方法监测在硝普钠存在下 ,西地非尔10、10 0、10 0 0nmol·L-1对cGMP水平的影响 ;采用离体器官水浴技术 ,将RCC用苯丙肾上腺素 (PE)收缩 ,观察西地非尔对NO供体硝普钠 (SNP)及促内皮依赖性NO释放剂氯化乙酰甲基胆碱介导RCC舒张作用的影响。结果　SNP可提高RCC中cGMP水平 ,西地非尔 10、10 0、10 0 0nmol·L-1可剂量依赖性使之升至更高水平。西地非尔使SNP、氯化乙酰甲基胆碱 (MCH)作用IC50 显著减小。结论　以上结果表明枸橼酸西地非尔通过NO/cGMP呈剂量依赖性增强MCH和SNP对RCC的舒张作用 ,对动物阴茎海绵体组织舒张功能有显著性改善作用 ,从而大大提高动物性功能。     

Toxicity of theophylline depends on plasma concentration by single and also repeated dosing in rats.

The purpose of this study was to evaluate the relationship between the in vivo toxicity and plasma concentration of theophylline. Theophylline was administered intravenously in single doses ( 50, 100, 150 and 200 mg kg(-1)once a day) or repeated doses (12.5, 25 and 90 mg kg(-1)/day for 28 days) in rats. Plasma concentrations of theophylline increased dose-dependently in both single and repeated doses, and there were no differences due to effects of 28-times repeated administration. Neither single dose at 50 mg kg(-1)nor repeated dose at 12.5 mg kg(-1)/day injections of theophylline showed toxic signs, in which plasma concentrations of theophylline were less than 110 and 22.5 microg ml(-1), respectively. Theophylline induced myocardial fibrosis in 25 mg kg(-1)/day and more treated groups: in which plasma concentrations of theophylline were more than 50 microg ml(-1). At doses of 100 mg kg(-1)(single) and 90 mg kg(-1)/day (repeated), theophylline caused tachypnea and excitement of movement. Each theophylline concentration in plasma was more than 194 microg ml(-1)in single 100 mg kg(-1)and 162 microg ml(-1)in repeated 90 mg kg(-1)/day injections, respectively. Death was observed at a dose of 200 mg kg(-1), in which the plasma concentration of theophylline was more than 264 microg ml(-1). Moreover, the recovery period from signs of toxic poisoning to normality in the 200 mg kg(-1)treated group was greater than that in the 150 mg kg(-1)and less treated groups. The results indicated that the in vivo toxicity of theophylline is highly dependent on plasma concentrations in rats which received single and also repeated doses of theophylline.     

Interleukin-12 was not involved in promotion of T helper cell differentiation induced by theophylline

AIM:ToinvestigatetheeffectoftheophyllineonthenaiveTcelldifferentiationandtheprobableroleofinterleukin-12(IL-12).METHODS:NaivecordbloodTcellsweretreatedwiththeophylline10mg/Lfor3dafterstimulationwithPHA100mg/L.DifferentiationofTcellswasanalyzedbyflowcytometry.Theophylline10mg/LandIL-12-mAb0.025mg/Lwereaddedincordbloodmononuclearcell(CBMC)culturesprimedwithLPS1mg/LtodetectthelevelsofIL-12andIL-12P40.Thewholebloodcultureswereobtainedfromtwelvehealthvolunteerswithorwithoutadministr…     

Salivary theophylline monitoring in asthmatic children

The usefulness of determination of salivary concentrations of theophylline for estimation of the serum concentration of the drug was tested in asthmatic children receiving daily 15-20 mg/kg of aminophylline. Theophylline was measured in saliva samples obtained after stimulation with citric acid and bromhexine, and in the blood serum, and the ratio of saliva: serum theophylline concentrations was calculated. The correlation between saliva and serum theophylline concentration was better for saliva samples obtained after bromhexine stimulation (r = 0.9496) than after citric acid stimulation (r = 0.8506). Using the mean value of the saliva: tissue theophylline concentration ratio of 0.6795, the serum theophylline concentration may be satisfactorily predicted (r = 0.9810). The stimulation of salivation with bromhexine is more suitable for the Abbott TDX Drug Monitoring System than the stimulation with citric acid, and the method is suitable for a routine monitoring of theophylline concentrations in the course of theophylline therapy.     

Effect of cigarette smoking on salivary epidermal growth factor (EGF) and EGF receptor in human buccal mucosa.

The mouth acts as a primary target for cigarette smoke which is associated with several oral diseases and cancer. The present study investigated the effect of cigarette smoking on salivary EGF and the buccal EGF receptor. Samples of whole saliva and buccal biopsy were obtained from 15 healthy volunteers (10 smokers and 5 non-smokers). The smokers smoked 20 or more cigarettes/day for more than 5 years. Salivary cotinine (a major metabolite of nicotine) was determined by radioimmunoassay (RIA). The salivary cotinine level was consistent with the self-reported smoking status (smokers, 106-530 ng/ml saliva; non-smokers, < 2 ng/ml saliva). As compared to the non-smokers, the salivary EGF concentration (determined by RIA) was 32% lower in those smokers whose salivary cotinine level was 250 ng/ml or higher (non-smokers, 2.21 +/- 0.16; smokers, 1.57 +/- 0.09 ng/ml saliva; mean +/- S.E.M., P < 0.01). There was no significant difference in 125I-labeled EGF binding to the buccal receptor between the two groups. However, EGF stimulated the autophosphorylation of a 170-kDa protein band in the sample of non-smokers, but not in the smokers. The immunoblot analysis using anti-EGF receptor antibody indicated that the smoking-related deficiency in EGF receptor autophosphorylation was due to the functional alteration of the receptor proteins. In conclusion, cigarette smoking reduces the salivary EGF level and impairs the function of buccal EGF receptor, which may be associated with the pathology of smoking-related oral disease.     

Sildenafil (Viagra) reduces arrhythmia severity during ischaemia 24 h after oral administration in dogs

Sildenafil (Viagra) prolongs repolarisation in cardiac muscle, an effect that could lead to ventricular fibrillation (VF). Sildenafil (2 mg kg(-1)) was given by mouth to 12 mongrel dogs and, 24 h later, these dogs were anaesthetised, thoracotomised and subjected to a 25 min occlusion of the anterior descending coronary artery. Haemodynamic parameters were similar in this and the control group, but there were fewer and less serious ventricular arrhythmias during occlusion in the sildenafil group (VF 17 vs 60%; ventricular premature beats 140+/-52 vs 437+/-127% and episodes of ventricular tachycardia 4.0+/-3.2 vs 19.3+/-7.7%, all P<0.05). However, reperfusion VF and indices of ischaemia severity (epicardial ST-segment mapping, inhomogeneity) were not modified by the drug. Sildenafil increased the QT interval, especially during ischaemia. Our conclusion is that ischaemia-induced ventricular arrhythmias are reduced by sildenafil, but this protection is less pronounced than that following cardiac pacing or exercise.     

Evaluation of passively absorbed saliva for determination of oral slow-release theophylline bioavailability in children

Assessment in young children of the bioavailability of slow-release theophylline formulations is hampered by the requirement for frequent blood sampling. Calculations of bioavailability from serial serum and passively absorbed saliva samples were therefore compared in six 9- to 12-year-old asthmatic children receiving multiple doses of Theo-Dur Sprinkle every 12 hours, using Theo-Dur tablets, a previously characterized formulation, as a reference. Results indicated 85 +/- 5 percent and 82 +/- 8 percent (mean +/- SEM) relative bioavailability based on serum and salivary measurements, respectively. Correlation coefficient for serum and passively absorbed saliva bioavailabilities was 0.90. Passively absorbed saliva provides an acceptably accurate, noninvasive method for theophylline bioavailability assessment and may be a useful alternative for bioavailability studies in young children.     

Protection by sildenafil and theophylline of lead acetate-induced oxidative stress in rat submandibular gland and saliva

The role of oxidative stress in lead toxicity has been proposed in many organs, however, no study has been performed in the salivary glands, which are important parts of the gastrointestinal tract with a high implication in health of the whole body. Recently, it has been proposed that increasing the levels of cGMP and cAMP in the cells may protect from the neurotoxicity of lead. The objective of this study was to determine the ability of lead acetate to produce oxidative stress in rat submandibular as the main salivary gland of the body and to study the role of pretreatment by specific phosphodiesterase inhibitors in the prevention of oxidative stress. Lead acetate (100 mg/kg), alone or in combination with theophylline (25 mg/kg) and sildenafil (5 mg/kg), was administered intraperitoneally to rats. After 2 hours and under general anaesthesia, the submandibular gland ducts were cannulated intraorally using microcannula, and pure saliva was collected for 30 min using pilocarpine (8 mg/kg) as a secretagogue. The submandibular glands were then isolated free under surgery. Oxidative stress in the gland and pure saliva were evaluated measuring lipid peroxidation (thiobarbituric acid reactive substances assay), total thiol groups content and total antioxidant capacity (the ferric reducing ability assay). Results showed significant oxidative stress in the gland and secretions as indicated by increased lipid peroxidation, decreased total antioxidant capacity and thiol group levels. The use of cAMP and cGMP phosodiesterase inhibitors, theophylline and sildenafil, prevented lead-induced increased lipid peroxidation and also protected from decreased thiol groups content and total antioxidant power of the gland and secretions. The same trend of effects was observed in gland and saliva. It is concluded that lead toxicity is mediated through oxidative stress in salivary glands, while increasing intracellular cAMP and cGMP levels may prevent lead-induced oxidative stress.     

Effects of obesity and ancillary variables (dialysis time, drug, albumin, and fatty acid concentrations) on theophylline serum protein binding

The effect of obesity on the serum protein binding of theophylline was investigated in man and rat along with other ancillary variables such as dialysis time, theophylline concentration, albumin concentration, and fatty acid type and concentration. The percent binding of theophylline first increased with dialysis time, reached equilibrium over 2 to 6 h, then diminished. This decrease was not due to instability of theophylline. Theophylline binding was linear over a concentration range of 15 to 150 micrograms ml-1. A similar degree of binding was found in normal humans (44.4 +/- 1.0%) and rats (41.5 +/- 0.5%). The binding ratio (bound/free) of theophylline was proportional to the albumin concentration (1 to 5%) and yielded a binding parameter (NK) of 1.47 x 10(-3) M-1. Over a normal physiological range, individual and mixed fatty acids had minimal effects on theophylline binding to albumin. However, binding significantly decreased as fatty acid (FFA) concentrations increased. The magnitude of the effect appeared to parallel the carbon chain number of the fatty acid. Theophylline binding in obese subjects decreased to a mean (SD) of 35.8 +/- 8.0 per cent compared to 43.0 +/- 6.1 per cent in normal subjects (p less than 0.05). Similar decreases were found in normal versus obese rats and in the saliva: serum ratio following theophylline administration to normal and obese human subjects. Obesity causes a moderate decrease in serum binding of theophylline which may be attributed to increased FFA rather than in vitro artifacts.     

Serum/saliva correlations for theophylline in asthmatics

Theophylline levels in mixed saliva (both stimulated and unstimulated) were compared with total and free (unbound) serum theophylline levels in 28 asthmatic outpatients using theophylline regularly. Stimulated saliva predicted both total and unbound serum theophylline concentrations within +/- 1 microgram/mL in 62.5% and 92.9%, respectively, of the samples examined. In addition, the total serum levels could be used to predict unbound serum concentrations to within +/- 1 mg/L in 100% of the cases that were examined. These results indicate that saliva levels predict the unbound serum theophylline levels with greater accuracy and precision than they predict total serum theophylline levels. In addition, total serum levels can be used to reliably predict unbound serum levels. The use of mixed stimulated saliva is recommended as a reliable non-invasive method for monitoring unbound serum theophylline levels. The therapeutic range for saliva, which corresponds to the accepted total serum concentration range of 10-20 mg/L, is approximately 5.6-11.3 mg/L.     

Effect of Theophylline Administered Intratracheally as a Dry Powder Formulation on Bronchospasm and Airway Microvascular Leakage in the Anaesthetized Guinea-pig

Summary: The effect of theophylline (a non-selective phosphodiesterase (PDE) inhibitor), dosed intratracheally (it) as a dry powder, on histamine- and platelet activating factor (Paf)-induced bronchospasm and antigen (ovalbumin, OA)-, histamine- and Paf-induced microvascular leakage (MVL) in the airways, was studied in the anaesthetized guinea-pig. Bronchospasm was measured as the increase in pulmonary inflation pressure (PIP). MVL was assessed by fluorometric assay of fluorescein isothiocyanate dextran (FITC-dextran) content in airway tissues and tracheobronchial lavage fluid. OA (200 μg), histamine (60 nmol) and Paf (4 nmol), all given it, significantly increased MVL by up to 350% over levels in undosed unchallenged animals. Theophylline (50-500 μg it, n=5-6) inhibited histamine-induced bronchospasm (30% inhibitory dose, ID₃₀: 258±30 μg) and Paf-induced bronchospasm (ID₃₀: 190±80 μg). An inhibition of 40-50% of maximal bronchospasm was the largest attained. Theophylline, at approximately the bronchospasm ID₃₀ dose (200 μg it, n=4-8), inhibited MVL induced by all agents by 30-80% in airway tissues and in lavage fluid samples. Theophylline (50-500 μg it, n=3) produced plasma drug levels of 0.13±0.07 to 0.83±0.39 μg/ml 10 min after dosing. Plasma levels were the same 60 min after dosing, suggesting retention of theophylline in the airways. The local concentration of theophylline retained in the airways should be sufficient to inhibit PDE activity. Direct application of theophylline (arguably by inhibition of the PDE isoforms PDE III, PDE IV and PDE V) thus has significant antiinflammatory and some bronchodilator effects at very low doses which should have no systemic toxicity. Theophylline applied as a dry powder locally in the airways may thus improve its documented usefulness in the treatment of asthma.     

Dose dependent pharmacokinetics of theophylline: Michaelis-Menten parameters for its major metabolic pathways.

Dose Dependency for pharmacokinetics of theophylline and the formation of its major metabolites, 3-methylxanthine (3-MX); 1-methyluric acid (1-MU); 1,3-dimethyluric acid (DMU), were examined by administering three single oral doses (250, 375, 500 mg) of theophylline to six healthy adult volunteers. The serum and urine concentrations of theophylline and the metabolites in serum and urine were determined by high-performance liquid chromatography. Total clearance of theophylline decreased and its half life increased over the range of doses administered (p<0.01). There was a significant dose related decrease in the fractional recovery of 3-MX and 1-MU (p<0.001) and a dose related increase in fractional excretion of DMU and unchanged theophylline (p<0.01 and p<0.001 respectively). No significant dose related changes were observed in the renal clearance of 3-MX, 1-MU and DMU, indicating linear urinary excretion kinetics of the metabolites. Theophylline metabolic clearance to 3-MX as well as to 1-MU decreased with increasing dose but clearance to DMU remained unnaffected by the size of dose. The individual Michaelis-Menten parameters Km and Vmax were estimated for six subjects receiving three different single doses. The Km values for theophylline metabolism to 3-MX, 1-MU and DMU were 2.4+/-0.6, 5.1+/-1.8+/- and 112.3+/-36.8 mg/L respectively and the Vmax values were 3.5+/-0.7, 7.5+/-2.6 and 112.3+/-36.8 mg/hr respectively. The Km values for the N-demethylation pathways (3MX and 1-MU) were lower corresponding to therapeutic serum concentrations of drug. These results suggest that the elimination kinetics of theophylline is nonlinear in the human in the therapeutic range of serum concenntrations and can be explained by saturable formation kinetics of 3-MX and 1-MU. In contrast to previous studies we didn't find obvious indication for nonlinear formation of DMU at therapeutic concentration range.     

Inhibitory effect of sildenafil on rat duodenal contractility in vitro: putative cGMP involvement

1. Sildenafil citrate (Viagratrade mark; Pfizer, Sandwich, Kent, UK), a phosphodiesterase 5 inhibitor, rises cGMP levels in smooth muscle cells. It relaxes both vascular and visceral smooth muscle. In order to assess the intestinal effects of sildenafil, we decided to investigate its actions on rat duodenal motor activity in vitro. 2. In isolated duodenal segments maintained in Tyrode's solution, sildenafil exhibited a concentration-dependent antispasmodic effect on acetylcholine (ACh)-induced phasic contractions, with an IC50 value of 26.7 micromol/L (95% confidence interval (CI) 2.0-55.3 micromol/L). 3. Sildenafil also relaxed the carbamylcholine (CCh)-induced sustained contraction with an IC(50) of 16.2 micromol/L (95% CI 9.5-27.6 micromol/L). Sildenafil produced significant additional relaxation of 25.2 +/- 8.1% of the CCh-induced contraction, beyond basal tone. 4. Sildenafil reduced the amplitude of spontaneous duodenal contractions with an EC50 of 9.6 micromol/L (95% CI 5.7-16.2 micromol/L). This effect was significantly more potent than the effects of zaprinast and papaverine, which also reduced duodenal contractions with EC50 values of 91.6 micromol/L (95% CI 46.0-182.2 micromol/L) and 78.5 micromol/L (95% CI 37.1-166.3 micromol/L), respectively. 5. In preparations treated previously with methylene blue (10 micromol/L) or 1H-[1,2,4]oxadiazolo(4,3-a)quinoxalin-1-one (ODQ; 10 micromol/L), the EC50 values for the sildenafil effect were significantly increased to 39.0 micromol/L (95% CI 23.9-63.4 micromol/L) and 43.8 micromol/L (95% CI 24.5-78.3 micromol/L), respectively. These values were significantly greater than those obtained with sildenafil alone. 6. In conclusion, sildenafil has myorelaxant and antispasmodic effects on rat duodenal segments in vitro. The contractile inhibitory effect of sildenafil on rat isolated duodenum is probably due to intracellular cGMP accumulation as a result of its decreased degradation.     

Chronic exposure to subcutaneously implanted methylxanthines. Differential elevation of A1-adenosine receptors in mouse cerebellar and cerebral cortical membranes

Upregulation of brain adenosine receptors in DBA/2J mice as affected by theophylline and caffeine, adenosine antagonists, was examined following subcutaneous drug implantation to ensure chronic exposure. Scatchard analysis of binding to membranes of cerebral cortex and cerebellum from individual mice showed a differential upregulation of (-)-N6-R-[G-3H]phenylisopropyladenosine ([3H]-L-PIA) binding density by theophylline. After 14 days of exposure to theophylline (serum concentration of 1.2 +/- 0.01 micrograms/ml measured by HPLC analysis), the Bmax for L-PIA binding to cerebellar membranes increased 22% over the control mice (statistically significant at P less than 0.01 level). Theophylline had no effect on the Bmax for L-PIA binding to cerebral cortical membranes. The observed increases in Bmax values of cerebellar (13.2%) and cerebral cortical membrane binding (14.2%) on chronic exposure to caffeine (7.1 +/- 0.5 micrograms/ml) were not statistically significant at the P less than or equal to 0.05 level. Neither methylxanthine affected the dissociation constant, KD, for L-PIA. The increased potential for adenosine receptor upregulation by theophylline compared to caffeine following chronic, low level exposure suggests that caffeine treatment for sleep apnea may be preferred to the standard theophylline therapy.     

Relationship between serum and saliva theophylline levels in patients with cystic fibrosis.

Theophylline levels in stimulated and unstimulated mixed saliva were compared with total and free (unbound) serum theophylline levels in 11 outpatients with cystic fibrosis (CF) who were using theophylline regularly. Stimulated saliva from CF patients predicted both total and unbound serum theophylline concentrations to within +/- 1 microgram/ml in 53.3 and 80.0%, respectively, of the samples examined. In addition, the total serum levels from CF patients could be used to predict unbound serum concentrations to within +/- 1 micrograms/ml in 100% of the cases examined. Furthermore, it was observed that prediction equations derived in a previous study with asthmatics employing identical methodology would allow both unbound and total serum theophylline levels to be predicted from saliva levels in CF patients with a degree of accuracy and precision that was approximately equal to or slightly better than the results obtained using prediction equations derived in other CF patients. These results indicate that saliva levels allow predictions of the unbound serum theophylline levels with greater accuracy and precision than they predict total serum theophylline levels. In addition, total serum levels can be used to reliably predict unbound serum levels. The use of mixed stimulated saliva is recommended as a reliable noninvasive method for monitoring unbound serum theophylline levels. The therapeutic range for saliva, which corresponds to the accepted total serum concentration range of 10-20 micrograms/ml, is approximately 5.55-11.3 micrograms/ml.     

Bosentan decreases the plasma concentration of sildenafil when coprescribed in pulmonary hypertension

AIMS: To determine whether bosentan decreases the plasma concentration of sildenafil in patients with pulmonary arterial hypertension. METHODS: Ten patients (aged 39-77 years) with pulmonary arterial hypertension in WHO functional class III received bosentan 62.5 mg twice daily for 1 month, then 125 mg twice daily for a second month. Sildenafil 100 mg was given as a single dose before starting bosentan (visit 1) and at the end of each month of bosentan treatment (visits 2 and 3). Sildenafil and its primary metabolite, desmethylsildenafil, were measured in plasma at 0 h and 0.25, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 18 and 24 h using liquid chromatography-tandem mass spectrometry. Statistical analysis was by repeated measures anova, using log transformed data where appropriate. RESULTS: Treatment with bosentan 62.5 mg twice daily for 4 weeks was associated with a two-fold increase in sildenafil clearance/F and a 50% decrease in the AUC (P < 0.001). Increasing the dose of bosentan to 125 mg twice daily led to a further increase in sildenafil oral clearance and decrease in the AUC (P < 0.001 vs. 62.5 mg bosentan). The ratio of AUC on bosentan treatment relative to that of visit 1 was 0.47 [95% confidence interval (CI) 0.36, 0.61] for visit 2 and 0.31 (95% CI 0.23, 0.41) for visit 3 (P < 0.001). Sildenafil C(max) fell from 759 ng ml(-1) on visit 1 to 333 ng ml(-1) on visit 3 (P < 0.01) and there was a significant decrease in the plasma half-life of sildenafil on the higher bosentan dose (P < 0.05). The AUC and plasma half-life of desmethylsildenafil was also decreased by bosentan in a dose-dependent manner (P < 0.01). CONCLUSIONS: Bosentan significantly decreases the plasma concentration of sildenafil when coadministered to patients with pulmonary hypertension.     

The effect of sildenafil on corpus cavernosal smooth muscle relaxation and cyclic GMP formation in the diabetic rabbit

Sildenafil, a type V phosphodiesterase inhibitor, enhances smooth muscle relaxation in normal human and rabbit corpus cavernosum. We investigated the in vitro effects of sildenafil on non-adrenergic, non-cholinergic and nitric oxide (NO)-mediated cavernosal smooth muscle relaxation in diabetic rabbits, since alterations in this pathway are recognised in diabetic erectile dysfunction. Diabetes mellitus was induced in male New Zealand White rabbits with alloxan. Cavernosal strips from age-matched control, 3- and 6-month diabetic animals were mounted in organ baths. Relaxation responses to electrical field stimulation (1-20 Hz) or sodium nitroprusside (10(-8)-10(-4) M) were assessed in the absence and presence of sildenafil (10(-8) and 10(-7) M). The effect of sildenafil on cGMP formation by the corpus cavernosum was also assessed following stimulation with sodium nitroprusside, A23187 and acetylcholine. Sodium nitroprusside-stimulated relaxations were significantly (P<0.03) impaired in the corpus cavernosum from both diabetic groups, (IC(50)=4.6 x 10(-6) M following 3 months of diabetes mellitus and 4.0 x 10(-6) M following 6 months of diabetes mellitus; compared to 7.5 x 10(-7) M for pooled age-matched controls). Sildenafil (10(-7) M) significantly enhanced sodium nitroprusside-stimulated relaxation in control (P<0.05) and diabetic groups (P<0.03). Electrical field stimulation-mediated relaxations of the corpus cavernosum were significantly impaired after 6-month diabetes mellitus and enhanced by sildenafil (10(-8) M). cGMP formation by the diabetic corpus cavernosum was impaired significantly, but restored towards normal by sildenafil. We suggest that the impairment of NO-mediated relaxation of the corpus cavernosum reflect, at least in part, a defect in guanylyl cyclase activity. These findings support the use of sildenafil as an effective, orally administered, treatment for diabetic erectile dysfunction.